Can the Speed of Light Be Changed and What Does It Mean for Space Exploration?

[Doc Al]

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.

 

[Doc Al]

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.

 

[bino]

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.

 

[Nenad]

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.

 

[bino]

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?

 

[Nenad]

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]

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

 

[bino]

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? don't they do something with the end points.

 

[Chronos]

yes i know this but how was this equation formed? i know that it is some how derived from time dilation. right? don't they do something with the end points.

No. Why would you need to?

 

[Doc Al]

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]

yes i know this but how was this equation formed? i know that it is some how derived from time dilation. right? don't they do something with the end points.

You could also measure the time it takes to pass you and divide that into the speed.

 

[quantumdude]

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!

 

[Nenad]

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]

You'd multiply the time by the speed.

Always check your units!

Uh, yeah - what he said. Hey, why am I not working right now?!

 

[Doc Al]

Both frames equally valid

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.

 

[Nenad]

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.

 

[Nenad]

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, please explain to me a little more about the case youve set up, its very interesting.

 

[Doc Al]

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]

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!

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, please 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.

 

[Nenad]

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.

 

[The Bob]

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 ©)

 

[Chronos]

Incorrect. Each frame in background independent. Simultaneity does not exist in either reference frame.

 

[The Bob]

Incorrect. Each frame in background independent. Simultaneity does not exist in either reference frame.

Ok, sorry.

The Bob (2004 ©)

 

[Doc Al]

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.

 

[Nenad]

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?

 

[Doc Al]

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.

 

[h8ter]

Why is it that light goes faster with the rotation of earth, and light goes slower against the rotation of earth?

 

[Nenad]

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). I've never heard of light being faster in ine direction. Do you have a source?

 

[pervect]

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.

 

[h8ter]

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.

 

[pervect]

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

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.

 

[h8ter]

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.

 

[bino]

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.

 

[Nenad]

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..). Let's 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.

 

[Doc Al]

length contraction

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.

 

[h8ter]

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.

 

[pervect]

If I had any reproducible evidence that disproved SR, I'd be standing in line to get my Nobel prize

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.

SR is really a well tested theory, and it has been for probably the last 50 years or so.

 

[bino]

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?

 

[Nenad]

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.

 

[Nenad]

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.

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.

 

[bino]

eventhough I am going almost the same speed?

 

[Nenad]

yes that's 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.

 

[bino]

so then if we were going the speed of light, light would still be going a lot faster than us?

 

[Doc Al]

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.

 

[bino]

thats interesting.

 

[bino]

so you find the length of a moving object by the time*speed?

 

[h8ter]

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]

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.

 

[Doc Al]

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.

 

[unicorn]

And what is your opinion about tachyons, do they exist? Sorry if anyone asked this before.