The Mystery of Light Slowing and Speeding Up - www.thefinaltheory.com

[geistkiesel]

Conservation of momentum.


Consider first an atom in the interior of an object. Far more likely than not, this atom is in some sort of stable equilibrium state with respect to other nearby atoms.

When this atom absorbs the photon, it absorbs the momentum contained in that photon, which changes its state of motion. The atom is no longer in equilibrium! The most likely eventuality is that the other nearby atoms will push it back into equilibrium causing it to emit another photon. Since the net effect is that the atom we were observing has returned to its equilibrium state, it retained none of the momentum of the original photon, and thus the emitted photon must have exactly the same momentum as the original photon (i.e. it travels in the original direction).

For atoms near the surface of an object, it isn't surrounded by other atoms so it doesn't experience quite the same restoring force, which causes the re-emitted photon to either be a reflection of the original, or bent from the original.

Yoy are not describing a universally observed process. Mossbauer Effect observations of the recoiless absorption and readmittance of photons tells us the consevation of momentum considerations is an incompete description of the process. The interior of matter, atoms for instance, is not physically, or geometrically, described by Mendeleyev's chart of the elements. The particuliar state of the subelements of an atom may not be scrutinized says the first and last law of quantum mechanical theory. Therefore, it is anybody's guess, what is going on!

 

[relative_sceptic]

All I can say is, go get a good book on relativity and just do the calculation. I would do if for you except that all my GR notes and books are in another country.

Please do this before posting any more specultions of what you 'suspect' relativity might say.

Matt

Oh dear! no need to be so defensive because you can't answer a simple question
I note that you still haven't answered it:-)

I have just been looking at some of your replies so far:-
>In fact, you can even resolve the whole thing - accelerations and all - >with just SR. It's in one of the usual texts on the >subject, but I can't >remember which one. Possibly the one by J. Martin.
>
>p.s. I like the fact that this final theory person keeps telling us physicists >what we do and don't understand. Surely we
>already know this?

You call yourself a physicist, and even seem to think you understand relativity, (I bet you also think you understand Quantum Theory), yet you can't answer this question without your texbooks.

BTW here's a quote (from Will Rogers) that you might be interested in:-
"it's not what people don't know that hurts them. It's what they do know that just ain't so."

Sorry to burst your bubble, but you won't find the answer to this question in any standard textbook - all you will find is avoidance of the obvious contradiction, at the very heart of the theory.
The standard ploy to avoid this question is to say that the one that ages slower is the one who experiences the acceleration(s), which is why I have added the part about identical accelerations.

>The question "which one experiences the time dilation" is ill posed. They each will observe time dilation in the other >twin's >frame. The only question you can then sensibly ask is 'when the twins return to the same frame which one is older?' and this >will depend in detail on the accelerations each one has experienced.
>
>Matt

I have proposed a situation where each twin (or clock) experiences identical accelerations, during separation and returning together - you did not reply to this
I'm assuming you would agree that in this situation the effects of acceleration (whatever they may be) can be ignored, and only the periods of uniform relative motion need be considered. (When considering the Twin/clock paradox, Einstein did not consider that the effects of acceleration were relevant).
Isnt it strange then, that when trying to avoid this
question, "physicists" since then have brought acceleration into it.

Basically this is the paradox:- when considering uniform relative motion, we have no right to say whether a clock is "moving" or "stationary", we can only say one is in motion relative to the other. Now in this case, if we want to calculate how much slower one clock has gone, how do we know which clock to perform our calculations on. The situation is entirely symmetrical. And which one we decide is stationary and which moving is an entirely arbitrary decision, and whichever we choose, we will get the result that it is running slower than the other clock. Clearly when the clocks come together they cannot both be slower than the other.

Also when we choose the Earth as the start and finish of the journeys, we have no right to assume that the Earth is at rest either.

In fact in the great debate between Dingle and McCrea on this subject, McCrea conceded at one point that this was a symmetrical situation, then proceeded to answer a different question.

So, I am still waiting to see a sensible answer to this question.
As I said before, I suspect that Relativity is unable to distinguish between the two in any meaningful way

I reserve my right to ask this question, it is up to the self-styled "experts" to answer it, if they can.

The fact that this debate is unresolved 99 years after the theory was first published, means I won't be holding my breath waiting for a solution.

regards
---Steve

 

[ram2048]

meh, my reply wasn't good enough either?

i said basically if the universe only included these two objects then yes they'd be the same. but the universe does NOT include just these two objects it includes the Earth the sun the stars everything. so when one accelerates it isn't in relation to the other object (although it IS but not trivially so) it is in relationship to its position in the universe as a whole.

hell if there's general relativity and special relativity I'm going to call mine universal relativity :|

 

[geistkiesel]

The place of acceleration in relativity theory.

that's why i was saying it's not the acceleration but the speed. if they both accelerated to the speed of light at the exact same rate, but one experienced a period of deceleration on return before taking the measurement, the entire period where their speeds were not the same is the calculated part where their times and aging would be different.

if acceleration IS the cause for time dialation, then it can only be measured by RATE of acceleration, because once you stop accelerating and are just cruising at a constant speed, your time would be back to normal.

How is acceleration separated from time dilation?. Is this a theoretical postulate or a convenient reply to an unwamted complexity or experimentally defined?

It seems to me that acceleration is a key to much, if not all of relativity theory. For instance, accleration places the acclerated body in a higher energy state than an unaccelerated state. Higher energy states of matter are in higher states of vibration modes that operate to dilate clocks. In an unaccelerated, low energy state, the molecular components of a dynamic entity have wide spectrum of efficient equilibrium, for required interactions, where higher energy state the efficiency of interactions decreases. Eventually a state of vibration can be so violent that efficiency (whatever that is) of intermolecular activity is effectively diminished. Energy exchanges are more swept up in performing trivial tasks of energy exchanges and storage and less to velocity increases for accelerated particles. Time dilation occurs for a similar reason: the frequency of completed "clock cycles" decreases with increased chaos at higher energy level: A form of ordered complexity struggling to perform all the required tasks in the processes demanded at the instant.

Therefore long durations at constant velocity are merely long durations of less efificient intermolecular activity. But all this is set, established, by the accelerations.

I have my "flat earth" model based somewhat on this. Ont he planet surface one will be hard pressed to find a deviation from flat as measured by a laser beam. Eventually, however, a moving object comes to the edge of flat zones, which are more like flat irregulalry shaped regions of flatness, flat plates, quantized plates scattered around as they are and difficult to detect, especiall if one isn't looking. When accelerating into orbit the higher energy state gives one a spherical perspective. when measuring the Earth which from this energy state is clearly measured spherical. Even the moon looks flat, until one achieves a very high energy state like an oribiting trajectory around the moon, but we know it isn't, flat, don't we?. Much of what we view and perceive as a particular shape is socially determined, such as beauty and acceoptable limits of fat, skinny, handsome, ugly ec.

here's the molecular theory on this one based on electron orbits. basically when traveling at a certain speed, the atoms in an object all get pulled forward because they're connected. electrons have to travel "more" to stay in orbit because of the motion (their orbits have become elliptical relative to the universe, but still circular to their perspective). since they still travel the same rate, but have larger orbits, it takes them more "time" to complete revolutions. at close to light speed, the electrons have a lot of trouble completing revolutions, because the relative paths are stretched out very far.

At light speed, the electrons cannot even complete a revolution because they'd have to travel faster than light to traverse along their path when going forward.

How practical is the electron in orbit model? Once we've got all the electrons jammed into their proper energy states in an atom, who is to say this is the way they spend their idle time? In one sense all electrons could be in the same "energy state" as a soup of some kind, a form of supeconducitivity, until a field is exerted. The permamnet superconducting state only appears at low temperature, low energy, when different interaction states are manifest and processes are implied, without violating exclusivity principals. Onlywhen acted upon, ( room temperature)when extracting or ionizing a particle do the energy states appearas significan, as we all observe.

Just some random musings, but as long as there is an implied "I dunno"
everybody gets their own perspective, kind of like SR theorists gets a percpetion unique to his inertial speed.

This isn't a righteous argunment, but maybe it is, the SR postulates are seemingly consistent regarding the laws of physics and the measurement of the speed of light, except for the blatant unphysical "postulates" that effectively separates inertial frames in such a way that the inertial levels have no physical law counter part that can describe the differences as expressed by SR theory, namely simultaneity. Very suspicious.

 

[ram2048]

well it'll have to all come down to my theory that motion = time, so when there is no motion in an atom no relative time is passing for it.

as far as electron orbits i have no idea if that's even real. i am going to assume that molecules or atoms HAVE to move in order for interaction to take place

and that high velocity impedes their movement-interaction in such a fashion that time dilation is caused.

but until some better time-dialation experiments come forth with new information it's pretty much anyone's game :D

 

[Alkatran]

But regardless, the point is that analysis does not stop simply because the abstract concept of "Work" calculated from the Work Function is zero. When a zero result from this purely abstract Work calculation occurs it simply means that a force did not result in the motion of an object in this case [i.e. Work = Force x (zero)Distance]. It does not mean zero effort or energy was expended by the applied force. Yet today's justification for all sorts of energy expended by Newton's gravitational force tries to get by on precisely that thin, flawed argument

I was reading through your post, hit into this, then started skimming. I'm in high school and I can see the flaws here. There is zero work done on the moon because its potential gravitational energy always stays the same (as does it's kinetic energy!). That means that (, gasp,) there is no work being done! You seem to be stuck visualizing the problem from the wrong angle, the fact that the moon is changing direction doesn't imply a change in energy since ENERGY IS NOT A VECTOR - The only thing that matters in determining the "energy" of the moon is it's height and speed, which remain almost constant (assuming it has a circular orbit, of course).

 

[relative_sceptic]

The one who is accelerating will age slower. This is absolute acceleration not relative acceleration. There is a difference.

Except it is possible to visualise a situation where they both experience exactly the same accelerations (but at different times) before returning to their starting point. One has traveled further from the starting point than the other before returning. So during their periods of relative uniform motion one is supposed to age slower, but which one?, since during these periods it is not possible say which is moving and which is stationary. It is not possible also to say that the starting point is stationary.

 

[relative_sceptic]

meh, my reply wasn't good enough either?

i said basically if the universe only included these two objects then yes they'd be the same. but the universe does NOT include just these two objects it includes the Earth the sun the stars everything. so when one accelerates it isn't in relation to the other object (although it IS but not trivially so) it is in relationship to its position in the universe as a whole.

hell if there's general relativity and special relativity I'm going to call mine universal relativity :|

You're right, but SR does treat them as if they are the only 2 objects in the universe, and does not include the other factors you have mentioned.

 

[relative_sceptic]

Okay, this is something that, in my opinion, gets overlooked to often when discussing this type of thing, and it leads to a lot of unnecessary confusion.

The first thing to realize is that acceleration does not cause time dilation from the view of the unaccelerated frame. (IOW if you are observing an object that is accelerating, you only have to deal with its velocity at any given moment to determine its time dilation, the fact that it is accelerating has no effect.

Now in the accelerated frame, things are different, If you are in this frame, three factors control how you will measure other objects time rates: the magnitude of the accelleration, the direction the object is with respect to the acceleration, and the distance of the the object.

The second thing is that time dialtion is not something that anyone experiences it is something that you measure as happening in other frames.

Now in your situation, from the Earth Frame, the twin that turned around last ages the least becuase he undergoes the longest duration of time dilation.

From either twins view, Earth time runs fast when they turn around and start heading back (when they are an accelerated frame once they retrun to uniform motion towards the Earth, they will once more measure time running slow on Earth). Since the twin that turns around last is further from the Earth when he turns around, he will measure Earth time as running that much faster during this time. He will return to Earth expecting more time as having passed on Earth than his brother will.

OK, except arent you treating the Earth as being "at rest". As far as I can see when the spaceship is traveling away from the Earth at a constant speed, you are equally entitled to say the Earth is moving away from the spaceship at constant speed, and the spaceship is stationary, so clocks on Earth should run slower.

 

[geistkiesel]

Basically this is the paradox:- when considering uniform relative motion, we have no right to say whether a clock is "moving" or "stationary", we can only say one is in motion relative to the other. Now in this case, if we want to calculate how much slower one clock has gone, how do we know which clock to perform our calculations on. The situation is entirely symmetrical. And which one we decide is stationary and which moving is an entirely arbitrary decision, and whichever we choose, we will get the result that it is running slower than the other clock. Clearly when the clocks come together they cannot both be slower than the other.

I trust we can alter the question slightlty by inserting that two frames had recently shared a comon stationary frame . Each frame knows its velocity is greater than the stationary common frame. Hiowever, the distance between the frames is huge and merely sending their current clock setting won't work in determining which is the faster frame with respect to the common stationary frame. How may the frames determine which is fastest. The frame clocks are identical with a stationary frame clock pulse rate = 1.

Each frame's clock is pulsing at some frequency where the signals are true pulses, | | | | | | | |. Would not the slowest frame receive a pulse rate from the faster at a slower rate than his own pulse rate?

Likewise, would not the fastest frame determine the pulse rate from the slower was generated at a higher frequancy than his own?

This seems rather trivial if true, having heard all the horror stories of relativity theory that seem to deny the ability to do this..

 

[geistkiesel]

that's why i was saying it's not the acceleration but the speed. if they both accelerated to the speed of light at the exact same rate, but one experienced a period of deceleration on return before taking the measurement, the entire period where their speeds were not the same is the calculated part where their times and aging would be different.

If we assume that acceleration increases the energy state of all matter in the the frame accelerated, and that for the elevated energy, translated into higher frequency rates for all affected matter, the efficiency of material dynamic processes becomes inversely less effecient in energy and force exchanges. This includes equilibrium state processes, velocity a constant. At relativistic velocities the accelerations have been enormous. The efficiency of the energy exchange and force exchnge processes decreases grossly as observed. Lower the energy level, increase the efficiency of process dynamics of the matter undergoing the process.

What is observed in relativistic accelerations? More and more energy used for storing and loading than accelerating, inversely proportionately less for velocity increases.

The lorentz term using velocity as the key is merely a measure of the limiting parameter for that particlular process under scrutiny. What is being ignored is the dynamics of complex energy flow in all material processes.

 

[ram2048]

very interesting. i'll have to look into that one :D

thanks

 

[geistkiesel]

hell if there's general relativity and special relativity I'm going to call mine universal relativity :|

ram2048, I have a problem. I calculated that an electromagnetic sphere whose radius was expanding at a rate equal to c would have a radius equal to c after one second which means the diameter would be 2c afte one second that means the oppositiely directed photons were expanding at a relative rate of 2c.
I was hushed an told be quite. Where is the fallacy in all of this?

 

[ram2048]

i don't see a problem with that... :D

 

[baffledMatt]

You call yourself a physicist, and even seem to think you understand relativity, (I bet you also think you understand Quantum Theory), yet you can't answer this question without your texbooks.

Hmm, sorry I didn't realize that having all the calculations for SR at the tips of ones fingers was a requisite for being a physicist. Does this go for all theories? I mean, should I also be able to solve the 2d Ising model without my books?

Well, I guess I'm not a physicist then... and there I was, doing so well in my PhD and everything...

Matt

 

[relative_sceptic]

I trust we can alter the question slightlty by inserting that two frames had recently shared a comon stationary frame . Each frame knows its velocity is greater than the stationary common frame. Hiowever, the distance between the frames is huge and merely sending their current clock setting won't work in determining which is the faster frame with respect to the common stationary frame. How may the frames determine which is fastest. The frame clocks are identical with a stationary frame clock pulse rate = 1.

Each frame's clock is pulsing at some frequency where the signals are true pulses, | | | | | | | |. Would not the slowest frame receive a pulse rate from the faster at a slower rate than his own pulse rate?

Likewise, would not the fastest frame determine the pulse rate from the slower was generated at a higher frequancy than his own?

This seems rather trivial if true, having heard all the horror stories of relativity theory that seem to deny the ability to do this..

I don't think you are allowed to say that a frame is "stationary", so you also cannot say that the two frames know they are traveling faster than the common frame. They might consider themselves to be stationary and the common frame moving away from them.

 

[relative_sceptic]

Hmm, sorry I didn't realize that having all the calculations for SR at the tips of ones fingers was a requisite for being a physicist. Does this go for all theories? I mean, should I also be able to solve the 2d Ising model without my books?

Well, I guess I'm not a physicist then... and there I was, doing so well in my PhD and everything...

Matt

There you go again, arrogance is quite common in PhD students, fortunately they usually get over it, I'm sure you will too.
What I am trying to point out tho is the contradiction here, I've seen numerous answers to this problem which merely try to avoid the issue or cloud the issue, by pages of calculations and spacetime diagrams, none of which really address the issue.
I'm also trying to say keep an open mind and don't be too sure of what you think you understand, and that you can't blindly accept everything you read in textbooks.
BTW I'm not a supporter of this new TOE guy, it sounds like a scam to sell books to me.

I like to think I can see logical contradictions in arguments, and the bull**** people use to cover them up.
But then who knows.

All I know is that a lot of people have have based a lot of their work on the principles of relativity and if it was accepted that there was some flaw in relativity, their work could be discredited, and their reputations would be diminished. They have a huge vested interest in maintaining the theory as flawless. In which case their motives have to be questioned, and also the validity of the arguments they put forward.
Unfortunately not all scientists have the highest motives, they are as prone to human weakness as everybody else.

Anyway that's enough of a rant, as far as SR is concerned I will just have to wait and hope that time will tell.

---steve

 

[baffledMatt]

By the way...

Mmmmmhhhh

So can someone tell me which one is older when they have both experienced identical accelerations on their journeys, but at different times?

---Steve

Are you aware that this scenario is not symmetric? So any discrepancy between the ages of the twins is not a problem.

Matt

 

[elenaedinburgh]

Thank God for you guys!

 

[vacuum]

Hahaha

The most amazing thing to me is that they've actually provided a link to this discussion on the mentioned site.

 

[Ponder Stibbons]

Spacebound twin shifts reference frames

Ignoring periods of acceleration, the spacebound twin's journey involves two inertial reference frames: One leaving, one returning. So there's three reference frames you're likely to want to consider things from.

From the earthbound reference frame, the earthbound twin undergoes no time-dilation and the spacebound twin undergoes some each way. (I say undergoes because you don't experience it, you see it happening to others.) The spacebound twin is x years younger on return.

From the departing reference frame, the earthbound twin undergoes constant time-dilation. The spacebound twin initially undergoes no TD, then undergoes MORE TD than the earthbound one on the return leg, and is x years younger on catching up with Earth.

From the inbound reference frame, the earthbound twin undergoes constant TD. The spacebound twin initially undergoes more TD, so much that even though he/she/it undergoes no TD on the return leg he/she/it is still x years younger than the earthbound twin when Earth arrives.

See? No paradox - unless you didn't know you had a twin!

 

[Muddler]

Stupid('s) question to Twin Paradoxon

Hi there!
If been thinking a lot about this whole "Twin Paradoxon"-issue.
I don't have a problem to understand, that there is a difference between who is being absolutely accelerated and who is not (since stating that the spacebound twin is "stationary" would mean, the whole rest of the universe has to be moved away from him - taking the two guys solely into account might be right for calculating but not for understanding how the whole thing would work out in "reality". For that kind of understanding a simple guy like me needs simple analogies).

My actual question is, if anyone could tell me why there has to be something like "time dilation" at all? And, if possible, without quoting a pile of formulas that I won't understand anyway.

What was Einsteins "idea" behind the theory that made him state that time has to be relative too?

What would be so awfully wrong about thinking that time is the same, no matter where you are and how fast you are moving?

I know this question might sound stupid to you, but if anyone would take the time and enlighten me, I would be really thankful!

 

[ram1024]

Time dilation exists because it was a necessary assumption (along with length contraction) to keep special relativity consistant.

you can assume that time is absolute and unchanging for all speeds, but then light speed would not be relatively unchanging <measured> to all observers

which is not so bad... :D

 

[Prometheus]

What would be so awfully wrong about thinking that time is the same, no matter where you are and how fast you are moving?

There is nothing wrong with this. Go ahead and believe so, if you like. Physics belived this way for a long time, in what is known as Newtonian physics.

However, scientists wanted to move beyond Newtonian physics, in order to better understand the nature of the world. If you want to join them, then you would have to realize that space and time interact in what is known as space-time. In this scenario, motion through time is dependent upon motion through space. You want to change the rate of motion through space, yet have no affect on the rate of motion through time. This is now understood, in Einsteinian physics, to be impossible.

However, there is nothing wrong with you for not wanting the increased complexity of understanding that is required for what little you might gain in your personal life. Feel free to continue with Newtonian physics, or whatever level of science you may have.

 

[jcsd]

Hi there!
If been thinking a lot about this whole "Twin Paradoxon"-issue.
I don't have a problem to understand, that there is a difference between who is being absolutely accelerated and who is not (since stating that the spacebound twin is "stationary" would mean, the whole rest of the universe has to be moved away from him - taking the two guys solely into account might be right for calculating but not for understanding how the whole thing would work out in "reality". For that kind of understanding a simple guy like me needs simple analogies).

My actual question is, if anyone could tell me why there has to be something like "time dilation" at all? And, if possible, without quoting a pile of formulas that I won't understand anyway.

What was Einsteins "idea" behind the theory that made him state that time has to be relative too?

What would be so awfully wrong about thinking that time is the same, no matter where you are and how fast you are moving?

I know this question might sound stupid to you, but if anyone would take the time and enlighten me, I would be really thankful!

It's possible to demonstarte time dialtion with a simple geometric argument and a few assumptions:

Imagine a beam of light traveling between an emitter and a detector (which are staionary relative to each other) and an observer (denoted by an 'A' in the diagram) moving perpendicualr realtive to the emitter and detector.

This is what is seen from the rest frame of the detector and emitter:

|----->|   A
           |
           | 
           |
           |

This is what is seen from the rest frame of the observer

     /|   A
    /
   /
  /
|/

It's clear to see that the beam of light traveled further from the point of view of our observer A. As the speed of light is constant in ALL rest frames this means that from the point of view of the observer A the light took longer to travel between the emitter and the detecot than it did it did from the point of view of someone in the rest frame and the emitter i.e. time has been dialated.

If we use the Newtonian kinematic equation for constant veocity:

x = ut

And let c be the speed of light, u the relative velcoity of the observer to our emitter/detector set-up, t' the time measured for the beam of light to travel from the emitter to the detector in the emitter/detectr set-up's rest frame and t the time measured for the beam of light to travel from the emitter to dector in A's rest frame then we can annote our second diagram with the appropiate lengths:

     /|   
ct  / |
   /  | ut'
  /   |
 /    |  
------
  ct'

using the Pythagorean theorum we can say:

c^2t^2 = u^2t&#039;^2 + c^2t&#039;^2

therfeore:

t&#039;^2 = t^2(1 - \frac{u^2}{c^2})

therfore:

t&#039; = \frac{t}{\sqrt{1-\frac{c^2}{u^2}}}

which is our formula for time dialation.

 

[tavi_boada]

Jack, it is not true that physics can't answer that question. An iluminating way to view it is with the analogy of waves on a cord. Suppose you start moving up and down the end of a rope of a certain density. The perturbations will propagate along the cord at a certain speed which is related to it's density. Now suppose you tie another cord with a different density to the opposite end of the first one. The perturbation traveling along the first rope will be transmitted faster on the new rope if it's density is smaller, and this is only non-relativistic classical physics. There will be reflections, the wave transmitted to the new rope will be less energetic,etc.

This analogy is not completely accurate because light doesn't propagate in a medium, but it helps.

 

[zoobyshoe]

which is our formula for time dialation.

I have read this example set up differently, where the emitter/detector were moving and the observer stationary.

In that case, I have wondered if the moving emitter/detector were moving at an appreciable fraction of the speed of light would the light actually be shown to have any component of movement in the direction of travel?

It isn't the same situation as tossing a ball up and down on a train where the ball already has momentum in the direction of train travel. The photon is created on the spot, and since quanta are not like anything else, I wonder if a stream of photons emmitted at 90º to the direction of travel wouldn't actually have the appearance of a curve away and opposite to the direction of travel. If the detector were far enough away and the speed of the emitter great enough, the photon might not even hit the detector before it (the detector) moved out of the way.

 

[jcsd]

I have read this example set up differently, where the emitter/detector were moving and the observer stationary.

I actuually thought that one up myself, but I was flicking through Feynman vol 1 and I noticed that he had almsot exactly the same demonstartion in it, so I may of unsuspectingly took the idea from there. Due to the relativity of constant motion there is no objective difference between the observer and the emitter/dector moving.

In that case, I have wondered if the moving emitter/detector were moving at an appreciable fraction of the speed of light would the light actually be shown to have any component of movement in the direction of travel?

The diagrams do imply that the dector/emitter is moving at very close to the speed of light (in fact if you study the actual lengths in the diagram they're moving at above the speed of light, but the diagram is only meant to be a rough sketch so don't draw any conclusions from that!)

I think you have to be clearer on what you mean by direction of travel' i.e. whose direction of travel relative to what?

 

[ram1024]

Due to the relativity of constant motion there is no objective difference between the observer and the emitter/dector moving.

i have outlined exactly why "changing the objective frame" doesn't hold true for dealing with light

you are on the right track, zooby. if you want to sift through 25 pages of arguments i have a thread "Today special relativity dies". it gives pretty good arguments from both sides in detail so you can see where each are coming from

 

[zoobyshoe]

In the case where the emitter/detector are moving the direction of travel is theirs. The light is emitted at 90º to this.

 

[zoobyshoe]

you are on the right track, zooby. if you want to sift through 25 pages of arguments i have a thread "Today special relativity dies".

I'll wait till the Reader"s Digest short version is issued.

I'm not really on a track here, so much as trying to separate what is "gedanken" from what is real. You can't see a beam of light to begin with, so it may also be that the path it takes is also a stipulation. I'm not quite sure.

 

[jcsd]

i have outlined exactly why "changing the objective frame" doesn't hold true for dealing with light

you are on the right track, zooby. if you want to sift through 25 pages of arguments i have a thread "Today special relativity dies". it gives pretty good arguments from both sides in detail so you can see where each are coming from

Your arguments are based on Gallilean relativity, which is odd as you also reject that.

 

[jcsd]

In the case where the emitter/detector are moving the direction of travel is theirs. The light is emitted at 90º to this.

In that case there must be a component in the direction they are travelling, the only case when this is not so is when the relative velocities are zero 9in which case they don't have a direction of motion).

For the case of 90 degrees, remember in special relativity light always travels in a straight line in all inertial refrence frames.

 

[ram1024]

Your arguments are based on Gallilean relativity, which is odd as you also reject that

i had no idea what "Galilean Relativity" was until i brought my thoughts to this forum. so my thoughts are not "based on" galilean relativity, but many of the principles remain the same.

i've never rejected it, i just don't know enough about it to see what's wrong with it... if anything.

 

[ram1024]

I'll wait till the Reader"s Digest short version is issued

i understand completely :D

it helps to view it internally, and find a self-rational view of how things would work. then tackle what scientists have concluded piece by piece, comparing it to your own view and re-structuring how you view things if need be.

you end up with a view of how things work AS MAKES SENSE TO YOU <which is important> and also consistant with how others have found things to be.

 

[reilly]

As to how light "speeds back up" after leaving a substance, here is the easiest way of looking at it.

Photons always travel at c. When they enter a transparent substance, however, they encounter molecules/atoms. As they do so, the molecules absorb the photons. When that happens the photons cease to exist.

Then after a short delay, the molecule , re-emits a photon traveling in nearly the same direction as the first. This new photon, upon creation, begins to travel at c until it encounters another molecule.

These slight delays between absorption and emission, increases the time it take from the time a photon enters a substance to the time one emerges form the other side.

This give the impression that light slowed down while traveling through the subtance.
(If you knew that some friends had left their home, which was 60 miles distant from you, at a given time, and they arived at your house 1 1/2 hrs later, It would seem to you that they drove the distancea 40 mph. Even if, while on the road, they drove at 60 mph, but stopped for gas along the way, got a quick bite to eat somewhere, had to fix a flat , etc. )

Light travels though a substance in similar fits and starts.

RA What you say is true, but the actual computations and detailed theory are dificult. (Among the early contributors are some of the marques names in physics, Rayleigh (explained why the sky is blue), Einstein and Smolukowski who investigated and showed the importance of fluctuation in local numbers of molecular scatterers, less well known is Mie who developed the theory of why the rainbow looks as it does.

The slowdown occurs through interference inside the material -- the slowdown is reflected in the so-called group velocity of a wave packet , all frequencies treavel at c-- the scattering results in changes in the frequency of the light. The frequency shifts are due to, among other things, molecular recoil, and sometimes due to so-called radiative broadening due to the lifetimes of the excited molecular states.

But, once outside, the light suffers no interference, and so goes at c. There are no contradictions; the theory has been tested countless times -- including the theory of radar we all depend on while flying.

The theory, like most in physics, is descriptive, as are Maxwell's equations. We physicists make no pretension that we understand how, or why charges emit radiation or produce fields. But the modern world is testimony that once we assume fields, the resulting theory is staggeringly useful, and remarkably accurate.

Regards,
Reilly Atkinson

 

[zoobyshoe]

In that case there must be a component in the direction they are travelling, the only case when this is not so is when the relative velocities are zero 9in which case they don't have a direction of motion).

But I'm trying to determine if your "there must be" is a stipulation or if it has been determined to be true. Will a photon emitted from a spaceship traveling at an appreciable fraction of c at 90º to the ships direction of travel actually have a component of motion in the direction of the ships travel? Or is this a stipulation to make the point about what the observer will see?

Imagine the emitter/detector as two ships both traveling in the same direction at the same speed .9999999c. They are side by side but separated by 300,000 miles. It will take well over a second for a photon to cover this distance.

If ship Emitter aims its photon gun at ship Detector and fires one round, will not ship Detector have vacated the target area by the time the photon arrives where it was aimed?

If someone on ship Emitter throws a rock at ship Detector it will, indeed, eventually hit ship Detector. The rock, though, has acquired momentum in the direction of Emitter/Detector's travel by virtue of its mass. A photon has no mass and I wouldn't be surprised to find out it behaved differently than a rock in the same circumstances.

 

[Muddler]

There is nothing wrong with this. Go ahead and believe so, if you like. Physics belived this way for a long time, in what is known as Newtonian physics.

However, there is nothing wrong with you for not wanting the increased complexity of understanding that is required for what little you might gain in your personal life. Feel free to continue with Newtonian physics, or whatever level of science you may have.

Hmmph!
That's just the kind of answer I needed.
I know you are brilliant and I'm a klutz, but I knew that before.
The problem is, I'd like to believe in Einsteinian physics, but it's not as easy for me to just accept it without understanding the problems that Einstein's theory claims to solve.
Time dilation is explained as a necessary consequence of relativity.
But why is it so important for lightspeed to be measured as a constant value?
I have no problem with lightspeed being constant and I know that experiments have shown a constant value for lightspeed even with moving emitters and detectors. But that was on earth (or near it) and the speed of the objects has always been small in relation to the speed of light.
Do you know of any experiment (references welcome!), where light-emitters have actually been accelarated to near-lightspeed? (And I mean lab-experiments, not any distant supernova or anything we measured and calculated already using Einstein's concepts)
You see my problem?
People always seem to say that relativity (with all its consequences) has to be true, because...because it needs to be true to work!
That simply doesn't satisfy me.
I know that many things can be accurately calculated using Einstein's formulas, but to me that's not the same as Einstein's idea of spacetime being real.
I always try to get a concept of physics as a whole, to understand what a formula or theory means.

I know, you are going to tell me, I won't be able to understand it without becoming a student of physics and getting a degree, but I'm arrogant enough to think, that if you are not able to make me understand doesn't necessarily mean that I'm the one who is stupid...

 

[ram1024]

skepticism is healthy as long as you can handle the criticism that comes with non-believing :D

basic physics is quite easy, and it's absolutely necessary just in order to get your foot in the door to understand anything.

the thinking part is more important than knowledge. according to basics:

1. knowing how to learn
2. knowing things
3. knowing how to apply "things"
4. knowing history and knowing how things have been used in the past
5. knowing society and the consequences and ramifications of using things

at that's that's the hiearchy as I've found it to be

 

[Prometheus]

Hmmph!
That's just the kind of answer I needed.
I know you are brilliant and I'm a klutz, but I knew that before.

I never said that I am brilliant or that you are a klutz. All I said was that you do not have to learn about relativity, and therefore that you do not have to accept its tenets, if you do not wish to.

But why is it so important for lightspeed to be measured as a constant value?

Let me take a stab at this one. How is our species aware of time? Fundamentally, we are aware of time by observing motion through space. (For example, to be aware of units of time such as the month and the year, we observe the motion of the moon and the sun through space.) Therefore, space is necessary in order to be aware of time. How is our species aware of space? By observing changes in space. Such changes require time. Therefore, to be aware of space requires time, and to be aware of time requires space. This is the nature of space-time. How are we aware of space and time. By light. Light emitted from objects in space reaches our eyes and our techincal instruments to inform us of objects in space. Without light, there can be no awareness of time or space. Further than this, without light, there is no motion through time or space. Light is not only that which informs us of time and space, light is the enabler of space-time. Light is the enabler of space-time, and light is the conveyer of information about space-time. Everything that we see emits light all of the time.

Our part of the universe was thrown far out in space from the Big Bang. All of space-time in this part of the universe moves at a fairly constant rate of motion through space, and therefore a fairly constant rate of motion through time. This includes our light. The light in this part of the universe moves at a fairly constant rate of motion through space, and a fairly constant rate of motion through time. Although the rate of motion through space-time is constant for the entire universe, the rate of motion of light through space only seems constant in this part of the universe, but is not so everywhere in the universe.

The speed of light seems constant because there is motion through space-time only when there is light. Light, once emitted, does not age. It therefore travels at the same rate of motion through space and time. All of the light that we can see in this part of the universe is roughly the same age, and therefore moves at basically the same speed. We are unable to detect any differences.

Your usage of the word lightspeed reflects an understanding that light is in motion through space. You must also understand that light is in motion through time. In other words, light is in motion through space-time, and that motion through space and time is symmetrical. Increases in motion through space result in symmetrical decreases in motion through time, and vice versa. When you use the word lightspeed, you seem to be using a Newtonian definition, whereby speed though space is meant. You should realize that everything in the universe moves at the speed of light; it is only the spatial and temporal components that are subject to change.

 

[zoobyshoe]

That's not a useful answer to muddlers question.

The question, itself, isn't put well. It is not important for light to be measured as constant. What happened is that when they have measured the speed of light, it always turns out to be constant. Even if you are, yourself, going at half the speed of light, a beam of light traveling in the same direction will pass you at the full speed of light, when it should seem only to be going half the speed of light.

Why it is like this is, really, a complete mystery. Einstein's solution to the problem was to theorize that, since light behaves that way, it must be because time is not absolute, that it can dilate in one reference frame relative to another by virtue of different relative velocities between the two reference frames.

Alot of people believe Einstein hit the nail on the head and explained the apparent problem with the constancy of the speed of light. Others have a lot of doubts.

Relativity is accepted by main stream physics, which doesn't mean you can't question it, but you get a great deal of resistence, of course.

 

[Muddler]

To Prometheus:
Sorry, no offense meant! I was just a bit frustrated about your "answering" my question by just talking about how complex physics are (by the way- I have to say that even your second response does not feel like an answer to my question to me...)

To Zoobyshoe:
You are right, my question wasn't put very well. What I really wanted to know is: have there been any experiments at higher speeds (e.g. half lightspeed as you stated) which prove that lightspeed is still constant with emitters/detectors moving that fast?
For I thought that all actual experiments where done using velocities which were small compared to lightspeed (and therefore our observations of constant lightspeed might not be as valid as we might think...).
It is easy to give examples of bodies moving at near-lightspeed when backed up by such an widely accepted theory as relativity, the question is which kind of examples are valid to prove it...

To all:
Just think about this one: instead of stating that lightspeed is the highest possible velocity in our universe you could as well say that lightspeed is the highest detectable speed (let's say for some reason as "spacetime-viscosity"). If we assume that any measurable effect in our universe can only be followed at lightspeed (just the way we are only able to perceive separate movement below frequencies of about 25 Hz - bad example, but I think it gets the idea...), then there would be no need for spacetime-dilation at all. I know this is pure speculation and therefore can't be disproved easily. But I don't find it harder to imagine that anything moving faster than light is just to quick to follow than trying to figure out, what warped spacetime looks like...

And finally:
As far as I understood Einstein's formula, any object (mass not zero) you try to accelerate to lightspeed (or above) will cause it's mass to go against infinite once you reach the "border", which means all additional acceleration-energy is then conversed directly into mass. If this is so, how comes all real fast moving particles we are able to observe have very little masses (or non at all) ?? And if you take E=mc² literally, doesn't that mean, that photons (which are said to have no mass) contain no energy at all??
The answer to that might be clear to you, but it keeps boggling my mind for sure...

 

[jcsd]

But I'm trying to determine if your "there must be" is a stipulation or if it has been determined to be true. Will a photon emitted from a spaceship traveling at an appreciable fraction of c at 90º to the ships direction of travel actually have a component of motion in the direction of the ships travel? Or is this a stipulation to make the point about what the observer will see? [p/quote]

I don't think I was partciualrly clear there must be, in the exmaple I showed were the light is emitted at 90 degrees to the direction of motion in the emitters rest frame, that's just a result of galliean relativity

Imagine the emitter/detector as two ships both traveling in the same direction at the same speed .9999999c. They are side by side but separated by 300,000 miles. It will take well over a second for a photon to cover this distance.

If ship Emitter aims its photon gun at ship Detector and fires one round, will not ship Detector have vacated the target area by the time the photon arrives where it was aimed?

No because the dector is at rest to the emitter so in that frame it doesn't even move and it just comes from self-cnsistenty that it must hit the dector in all rest frame.

If someone on ship Emitter throws a rock at ship Detector it will, indeed, eventually hit ship Detector. The rock, though, has acquired momentum in the direction of Emitter/Detector's travel by virtue of its mass. A photon has no mass and I wouldn't be surprised to find out it behaved differently than a rock in the same circumstances.

Rocks and photons do behave diffreently, but there's no need to consider the photons momantum here even as the importnat fact here is that light always travels at c.

 

[jcsd]

To Zoobyshoe:
You are right, my question wasn't put very well. What I really wanted to know is: have there been any experiments at higher speeds (e.g. half lightspeed as you stated) which prove that lightspeed is still constant with emitters/detectors moving that fast?
For I thought that all actual experiments where done using velocities which were small compared to lightspeed (and therefore our observations of constant lightspeed might not be as valid as we might think...).
It is easy to give examples of bodies moving at near-lightspeed when backed up by such an widely accepted theory as relativity, the question is which kind of examples are valid to prove it...

I think there's 2 different things at work here:

1. the model that is special realitvity

2. evidence for that model.

So far we've only adressed the model, but be assured there is ALOT of evidence for special relativity.

 

[Muddler]

I think there's 2 different things at work here:

1. the model that is special realitvity

2. evidence for that model.

So far we've only adressed the model, but be assured there is ALOT of evidence for special relativity.

Of course there is! That's why the theory of relativity is still used.
I'm not trying to discredit the whole theory, all I wanted to know is, what kind of proof we have to rightfully assume lightspeed to be constant under all thinkable (or better: testable) circumstances. If you have references for such experiments, I'd be real happy!

 

[ram1024]

Tom Mattson is currently on a mission (albeit slightly MIA) to collect his available data for speed of light trials.

i'm thinking there was a mathematical calculation error personally, hopefully i can pinpoint where it is and convince you guys to see it from my perspective (which seems to be the hard part) :D

 

[russ_watters]

...all I wanted to know is, what kind of proof we have to rightfully assume lightspeed to be constant under all thinkable (or better: testable) circumstances. If you have references for such experiments, I'd be real happy!

We've got quite a collection in THIS thread.

 

[reilly]

One can always hope that tunnel vision of SR will expand -- at what cost, who knows. There are a few points that typically get lost in these endless discussions of the validity of SR.

First, physics is a rough and tumble sport, and physics is full of predators. That is, at the first sign of weakness or fuzziness in a theory, and experiment, a calulation, physicists will jump all over the offending offering. So, SR has been cross-examined to an almost infinite degree. Someone earlier in this thread wrote about vested interests protecting SR. Nothing could be further from the truth. Any physicist would love to be the one to poke a hole in SR; that would mean immortalitiy. Just has not happened. The seminars in physics departments can be terribly vicious. Those challenging SR would last at most minute or two before being torn to intellectual shreds in any physics department seminar. Most posts here are gentle compared to comments from most professional physicists.

Second, physics like the law depends greatly on circumstantial evidence, mostly in the form of two way logic chains. The entire enterprise of particle physics depends critically on SR, usually with respect to relativistic kinematics -- and relativistic QM and field theory. That is, if the assumption that the speed of light is constant is not true, then many parts of physics would simply be wrong. That is, the evidence supporting SR is overwhelming. So overwhelming that it takes several years of course work to learn about the extent of the fabric of SR. About almost direct measurements of c: the pi 0 meson decays into two photons. if I'm not mistaken there's lots of data on the photon frequencies for a variety of pi 0 speeds. Circumstantial evidence to be sure, but it supports SR, and isotropy of c.

Is it possible that SR is wrong? Of course. But if it is, the odds are that the problems will emerge in areas about which we don't know much. Certainly we don't know much about photons that carry, say the energy of an asteroid. Perhaps at enormously high frequencies there might be problems. This suggests, perhaps, problems with relativistic field theory. There is, undoubtedly massive opportunity in the ultra-ultra hight frequency aries of physics.

It seldom pays to look for problems where the light has exposed all the nits and nats.

Regards,
Reilly Atkinson

 

[geistkiesel]

One can always hope that tunnel vision of SR will expand -- at what cost, who knows. There are a few points that typically get lost in these endless discussions of the validity of SR.

First, physics is a rough and tumble sport, and physics is full of predators. That is, at the first sign of weakness or fuzziness in a theory, and experiment, a calulation, physicists will jump all over the offending offering. So, SR has been cross-examined to an almost infinite degree. Someone earlier in this thread wrote about vested interests protecting SR. Nothing could be further from the truth. Any physicist would love to be the one to poke a hole in SR; that would mean immortalitiy. Just has not happened. The seminars in physics departments can be terribly vicious. Those challenging SR would last at most minute or two before being torn to intellectual shreds in any physics department seminar. Most posts here are gentle compared to comments from most professional physicists.

Second, physics like the law depends greatly on circumstantial evidence, mostly in the form of two way logic chains. The entire enterprise of particle physics depends critically on SR, usually with respect to relativistic kinematics -- and relativistic QM and field theory. That is, if the assumption that the speed of light is constant is not true, then many parts of physics would simply be wrong. That is, the evidence supporting SR is overwhelming. So overwhelming that it takes several years of course work to learn about the extent of the fabric of SR. About almost direct measurements of c: the pi 0 meson decays into two photons. if I'm not mistaken there's lots of data on the photon frequencies for a variety of pi 0 speeds. Circumstantial evidence to be sure, but it supports SR, and isotropy of c.

Is it possible that SR is wrong? Of course. But if it is, the odds are that the problems will emerge in areas about which we don't know much. Certainly we don't know much about photons that carry, say the energy of an asteroid. Perhaps at enormously high frequencies there might be problems. This suggests, perhaps, problems with relativistic field theory. There is, undoubtedly massive opportunity in the ultra-ultra hight frequency aries of physics.

It seldom pays to look for problems where the light has exposed all the nits and nats.

Regards,
Reilly Atkinson

Reilly take Enstein;s gedunken experiment where two photons are emitted simultaneously at A and B just as the moving observer is at the midpoint M of the A and B sources. As the moving frame continues it first detects the B phtobn and later the A photon coming from the rear. Einstein uses this sequential observtion of the pohotons as a definition of the loss of simultaneity and says that the observers in the moving frame "must therefore" conclude the photons were notwemitted simulataneously in the moving frame.

Let ius redesignethe experiment. At M the midpoint of gthe A and B photon sources, we insert some mirrors (\/) that deflect the A and B photons simultaneously into the moving frame, simultaneously. The photons are reflected when side by side. Tell us how the moving observers are able to, 1). Detect the photons were not emitted simultaneously in the moving frame and 2), which photon came from which source and 3) how simultaneity can possibly have any relevance to this problem that AE used as an example for the loss of simultaneity and the discarding of absolute time, among other aspects of SR.
If you can't answer this one you just kissed special relativity goodbye.

      M
  A-->\/<--B  stationary frame.
      ||
########### detectors in the moving  --> frame.
     A'B'

 

[russ_watters]

If you can't answer this one you just kissed special relativity goodbye.

Your continuing misunderstandings of SR do not constitute evidence that it is wrong.