View Full Version : Altering the speed of light
How might the speed of light be altered and what implications might this have for space travel?
Simfish
Aug20-04, 07:11 PM
IIRC, the speed of light can actually be modified in everyday circumstances. Or so as the textbook says, light is refracted when it travels between air and water because its speed is slightly different in water and in air. Similar when light travels between other media.
And the speed of light is defined to be what it is in a vacuum.
Simfishy said it, light speed is altered every day. To answer your second question, it won't have any implications on space travel. The speed of light cannot be increased if that is what you were thinking.
That is what I was thinking. If nothing can travel faster than light, what if there were a device attached to a spaceship that could speed up light around the ship?
rgoudie
Aug20-04, 10:01 PM
what if there were a device attached to a spaceship that could speed up light around the ship?
It is not the light particles themselves that limit speed. It is believed that light particles move as fast as this Universe apparently allows. This maximum speed, c, and the speed that light travels have effectively become interchangeable.
That being said, there is no proof that nothing in the Universe may travel faster than c.
-Ray.
But how could the speed of light particles so coincidentally also be the divine "maximum speed that the universe allows"? Is it just because we have yet to discover things that go faster than light? Does the maximum speed that observable matter goes automatically mean that no matter can be "pushed" faster than it has ever gone before?
A similar discussion has been going on here for a while, maybe you'll find some answers.
http://www.physicsforums.com/showthread.php?t=36548
jtolliver
Aug21-04, 02:08 AM
But how could the speed of light particles so coincidentally also be the divine "maximum speed that the universe allows"?
Because light is massless it must go at the speed of light(yes, this term sucks for this purpose)
Is it just because we have yet to discover things that go faster than light? Does the maximum speed that observable matter goes automatically mean that no matter can be "pushed" faster than it has ever gone before?
If you look at the formulas for lorentz transformations you might notice they look almost like rotations. You can introduce 4-vectors(the name comes from the fact that they have 4 components), with a time component in addition to the spatial ones. The only real difficulty is that the dot product must be given by
\vec{u} \dot \vec{v} = u_x v_x + u_y v_y + u_z v_z - u_t v_t
The negative sign is because of the fact that lorentz transformations aren't quite rotations, and c doesn't appear because i just chose the units so that its 1. A vector \vec{v} is called spacelike if \vec{v} \dot \vec{v} is greater than 0, lightlike if it is 0, and time like if it is less than 0. The velocity classically has a magnitude and a direction. In relativity we only need the direction it is moving in spacetime, and can choose the magnitude to be whatever is most convenient(as long as this does not do something like mapping a spacelike vector into a timelike vector). The relativistic velocity is called the 4-velocity, and is usually denoted by u. The x-component of the classical velocity is given by v_x=\frac{u_x}{u_t}, and likewise for the other components. For a particle moving in a timelike direction the classical velocity must be less than 1(or c if you didn't set it to 1), for a particle moving in a lightlike direction it must equal 1, and for a particle with moving in a spacelike direction it must be greater than 1. The energy and momentum, instead of satisfying E=p^2/2m, satisfy the equation E^2-p^2=m^2. The energy is essentially the time component of the momentum, and its norm squared is -m^2. To see that this gives classical physics in the low velocity limit, you can expand E in a power series in terms of p. Since the square of the norm of the momentum is negative for nonzero m, and the velocity points in the same direction as the momentum, the velocity must be timelike for massive particles, and thus they obey the speed limit. Massless particles(like the photon) likewise must have a lightlike velocity, and must go at the universal speed limit. Particles whose mass squared is negative(called tachyons) must go above the universal speed limit, however they have not been observed.
pervect
Aug21-04, 02:15 AM
How might the speed of light be altered and what implications might this have for space travel?
Well, all you really need to do is to get the standards committe that sets the value of the speed of light to change their minds about what this defined constant is.
Viola! You will have changed the speed of light :-)
I assume you're actually talking about 'c', BTW. The actual speed of light (EM radiation) does decrease when it travels through a dielectric.
Anyway, to try and imagine changes to physics that aren't too major that could result in a different universe with a different "speed of light" is somewhat interesting.
Speeding up space travel is a poor motivation for increasing 'c', though. We can't reach anywhere near 'c' at the moment. And one can much more easily imagine human beings living longer and having more patience for longer space trips than one can imagine actually changing the fundamental constants of the universe.
But there are a few things one can say speculatively about a different universe where the speed of light might be "different", in ways that are more interesting than a passive change in units.
Let's assume we want to keep both Maxwell's equation, and Schrodinger's equation. Then, to change the speed of light, we need to change either \mu_0 or \epsilon_o .
Of the two choices, changing u_0 has the least side effects. Basically, as the speed of light goes up, the magnetic field is going to go down. I'm really not sure what effect this would have on cosmology though - even though this is obviously an important question when designing hypothetical universes.
Changing \epsilon_0 is going to have some major side effects. The first one is that the Bohr radius, the radius of the hydrogen atom, is going to change its size. This also implies a change in its energy levels. This has the potential to upset a lot of basic chemistry, I would guess that the chemistry would be different enough that life from our universe would die. (Note: this is just a guess, it's very speculative). The further domino-like consequences of such a change are rather hard to even guess at, we can say that halving \epsilon_0 would increase the speed of light by a factor of 1.4, while halving the size of the hydrogen atom. Note this would actually "increase" the distance to the nearest star in terms of the multiple of the Bohr radius. I don't have a clue as to what would be likely to happen to cosmological issues for this sort of change.
How might the speed of light be altered and what implications might this have for space travel?
we wouldn't need to speed up light in order to have fantastic space travel. Special Relativity has stated: As a body moves closer and closer to the speed of light, time befins to flow slower and slower for him, and distance contracts. If we wanted to get on the other side of the universe, it would take us 0.00001seconds if we were to be traveling at the speed of light. (0.00001s is still too much, it would be less, but Im just giving you an idea)
When traveling at high speeds:
d_o = d \sqrt{1- \frac{v^2}{c^2}}
d_o is the distance experienced by the traveler, and d is the actual distance passed.
You can play around with the equation and see what it implicates.
we wouldn't need to speed up light in order to have fantastic space travel.
Yes, but speeding up light might allow relatively great speeds in which the infinite mass/ infinite energy problem could be solved (not to mention the chronology problem). What made me think of this was the conjecture, using the Varying Speed of Light theory, that there may be vast "superhighways" in deep space used by aliens for interstellar (intergalactic?) travel wherein light actually travels much faster. If the fundamental properties of these areas could be measured, could they not be replicated?
rgoudie
Aug21-04, 01:58 PM
If we wanted to get on the other side of the universe, it would take us 0.00001seconds if we were to be traveling at the speed of light.
Of course, this is not the case in real life. It takes light more than 1 second to travel from the Moon to the Earth, let alone across the Universe. :wink:
In fact, light particles may travel for billions of years on their journeys through the Universe.
-Ray.
russ_watters
Aug21-04, 02:49 PM
Clarification: the speed of light is constant. It does not change when light is refracted. In refraction, light is absorbed and re-emitted making for the appearance that it has slowed down.
rgoudie
Aug21-04, 02:53 PM
Clarification: the speed of light is constant. It does not change when light is refracted. In refraction, light is absorbed and re-emitted making for the appearance that it has slowed down.
Where did you get this from?
-Ray.
The Bob
Aug21-04, 03:39 PM
When traveling at high speeds:
d_o = d \sqrt{1- \frac{v^2}{c^2}}
d_o is the distance experienced by the traveler, and d is the actual distance passed.
Time Dilation. I understand this but it makes no difference to the speed of light. I read, unless it has changed, that even if we measured light from a moving vehicle or from a stationary point, the speed of light would be the same.
The Bob (2004 ©)
P.S. I then think about the Earth moving and it not being a stationary point. Frame of References are so easy to understand but difficult to get around. :biggrin:
Reminds me of what Hawking said about the moving train and the bouncing ball.
If we wanted to get on the other side of the universe, it would take us 0.00001seconds if we were to be traveling at the speed of light.
Of course, this is not the case in real life. It takes light more than 1 second to travel from the Moon to the Earth, let alone across the Universe. :wink:
In fact, light particles may travel for billions of years on their journeys through the Universe.
True, but irrelevant to Nenad's point. Yes, as seen by us, it takes light many years to traverse galactic distances. But if we traveled at near light speed, that distance would shrink to a mere pittance. To our clocks it would take almost no time at all. :wink:
pervect
Aug21-04, 04:09 PM
Yes, but speeding up light might allow relatively great speeds in which the infinite mass/ infinite energy problem could be solved (not to mention the chronology problem). What made me think of this was the conjecture, using the Varying Speed of Light theory, that there may be vast "superhighways" in deep space used by aliens for interstellar (intergalactic?) travel wherein light actually travels much faster. If the fundamental properties of these areas could be measured, could they not be replicated?
The varying speed of light theory, if it's the one some guy was pushing on rec.arts.sf.science, has a fatal flaw. You expect to see one of \epsilon_0 or \mu_0 to change with c = 1/\sqrt{\epsilon_0 \mu_0}
If the speed of light is to be very great, one of the two must not only change, but change a whole lot - it must tend to zero.
This implies that a region with a high speed of light would have no magnetic field, or a significantly different value for the permittivity of free space.
Measurements of the galactic magnetic field have been made, it's non-zero (this was done by observing the Zeeman splitting in various spectral lines). Changes in the value of the permittivity would be even more obvious than changes in the Zeeman effect (the spectral lines frequencies would be wrong in a very glaring way) and aren't found either.
Note: some people *think* they may have found a change in the fine structure constant. This hasn't been widely accepted, and the magnitude of the supposed change is very small - on the order of .001 percent. Not enough to fuel any visions of "galactic superhighways" even if it is true (and it's probably just a very small measurment error of some sort).
rgoudie
Aug21-04, 04:12 PM
True, but irrelevant to Nenad's point. Yes, as seen by us, it takes light many years to traverse galactic distances. But if we traveled at near light speed, that time passage would shrink to a mere pittance. To our clocks it would take almost no time at all. :wink:
If I effect the modification above in red, then I understand what was meant. The time experienced by the entity travelling at c.
D'oh!
-Ray.
is the speed of light constent?
pervect
Aug21-04, 04:22 PM
we wouldn't need to speed up light in order to have fantastic space travel.
This is another good point which is rarely mentioned. *IF* we had a spaceship that could accelerate continuously at 1g, we can travel a LOT further in 20 years of ship-time (proper time) than we could if acceleration were non-relativistic.
It turns out to be pretty implausibile to have a spaceship that can continuously accelerate at 1g for such a long period, however.
A perfectly effecient photon rocket would require a mass ratio of about e^{20} to do this iirc
http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html
gives a mass ratio of 62,000 to reach the center of the galaxy, for instance. This assumes perfect efficiency, which is highly unlikely. In fact, it's pretty unlikely that such a high-thrust high-ISP drive could exist, it would probably melt under its own waste heat considering the magnitude of the energies involved.
There are also some rather interesting problems in dealing with interstellar gas when travelling at such velocities.
It *really* is a lot simpler to just travel slower, and let the trip take longer, by going for a biological solution to allow longer lifespans and/or hibernation and/or artifical intelligence and/or downloading personalities into computer hardware, than it is to try and get velocities with significant time dilations.
the only problem with that would be by the time the ship leaves and then comes back from far out in space so much time has past here on earth that it would be pointless.
If I effect the modification above in red, then I understand what was meant. The time experienced by the entity travelling at c.
I meant it as I said it. The distance shrinks to a pittance. Of course it doesn't take much time to traverse such a small distance.
it wouldnt take much time for the thing going c but it with take a long time for it for something standing still.
still the distance would not change.
still the distance would not change.
Not sure what you mean. Observers moving across the galaxy at near light speed would measure the galactic distance to be severely contracted.
no the distance between two points would be the same no matter where you are. it would just take less time from point to point going at or near light speed.
Jeez Pervect, I wish I knew enough to be able to argue with you.
plum do you think that there can be things moving faster then the speed of light?
http://www.newscientist.com/news/news.jsp?id=ns99992796
Of course, this is not the case in real life. It takes light more than 1 second to travel from the Moon to the Earth, let alone across the Universe. :wink:
In fact, light particles may travel for billions of years on their journeys through the Universe.
-Ray.
Thats is in your frame of reference. If you are on that beam of light (in its frame of refernce), you will be there instantaneously. Thats the great thing about SR.
no the distance between two points would be the same no matter where you are. it would just take less time from point to point going at or near light speed.
I dont know where you learned your special relativity (if you even did :uhh: ) But the distance DOES change with varying speed.
pervect
Aug21-04, 08:26 PM
still the distance would not change.
bino, distance is not an invariant. It depends on the observer.
maybe im not understanding what your trying to say but if im traveling in a car going 100 mph past two trees 20 feet apart from each other. then i go past again but only go 1 mph the distance between the two trees is still 20 feet
pervect
Aug22-04, 02:51 AM
maybe im not understanding what your trying to say but if im traveling in a car going 100 mph past two trees 20 feet apart from each other. then i go past again but only go 1 mph the distance between the two trees is still 20 feet
If two trees are 20 feet apart when you are standing still, if you go past them at 80% of the speed of light, they are only 12 feet apart.
This is called "length contraction" and is a consequence of relativity.
see for example
http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/specrel/lc.html
geometer
Aug22-04, 11:13 AM
bino, distance is not an invariant. It depends on the observer.
Actually, this is not true. In Relativity, the distance between two space-time points is invariant. This is actually very easy to show mathematically.
And, it's not distance that contracts when you move close to the speed of light - YOU contract in the direction of your travel.
pervect
Aug22-04, 12:15 PM
Actually, this is not true. In Relativity, the distance between two space-time points is invariant. This is actually very easy to show mathematically.
And, it's not distance that contracts when you move close to the speed of light - YOU contract in the direction of your travel.
I think you're confused. The Lorentz interval is the invariant in relativity. This is the difference of the square of the distance, and c^2 times the square of the time. Time is not an invariant. Space is not an invariant. The Lorentz interval *is* invariant. Note that the Lorentz interval along a light beam is always equal to zero.
As far as contraction goes, see the old "barn and the pole' paradox. From the point of view of the pole vaulter, the barn he's running through contracts. From the point of the view of the barn, the pole vaulter contracts.
the way i read it was that i or my ship would be contracted in size not the distance between the trees
the way i read it was that i or my ship would be contracted in size not the distance between the trees
You have it exactly backwards.
Bino you might want to do a little reading, then come back.
http://casa.colorado.edu/~ajsh/sr/sr.shtml
russ_watters
Aug22-04, 02:39 PM
http://www.newscientist.com/news/news.jsp?id=ns99992796 From the article: While the peak moves faster than light speed, the total energy of the pulse does not. This means Einstein's relativity is preserved, so do not expect super-fast starships or time machines anytime soon.
More on refraction: The high school explanation really gets on my nerves because it gives people the wrong idea about light - and the belief that C isn't constant interferes with later learning.
Think about the issue this way: how does light know its in a medium? What happens when light enters glass? It hits an atom. When it hits an atom in a transparent media like glass, the photon is absorbed and re-emitted in the same direction it started in. There is a delay between the absorption and re-emission that causes the appearance of a change in speed.
Since refraction depends on hitting atoms, density matters: thats why the index of refraction in air is higher: fewer atoms to hit, so each photon travels further without hitting anything.
More on this at the bottom of THIS (http://online.cctt.org/physicslab/content/Phy1/lessonnotes/refractionoflight/refraction.asp) page.
isn't c^2 faster than c. how can you have that if nothing is faster than c?
pervect
Aug22-04, 03:19 PM
isn't c^2 faster than c. how can you have that if nothing is faster than c?
c^2 isn't a velocity. Have you been taught the concept of units yet? I don't know anything about your background. Comparing c^2 to c is a little bit like asking "what's longer, a yard, or a square yard".
wouldn't c be the speed of the ship? assuming it could reach c.
pervect
Aug22-04, 03:35 PM
From the article:
More on refraction: The high school explanation really gets on my nerves because it gives people the wrong idea about light - and the belief that C isn't constant interferes with later learning.
I've usually taken the position that 'c' is what's actually constant, the speed of transmission of energy through a media, which is what "speed of light" means if you take it literally, is not.
ok are you saying that c is not constant?
employee #416
Aug22-04, 04:28 PM
No, he means the rate at which light is absorbed and emitted is not constant. I think. :redface:
employee #416
Aug22-04, 04:38 PM
Yeah, I think the reason why emission and absorption is not constant is that light is absorbed through different densities. If it is absorbed in a material that has a low density, it will be absorbed less, but pass it through a dense material, and it will be absorbed fast. Emission of the photons occurs as a result of absorption.
according to http://www.fourmilab.to/cship/lorentz.html the length of the ship and the lattice only appears to be contracted. it is not actually smaller it just looks like it is smaller.
why is light sucked into black holes?
employee #416
Aug22-04, 04:49 PM
bino, honestly, I agree with you about the appearance to be contracted. It's all just a way of saying our eyes are unable to measure things that move at relativistic speeds, but opinionated comments are, unfortunately, not allowed on this forum. :cry:
Light does not get "sucked" into black holes, rather it falls into black holes. The gravitational pull of a black hole is large due to it's seemingly infinite density. This pull creates an escape velocity that is larger than the speed of light. Inevitably, light is unable to escape.
Light does not get "sucked" into black holes, rather it falls into black holes. The gravitational pull of a black hole is large due to it's seemingly infinite density. This pull creates an escape velocity that is larger than the speed of light. Inevitably, light is unable to escape.
that is once youre in the event horizon. Light can be deflected or bent from a black hole towards another object. The reason for this is that light has a mass, but it has no rest mass. So gravity has an effect on light particles. :rofl:
employee #416
Aug22-04, 04:54 PM
Yes, that light is also shifted. Gravitational-red shift takes place.
so in other words c cant outrun a black hole. or is it that it is just absorbed by the hole atoms?
according to http://www.fourmilab.to/cship/lorentz.html the length of the ship and the lattice only appears to be contracted. it is not actually smaller it just looks like it is smaller.
yes it will look smaller to the observer. The person in the spaceship will measure the space ship to be normal length. But the reason space contracts is because the observer sees the space as moving by him at high speed and contracting. Making distance differen at different speeds.
so in other words c cant outrun a black hole. or is it that it is just absorbed by the hole atoms?
look up black holes on the search, it will give you threads talking and explaining black holes. Its a lot easier than me answering all of your questions.
so if the ship looks like it is getting smaller as it gets closer to c would the ship then dissapper if it hits c?
Tom Mattson
Aug22-04, 05:01 PM
I've usually taken the position that 'c' is what's actually constant, the speed of transmission of energy through a media, which is what "speed of light" means if you take it literally, is not.
ok are you saying that c is not constant?
See the part in blue. He just said that it is constant.
Yeah, I think the reason why emission and absorption is not constant is that light is absorbed through different densities.
The average speed of light is different in different media because they have different indices of refraction.
If it is absorbed in a material that has a low density, it will be absorbed less, but pass it through a dense material, and it will be absorbed fast. Emission of the photons occurs as a result of absorption.
It has to do not only with the number of absorbers per unit area, but also the length of time that each atom holds the photon.
according to http://www.fourmilab.to/cship/lorentz.html the length of the ship and the lattice only appears to be contracted. it is not actually smaller it just looks like it is smaller.
No, if an observer who is watching the ship zoom by measures the length of the ship, he will really measure it to be less than the proper length of the ship (the length in the ship's rest frame). Conversely, the people on the ship will really measure the rods of the lattice to be shorter than their proper length. It's not an optical illusion.
why is light sucked into black holes?
The photons are just following the geodesic, as they always do. In the case of black holes, the geodesic leads irrevocably to the center of attraction, with no path of escape.
Tom Mattson
Aug22-04, 05:02 PM
bino, honestly, I agree with you about the appearance to be contracted. It's all just a way of saying our eyes are unable to measure things that move at relativistic speeds, but opinionated comments are, unfortunately, not allowed on this forum. :cry:
It's not just opinionated, it's also wrong.
theoretically yes. You saw the graph. And just to add, the ship cannot ever reach c, anything with mass cannot move at c. It can go 0.9999999999999....c, but never 1c. At 1c, there is an assymptote.
they both get shorter in retrospect of each other?
yes. It all depends on the frame of reference. The guy on the ship will see a person in space contract and himself as being normal, but a guy in sace will see the ship contract and will view himself as being fine.
so wouldnt they counter balance each other?
If two trees are 20 feet apart when you are standing still, if you go past them at 80% of the speed of light, they are only 12 feet apart. and if my ship i was 20 feet in length at rest, and i go 80% the speed of light the ships length would be 12 feet. is that right?
Tom Mattson
Aug22-04, 05:33 PM
they both get shorter in retrospect of each other?
Yes: Each claims that the other is shorter, and that nothing is out of the ordinary with regards to their own length.
so wouldnt they counter balance each other?
No, because each claims that they are at rest, and that the other is moving.
If two trees are 20 feet apart when you are standing still, if you go past them at 80% of the speed of light, they are only 12 feet apart.
Assuming you have done the calculation correctly, yes. That is, the trees are 12 feet apart in your frame.
and if my ship i was 20 feet in length at rest, and i go 80% the speed of light the ships length would be 12 feet. is that right?
It would be shorter in the frame of the trees. You must specify the frame of reference.
if a ship going one direction going 90% c and i was going the opposite at 90% and we fly past each other, what would happen then?
employee #416
Aug22-04, 05:44 PM
It has to do not only with the number of absorbers per unit area, but also the length of time that each atom holds the photon.
So, in other words, when measuring the density of emission and absorption, the amount of time should be included. How can that factor be determined?
It's not just opinionated, it's also wrong.
Or maybe you're wrong. Just because opinions contradict with the standard model, doesn't make them wrong. You are unable to use the standard model to counter new theories or opinionated ideas.
No, if an observer who is watching the ship zoom by measures the length of the ship, he will really measure it to be less than the proper length of the ship (the length in the ship's rest frame). Conversely, the people on the ship will really measure the rods of the lattice to be shorter than their proper length. It's not an optical illusion.
Has anything moving at relativistic speeds ever been measured? I'm not saying by equations, but by means of physical rulers. Until then, you are unable to claim it not to be an optical illusion. Just because a formula is derived from the transformation of triangles (might I add the way our eyes measure distances is through triangles...this is not always accurate) does not mean it is necessarily true.
if a ship going one direction going 90% c and i was going the opposite at 90% and we fly past each other, what would happen then?
then you would have to use relativistic velocity addition. Find the relative speed to eachoter, and calculate the contraction. In this case, they could both contract according to achother and they would both be right. Ive give you an example of relativistic addition.
u' = \frac{u + v}{1 + \frac{uv}{c^2}}
u' = \frac{0.9c + 0.9c}{1 + \frac{(0.9c)(0.9c)}{c^2}}
u' = \frac{1.8c}{1 + \frac{0.81c^2}{c^2}}
u' = \frac{1.8c}{1.81}
u' = 0.994c
the pictures didnt come through to me.
employee #416
Aug22-04, 06:01 PM
Yea, LaTeX messed up I guess. I can't see it either.
Tom Mattson
Aug22-04, 06:06 PM
So, in other words, when measuring the density of emission and absorption, the amount of time should be included. How can that factor be determined?
You can determine the index of refraction by sending a light pulse in and measuring the speed with which it comes out. The ratio of the speed of light in vacuum (c) to the speed of light in the medium (c') is the index of refraction (n). Simply put, n=c/c'.
Or maybe you're wrong. Just because opinions contradict with the standard model, doesn't make them wrong. You are unable to use the standard model to counter new theories or opinionated ideas.
No, you're wrong, and there's no "maybe" about it. While it's true that one theory cannot be used to falsify another theory, it is also true that experimental evidence can falsify a theory. And Galilean relativity (the only kind in which there is no length contraction) has been falsified experimentally.
Has anything moving at relativistic speeds ever been measured? I'm not saying by equations, but by means of physical rulers. Until then, you are unable to claim it not to be an optical illusion. Just because a formula is derived from the transformation of triangles (might I add the way our eyes measure distances is through triangles...this is not always accurate) does not mean it is necessarily true.
Length contraction has not been measured directly, but the invariance of the speed of light has been, as has time dilation. It is not logically possible for the speed of light to be absolute and for time to not be absolute, and simultaneously have space be absolute.
Tom Mattson
Aug22-04, 06:10 PM
if a ship going one direction going 90% c and i was going the opposite at 90% and we fly past each other, what would happen then?
You will observe a length contracted ship go past you at 0.994475c and whose length is contracted from its proper length by a factor of 1/0.43589.
Each claims that the other is shorter, and that nothing is out of the ordinary with regards to their own length. how can it be that the length of an object can get shorter to someone but not to someone else? i could understand it if it only looks shorter to the observer. it is like looking at a barn from 1ft away and looking at it from 200 ft away. the barn is smaller from farther away.
employee #416
Aug22-04, 06:25 PM
You can determine the index of refraction by sending a light pulse in and measuring the speed with which it comes out. The ratio of the speed of light in vacuum (c) to the speed of light in the medium (c') is the index of refraction (n). Simply put, n=c/c'.
Heh, first year physics. :redface: You use index of refraction in Snell's law to find the angle at which light is bent, right? This can also be interpreted as the angle at which light is absorbed and emitted from the old medium to the new medium?
No, you're wrong, and there's no "maybe" about it. While it's true that one theory cannot be used to falsify another theory, it is also true that experimental evidence can falsify a theory. And Galilean relativity (the only kind in which there is no length contraction) has been falsified experimentally.
Hehe, Tom, you cease to amaze me. Experimental evidence relies on our eyes as a confirmation, right? What our eyes see is not what is really happening. Just because something appears to be shorter, does not make it shorter. The true length is ALWAYS there. Things only appear to not be there. If a color-blind person needed a ruler that was blue and said, "Pass me the green ruler." You know the ruler is blue, but the color-blind person sees it as green, because he can not distinguish between colors. Optical illusion.
Length contraction has not been measured directly, but the invariance of the speed of light has been, as has time dilation. It is not logically possible for the speed of light to be absolute and for time to not be absolute, and simultaneously have space be absolute.
I would seriously argue you on that statement. I would really like to stay being a member on this site. Can you provide me with a link on how time dilation works and how it is derived? Lenght contraction is very well an optical illusion that people view as reality. I'm assuming the same about time dilation, but am fully knowledgeable in that area.
Each claims that the other is shorter, and that nothing is out of the ordinary with regards to their own length. how can it be that the length of an object can get shorter to someone but not to someone else? i could understand it if it only looks shorter to the observer. it is like looking at a barn from 1ft away and looking at it from 200 ft away. the barn is smaller from farther away.
This is how our eyes are at flaw of measuring things. Lorentz transformation relies on the way our eyes measure things. It takes a triangle and transforms it to come up with 4 vectors. Blah blah blah blah. So, Lorentz transformations state that an object's length contracts as it is moving at relativistic speeds. A barn LOOKS smaller when viewed from farther away, but we konw the true length is there, right? Is that not a way of saying our eyes can not measure the true size just as our eyes are unable to measure the true length of things moving at relativistic speeds?
Tom Mattson
Aug22-04, 06:30 PM
Each claims that the other is shorter, and that nothing is out of the ordinary with regards to their own length. how can it be that the length of an object can get shorter to someone but not to someone else?
Length contraction is a function of speed. In a frame in which the speed of an object is 0, the length is said to be the "proper length". The reason each observer claims that the other is shortened from the proper length and nothing is amiss with their own dimensions is that each observer regards himself at rest, and the other moving. That is, each observer imputes a nonzero speed to the other, and since length contraction is a function of speed, each observer would measure a shortened length for the other.
Now that's about a fundamental an explanation as anyone can give. If you want to know why this phenomenon of length contraction is a function of speed in the first place, or why it occurs at all, the only answer anyone can give is, "Because that's the way it is".
We happen to inhabit a universe in which there is an ultimate speed limit. Two direct consequences of that are time dilation and length contraction.
i could understand it if it only looks shorter to the observer. it is like looking at a barn from 1ft away and looking at it from 200 ft away. the barn is smaller from farther away.
That's not a very useful analogy, because that's not the nature of relativistic length contraction.
You will observe a length contracted ship go past you at 0.994475c and whose length is contracted from its proper length by a factor of 1/0.43589.
interesting.
Tom Mattson
Aug22-04, 06:46 PM
Heh, first year physics. :redface: You use index of refraction in Snell's law to find the angle at which light is bent, right? This can also be interpreted as the angle at which light is absorbed and emitted from the old medium to the new medium?
Yes, the index of refraction of a medium is also the ratio of the speed of light in vacuum to the speed of light in the medium.
Hehe, Tom, you cease to amaze me. Experimental evidence relies on our eyes as a confirmation, right?
No. In fact, relativistic measurements do not involve human senses at all, but rather electronic and mechanical subsitutes. Of course, our eyes read the dials, but that's hardly relevant.
What our eyes see is not what is really happening. Just because something appears to be shorter, does not make it shorter.
If something is measured to be shorter, then it is shorter. Measurements are what tell us what is real.
The true length is ALWAYS there.
No, it isn't. You're stuck in pre-relativistic thinking here. One thing SR teaches us is that there is no preferred frame, and there is no "real" length of objects.
Things only appear to not be there. If a color-blind person needed a ruler that was blue and said, "Pass me the green ruler." You know the ruler is blue, but the color-blind person sees it as green, because he can not distinguish between colors. Optical illusion.
This is an irrelevant argument by analogy. If you want to talk about SR, then why not just stick to SR?
Tom: Length contraction has not been measured directly, but the invariance of the speed of light has been, as has time dilation. It is not logically possible for the speed of light to be absolute and for time to not be absolute, and simultaneously have space be absolute.
416: I would seriously argue you on that statement.
And I would tell you to open a physics book and study, because this is really basic stuff.
I would really like to stay being a member on this site.
Then stop being so arrogant. You have obviously not studied physics, and here you are telling us that you can do our jobs better than we can.
Can you provide me with a link on how time dilation works and how it is derived? Lenght contraction is very well an optical illusion that people view as reality. I'm assuming the same about time dilation, but am fully knowledgeable in that area.
I repeat: In SR, neither length contraction nor time dilation are illusory. Lifeless detectors can be used to measure these effects, and they cannot be tricked the way human minds can.
Here is the original paper by Einstein:
On The Electrodynamics of Moving Bodies (http://www.fourmilab.ch/etexts/einstein/specrel/specrel.pdf)
This is how our eyes are at flaw of measuring things. Lorentz transformation relies on the way our eyes measure things. It takes a triangle and transforms it to come up with 4 vectors. Blah blah blah blah. So, Lorentz transformations state that an object's length contracts as it is moving at relativistic speeds. A barn LOOKS smaller when viewed from farther away, but we konw the true length is there, right? Is that not a way of saying our eyes can not measure the true size just as our eyes are unable to measure the true length of things moving at relativistic speeds?
This is completely wrong. The Lorentz transformation has nothing to do with human eyes or optical illusions. It states what is really happening, and all experimental tests of its predictions have come out positive. If you want to be allowed to post here, then you are going to have to stop posting your opinions that are based only on your own incredulity and ignorance.
yes it is a cheap analogy but if you take a picture of a barn then measured it the barn would still be smaller. the same as if you take a picture of something going near light speed. the object would be smaller.
Bunches of question on light being answered .. I got one!
Light moving through a gravitational field will have its direction of travel changed. Is it proper to say that that light is accelerated?
Tom Mattson
Aug22-04, 06:58 PM
yes it is a cheap analogy but if you take a picture of a barn then measured it the barn would still be smaller. the same as if you take a picture of something going near light speed. the object would be smaller.
But it's still irrelevant. We don't measure the lengths of objects by photographing them. We measure the lengths of objects by simultaneously recording the locations of their endpoints in some coordinate system, and subtracting the coordinates.
Tom Mattson
Aug22-04, 06:59 PM
Bunches of question on light being answered .. I got one!
Light moving through a gravitational field will have its direction of travel changed. Is it proper to say that that light is accelerated?
From a Newtonian point of view, yes. But from a general relativistic point of view, no. Light follows geodesics, and in GR there is no acceleration along a geodesic.
I understand .. Thanks Tom.
but wouldnt the end points change as i got closer?
Tom Mattson
Aug22-04, 07:02 PM
but wouldnt the end points change as i got closer?
No. They are fixed in space.
wouldnt they be if i were going faster?
Tom Mattson
Aug22-04, 07:11 PM
wouldnt they be if i were going faster?
Wouldn't they be what if you were going faster?
It doesn't matter if you are moving past the barn or not. If you simultaneously record the locations of the endpoints of a rod in your coordinate system, then the difference in coordinates is the length of the barn in your frame.
wouldnt they still be fixed endpoint?
Tom Mattson
Aug22-04, 07:14 PM
wouldnt they still be fixed endpoint?
The location of the endpoints--at the time you made the length measurements--are fixed.
and if i measured the length from 1ft away then i measured it from 200ft away. the measurements would be different.
the object is getting smaller right?
Tom Mattson
Aug22-04, 07:20 PM
and if i measured the length from 1ft away then i measured it from 200ft away. the measurements would be different.
No, it wouldn't. The measurement of length is a function of the relative speed between the observer and the observed. It has nothing to do with the coordinates of the person doing the observation.
edit to add:
the object is getting smaller right?
The object isn't "getting smaller". If a rod is moving, then it is smaller than it is in its own rest frame. But nothing actually happens to the rod. It's not as though the rod is physically shrinking by some compressive force.
No, it wouldn't. The measurement of length is a function of the relative speed between the observer and the observed. It has nothing to do with the coordinates of the person doing the observation.
edit to add:
The object isn't "getting smaller". If a rod is moving, then it is smaller than it is in its own rest frame. But nothing actually happens to the rod. It's not as though the rod is physically shrinking by some compressive force.
that just proves my point neither the ship or the lattes is physically getting smaller.
employee #416
Aug22-04, 08:00 PM
Proves my point also. :rofl:
pervect
Aug22-04, 10:45 PM
Yeah, I think the reason why emission and absorption is not constant is that light is absorbed through different densities. If it is absorbed in a material that has a low density, it will be absorbed less, but pass it through a dense material, and it will be absorbed fast. Emission of the photons occurs as a result of absorption.
Our eyes would see Terrel rotation, not Lorentz contraction.
http://www.math.ubc.ca/people/faculty/cass/courses/m309-01a/cook/terrell1.html
employee #416
Aug22-04, 10:55 PM
I wasn't even talking about contraction. Nowhere in there did i mention Lorentz transformation. I was talking about emission and absorption of photons and that's strictly it.
pervect
Aug22-04, 10:59 PM
Or maybe you're wrong. Just because opinions contradict with the standard model, doesn't make them wrong. You are unable to use the standard model to counter new theories or opinionated ideas.
He's not wrong.
When opinions are in opposition to observed facts, especially well-observed facts that have been confirmed by a multitude of observers, the opinions are wrong.
Has anything moving at relativistic speeds ever been measured? I'm not saying by equations, but by means of physical rulers.
We see muons reach the earth's surface.
This is proof of both time dilation (from our point of view), and the Lorentz contraction (from the muon point of view). Otherwise, muons simply wouldn't be able to reach the earth's surface.
pervect
Aug22-04, 11:10 PM
that just proves my point neither the ship or the lattes is physically getting smaller.
The length of an object is not the same for a moving observer and a stationary one.
The phrase "physically getting smaller" is unfortunately ambiguous. Measurements made of a moving object *will* show that it's length contracts.
Tom Mattson
Aug23-04, 01:41 AM
that just proves my point neither the ship or the lattes is physically getting smaller.
It does not. Your statement that the ship "is physically getting smaller" implies that something is happening to the ship. That is not the case. The fact of the matter is that there is no single "length of the ship". But in your mind, you are at least tacitly denying this, and so you think that when someone measures a length of the ship that differs from the proper length, that something must have been done to the ship to make it so. But that is not right, because there is in fact nothing special about the so-called proper length, other than the fact that it is the length that is measured when the ship happens to be not moving.
Tom Mattson
Aug23-04, 01:42 AM
Proves my point also. :rofl:
By what twisted logic do you reach that conclusion? Recall that your point was that length contraction is an illusion. Nothing I have said supports that view. Indeed, everything I have said specifically denies it.
employee #416
Aug23-04, 02:36 AM
Silly Tom!! Ok, maybe you were not saying what I thought. All-in-all lenght contraction is an illusion. Refer to the barn example that bino threw out. The bar up close appears to be normal size, but when you inch away from it, it appears to get smaller. It looses measurement off of height and width from the front view. When you are far away from the barn, it looks fairly small. You know that the true lenght is not that small. Your eyes are playing tricks on you. Do you agree with that? When something is moving at relativistic speeds, your eyes are unable to measure it anywhere near accurate, so it APPEARS TO CONTRACT, when you know that the true length is still in tact.
Tom Mattson
Aug23-04, 03:10 AM
All-in-all lenght contraction is an illusion.
This is the final time I am going to correct you on this. According to SR, the length of any moving object is really less than the length of the same object when it is stationary. Period.
Refer to the barn example that bino threw out. The bar up close appears to be normal size, but when you inch away from it, it appears to get smaller. It looses measurement off of height and width from the front view. When you are far away from the barn, it looks fairly small. You know that the true lenght is not that small. Your eyes are playing tricks on you. Do you agree with that?
Yes.
When something is moving at relativistic speeds, your eyes are unable to measure it anywhere near accurate, so it APPEARS TO CONTRACT, when you know that the true length is still in tact.
Wrong. First of all, the two situations are not analogous. The apparent shrinking of an object with increasing distance is a bonafide optical effect. Length contraction in SR is not. Second, I have already told you that this has nothing to do with human eyes or human minds. Lifeless mechanical or electronic sensors would register the result predicted by SR. And third, there simply is no "true length" of any object. The length of an object varies with its state of motion.
ArmoSkater87
Aug23-04, 03:57 AM
employee, by denying length contraction, you are denying time dilation, and therefore you are wrong because time dilation has been physically measured. Precise atomic clocks have been placed in airplanes and observed after a day of flight and apparently the time had been dilated. Not only that...but the amount of time that was dilated fit the model of time dilation exactly. T = T_0 / sqrt(1-v^2/c^2)
employee #416
Aug23-04, 05:02 AM
Heh, don't babble to me about what I'm denying and what I'm accepting. In the end, you are right though. :biggrin:
Time contraction is also an illusion. Time only seems slower at high velocities, because our eyes can't measure things as fast as it can moving at non-relativistic speeds. This lag in the eye's calculation gives the illusion that time is running slower. This may not be relevant, but I'll take a stab at it. Turn on a strobe light. How does everything look in motion? Slower than it actually is, eh? Our eyes are tricked. We measure things only if visible. If things go in and out of visiblity the eye measure slower than normal. This is an illusion, but we know that time is the same, right?
How can we rely on equations, that are derived from methods our eyes use for measurements? Our eyes do not measure everything accurately. If something is too fast for our eyes to measure, our eye distorts it. If an object is not moving, our eye is not accurate in measuring any dimension of that object. It's all estimated, until a tool for measuring is pulled out for clarity.
An object has a length of 100cm. It is traveling at relativistic speeds. Lets make that speed .95c. It appears to be shorter or is shorter? I'd go with the former. Length does not just disappear into thin air. The true length will ALWAYS be there. The time experienced by that moving object is the same as a person in a difference reference frame. It just seems slower.
Haha, just saw your post Tom Mattson. :rofl:
This is the final time I am going to correct you on this. According to SR, the length of any moving object is really less than the length of the same object when it is stationary. Period.
No, I'm going to correct you. It only appears to be shorter. The physical length of an object traveling at relativistic speeds is always there.
By true lenght, I'm referring an object measured while on the ground or table.
Second, I have already told you that this has nothing to do with human eyes or human minds. Lifeless mechanical or electronic sensors would register the result predicted by SR.
They are measruing wrong. No lenght is lost due to motion. That's just stupid. Magically that length returns when an object is decelerated to non-relativistic speeds. No, it was always there. I'm pretty sure this has to do with the human eye. TRIANGLES!! The whole formula is derived from the transformation of triangles. I'm pretty sure if you were to mess with it, you could get at the method the human eye uses to measure things.
Why is it an eye trick? Ok, take an object with two points. The point at the head end is point A, while the point at the back end is point B. This object, at rest, has a length of AB. Give this object a velocity that is non-relativistic, and your eyes notice no drastic affects in measuring the length. Give it relativistic speeds, and your eyes notice a huge difference. When it tries to calculate the distance from A to B it is smaller than what the distance is at rest. When point A crosses the eye, almost immidiately point B crosses the same path A has just crossed. Thus making measurment SEEM contracted. No length contraction is taking place.
This is probably all jumbled up...I have school in 2 hours and I haven't slept, so whatever.
ArmoSkater87
Aug23-04, 05:53 AM
Time contraction is also an illusion. Time only seems slower at high velocities, because our eyes can't measure things as fast as it can moving at non-relativistic speeds. This lag in the eye's calculation gives the illusion that time is running slower. This may not be relevant, but I'll take a stab at it. Turn on a strobe light. How does everything look in motion? Slower than it actually is, eh? Our eyes are tricked. We measure things only if visible. If things go in and out of visiblity the eye measure slower than normal. This is an illusion, but we know that time is the same, right?
You are not understanding what im talking about. I mean AFTER the airplanes fly for a day, the clock that was on it is compared to the one that was on the ground. So you are saying when we look at these two clocks next to each other, the difference somehow is an illusion??:rofl::rofl::rofl: Not to mention that the difference magically with illusions fits the model.:rofl:
How can we rely on equations, that are derived from methods our eyes use for measurements? Our eyes do not measure everything accurately. If something is too fast for our eyes to measure, our eye distorts it. If an object is not moving, our eye is not accurate in measuring any dimension of that object. It's all estimated, until a tool for measuring is pulled out for clarity.
An object has a length of 100cm. It is traveling at relativistic speeds. Lets make that speed .95c. It appears to be shorter or is shorter? I'd go with the former. Length does not just disappear into thin air. The true length will ALWAYS be there. The time experienced by that moving object is the same as a person in a difference reference frame. It just seems slower.
Once again, like Tom said...this has nothing to do with your eyes, we arent the ones observing the length contraction, its the electronic sensors. I guess the sensors are tricked by their sillicon chips right?? We only observe the data from the sensors, or are the computer screens also an illusion that makes us think that there is contraction going on?? Wait, what if you print the data out, im sure the paper deflects the light in such a way that the numbers printed on the paper change before they enter our eyes. Ahh...those damn illusions, dont you just hate them??:rofl:
No, I'm going to correct you. It only appears to be shorter. The physical length of an object traveling at relativistic speeds is always there.
By true lenght, I'm referring an object measured while on the ground or table.
Humm...you keep saying this without any actualy evidence or data. Its funny to see you say something that is consistent with all observations is wrong and an illusion, and yet you have nothing to actually support your arguement. And please dont quote again with something that has to do with our eyes and illusions.
They are measruing wrong. No lenght is lost due to motion. That's just stupid. Magically that length returns when an object is decelerated to non-relativistic speeds. No, it was always there. I'm pretty sure this has to do with the human eye. TRIANGLES!! The whole formula is derived from the transformation of triangles. I'm pretty sure if you were to mess with it, you could get at the method the human eye uses to measure things.
Why is it an eye trick? Ok, take an object with two points. The point at the head end is point A, while the point at the back end is point B. This object, at rest, has a length of AB. Give this object a velocity that is non-relativistic, and your eyes notice no drastic affects in measuring the length. Give it relativistic speeds, and your eyes notice a huge difference. When it tries to calculate the distance from A to B it is smaller than what the distance is at rest. When point A crosses the eye, almost immidiately point B crosses the same path A has just crossed. Thus making measurment SEEM contracted. No length contraction is taking place.
This doesnt help your case at all and doesnt counter any part of what Tom said in the quote you quoted. Your arguement again has to do with the way the eye sees things, which is not the case. We dont know length contraction is true because we observe with our EYES something moving at relativistic speeds. I mean...WTF? We cant even make out details on a car moving by on a highway...and thats like 60mph, oh soooo relativistic isnt it?!?:rofl:
Anyways...you cant use "illusions with eyes" as a way to defend your case because your eyes only play a role in reading data on a computer or a piece of paper.
Btw...Tom, take it easy, I know the rage you are feeling from such arguements, I feel the same way.:smile:
russ_watters
Aug23-04, 07:34 AM
Minor nitpick - these two statements contradict each other: If something is measured to be shorter, then it is shorter. Measurements are what tell us what is real.
...there is no "real" length of objects. I know what you mean, but I think it may be less confusing to others if the second statement read 'every measured length of objects is "real."' You mean there is no single real length and a bunch of illusions.
russ_watters
Aug23-04, 07:41 AM
Time contraction is also an illusion. Time only seems slower at high velocities, because our eyes can't measure things as fast as it can moving at non-relativistic speeds. This lag in the eye's calculation gives the illusion that time is running slower. How do our eyes effect the tick rate of clocks on GPS satellites?They are measruing wrong. Explain this: are you saying that every scientist who accepts the validity of Relativity is wrong? Are you saying every scientist who uses it is wrong?
GPS satellites have their clock tick rates calibrated according to Relativity prior to launch. This allows the clocks to stay in sync with clocks on the ground. How is this possible if the scientists are screwing up? Dumb luck?
As others have noted, you can program a computer to do all of this for you and give you the answer: how can human eyes affect the operation of computers?
employee #416, do you realize the implications of what you are saying? Its absurd. This whole issue boils down to you refusing to accept reality at face value because you don't like how reality is.
i understand what each of you is saying. both sides make very good points. some sides better points than others. you have to keep in mind that the length contracts only from the point of view of the stationary object. thats where the disagreement comes from. the ship looks shorter because it is shorter from the point of view of the lattes. the measurements from the equipment are correct from their point a view. the measurement are taken from a point in time. at that point in time the ship will measure to be shorter than its real length. but from the point of view of the ship it length has not changed so the equipment on the ship will say that same thing that it is in fact the same length as when it was stopped. it all matters on the point of view.
hence the name 'relativity'
Tom Mattson
Aug23-04, 01:06 PM
Heh, don't babble to me about what I'm denying and what I'm accepting. In the end, you are right though. :biggrin:
The only one here babbling is you.
Time contraction is also an illusion. Time only seems slower at high velocities, because our eyes can't measure things as fast as it can moving at non-relativistic speeds. This lag in the eye's calculation gives the illusion that time is running slower. This may not be relevant, but I'll take a stab at it. Turn on a strobe light. How does everything look in motion? Slower than it actually is, eh? Our eyes are tricked. We measure things only if visible. If things go in and out of visiblity the eye measure slower than normal. This is an illusion, but we know that time is the same, right?
I repeat: Our eyes have nothing to do with it. When time dilation is measured in muon decay, the time of creation is recorded, and the time of decay is recorded. The particle lives longer in the lab frame than it does in its rest frame. And no, the decay is not too fast for the equipment.
Particle phyisicists use time dilation every day to prolong the lifetime of unstable particles so that they can study them. But once again, here you are, the arrogant, ignorant internet bozo, thinking that you know better than the people who work with it every day, when you have never even studied it once.
How can we rely on equations, that are derived from methods our eyes use for measurements? Our eyes do not measure everything accurately. If something is too fast for our eyes to measure, our eye distorts it. If an object is not moving, our eye is not accurate in measuring any dimension of that object. It's all estimated, until a tool for measuring is pulled out for clarity.
Our eyes don't take the measurements in modern physics. Why are you ignoring me?
An object has a length of 100cm.
Correction: An object has a length of 100cm in its rest frame.
It is traveling at relativistic speeds. Lets make that speed .95c. It appears to be shorter or is shorter?
It is shorter in the frame of the person watching the object fly by. It is still 100 cm in its rest frame.
I'd go with the former.
No one cares what you would go with. All experimental confirmations of SR contradict you.
That's why you are a crackpot.
Length does not just disappear into thin air.
The universe is not oblgated to behave according to your preconceived notions.
The true length will ALWAYS be there.
Correction: There is no "true length" of any object.
The time experienced by that moving object is the same as a person in a difference reference frame. It just seems slower.
No, it is slower.
No, I'm going to correct you.
Again, your arrogance is absolutely staggering. What on Earth makes you think you know anything about this? You have very clearly not studied it.
It only appears to be shorter. The physical length of an object traveling at relativistic speeds is always there.
Wrong. There is no preferred frame of reference, and so there is no true "physical length" of an object. You are just clinging to a faulty view of space and time that was used by Newton and is now known to be false.
By true lenght, I'm referring an object measured while on the ground or table.
That is called the proper length, but there is nothing special about it. The idea of the length of an object has no meaning apart from specifying its state of motion.
They are measruing wrong. No lenght is lost due to motion. That's just stupid.
Oh, well now I'm convinced. :rofl:
I'll just scrap all of those experimental tests of relativity because, "that's just stupid".
Learn to formualte an argument, kid. :rolleyes:
Magically that length returns when an object is decelerated to non-relativistic speeds. No, it was always there.
Wrong. The length contraction formula applies at all speeds, not just relativistic speeds.
I'm pretty sure this has to do with the human eye.
I've already told you this is wrong, so the question is, why the hell are you persisting in it?
TRIANGLES!! The whole formula is derived from the transformation of triangles.
You are hopeless.
First, you ask me for a link that contains the derivation of these phenomena, and I gave it to you. You have obviously not even looked at it, because it very clearly shows how the Lorentz transformation is derived from the postulates of relativity and Maxwell's electrodynamics.
"TRIANGLES!!" Pfffft. Get a clue.
I'm pretty sure if you were to mess with it, you could get at the method the human eye uses to measure things.
I'm absolutely sure that you have no idea of what you're talking about.
Why is it an eye trick?
It isn't an eye trick.
Ok, take an object with two points. The point at the head end is point A, while the point at the back end is point B. This object, at rest, has a length of AB. Give this object a velocity that is non-relativistic, and your eyes notice no drastic affects in measuring the length. Give it relativistic speeds, and your eyes notice a huge difference. When it tries to calculate the distance from A to B it is smaller than what the distance is at rest. When point A crosses the eye, almost immidiately point B crosses the same path A has just crossed. Thus making measurment SEEM contracted. No length contraction is taking place.
Wrong. Look at the Lorentz transformation, and you'll see no reference is made to human eyes, human minds, or the means of measurement.
You keep posting this same garbage, and I keep telling you that it is not reflective of relativity at all. Why do you do that? It is just not rational. You say that you want to be a member of this Forum, and you know that we do not allow unsubstantiated nonsense here. So why is that all you ever post? It makes no sense.
Tom Mattson
Aug23-04, 01:11 PM
Minor nitpick - these two statements contradict each other: I know what you mean, but I think it may be less confusing to others if the second statement read 'every measured length of objects is "real."' You mean there is no single real length and a bunch of illusions.
OK, I'll explain.
If something is measured to be shorter, then it is shorter. Measurements are what tell us what is real.
And this is what is "real": The length of an object is depends on its state of motion relative to an observer. It is not a determinate quantity until its state of motion relative to an observer is specified.
...there is no "real" length of objects.
Meaning that since the length of an object is determined by its state of motion relative to an observer, and since there is no preferred reference frame, it cannot be said that the length measured in any reference frame is any more "real" than that measured in any other frame. All reference frames have an equally valid experimental point of view.
Note: some people *think* they may have found a change in the fine structure constant. This hasn't been widely accepted, and the magnitude of the supposed change is very small - on the order of .001 percent. Not enough to fuel any visions of "galactic superhighways" even if it is true (and it's probably just a very small measurment error of some sort).AFAIK, there are two types of observation which have been done, to see if alpha is varying over cosmological time (roughly, billions of years) - Oklo and astronomical. The former refers to a natural reactor, in uranium ore in Africa; from an analysis of the decay products, alpha has been shown to be constant to 1 part in 10 million, over a billion years or three. The astronomical observations are of several kinds; the most accurate - in several senses - show that alpha has not changed by more than 1 part in ~100,000, over ~10 billions years. There were some earlier studies, with lower accuracy, which could be interpreted as evidence for a small time variation; these observations used a technique that requires a rather long chain of calculations and many inputs (so the results were always in some doubt).
employee #416, I see that you have a different opinion from many other posters here; can you point to experimental evidence that supports your opinion? In particular, how are the muon decay experiments, and the actual functioning of the GPS system consistent with your opinion? No hand-waving please, just the numbers and the math.
Alkatran
Aug23-04, 06:00 PM
Oh fun fun, crackpot smashin time
Heh, don't babble to me about what I'm denying and what I'm accepting. In the end, you are right though. :biggrin:
Time contraction is also an illusion. Time only seems slower at high velocities, because our eyes can't measure things as fast as it can moving at non-relativistic speeds. This lag in the eye's calculation gives the illusion that time is running slower. This may not be relevant, but I'll take a stab at it. Turn on a strobe light. How does everything look in motion? Slower than it actually is, eh? Our eyes are tricked. We measure things only if visible. If things go in and out of visiblity the eye measure slower than normal. This is an illusion, but we know that time is the same, right?
Maybe things appear to go slower lalalla bu it doesn't matter: The effect is getting larger. The objects continue to move slower/faster through time and the gap between them increases. Think of two clocks, one is stationary and one is moving at near lightspeed. Let's say when they're a lightyear apart, they're synchronized (in the rest frame with Clock 1, of course). By the time Clock 2 meets Clock 1, Clock 2 well have a few extra days, maybe a few extra years, depending on the speed, on it. Is that still an optical illusion? I've never seen an illusion that could rotate a clock hand 360 degrees.
How can we rely on equations, that are derived from methods our eyes use for measurements? Our eyes do not measure everything accurately. If something is too fast for our eyes to measure, our eye distorts it. If an object is not moving, our eye is not accurate in measuring any dimension of that object. It's all estimated, until a tool for measuring is pulled out for clarity.
I can guarantee you they don't use human eyes to measure particles inside a particle accelerator. There's a big slab of matter (metal?) in the way.
An object has a length of 100cm. It is traveling at relativistic speeds. Lets make that speed .95c. It appears to be shorter or is shorter? I'd go with the former. Length does not just disappear into thin air. The true length will ALWAYS be there. The time experienced by that moving object is the same as a person in a difference reference frame. It just seems slower.
Haha, just saw your post Tom Mattson. :rofl:
No, I'm going to correct you. It only appears to be shorter. The physical length of an object traveling at relativistic speeds is always there.
By true lenght, I'm referring an object measured while on the ground or table.
In a way this is true, an object can never be longer than its proper length.
They are measruing wrong. No lenght is lost due to motion. That's just stupid. Magically that length returns when an object is decelerated to non-relativistic speeds. No, it was always there. I'm pretty sure this has to do with the human eye. TRIANGLES!! The whole formula is derived from the transformation of triangles. I'm pretty sure if you were to mess with it, you could get at the method the human eye uses to measure things.
I like the "TRIANGLES!!" remark, which clears up the whole thing for me.
Just so you know, the length is always "there", the problem is that you're looking at the object skewed through time. I'll include a link for a nice explanation of this at the bottom of this post.
Why is it an eye trick? Ok, take an object with two points. The point at the head end is point A, while the point at the back end is point B. This object, at rest, has a length of AB. Give this object a velocity that is non-relativistic, and your eyes notice no drastic affects in measuring the length. Give it relativistic speeds, and your eyes notice a huge difference. When it tries to calculate the distance from A to B it is smaller than what the distance is at rest. When point A crosses the eye, almost immidiately point B crosses the same path A has just crossed. Thus making measurment SEEM contracted. No length contraction is taking place.
But this effect would be reversed if you measured B followed by A, making the object appear longer.
This is probably all jumbled up...I have school in 2 hours and I haven't slept, so whatever.
Don't worry about the lack of sleep, it would be jumbled anyways.
Here is an excellent site on special relativity (http://casa.colorado.edu/~ajsh/sr/paradox.html)
lets say there is a star 44000 lightyears away. how long will it take to get there going light speed?
lets say there is a star 44000 lightyears away. how long will it take to get there going light speed?
Assuming that you mean that according to Earth-frame measurements the star is 44000 lightyears away, and that you are sailing by in a rocket at close to c (say 0.99c with respect to the Earth): the distance as seen by you in your rocket frame will be contracted--and it will take you about 6270 years to get there according to your rocket-frame clock.
how long from earths point of view?
Alkatran
Aug23-04, 07:08 PM
how long form earths point of view?
44 000 years, of course. (well, approximately, the earth is rotating around the sun which is rotating around the galaxy...)
Assuming that you are going at o.99c. In earths point of view, they will see your trip takes:
t_o = t\sqrt{1 - v^{2} /c^{2}}
6270y = t\sqrt{1 - 0.99c^{2} /c^{2}}
\frac {6270y}{0.141} = t
t = 44468 years
light has no rest mass. It has relativistic mass, and momentum.
6270y = t\sqrt{1 - 0.99c^{2} /c^{2}}
6270y = t\sqrt{1 - 0.9801c^{2} /c^{2}}
6270y = t\sqrt{1 - 0.9801}
6270y = t\sqrt{0.0199}
6270y = t(0.141)
\frac {6270y}{0.141} = t
t = 44468 years
what is lights relativistic mass?
6270y = t\sqrt{1 - 0.99c^{2} /c^{2}}
6270y = t\sqrt{1 - 0.9801c^{2} /c^{2}}
6270y = t\sqrt{1 - 0.9801}
6270y = t\sqrt{0.0199}
6270y = t(0.141)
\frac {6270y}{0.141} = t
t = 44468 years
got yeah! that makes sense.
listen, bino, Im not gonna sit here and spoonfeed you all night, look it up on a google search, or on another forum. Trust me, its a lot better than asking me 1000 questions and its a lot faster. Sorry for the outburst.
Assuming that you are going at o.99c. In earths point of view, they will see your trip takes:
t_o = t\sqrt{1 - v^{2} /c^{2}}
6270y = t\sqrt{1 - 0.99c^{2} /c^{2}}
\frac {6270y}{0.141} = t
t = 44468 years
Perfectly correct, of course, but the simplest way to look at it from the Earth's viewpoint is t = D/v = 44000/0.99{ yr} = 44400{ yr}.
Tom Mattson
Aug23-04, 07:36 PM
Bino,
Physics is best learned by working out problems. You're obviously curious and interested, and I think you'll benefit from this:
Special Relativity (http://www.physics.nyu.edu/hogg/sr/sr.pdf)
It's an excellent textbook in relativity, and it's free.
ok hypothetically, if i were in a ship that was going the speed of light. how long would it take to get to that star 44000 lightyears away? from the point of view of the ship.
Tom Mattson
Aug23-04, 09:27 PM
ok hypothetically, if i were in a ship that was going the speed of light. how long would it take to get to that star 44000 lightyears away? from the point of view of the ship.
It wouldn't take any time at all from that point of view. As Einstein said, the speed of light plays the role of an infinitely great speed in SR.
how is it that we can measure the speed of light if it doesnt take any time for it to get from one place to another?
Chronos
Aug23-04, 11:51 PM
how is it that we can measure the speed of light if it doesnt take any time for it to get from one place to another?It does take time for light to travel any distance, unless you are a photon. In which case time and space cease to exist. Ordinarily, I would ask what part of relativity do you not understand. In this case, I would say the answer is all of it.
what_are_electrons
Aug24-04, 12:23 AM
This thread seems to contain a lot of hypthetical ideas akin to theories. How has it survived? Perhaps the speed of our Mentors has dropped out of light speed.
ArmoSkater87
Aug24-04, 01:53 AM
light has no rest mass. It has relativistic mass, and momentum.
Actually light cant have relativistic mass because of SP equations...
m = \frac{m_0}{\sqrt{1-\frac{v^2}{c^2}}}
As you can see, if something has a rest mass(m_0) of zero, then the relativistic mass is zero as well because zero divided by anything is zero.
It wouldn't take any time at all from that point of view. As Einstein said, the speed of light plays the role of an infinitely great speed in SR.
Lightspeed is a constant finite speed, I thought this was the basis of SR.
Or is it because this...
u' = \frac{u+v}{1-\frac{uv}{c^2}}
The light from the star coming towards u at c, and you going towards it at c
u' = \frac{c+c}{1-\frac{c^2}{c^2}}
u' = \frac{2c}{0}
u' = infinity
Tom Mattson
Aug24-04, 02:00 AM
This thread seems to contain a lot of hypthetical ideas akin to theories. How has it survived? Perhaps the speed of our Mentors has dropped out of light speed.
Those who are politely asking questions are being accomodated.
Those who are rudely making unscientific assertions have been banned.
Does that answer your question?
Tom Mattson
Aug24-04, 02:09 AM
Lightspeed is a constant finite speed, I thought this was the basis of SR.
Or is it because this...
u' = \frac{u+v}{1-\frac{uv}{c^2}}
The light from the star coming towards u at c, and you going towards it at c
u' = \frac{c+c}{1-\frac{c^2}{c^2}}
u' = \frac{2c}{0}
u' = infinity
No, that's not an equation of relativity (if you're adding in the numerator, you should adding in the denominator, and the same goes for subtracting).
"c" plays the role of an infinite velocity because it is unattainable.
Actually, while the above statement is true, I shouldn't have said that it "takes no time at all" for light to travel a distance, because SR actually makes no predictions about what happens at light speed. So I officially withdraw that comment.
Tom Mattson
Aug24-04, 02:53 AM
how is it that we can measure the speed of light if it doesnt take any time for it to get from one place to another?
You have to be careful. I said that "it takes no time at all", meaning that it takes no time in the reference frame of the light. In the lab frame however, it takes a finite time, and the speed of a light pulse is easily measured by recording the position of emission, the position of detection, and the time interval between those two events.
But as I just said to Armo, I should not have said that "it takes no time at all" in the photon frame, because SR actually makes no predictions on the experimental results obtained from the photon frame. The time it takes to traverse a distance is actually undefined.
ok. from the view point of the lattes the ship has compressed because the ship is moving so fast, but from the view point of the ship the lattes is the one that is going by so fast and that is why the lattes is compressed. correct? so then from the view of light we would be moving that fast. so then from the frame of light we would be compressed. how can this be?
??? Read the book posted a while ago about special relativity. It helps a lot. If thwo abjects are in the same frame of reference, (travelling at the same speed in the same direction) then they see no difference in themselves. There is no dilation or compression.
Tom Mattson
Aug24-04, 02:11 PM
ok. from the view point of the lattes the ship has compressed because the ship is moving so fast, but from the view point of the ship the lattes is the one that is going by so fast and that is why the lattes is compressed. correct?
Not really. I kept saying before that nothing actually happens to either the ship or the rod. It's not as if some physical force is pushing on them to cause them to be shorter. They simply are shorter in other frames of reference.
so then from the view of light we would be moving that fast. so then from the frame of light we would be compressed. how can this be?
As I said, SR makes no predictions about what would be seen from an inertial frame moving at speed c. The Lorentz factor is undefined there. We can talk about things that happen in inertial frame as its speed approaches c, but if you want to keep talking about frames that move at the speed of light, then SR has no answers for you, and so neither do I.
Now if you want to talk about frames moving with speeds less than c, we can get somewhere.
but from the frame of reference of the light we would be the ones moveing at the speed of light. right? you know when your driving in a car the objects closer tothe car look like there are moving faster than the objects farther away. idont remember what thats called but why doesnt that have an effect on the Lorentz equation?
russ_watters
Aug25-04, 07:40 AM
but from the frame of reference of the light we would be the ones moveing at the speed of light. bino, Tom just said under SR, there is no such thing as "the frame of reference of the light."
i know what he said. its just that there has to be a frame of reference for light. that is what i dont understand.
when traveligna th the speed of light, mass becomes infinite, time becomes 0, and distance becomes 0. So in essence, you are everywhere and anywhere in the universe at once. This is why it is hard to talk about lights frame of reference. Do you understand now.
Tom Mattson
Aug25-04, 10:30 PM
i know what he said. its just that there has to be a frame of reference for light. that is what i dont understand.
There isn't a reference frame for light. That is, there is no frame in which light can be considered at rest. As I noted earlier, and as Einstein himself noted in his original paper, c plays the role of an infinite speed in SR.
when traveligna th the speed of light, mass becomes infinite, time becomes 0, and distance becomes 0. So in essence, you are everywhere and anywhere in the universe at once.
You have to be a bit careful when talking about what happens at light speed. This is the same mistake I made earlier when I got careless and said that it "takes no time at all" for a photon to travel a distance, from it's own frame. The reason this is not right is that the Lorentz factor has a "zero denominator" when v=c. SR literally makes no prediction about what happens at v=c, because the Lorentz transformation is undefined there.
is it that there in on frame of reference for light or is it that we just dont have equation to predict lights frame of reference? and what about this? you know when your driving in a car the objects closer tothe car look like there are moving faster than the objects farther away. i dont remember what thats called but why doesnt that have an effect on the Lorentz equation?
is it that there in on frame of reference for light or is it that we just dont have equation to predict lights frame of reference?
According to special relativity there is no possible reference frame for light.
and what about this?
you know when your driving in a car the objects closer tothe car look like there are moving faster than the objects farther away. i dont remember what thats called but why doesnt that have an effect on the Lorentz equation?
The effect you describe here is an optical illusion called the "parallax effect". It has no bearing on the Lorentz transformations, because those equations relate actual measurements not just how things "appear". The predictions of relativity are real effects, not just illusions of perception.
For more information on the parallax illusion, see this: http://www.campusprogram.com/reference/en/wikipedia/p/pa/parallax.html
Alkatran
Aug26-04, 03:36 PM
Light moves relative to everything at c. Light moves relative to itself at c. But since light has no time...
It's all very confusing, non-logical, random, lalalala... you know all that fun stuff that happens when you divide by 0.
we astablished in earlier conversation that neither the ship nor the lattes are actually getting smaller that they only appear to be getting smaller from each others view. and with parallax all objects move backward relative to the car, and for nearby objects the speed of change in direction is what the observer considers the normal consequence of his own movement; however, for distant objects the backward change in direction is slow and much less obvious than the forward change in direction relative to nearby objects. It seems as if distant objects move a little slower. it seems that it should have an effect.
Chronos
Aug27-04, 04:20 PM
we astablished in earlier conversation that neither the ship nor the lattes are actually getting smaller that they only appear to be getting smaller from each others view. and with parallax all objects move backward relative to the car, and for nearby objects the speed of change in direction is what the observer considers the normal consequence of his own movement; however, for distant objects the backward change in direction is slow and much less obvious than the forward change in direction relative to nearby objects. It seems as if distant objects move a little slower. it seems that it should have an effect.Try reading this and see if it helps. It gives a nice history of physics leading up to relativity, the problems earlier researchers encountered, and how relativity solved them.
http://www.mathpages.com/rr/s2-05/2-05.htm
we astablished in earlier conversation that neither the ship nor the lattes are actually getting smaller that they only appear to be getting smaller from each others view.
I don't know what you mean by "appear". You seem to think that the SR length contraction is an optical illusion in the same sense that the parallax effect is. Not true. All measurements of objects will confirm that they actually do have a shorter length when observed from a frame in which they are moving. They don't just appear to be shorter; in the moving frame they are shorter.
On the other hand, if you mean that the length of a ship in its own rest frame doesn't change just because a moving observer happens to pass by: That's certainly true! :smile: (SR is strange, but not that strange.)
and with parallax all objects move backward relative to the car, and for nearby objects the speed of change in direction is what the observer considers the normal consequence of his own movement; however, for distant objects the backward change in direction is slow and much less obvious than the forward change in direction relative to nearby objects. It seems as if distant objects move a little slower. it seems that it should have an effect.
Parallax, on the other hand, is just a perceptual illusion. Nearby objects merely appear to go by faster compared to background objects. But clearly the actual speed of the objects with respect to you does not depend on the angle of view. Once you understand what causes the parallax illusion, you can account for it. The SR effects depend only on the actual speed, so parallax has no effect.
The object isn't "getting smaller". If a rod is moving, then it is smaller than it is in its own rest frame. But nothing actually happens to the rod. It's not as though the rod is physically shrinking by some compressive force.
therefor it just appears contracted from the view of the object at rest.
therefor it just appears contracted from the view of the object at rest.
I still don't understand what you mean by "appears". I can only assume you mean to contrast "appears contracted" with "really is contracted".
Note that Tom does not say the rod "appears" contracted, he says "If a rod is moving, then it is smaller than it is in its own rest frame." (Emphasis mine.)
Perhaps we are arguing semantics, but I think it's important. An analogy: You look into a spherical mirror, your image is distorted. Is the distortion real or apparent? I assume you would agree that you only appear distorted due to how the mirror reflects light. On the other hand, what if I wish to measure the length of my desk? I apply a ruler and get a certain number of centimeters. Is the length of my desk the actual length (in my rest frame, of course) or is it just the apparent length? Again I assume you would agree that it makes sense to say that the measured length is the actual length, not just an illusion or a trick of light.
Now of course there are practical difficulties in measuring the length of desk that is moving past you at an appreciable fraction of light speed--but lets do the thought experiment anyway. Pretend we have incredibly accurate clocks and detectors. We arrange to measure the position of each end of the moving desk at a precise instant of time according to our (stationary) clocks and metersticks. This is what I mean by the measuring the length of the moving desk. We find that its length is smaller compared to what it would measure if it were at rest. I see no justification for saying that the length of the desk merely "appears" smaller: by any normal definition of "length" it really is smaller.
This contraction is a property of space-time; there is no physical force that reaches out and compresses the desk. But it is real nonetheless.
pervect
Aug28-04, 01:23 PM
I still don't understand what you mean by "appears". I can only assume you mean to contrast "appears contracted" with "really is contracted".
This discussion is starting to get a bit philosophical, but I thought I'd trhow in my $.02, in the hope that it well help more than confuse the issue (we'll have to see how it works out).
If one defines a "real" property of a body as a property that does not depend on the observer, one that is intrinsic only to the body itself, then space and time both fail to be "real" properties. The Lorentz interval, however, which is a mathematical combination of both space and time, does not fail this test, so it qualifies as "real".
This puts space and time in an interesting philosophical situation. Neither one is "real" by itself, but when combined properly, they form a "real" entity.
So one might say that space and time are illusions, as many mystics have done. And to some extent this is correct. On the other hand, it's a bit hard to explain how two illusions, combined together, form something that is real, if one takes this philosophical approach.
Fortunately, however, it usually doesn't matter which quantites one considers to be "real" when doing physics. I will note, however, that it's generally easier to avoid making mistakes by focusing on the quantites which don't change (are invariant) when doing calculations. In relativity, this approach would be to focus on the Lorentz interval.
Tom Mattson
Aug28-04, 01:32 PM
therefor it just appears contracted from the view of the object at rest.
The rod is shorter than its proper length in the moving frame.
How many times are you going to make me say it?
This discussion is starting to get a bit philosophical, but I thought I'd trhow in my $.02, in the hope that it well help more than confuse the issue (we'll have to see how it works out).
its not philosophical at all. Its Special Relativity.
The rod is shorter than its proper length in the moving frame.
I thought it had proper length in the moving frame. To an outside observer it is shorter. Relative to it's own frame, the rod is proper length.
Tom Mattson
Aug28-04, 02:16 PM
I thought it had proper length in the moving frame.
The rod is its proper length only in a frame that is at rest relative to the rod. When I say that the rod is shorter "in the moving frame", I mean that the rod is moving, and the observer who measures the length is watching it go by.
To an outside observer it is shorter. Relative to it's own frame, the rod is proper length.
That's right.
Ok, I see what you were saying now. I probably just have poor reading comprehension skills. :rofl:
the rod is shorter when it is moving but only to the at rest observer. but if we are going the same speed as the rod then we know that it is not actually shorter.
the rod is shorter when it is moving but only to the at rest observer. but if we are going the same speed as the rod then we know that it is not actually shorter.
Be carefull with the word 'actually'. If you do enter the frame of reference of the rod (light speed), you lill measure it to be rest length, but it you do not enter its frame, and you are at rest while iti s moving, the rod is then 'actually' shorter, meaning it is shorter.
Tom Mattson
Aug28-04, 04:26 PM
the rod is shorter when it is moving but only to the at rest observer. but if we are going the same speed as the rod then we know that it is not actually shorter.
What is it with you?
DocAI just described how the measurement process would be carried out. You simultaneously record the locations of the endpoints of a rod as it moves by, and subtract the coordinates. The distance between the points is the length of the rod, and that distance varies with speed.
Haven't you looked at that textbook yet?
if a ship travels from earth moving at .99c to a destination 44000 lightyears away. from the view of the ship the trip would take 6270 years but from the view of earth it would take 44468 years. but from the view of the ship the earth would be moving at .99c. then wouldn't those numbers be switched?
Tom Mattson
Aug28-04, 04:38 PM
if a ship travels from earth moving at .99c to a destination 44000 lightyears away. from the view of the ship the trip would take 6270 years but from the view of earth it would take 44468 years. but from the view of the ship the earth would be moving at .99c. then wouldn't those numbers be switched?
No, because the distance between the Earth and the destination is shorter in the ship frame.
i have no problem saying that the length of the ship will be measured shorter. i completely agree with that. but the length is not physicaly getting smaller.
Tom Mattson
Aug28-04, 04:45 PM
i have no problem saying that the length of the ship will be measured shorter. i completely agree with that. but the length is not physicaly getting smaller.
At last, something I can agree with!
The rod is not physically getting smaller--it simply is smaller than it is in its rest frame.
right
like i said earlier
you have to keep in mind that the length contracts only from the point of view of the stationary object. thats where the disagreement comes from. the ship looks shorter because it is shorter from the point of view of the lattes. the measurements from the equipment are correct from their point a view. the measurement are taken from a point in time. at that point in time the ship will measure to be shorter than its real length. but from the point of view of the ship its length has not changed so the equipment on the ship will say that same thing that it is in fact the same length as when it was stopped. it all matters on the point of view.
onward and forward.
the ship moving at .99c, 44000 lightyears away. and the earth moving at .99c, 44000 lightyears away. those are the same, the only difference is what is moving from each others perspective.
the ship moving at .99c, 44000 lightyears away. and the earth moving at .99c, 44000 lightyears away. those are the same, the only difference is what is moving from each others perspective.
Not true. The two frames will disagree as to the distance, since they are in relative motion.
i dont mean that they are moving at the same time. sorry. i mean that the ship moving away from earth is the same as the earth moving away from the ship.
Tom Mattson
Aug28-04, 05:23 PM
right
like i said earlier
onward and forward.
the ship moving at .99c, 44000 lightyears away. and the earth moving at .99c, 44000 lightyears away. those are the same, the only difference is what is moving from each others perspective.
No, and I already answered that:
No, because the distance between the Earth and the destination is shorter in the ship frame.
pervect
Aug28-04, 05:31 PM
its not philosophical at all. Its Special Relativity.
Guess my remarks didn't resolve much.
A statement about what is "actually" happening or what is "really happening" tends to be a sign that a philosophical discussion is occuring.
Generally, philosophy is pretty harmless (except for being a potential source of undending debate), and it usually doesn't matter what one thinks is "real", and what one thinks is "appearance". There are a few exceptions, basically they occur when someone does philosophy badly.
An example of bad philosophy would be to insist that lengths don't change with motion, because of some philosphical belief about them being real.
Another example of bad philosophy would be to claim that time and space are illusion, and then to turn around ans inconsistently start talkig about the "true" length, or the "real" time.
i dont understand how they could be different? one is going .99c for 44000 lightyears while the other is at rest. and the same goes for the other.
Tom Mattson
Aug28-04, 05:34 PM
i dont understand how they could be different? one is going .99c for 44000 lightyears while the other is at rest. and the same goes for the other.
The distance between Earth and destination is different for the two observers for the exact same reason the length of a rod is different in different frames: Length contraction.
Look at the Lorentz transformation, and you can derive it for yourself.
hey bino, how many posts do you have on this thread, like 80? lol. Just read the book Tom posted for you earlier, then come with the questions.
i understand that
The distance between Earth and destination is different for the two observers for the exact same reason the length of a rod is different in different frames: Length contraction.
what i dont understand is in the point of view from the earth the ship is moving but in the point of view from the ship the earth is moving. right? so then from the point of view of the ship the earth would then take 44468 years to go 44000 lightyears. and from the point of view from the earth the trip only took 6270 years.
i understand that
what i dont understand is in the point of view from the earth the ship is moving but in the point of view from the ship the earth is moving. right? so then from the point of view of the ship the earth would then take 44468 years to go 44000 lightyears. and from the point of view from the earth the trip only took 6270 years.
no, in both points of wiew, it takes the other 6270 years to do the trip, but one of them is wrong. The person in motion is wrong and finds out he is wrink when the ship stops.
ok lets think about it this way.
the starting point =
a b
< >
a< --------------------- >b
resting 44000lightyears moving
from the point of view of a, b has moved 44000 lightyears away at .99c.
now back to start =
a b
< >
a< --------------------- >b
moving 44000lightyears resting
from the point of view of b, a has moved 44000 lightyears away at .99c.
how is that not the same?
nenad what are you talking about?
ok lets think about it this way.
the starting point =
a b
< >
a< --------------------- >b
resting 44000lightyears moving
from the point of view of a, b has moved 44000 lightyears away at .99c.
now back to start =
a b
< >
a< --------------------- >b
moving 44000lightyears resting
from the point of view of b, a has moved 44000 lightyears away at .99c.
how is that not the same?
Oh my God, We have been through this like 1000 times. Do you not listen. To BOTH observers, what you are saying is true, but one of them is WRONG since one of them is not in real motion. Think of it this way: The way time/length/mass knows who is in motion is the one who accelerates. Both observers wee that the other observers time is slowing down, but one of them is Wrong.
Do you understand now?
pervect
Aug28-04, 11:47 PM
Oh my God, We have been through this like 1000 times.
I dunno, I have a suspicion that bino is pushing is own "hidden" agenda, as opposed to really trying to learn relativity, but I tend to be rather grumpy and suspicious a lot of the time.
you figured me out, pervect. im on a secret mission to a hidden planet 44000 lightyears away and i need to tell my wife when to expect me home for dinner.
oh shoot i guess it's not a secret anymore.
ok lets think about it this way.
.....
from the point of view of a, b has moved 44000 lightyears away at .99c.
.....
from the point of view of b, a has moved 44000 lightyears away at .99c.
how is that not the same?
You don't seem to be catching on to the fact that the viewpoints are not symmetric. Since the two frames are in relative motion, they measure different distances. So just saying they are "44,000 ly apart" means nothing unless you specific who is measuring what.
Let's try to be very clear as to what's going on. Let's say that exactly 44,000 ly from earth there is a marker floating in space. The marker is at rest with respect to the earth. The distance is measured from the earth's frame. Make sense so far? A rocket heading toward earth at 0.99c passes the marker on its way.
Let's describe the trip from marker to earth from (1) the earth frame and (2) the rocket frame. We've analyzed this to death, so I'll summarize:
From the earth frame:
Distance traveled by rocket: 44,000 ly
Speed of rocket: 0.99c
Time of travel: t = D/v = 44,444 years
From the rocket frame:
Distance traveled by earth: 44,000 x 0.141 = 6204 ly (Lorentz contraction)
Speed of earth: 0.99c
Time of travel: t = D/v = 6,267 years
Note that to the rocket observer, the distance from marker to earth is only 6204 ly. This is key to understanding what's going on.
Note that having a marker, as I introduced above, is a key to an unambiguous statement of the problem. Just saying "The rocket is a distance X from earth" is not good enough, since it gives a distance without saying who measured what.
ok. that makes sence to me. but from the frame of the rocket it is at rest and that the marker and the earth are moving?
but from the frame of the rocket it is at rest and that the marker and the earth are moving?
That is correct.
so then would not the numbers be swiched?
HallsofIvy
Aug29-04, 03:41 PM
That was exactly what Doc Al did:
From the earth frame:
Distance traveled by rocket: 44,000 ly
Speed of rocket: 0.99c
Time of travel: t = D/v = 44,444 years
From the rocket frame:
Distance traveled by earth: 44,000 x 0.141 = 6204 ly (Lorentz contraction)
Speed of earth: 0.99c
Time of travel: t = D/v = 6,267 years
ok so from that. i got that the ship would arrive to earth 38177 years before anyone on earth noticed the ship was here. or is it that everyone on the ship is 38177 years younger than what they would be on earth? why would the lorentz contraction take affect only from the ships viewpoint?
ok so from that. i got that the ship would arrive to earth 38177 years before anyone on earth noticed the ship was here.NO
or is it that everyone on the ship is 38177 years younger than what they would be on earth? YES
why would the lorentz contraction take affect only from the ships viewpoint?Because the ship is the one in motion, NOT the earth.
So just saying they are "44,000 ly apart" means nothing unless you specific who is measuring what.
if they both are sitting at rest 44000 lys from each other the distance is the same from both points of view. right? say one of them can instantly go straight to .99c. now as soon as that one starts the distance for that one shrinks. but it stays the same for the one that stays at rest.
ok so from that. i got that the ship would arrive to earth 38177 years before anyone on earth noticed the ship was here.
No. That's kind of silly, isn't it?
or is it that everyone on the ship is 38177 years younger than what they would be on earth?
No. It's not so simple. The rocket and the earth would disagree as to what time the rocket passed the marker.
why would the lorentz contraction take affect only from the ships viewpoint?
What makes you think that the Lorentz contraction only works from the ship's viewpoint? In this example, only one distance was given: 44,000 km, measured from the earth. So, only the rocket sees that "length" as moving. But the Lorentz transformation certainly works both ways. For example, if the rest length of the rocket was length L, the earth observers would see it contracted to only (0.141)L.
Because the ship is the one in motion, NOT the earth.
but from the point of view of the ship the earth is in motion and not the ship.
but from the point of view of the ship the earth is in motion and not the ship.
Of course. From the earth frame, the rocket moves; from the rocket frame, the earth moves.
So, only the rocket sees that "length" as moving. But the Lorentz transformation certainly works both ways. For example, if the rest length of the rocket was length L, the earth observers would see it contracted to only (0.141)L.
so then from the rockets view everything is shrunk except itself but from earths view only the ship is shrunk?
so then from the rockets view everything is shrunk except itself but from earths view only the ship is shrunk?
No. It's simple: Every frame measures anything moving as being shorter that it would be if it wasn't moving. That's true for the rocket, the earth, everybody. So, if you want to know if something is "shrunk" from a certain viewpoint, just ask "Is it moving from that viewpoint?". If the answer is yes, then it is measured to be "shrunk"; if no, then not shrunk. Got it?
so from the view point from earth only the ship is moving but from the view point of the ship everything is moving. i think that is what i was not grasping.
An object is hurled towards a another object that has emitted light. The object that is traveling towards the emitting source has a velocity of .5c. Does the wavelength of light shift and become red? I was just wondering. After this is answered, I have another question. :redface:
An object is hurled towards a another object that has emitted light. The object that is traveling towards the emitting source has a velocity of .5c. Does the wavelength of light shift and become red? I was just wondering. After this is answered, I have another question. :redface:Observers on each object will record EM emissions (e.g. the yellow sodium D lines) from the object they see as moving towards them as being 'blueshifted' wrt the same emissions at rest wrt themselves.
No. It's not so simple. The rocket and the earth would disagree as to what time the rocket passed the marker. Doc Al, I dont understand what you're talking about, it would be this simple. The peson on the rocket would age much less than if he was on earth during the trip.
Doc Al, I dont understand what you're talking about, it would be this simple. The peson on the rocket would age much less than if he was on earth during the trip.
It's certainly true that the earth observers will measure the time for the trip to be longer (44,444 yrs) than the time measured by the rocket observer (only 6267 yrs). Since the rocket observer carries his clock with him, that 6267 yrs can certainly be thought of as an "age" of someone: imagine that someone (Methuselah?) was born in the rocket at the exact moment that the rocket passed the marker. How old would that person be when the rocket passes earth? Everyone would agree that the person would be 6267 years old (according to his own calendar and biological clock).
But where is the corresponding person (twin?) in the earth frame? And how old will he be when the rocket passes earth? According to who? Things are tricky now since we first have to agree on when that person was born. Let's be very clear. Let's say that a person is born on earth exactly at the moment that the rocket passes the marker. But according to who? The two frames will disagree as to when the rocket passed the marker!
Simultaneity of space-separated events is frame-dependent.
Let's work out the details. Let's put a clock on that marker, synchronized with the earth clock. That's no problem, since they are in the same frame. Let's assume that according to the earth frame the rocket passes the marker exactly when the clocks read zero. Will the rocket observer agree? No! To the rocket observer the earth and marker clocks are wildly out of synch! To the rocket observer, the clock (calender, I guess) on earth reads 43,560 yrs when the rocket passes the marker. Since the rocket arrives when the earth clock reads 44,444 yrs, the rocket observer would say that Methuselah is only 884 earth-years old. This makes sense, since the rocket sees the earth clocks as running slow. Of course, the earth frame will drag out a 44,444 year old geezer and say that he was born exactly the moment that Methuselah was. Of course the rocket guys would laugh--they know that this earth man was born way before they came anywhere near that marker, long before Methuselah was born.
I hope this makes sense to you. (And that I explained it correctly.)
The moral of this story: There's a reason that the infamous twin "paradoxes" of SR always arrange for the twins to start out together (just like real twins!), then go their merry ways, and then be reunited. After all is said and done, once they are reunited there is no frame-dependent ambiguity. Every observer in every frame will agree as to which twin is older.
so the if they switch twins and took the older one back to the marker. would they then become the same age if methuselah stayed on earth?
Observers on each object will record EM emissions (e.g. the yellow sodium D lines) from the object they see as moving towards them as being 'blueshifted' wrt the same emissions at rest wrt themselves.
Ok, I can agree with that. Now, throw in an outside observer. He observes the one object headed towards the light source. The object heading towards the light source sees the light as shifted to a different frequency. Does the man see the light as its original frequency and wavelength?
Now, throw in an outside observer. He observes the one object headed towards the light source. The object heading towards the light source sees the light as shifted to a different frequency. Does the man see the light as its original frequency and wavelength?
The shift in frequency seen by any observer depends on the relative velocity of the source with respect to that observer.
so the if they switch twins and took the older one back to the marker. would they then become the same age if methuselah stayed on earth?
Sorry, but I really have no idea what you are asking.
im asking if once the rocket arrived on earth if the twin that was on earth then got on the ship and the twin that was on the rocket switched places. then the ship flew back to the marker if the twins would then become the same age again.
It's certainly true that the earth observers will measure the time for the trip to be longer (44,444 yrs) than the time measured by the rocket observer (only 6267 yrs). Since the rocket observer carries his clock with him, that 6267 yrs can certainly be thought of as an "age" of someone: imagine that someone (Methuselah?) was born in the rocket at the exact moment that the rocket passed the marker. How old would that person be when the rocket passes earth? Everyone would agree that the person would be 6267 years old (according to his own calendar and biological clock).
But where is the corresponding person (twin?) in the earth frame? And how old will he be when the rocket passes earth? According to who? Things are tricky now since we first have to agree on when that person was born. Let's be very clear. Let's say that a person is born on earth exactly at the moment that the rocket passes the marker. But according to who? The two frames will disagree as to when the rocket passed the marker!
Simultaneity of space-separated events is frame-dependent.
Let's work out the details. Let's put a clock on that marker, synchronized with the earth clock. That's no problem, since they are in the same frame. Let's assume that according to the earth frame the rocket passes the marker exactly when the clocks read zero. Will the rocket observer agree? No! To the rocket observer the earth and marker clocks are wildly out of synch! To the rocket observer, the clock (calender, I guess) on earth reads 43,560 yrs when the rocket passes the marker. Since the rocket arrives when the earth clock reads 44,444 yrs, the rocket observer would say that Methuselah is only 884 earth-years old. This makes sense, since the rocket sees the earth clocks as running slow. Of course, the earth frame will drag out a 44,444 year old geezer and say that he was born exactly the moment that Methuselah was. Of course the rocket guys would laugh--they know that this earth man was born way before they came anywhere near that marker, long before Methuselah was born.
I hope this makes sense to you. (And that I explained it correctly.)
The moral of this story: There's a reason that the infamous twin "paradoxes" of SR always arrange for the twins to start out together (just like real twins!), then go their merry ways, and then be reunited. After all is said and done, once they are reunited there is no frame-dependent ambiguity. Every observer in every frame will agree as to which twin is older.
I still don't get why you chose to make things so compliaced. In the end, the observer on the rocket ages less than the observer on earth. There is not assumptions or ambiguity.
how do they measure the length of the moving object? i know they have an event happen simultaneously but how do they then measure that?
how do they measure the length of the moving object? i know they have an event happen simultaneously but how do they then measure that?
If you know the moving objects speed and rest length, then you can measure its moving length using:
d_{rest} = d_{moving} \sqrt{1-v^{2} / c^{2}}
quibton
Aug31-04, 10:53 PM
Bino says "Each claims that the other is shorter, and that nothing is out of the ordinary with regards to their own length. how can it be that the length of an object can get shorter to someone but not to someone else? i could understand it if it only looks shorter to the observer. it is like looking at a barn from 1ft away and looking at it from 200 ft away. the barn is smaller from farther away."
The observer is quantified by a specific physics value when in "motion". This quantity revolves around what the difference means between the ability to "accelarate" in relation to the ability to be in "motion". Either relative view piont could suggest an abstract, illusionary or real effect of the barn or not even if the barn is the same from piont 1 (before calulating what it could be after). Relativity was discovered to exaplain away probably one of the most complex problems in physics i,e were is everything in relation to everything else, considering we know what those things are anyway? Acceleration is not motion. The effects of what could happen due to the "inertia" qualities of space time within an accelerated "body" relative to the outside space time effect is not entirely understood, especially in the subjective, temporal, biological human context, even if we, being a human construct of space time have allready denoted a value of it, for a certain point that represents a certain property that is used in many equations to explain it, in its final terms. Your questions are very clever. Keep asking them
Quibtonite
Claire
If you know the moving objects speed and rest length, then you can measure its moving length using:
d_{rest} = d_{moving} \sqrt{1-v^{2} / c^{2}}
yes i know this but how was this equation formed? i know that it is some how derived from time dilation. right? dont they do something with the end points.
yes i know this but how was this equation formed? i know that it is some how derived from time dilation. right? dont they do something with the end points.No. Why would you need to?
Regarding my analysis of relative "aging" for observers in different frames in the rocket-earth scenario (post #198):
I still don't get why you chose to make things so compliaced.
Get used to it. That's the way SR and the world works. It's only as "complicated" as it needs to be to accurately describe the situation.
In the end, the observer on the rocket ages less than the observer on earth.
Nonsense. You seem to think that the rocket observer is somehow the one who is really moving. Not so. SR "time dilation" works for both frames.
In post #187 you state:
Because the ship is the one in motion, NOT the earth.
Oh really? This leads me to conclude that you are missing the point of SR.
There is not assumptions or ambiguity.
You won't find any ambiguity in my analysis or in what SR states.
russ_watters
Sep1-04, 08:53 AM
yes i know this but how was this equation formed? i know that it is some how derived from time dilation. right? dont they do something with the end points. You could also measure the time it takes to pass you and divide that into the speed.
Tom Mattson
Sep1-04, 09:30 AM
You could also measure the time it takes to pass you and divide that into the speed.
You'd multiply the time by the speed.
Always check your units! :wink:
Nonsense. You seem to think that the rocket observer is somehow the one who is really moving. Not so. SR "time dilation" works for both frames.
I understand that both observers see the other as the one in motion, and the effects of SR taking effect on the other, and not themselves, but one of them is obviously wrong, and once the two observers join the same frame of reference, then the wrong observer sees that he is wrong.
russ_watters
Sep1-04, 12:28 PM
You'd multiply the time by the speed.
Always check your units! :wink: Uh, yeah - what he said. Hey, why am I not working right now?! :blushing:
I understand that both observers see the other as the one in motion, and the effects of SR taking effect on the other, and not themselves, but one of them is obviously wrong, and once the two observers join the same frame of reference, then the wrong observer sees that he is wrong.
Sorry, Nenad, that's not how SR works. Both observers make measurements with respect to their own inertial frames. Both frames are equally "correct". One is not "obviously wrong". That statement makes me think that you really do view one frame as being "right" and the other "wrong"--that's not how SR works. In fact it misses the entire point of relativity.
ok, this is the way I was taught, that the fame in motion is the frame in which canges occur such as time dilation, mass dialtion and length contraction. I was also taught that in a case with two abservers, one of them will be wrong in his assumptions that he is in motion and not the other. So youre telling me that both observers are right, and they both end up agreeing in the end with nobody changing their mind. Hmm, this makes me think. But how would the time dilation work out for both observers?(twin paradox case) They will both assume that they are aging much more than the other observer, (as a result of their assumptions that the moving frames time is slowing down)?? Just help me with this example, I will get the rest from books.
Simultaneity of space-separated events is frame-dependent.
Let's work out the details. Let's put a clock on that marker, synchronized with the earth clock. That's no problem, since they are in the same frame. Let's assume that according to the earth frame the rocket passes the marker exactly when the clocks read zero. Will the rocket observer agree? No! To the rocket observer the earth and marker clocks are wildly out of synch! To the rocket observer, the clock (calender, I guess) on earth reads 43,560 yrs when the rocket passes the marker. Since the rocket arrives when the earth clock reads 44,444 yrs, the rocket observer would say that Methuselah is only 884 earth-years old. This makes sense, since the rocket sees the earth clocks as running slow. Of course, the earth frame will drag out a 44,444 year old geezer and say that he was born exactly the moment that Methuselah was. Of course the rocket guys would laugh--they know that this earth man was born way before they came anywhere near that marker, long before Methuselah was born.
I hope this makes sense to you. (And that I explained it correctly.)
Doc Al, I think I got it. Since the rocket observer is in motion, simoutanaety in a rest frame is not simoutaneous to him. The he passes the marker, the signal from the marker would read 0 time has passed and it is just starting to count, but since the signal from earth comes later than the signal form the marker (simoutanious signals in a rest frame), the ship sees that the signal from earth reads that 43,560 yrs has passed, making him think that the earth time is not syncronized with the marker time. Is this right? If its not, plz explain to me a little more about the case youve set up, its very interesting.
ok, this is the way I was taught, that the fame in motion is the frame in which canges occur such as time dilation, mass dialtion and length contraction.
But the frames are in relative motion. Relativity teaches that either frame is perfectly entitled to view itself as being at rest.
I was also taught that in a case with two abservers, one of them will be wrong in his assumptions that he is in motion and not the other.
This is a serious misconception. Any inertial frame is just as good as another for the purpose of making observations. Relativity tells us that certain quantities (length, time, clock synchronization) are frame dependent. The Lorentz Transformations describe how the space-time coordinates of an event (and thus measurements of length and time) transform between frames.
So youre telling me that both observers are right, and they both end up agreeing in the end with nobody changing their mind.
Yes, both observers are "right" in the sense that their clocks and measuring sticks really do work according to SR. Whether they have to change their minds or not depends on their level of sophistication: Observers who understand SR expect measurements to be different in different frames.
Hmm, this makes me think. But how would the time dilation work out for both observers?(twin paradox case) They will both assume that they are aging much more than the other observer, (as a result of their assumptions that the moving frames time is slowing down)?? Just help me with this example, I will get the rest from books.
Let's get this clear first: between inertial frames in relative motion, time dilation (and length contraction, and clock synchronization effects) work exactly the same for both observers.
The twin "paradox" -- which, by the way, has nothing to do with the example we've been discussing -- involves a little more analysis. I won't attempt it here; pick up any book on relativity. (David Hogg's book discusses it.) I'll just make a few comments that might help. The twins begin in one frame, but one remains in that frame while the other accelerates then rejoins that frame. That accelerating twin ends up traveling a different (curved) path through space-time--one that always has a shorter proper time.
Since one twin accelerates, he does not remain in a single inertial frame. So, you cannot simply apply SR from that twin's frame as if it did. But the view of the stay-at-home twin is always from a single inertial frame, so SR works just fine for him. He sees the other twin's clock as being slow. You can certainly analyze the twin paradox from both twin's viewpoints even within SR--but that involves the accelerating twin changing inertial frames at some point during his journey. But rest assured, a complete account of both twins unambiguously shows that they both agree that the accelerated twin ends up younger. So, it's not that one is wrong and the other right: they are both right, and they both agree.
Doc Al, I think I got it. Since the rocket observer is in motion, simoutanaety in a rest frame is not simoutaneous to him.
Now you're talking sense... finally! :smile:
The he passes the marker, the signal from the marker would read 0 time has passed and it is just starting to count, but since the signal from earth comes later than the signal form the marker (simoutanious signals in a rest frame), the ship sees that the signal from earth reads that 43,560 yrs has passed, making him think that the earth time is not syncronized with the marker time. Is this right? If its not, plz explain to me a little more about the case youve set up, its very interesting.
It's "kind of" right. Let me rephrase it. First, as you point out, simultaneity is frame dependent. SR predicts that the two clocks (marker clock and earth clock) that are in synch according to marker-earth frame will not be in synch according to the rocket frame. (As I showed earlier, according to the rocket frame when the marker clock reads 0 the earth clock reads 43,560 yrs.)
Just for fun, let's say that the rocket observer has a super telescope that allows him to see the earth clock. When the rocket passes the marker (just when the marker clock reads 0) the rocket observer looks through the telescope. After accounting for the time of travel of the light (and time dilation) he will deduce that the earth clock must be reading 43,560 yrs at the moment he passes the marker. It all fits together.
Just for fun, let's say that the rocket observer has a super telescope that allows him to see the earth clock. When the rocket passes the marker (just when the marker clock reads 0) the rocket observer looks through the telescope. After accounting for the time of travel of the light (and time dilation) he will deduce that the earth clock must be reading 43,560 yrs at the moment he passes the marker. It all fits together.
Im kind of getting it, but the one think I do not understand is why the two clocks would be out of sync. They are in the same frame, and if the moving frame has this 'super telescope', why would the time passed on earth be different than time passed on the marker. Both the marker and earth are in the same frame of reference. If you could just help me out here that would be great.
Im kind of getting it, but the one think I do not understand is why the two clocks would be out of sync. They are in the same frame, and if the moving frame has this 'super telescope', why would the time passed on earth be different than time passed on the marker. Both the marker and earth are in the same frame of reference. If you could just help me out here that would be great.
If I am correct, the objects are in the same frame of reference but in different states: stationary or moving. Therefore it is like a frame in a frame and so the time changes with it.
The Bob (2004 ©)
Incorrect. Each frame in background independent. Simultaneity does not exist in either reference frame.
Incorrect. Each frame in background independent. Simultaneity does not exist in either reference frame.
Ok, sorry.
The Bob (2004 ©)
Im kind of getting it, but the one think I do not understand is why the two clocks would be out of sync.
Whether two clocks in the same frame are synchronized or not is not an intrinsic property of the clocks--it depends on what frame is observing those clocks. This is the meaning of the "relativity of simultaneity". The marker clock and the earth clock are in the same frame, and they are synchronized according to the earth-marker frame. But the rocket observer will observe them to be out of synch according to the rocket frame.
They are in the same frame, and if the moving frame has this 'super telescope', why would the time passed on earth be different than time passed on the marker.
Because the rocket observer wants to know what time is it on earth right now--the moment he passes the marker. But "right now" means different things to each observer. To the earth frame "right now" means when both clocks read 0. But the rocket frame sees the earth clock being way out of synch with the marker clock. And, since the earth clock is moving, the rocket observer sees that it operates slowly compared to his own clock. And don't forget that the rocket observer measures his distance to the earth to be shorter that what the earth frame measures it to be.
To make sense out of these things, one cannot consider length contraction or time dilation as separate, independent effects. One must consider all the relativistic effects--length contraction, time dilation, simultaneity--working in concert. To consider one effect while ignoring the others will result in logical contradiction.
Whether two clocks in the same frame are synchronized or not is not an intrinsic property of the clocks--it depends on what frame is observing those clocks. This is the meaning of the "relativity of simultaneity". The marker clock and the earth clock are in the same frame, and they are synchronized according to the earth-marker frame. But the rocket observer will observe them to be out of synch according to the rocket frame.
Because the rocket observer wants to know what time is it on earth right now--the moment he passes the marker. But "right now" means different things to each observer. To the earth frame "right now" means when both clocks read 0. But the rocket frame sees the earth clock being way out of synch with the marker clock. And, since the earth clock is moving, the rocket observer sees that it operates slowly compared to his own clock. And don't forget that the rocket observer measures his distance to the earth to be shorter that what the earth frame measures it to be.
To make sense out of these things, one cannot consider length contraction or time dilation as separate, independent effects. One must consider all the relativistic effects--length contraction, time dilation, simultaneity--working in concert. To consider one effect while ignoring the others will result in logical contradiction.
I understand, basically the two clocks are out of sync because of simultaneity, the earth and the marker both start their clocks at the same tie, but because the rocket is in motion, the clock start is NOT simoutaneous according to the rockets referance frame, maing the clocks out of sync. Right?
I understand, basically the two clocks are out of sync because of simultaneity, the earth and the marker both start their clocks at the same tie, but because the rocket is in motion, the clock start is NOT simoutaneous according to the rockets referance frame, maing the clocks out of sync. Right?
You got it.
Why is it that light goes faster with the rotation of earth, and light goes slower against the rotation of earth?
Why is it that light goes faster with the rotation of earth, and light goes slower against the rotation of earth?
Light is a constant speed no matter in which direction you point it at (when in the same medium). Ive never heard of light being faster in ine direction. Do you have a source?
Why is it that light goes faster with the rotation of earth, and light goes slower against the rotation of earth?
If you synchronize your clocks in the manner proposed by Einstein, the speed of light is independent of direction. So it's not really true that light goes faster or slower from east/west or from west/east.
But also note that is impossible to synchronize all clocks on a rotating planet or disk according to Einstein's "clock in the middle" method. See for instance
http://www.smcm.edu/nsm/physics/SMP03S/KeatingB.doc.pdf
This has been the source of a *lot* of confusion, as a brief websearch will reveal :-(.
There is a common synchronization method widely used, for instance in the definition of TAI time, that does allow all the clocks on a rotating object to be synchronized. This is not Einstein's method, of course, since we've already mentioned that it's impossible to do this via Einstein's method. One first thinks, perhaps, of emitting a signal from the center of the earth and synchronizing outwards - when the obvious practical difficulties with this method raise their head, one thinks of synchronizing only along north-south lines to master clocks at one or both of the poles.
Before one gets too excited about the existence of such alternate synchronization methods, one should realize that Einstein's method, and only Einstein's method, allows one to keep Newtonian momentum p=mv or relativistic momentum p=mv/sqrt(1-(v/c)^2) as a conserved quantity.
So before one gets too excited by various commonly-found-on-the-web-but-ill-informed claims about the "one-way" speed of light being different from e-w or w-e, remember to check whether or not, by the definitions used, that a body of mass m moving east at a velocity v will come to a stop when colliding with a body moving west at a velocity v, according to the particular coordinate scheme used to measure velocity. It can, in fact, be shown that only an isotropic synchronization scheme such as Einstein's will conserve momentum. I'll mention that the isotropy requirement comes from Noether's theorem, but I think it would be getting to technical and wandering too far afield to go into any more detail at this point.
So, how do you explain the sagnac effect? It shows how rotation alters the speed of light. Well, how energy fields alters the speed of light. Although the MM experiment "disproved" the aether, this was only done by disproving it through Maxwell's equations. So, is there any explanation without throwing in Maxwell's equations (since they only deal with detectors and emitters AT REST...not moving). Please try not to be bias when explaining this. I want a good explanation of it. :smile:
So, how do you explain the sagnac effect? It shows how rotation alters the speed of light.
Did you read the reference I posted?
I'm looking at the section right now which starts out as
The sagnac effect, and indeed all of the "pardoxes" described in this paper, can be explained by the impossibility of synchronizing all clocks on the disk such that all observers will agree that they are in fact synchronized.
I would guess you probably didn't read it, especially from the rapidity of your response :tongue2:
The paper really is worth reading IMO - it's quite good, and goes into a lot more detail than I can. It talks in detail about what happens when various observers make a "round trip" around the disk, and compare their clocks, for instance.
Another quote caught my eye, the concluding quote from the URL I cited previously (and repeated below):
http://www.smcm.edu/nsm/physics/SMP03S/KeatingB.doc.pdf
In the words of Rizzi and Tartaglia [reference omitted], "... a rotating disk does not admit a well-defined "proper frame"; rather, it should be regarded as a class of infinite number of local proper frames, considered in different points and different times, and glued together according to some convention.
Haha, I couldn't read it because work didnt have acrobat reader (I'm not supposed to download programs to computer). I'll read it in a minute or tomorrow and post a response. I do know that the sagnac effect is accepted by relativists. I read that somewhere. That is very contradictive. Thanx for the link--again. I'll have a response ASAP after I read it.
d_{rest} = d_{moving} \sqrt{1-v^{2} / c^{2}}
if you use the actual numbers does it still work?
44000lightyears = d_{moving} \sqrt{1-269813212m/s^2/299792458m/s^2}
44000 = d_{moving} \sqrt{1-0.809999999}
44000 = d_{moving} \sqrt{0.190000001}
44000 = d_{moving}0.435889896
44000/0.435889896=d_{moving}
100942.923=d_{moving}
i had to have done something wrong here.
d_{rest} = d_{moving} \sqrt{1-v^{2} / c^{2}}
if you use the actual numbers does it still work?
44000lightyears = d_{moving} \sqrt{1-269813212m/s^2/299792458m/s^2}
44000 = d_{moving} \sqrt{1-0.809999999}
44000 = d_{moving} \sqrt{0.190000001}
44000 = d_{moving}0.435889896
44000/0.435889896=d_{moving}
100942.923=d_{moving}
i had to have done something wrong here.
its a colt easier if you take your speed and convert it into a decimal of the speed of light. (ie: 0.8c, 0.5c etc..). Lets say you have 2,000,000m/s. To convert it, you would do the following:
\frac{2,000,000m/s}{300,000,000m/s/c} = v
v = 0.0066c
use this method, its a lot easier to work with, and units cancel out a lot easier.
d_{rest} = d_{moving} \sqrt{1-v^{2} / c^{2}}
if you use the actual numbers does it still work?
....
i had to have done something wrong here.
You need to interpret the length contraction equation properly. I prefer to write it like this:
L = L_0 \sqrt{1 - v^2/c^2}
Where L_0 is the proper length of the object (measured in its rest frame) and L is the length of the object when measured from the frame in which it moves with speed v.
It's unreal how that paper is biased to the support of SR!! Do you have any evidence that disregards SR? That's what I'm truly looking for. SR has not been proven, so it is a possibility that the Sagnac effect is present. I was talking to my physics teacher today about the Lorentz Transform, and he said he doesn't think that is a good explanation for what is really happening. Sometimes he talks crazy though. :rofl:
If I had any reproducible evidence that disproved SR, I'd be standing in line to get my Nobel prize :biggrin:
One might guess from the fact that SR is a well accepted theory that very well-known results like the Sagnac effect don't falisfy it. (I've never quite understood why this wasn't obvious to people - I've got a somewhat off-topic guess that it may have to do with the prevalence of lying in American society today, but that's just a wild-assed-guess.)
I've also never quite understood why people make up their minds in advance that SR must be wrong, and then go looking for anything that might support their preconceived ideas. :grumpy:
SR is really a well tested theory, and it has been for probably the last 50 years or so.
if i were moving at .90c would the speed of light look slower or would it still be moving as fast as if i were standing still?
if i were moving at .90c would the speed of light look slower or would it still be moving as fast as if i were standing still?
the speed of light would still look like normal. It would still move at a speed of c.
It's unreal how that paper is biased to the support of SR!! Do you have any evidence that disregards SR? That's what I'm truly looking for. SR has not been proven, so it is a possibility that the Sagnac effect is present. I was talking to my physics teacher today about the Lorentz Transform, and he said he doesn't think that is a good explanation for what is really happening. Sometimes he talks crazy though. :rofl:
SR has been one of the most remarkably accurate theories known to man. It the only theory that works as wee as it does, and giver results that are as accurate as they are.
eventhough im going almost the same speed?
yes thats the thing about light, its speed is always c, no matter in waht frame youre in. Even if yuo send two beams of light at each other, the speed at which they approach eachoter is not c+c, it is just c.
so then if we were going the speed of light, light would still be going a lot faster than us?
so then if we were going the speed of light, light would still be going a lot faster than us?
As has been mentioned several times in this (seemingly endless) thread, one cannot go at the speed of light. So, let's say you were in your rocket going at 0.99c with respect to the earth. Someone (anyone!) fires off a beam of light. Observers on both rocket and earth will measure that beam as traveling at speed c with respect to themselves. The logical consequences of this fact lead to all the SR "effects" that we've been discussing throughout this thread: length contraction, time dilation, and simultaneity.
So, to answer your question directly. Everyone will always measure light as moving at speed c with respect to themselves. So, if that's what you mean by "going a lot faster", then yes. But another observer, watching you go by at say 0.99c, also measures that light as going at speed c with respect to him, so as far as he is concerned the light is only going 0.01c faster than you. :smile:
so you find the length of a moving object by the time*speed?
Why is it that when objects only loose length when traveling at relativistic speeds? Well, it is noticeable at relativistic speeds. What actually defines the magnitude of relativistic speed? When do you start applying the Lorentz Transform and why?
In addition to the statement about length contration, I would like to say that length is not PHYSICALLY lost. In one reference frame the length of an object at relativistic speeds is contracted, while relative to that object it is the same. It is not physically lost, because it is contracted and proper in two reference frames. This is contradictory. Nothing can loose length and keep it at the same time. Just my two coins going in.
ArmoSkater87
Sep4-04, 12:58 AM
Why is it that when objects only loose length when traveling at relativistic speeds? Well, it is noticeable at relativistic speeds. What actually defines the magnitude of relativistic speed? When do you start applying the Lorentz Transform and why?
Since everyday speeds are nothing compared to the speed of light, the length contraction/time dilation/mass increase are neglected. When moving at relativistic speeds (close to the speed of light) these effects are very noticable. For example, mass is a little more than 2 times greater at .9c than the rest mass. Which shows that you have to get very close to the speed of light for the mass to start sky rocketing.
In addition to the statement about length contration, I would like to say that length is not PHYSICALLY lost. In one reference frame the length of an object at relativistic speeds is contracted, while relative to that object it is the same. It is not physically lost, because it is contracted and proper in two reference frames. This is contradictory. Nothing can loose length and keep it at the same time. Just my two coins going in.
Correct, nothing is physically happening to it, there is no force making it contract. It simply IS shorter at a certain velocity.
so you find the length of a moving object by the time*speed?
As was discussed several posts ago, one way of measuring the length of a moving object is to time how long it takes to pass you, then multiply that time by its speed.
And what is your opinion about tachyons, do they exist? Sorry if anyone asked this before.
What is the barrier when you start considering speeds relativistic?
Correct, nothing is physically happening to it, there is no force making it contract. It simply IS shorter at a certain velocity.
How is it simply shorter and at the same time simply the same size as it is when considered at rest to itself?
Tom Mattson
Sep4-04, 10:41 AM
What is the barrier when you start considering speeds relativistic?
There isn't one. All speeds are relativistic. Now as to the related question, "When do you have to use relativity, and when can you get away with not using it?" the answer is another question: "How accurate do your calculations need to be?"
How is it simply shorter and at the same time simply the same size as it is when considered at rest to itself?
It is shorter than its proper length according to an observer watching it move by.
It is exactly its proper length in its rest frame.
You have to qualify observational statements with the frame in which the observation is made to make any sense.
How can it have two lengths at the same time? Isn't that impossible. I know this is in regards to different inertial reference frames, but reference frames doesn't make something heavier or lighter depending on the speed of one related to another. That would make something have two different masses at the same time.
A good explanation would help me understand.
Tom Mattson
Sep4-04, 11:05 AM
How can it have two lengths at the same time?
Because it happens to be a feature of the universe we live in that the length of an object is a function of its speed.
Isn't that impossible.
No, it isn't. In fact, it's quite impossible for it not to be that way!
I know this is in regards to different inertial reference frames, but reference frames doesn't make something heavier or lighter depending on the speed of one related to another. That would make something have two different masses at the same time.
The concept of relativistic mass can be accepted or abandoned at will, but we are stuck with length contraction and time dilation. So, I'll be confining my remarks to the latter two phenomena.
A good explanation would help me understand.
It all starts with Maxwell's equations of electrodynamics. This is how Einstein derived Special Relativity from two postulates:
1. The laws of physics must be the same in every inertial frame.
2. The speed of light must be the same in every inertial frame.
The first postulate means that you should not be able to tell whether you are moving or at rest merely by performing an experiment in a closed laboratory. What it really amounts to is that there is no such thing as a state of absolute rest. Equivalently, it means that there is no preferred inertial frame of reference.
The second postulate means that, for any light pulse, its speed will be measured to be 'c', no matter what the relative motion between the source and the observer. So if a source is stationary in your frame and you measure the speed of a pulse, it is 'c'. And if that same source comes at you at 0.5c and you measure the speed of another pulse, you still measure the speed to be 'c' (not 1.5c!).
That second postulate gives an inkling of length contraction and time dilation: Space and time cannot possibly be reckoned the same for all observers, if the speed of light is reckoned the same for all observers.
Now back to Maxwell. What Einstein did was pose the question, "What sort of coordinate transformation would leave Maxwell's equations in the same form for all inertial observers?" This question is relevant because of the first postulate. If the laws of physics have to be the same for everybody, then the equations have to be the same for everybody. Einstein didn't just pose the question, he also answered it: The coordinate transformation is the Lorentz transformation.
And derivable from the LT are the formulas for length contraction and time dilation. So the best way I can think of the "explain" these phenomena is to say that they are deduced from the postulates of SR, which in light of all the experimental data are eminently reasonable, and the covariance of Maxwell's equations, which are well-confirmed experimentally.
The concept of relativistic mass can be accepted or abandoned at will, but we are stuck with length contraction and time dilation.
We are not necessarily stuck with length contraction or time dilation. I've seriously been a firm believer in Einstein's theories, but as of lately, I've kind of trailed off thinking less of what he has theorized.
Time dilation has been tested, and scientist would even say it is proven to exist. I would have to argue that statement. Length contraction has never been observed, nor has mass increase been observed (Not sure about the mass increase, but I'm thinking it hasn't been measured, so dont go too hard on that one).
Would you like to explain to me exactly how light keeps it's constant velocity? I am in accordance with Maxwell saying the frequency is inversly proportional to the wavelength only when the source and detector are stationary. What I do not believe is that this is true when velocity of the source of detector is thrown in. I have no belief that the Lorents Transform did a good job in explaining this phenomenon. So, saying what you just said, has not influenced my thought. Can you go more indepth? I'm going astray; I need to get back on path with physics. :rofl:
Tom Mattson
Sep4-04, 02:13 PM
We are not necessarily stuck with length contraction or time dilation.
Yes we are.
Time dilation has been tested, and scientist would even say it is proven to exist. I would have to argue that statement.
There's nothing to argue. Time dilation has been observed, and in the precise quantities predicted by relativity.
Length contraction has never been observed,
That's true. But the invariance of the speed of light has been observed, and so has time dilation. It is not logically possible for space to be absolute, when the speed of light is absolute and time is not.
nor has mass increase been observed (Not sure about the mass increase, but I'm thinking it hasn't been measured, so dont go too hard on that one).
As I already said, "mass increase" is a matter of convention, not physics. If you define mass as m=γm0, then you will observe that that quantity increases with speed. It's done all the time in particle accelerators. But most particle physicists define mass as the norm of the 4-momentum, and as such it is a Lorentz invariant.
Would you like to explain to me exactly how light keeps it's constant velocity?
No one knows why. We only know that it is true.
I am in accordance with Maxwell saying the frequency is inversly proportional to the wavelength only when the source and detector are stationary. What I do not believe is that this is true when velocity of the source of detector is thrown in.
It doesn't matter if you believe it or not. The speed of light has been measured from moving sources. The most direct test has been performed by T. Alvager, et al, Physical Letters 12, 260 (1964).
Look it up.
I have no belief that the Lorents Transform did a good job in explaining this phenomenon.
The Lorentz transform doesn't explain the phenomena, it predicts them. I said that the explanation is in terms of the postulates: Time dilation and length contraction are necessary, deductive consequences of the postulates.
But since the postulates and the transforms have survived every experimental test with flying colors, I'll say it again: it doesn't matter in the slightest what you believe.
say there is a ship going .90c we figured out the length of the ship from the viewpoint of something going .30c. if we were standing still and shot two knives that go .30c, the same distance apart from each other as the ship's length we figured earlier, would we miss the ship or would the ship get cut into three portions?
Tom Mattson
Sep4-04, 02:57 PM
say there is a ship going .90c we figured out the length of the ship from the viewpoint of something going .30c. if we were standing still and shot two knives that go .30c, the same distance apart from each other as the ship's length we figured earlier,
You need to be more specific. First, are the knives moving perpendicular to the path of the ship, or antiparallel to it? This matters because length contraction is only in the direction of relative motion. So, if the knives are moving perpendicular to the path of the ship, then a person in the frame of the knives would agree with an observer in the lab frame as to the length of the ship.
Second, you should assign spacetime coordinates to each event, and state where the ship is when the knives are launched.
would we miss the ship or would the ship get cut into three portions?
There's a false dilemma here, because those aren't the only 2 options. Depending on when you shoot the knives, it's possible that only 1 knife will hit the ship.
the ship's and the knives' path are to intersect at the exact same time.
why doesnt time move slower at the equator than at the poles?
Tom Mattson
Sep4-04, 06:32 PM
the ship's and the knives' path are to intersect at the exact same time.
That doesn't help, because you have to say which knife is to intersect the ships path when the ship gets there. As I already said, in the frame of the knives, the ship is too short to be hit by both of them.
Tom Mattson
Sep4-04, 06:33 PM
why doesnt time move slower at the equator than at the poles?
Why would you think that time dilation is inapplicable here?
so if i lived on the equator i would live longer than if i lived on the northpole? granted i dont die of any other reason other than old age.
the ship's and the knives' path are to intersect at the exact same time.
You haven't given enough information but if we assume that the knifes are fired simulataneously in the gun's refernce frame in such a manner that the front of the ship is 'clipped' by the knife on the right.
What happens in the gun's frame is simply that the knife 'clips' the front of the ship, but the knife on the left misses the ship completely due to the fact that the length of the ship is contarcted in this frame.
In the shi's frame the length of the gun is contracted, howver the knifes are not fired simulatanoeusly; the knife on the right fires first and the ships front is 'clipped', then the ship moves on and the knife on the left fires missing the ship completely.
The lengths of the knifes are the same in both frames.
the knives are the same length apart from each other so that one would slide past right in front of the ship and one would slide right behind the ship. they both cross the ships path at the same time.
Tom Mattson
Sep4-04, 06:50 PM
the knives are the same length apart from each other so that one would slide past right in front of the ship and one would slide right behind the ship. they both cross the ships path at the same time.
It's not possible to tell for certain from your language, but you seem to think that the ship should fit snugly between the two knives, which is wrong. As I've said twice already, the ship has the same length in the frame of the knives as it has in the frame of the knife launcher.
Tom Mattson
Sep4-04, 06:52 PM
so if i lived on the equator i would live longer than if i lived on the northpole? granted i dont die of any other reason other than old age.
Longer as measured by whom? You would not notice your life being any longer, of course, because relativistic effects always turn up in the other guy's frame.
It seems like you have not looked at that relativity textbook I linked you to. If you learn the material in that link, you can answer all these questions for yourself.
the knives are the same length apart from each other so that one would slide past right in front of the ship and one would slide right behind the ship. they both cross the ships path at the same time.
As Tom Mattson says length is frame dependent and the length of the ship is contracted (i.e. smaller) in the gun's and the knife's frame, only the proper lengths are the same.
why would one be shot off sooner than the other, from the view of the ship, if they are both shot at the same time from the view of the gun?
Of course you could mean that the length of the ship is L in the gun's frame (which means that the proper length of the ship would actually be greater than 2L) in which case both front and back will be clipped under the previous assumptions (simultaneously in the gun's frame, non-simultaneously in the ship's frame) .
why would one be shot off sooner than the other, from the view of the ship, if they are both shot at the same time from the view of the gun?
Because of the failure of simultaneity at distance in relativity - i.e. events that are simultaneous and seperated by distance in one frame are not simultaneous in another frame.
Tom Mattson
Sep4-04, 07:28 PM
why would one be shot off sooner than the other, from the view of the ship, if they are both shot at the same time from the view of the gun?
Because simultaneity is relative. Events that are spatially separated and are simultaneous in one inertial frame, are not simultaneous in any other inertial frame.
It's all spelled out quite clearly in that book I linked you to.
edit: jcsd already got it, I see.
Here's that link again, in case you change your mind about reading it:
Special Relativity (http://www.physics.nyu.edu/hogg/sr/sr.pdf)
that does not make sense. say im traveling in a ship that its width is longer than its length and another ship flies perpendicular to me at a speed of .90c then my ship will look like its slanted to the right? both of my side are moving at the same time in the view of my ship.
Tom Mattson
Sep4-04, 07:34 PM
that does not make sense. say im traveling in a ship that its width is longer than its length and another ship flies perpendicular to me at a speed of .90c then my ship will look like its slanted to the right?
In general extended objects are rotated in a frame in frames that are moving relative to those objects.
both of my side are moving at the same time in the view of my ship.
And as we keep repeating, simultaneity is relative. Two events that are spatially separated and simultaneous in one inertial frame are not simultaneous in any other inertial frame.
so then things that are farther in front of the ship are then closer together from the ship view?
Tom Mattson
Sep4-04, 07:48 PM
so then things that are farther in front of the ship are then closer together from the ship view?
I can't answer that, because this question is ill formulated. You haven't specified the state of motion of the "things" in front of the ship. If they are stationary with respect to the ship, then the distance between the ship and the things is a proper length, and it would be shorter from the point of view of someone watching the ship pass by. If the things are stationary with respect to the onlooker, than the distance will be shorter from the point of view of the ship.
Bino, please read the link I gave you. You keep asking the same type of questions over and over and over and over and over and over...., and this rapid fire questioning is getting tiresome. Please take some of the responsibility of your own education. You'll be the better for it.
russ_watters
Sep4-04, 08:20 PM
so if i lived on the equator i would live longer than if i lived on the northpole? granted i dont die of any other reason other than old age. Well, you also have to consider gravitational time dilation since the earth isn't a perfect sphere...
Just to amplify a few things about this last point.....
One of the very interesting facts of life is that all clocks on the Earth's surface at sea-level (the geoid) run at the same rate. The reduced gravitational potential at the Earth's equator due to it's equatorial bulge exactly cancels out the time dilation due to the rotational motion.
Atomic clocks are precise enough nowadays that these issues are actually important - one of the primary clocks at Denver, Colorado, has to have it's contribution to atomic time (TAI time) adjusted because of it's altitude above sea level.
i don't understand how the michelson-morley experiment could have worked in the first place. everthing is fixed to the earth the speed of light could not have changed anyway. how does that have to do with the rotation of the earth?
First of all, I really agree that you should do some reading on special relativity and general relativity before you come back to ask another set of questions.
In reply to your question, first of all, not everything is fixed to the Earth. For example, winds experience forces and move in interesting patterns due to Earth's rotation. That is because the Earth is strictly an inertial reference frame. Since people thought that light was supposed to move at c only when measured at an inertial reference frame, c measured in different directions with respect to the motion of the planet were supposed to have different speeds. That was the whole idea of the Michelson-Morley experiment.
It's like measuring the time taken for a boat to go and come back across a river of width k units, and then comparing the time to the time measured when the boat moves upstream for k units and then downstream. There would be some difference in the times if the water in the river were running.
It doesn't only depends on the rotation of the Earth...it also depends on Earth's orbiting around the sun, and all other accelerating movements of the Earth.
Anyway, relativity explained the results very beautifully.
"Since people thought that light was supposed to move at c only when measured at an inertial reference frame, c measured in different directions with respect to the motion of the planet were supposed to have different speeds. That was the whole idea of the Michelson-Morley experiment."
their experiment could not do what they thought it would since the whole experiment was moving along at the same speed as the earth. (it would be more like if someone was throwing a ball in a box the ball will be moving at the same speed no matter what direction i throw it in front to back, side to side even if the box was moving.) from the frame of the person in the box.
It's like measuring the time taken for a boat to go and come back across a river of width k units, and then comparing the time to the time measured when the boat moves upstream for k units and then downstream. There would be some difference in the times if the water in the river were running.
i think i read somewhere that flowing water has an effect on the speed of light also. light moves faster going downstream than it would if it was going upstream or if the water was not flowing. ill try to find out where i read that.
i don't understand how the michelson-morley experiment could have worked in the first place. everthing is fixed to the earth the speed of light could not have changed anyway. how does that have to do with the rotation of the earth?
the reason for the Michelson experiment is to test for an 'ether' that light was supposed to travel through, since it was thought to be a 'wave'. And since the earth torates around the sun and rotates on itrs axis, it was thought that this ether was raming into it, since it was supposed to be stationary. The point of their experiment was king for like sending a boat upstream and downstream, the ether was like water, so the light should go faster in one direction than in the other.
ok so then its important because it debunked the ether theory.
but how does that equate into light being the same speed for all frames?
It all starts with Maxwell's equations, which predicted light to move at a certain speed c. However, there wasn't any implication of which reference frame we would measure speed at. It seemed as if there was one unique reference frame at absolute rest. That would be the frame which "ether" would exist at.
If ether existed, they would have measured a difference in the speed of light going "upstream, downstream" and "across the river", which is actually just the difference between Earth's reference frame and the "frame at absolute rest". However, they didn't measure any difference.
Einstein solved this problem by suggesting that light perhaps was at the same speed c for all frames, not just one. Nobody know why it is like that, but nowadays it seems that it just explains the phenomena beautifully. However, consequences of SR changes our views and makes classical physics no longer applicable at great speeds.
russ_watters
Sep6-04, 11:49 AM
but how does that equate into light being the same speed for all frames? Because ether theooy is what says that light speed is not the same in all frames. If ether theory were correct, then measuring the speed of light traveling east, you'd get C+1000mph, and measuring the speed of light traveling west, you'd get C-1000mph. That's (basically) what the M&M experiment was trying to find.
right right. but their test was not tested in different frames the whole thing was only in one frame. or is that they thought that the ether was moving around the surface of the earth? because the way im thinking, they were thinking, is that the ether is going around the outside of earths atmosphere.
People thought about ether dragging theories for a while, but couldn't reconcile the results with stellar aberration results. If the earth was dragging the ether around it as it moved, this should have some optical effects on observing stars (depending on the exact variety of theory being used) - no such effects were found.
Of course, nowadays we don't have to rely on the limited experimental results that were available when relativity was first being formulated, we have a whole host of experimental confirmations of relativity. See for instance
http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.htmlhttp://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html
For instance, we have measured the speed of "light" (gamma rays) emitted from the decay of fast (.99975) pi mesons with a resolution of 400ppm, and found no change. That's just one of a huge number of experiments.
Modern high particle accelerators wouldn't work at all without relativity - the early cyclotron designs gave way to the synchrotons. GPS wouldn't work the way it does without relativity. These are examples of the large number of "informal" tests of relativity - things that simply wouldn't work if relativity were not true, things that are used every day. With the advent of atomic clocks, some of the predictions of general relativity, formerly of only theoretical interest, are of practical importance. As I mentioned before, the accuracy of the Boulder clock is such that the small relativistic shift in frequency due to it's altitude is about 40x as large as the frequency stability of the clock itself.
seems like i read somewhere that in some 1999 issue of "Nature" there was an article that said that scientists managed to slow down light by a large factor by using a high density clump of Bose-Einstein condensate...
if this is true, what applications can it have?
Tom Mattson
Sep6-04, 05:57 PM
right right. but their test was not tested in different frames the whole thing was only in one frame.
Look at the MMX apparatus. There is a beam of light going in two different directions. So relative to the ether, the two beams should have had two different velocities.
was the ether sapossed to moving around the surface of earth or around the atmosphere of earth?
Tom Mattson
Sep6-04, 07:46 PM
was the ether sapossed to moving around the surface of earth or around the atmosphere of earth?
Read Chapter 1 of the book I linked you to. It explains everything.
i did thats where i got my question from. alls it said was that it was believed that earth moved through the ether. but it didnt say if it went around the surface or atmosphere of earth? becuase if it went around the surface then they should have figured that they would be able to feel it but if it went around the atmosphere then their experement could not have measured anything. either way it was doomed. and i still dont see how it would prove the speed of light is constant? pervect i looked over the website you posted and it had a lot of experiments that where for and against SR. do you any other sites maybe one that has more discriptions of the experiments.
Tom Mattson
Sep7-04, 06:06 PM
alls it said was that it was believed that earth moved through the ether.
You didn't read it very carefully then. It also said that the two beams were moving perpendicularly to each other. That means that the light beams should have had two different speeds, if the Earth were truly moving through the aether. The book is both specific and quantitative on this point. I honestly don't understand how you could have missed it.
but it didnt say if it went around the surface or atmosphere of earth?
It says that, if the aether exists, then the Earth should be moving through it. It says so explicitly on page 3, middle left column and on page 4, upper right column.
becuase if it went around the surface then they should have figured that they would be able to feel it but if it went around the atmosphere then their experement could not have measured anything. either way it was doomed.
The aether doesn't move around anything. It's an inertial frame!
if the earth moves through it then the ether has to either move around the earth or move through the earth.
i understand what the apparatus was suppose to do and what it looked like. i don't see how it could be considered a valid test to prove anything.
I suggest somebody end this thread right now. LOCK DOWN.
nenad, but don't you like the way bino always replies in one at most two sentences, never uses capital leters, and always asks a question at the end?
i understand what the apparatus was suppose to do and what it looked like. i don't see how it could be considered a valid test to prove anything.Read Chapter 1 of the book I linked you to. It explains everything.bino, did you?
Tom Mattson
Sep8-04, 10:25 AM
if the earth moves through it then the ether has to either move around the earth or move through the earth.
The hypothetical aether does not interact with matter, so the motion of the Earth through the aether does not affect it in any way.
i understand what the apparatus was suppose to do and what it looked like. i don't see how it could be considered a valid test to prove anything.
No, I don't think you do understand what it was supposed to do. When I told you that you should read Chapter 1, I did not mean for you to simply look at the pictures. I meant for you to read the text and follow the math. The aether model makes predictions regarding the MMX, and those predictions were not met.
Alkatran
Sep8-04, 10:33 AM
You drive up to a four way intersection behind a car which is going the same speed as you. He doesn't stop and neither does a car coming from the other direction. They are both going 40 mph and ram into each other at the midpoint of the intersection.
If they had been going the same direction they wouldn't have hit together, for the same reason you didn't hit into the car in front of you. SO:
If a beam of light is moving in a different direction than another beam of light, it is NOT in the same inertial frame, because they can collide.
bino is just playing dumb, he knows how to read, I say READ THE SR BOOK and stop asking questions which could be answered easily by the book.
bino is just playing dumb, he knows how to read, I say READ THE SR BOOK and stop asking questions which could be answered easily by the book.
that's my opinion too, his unique style of capitalization and short two-line responses appears to me to be a calculated style to make him look dumb. in other words i think he's trolling.
i read up to page 11 in the book i have not had time to read further yet. but i did read all about the m&m experiment. so then the ether was suppose to interact only with the light and has no effect on anything else? that makes sense. but then it still only proves there is no ether.
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