# Thread: Time Dilation

1. okay..but i have a question on the subject of light-clocks.

and maybe i've got this all wrong...but i have to ask.

a frame or light-clock with a relativistic velocity may experience time dilation...but be unaware that it's time rate is different to another that has no velocity....because it has nothing to reference itself against.

we agree that due to the velocity, a perpendicular light-clock will return a symmetrical result...and one angled at eg: 90dg..an asymmetrical result.

whereas, if neither were experiencing motion, they would both return a symmetrical result.

so we should therefore be able to combine them in a test of absolute motion.

because if either of the 2 returned an asymmetric result, it would immediately signal that there is motion....regardless of whether it can be felt or observed.

but then, isn't this the same setup that was used by mitchelson-morley to prove the obverse....that we can detect no absolute motion in this manner?

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No, it's not the same. Michelson and Morley tried to detect differences in the speed of light in two perpendicular directions. They didn't try to use the light as a clock.

But we do not have to think about perpendicular directions at all. In Percival's frame light will seem to take more time traversing the northbound train from south to north than from north through south. But in Nicholas' frame, with its slanted lines of simultaneity, light will take the same time to traverse the train in both directions.

If two light beams are emitted forward and backward simultaneously (in Nicholas' frame), they will simultaneously (in Nicholas' frame) reach the other end of the train. The two lines of simultaneity and the worldlines of the front and back of the train form a parallelogram both of whose diagonals are slanted by 45 degrees from the horizontal. I.e. both of whose diagonals are light rays.

Light rays emitted in an East-West direction would be represented by the diagonals of a rectangle, normal to the diagram and lying in a plane of simultaneity, which is also normal to the diagram and intersects it in one of Nicholas' lines of simulaneity.

3. i'm not proposing that they did use the light for a clock....but instead for a test of relative propagation speed of light against a moving body.

there should be asymmetry in both setups....or...put another way...a velocity based doppler shift.

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There is no difference, and we can calculate this in Percival's frame.

First, something with speed C is overtaking something at distance D' with speed V. This will take a time T1, where T1 * C = D' + T1 * V.

Next, something with speed C is meeting something at distance D' with speed V. This will take time T2, where T2 * C = D' - T2 * V.

T1 + T2 = D' / (C - V) + D' / (C + V) = 2CD' / (C * C - V * V)

The perpendicular signal, on the other hand, must travel twice the hypotenusa of a rectangular triangle with sides D" and T3 * V, where T3 is the time needed to travel this hypotenusa once. Hence T3 * C squared is equal to D" squared plus T3 * V squared, or T3 = CD" / sqrt(C * C - V * V)

Now, for the parallel signal we find T1 + T2 = 2D' / (1 - (V/C)^2)
And for the perpendicular signal we find 2T3 = 2D" / sqrt(1 - (V/C)^2)

If D' and D" are equal in Nicholas' frame, then D'/D" in Percival's frame must, by the Lorentz contraction, be equal to sqrt(1 - (V/C)^2), making both expressions equal.

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This thread is on "Time Dilation", correct?

If this is indeed the case, there is a direct, incontrovertible proof that time dilation exists, it is measurable and it is a real effect. It stems from an experiment done by ....two antirelativists H.Ives and Stilwell. They set up to demonstrate that the transverse Doppler effect predicted by the 1905 Einstein paper was flawed. Luckily, I_S were VERY good experimenters and they proved...Einstein right!
The "Ives-Stilwell" experiment has become an "acid test" for "alternate theories". Most "aether" based theories pass the MM and Kennedy-Thorndike experiments thru clever tricks (most of them invoke the FitzGerald contraction ,conveniently "forgetting" that it was refuted by...another antirelativist, Trouton in 1903 and 1908). But they cannot pass the Ives-Stilwell test!
It is interesting that the antirelativists had such a great contribution in proving relativity. (BTW Michelson died a convinced "anti").

6. Relmuis

i'm talking about one reference frame....with basically an L shaped arrangement of the 2 light-clocks...in a manner similar to Lisa/Ligo.

if there is no motion...both light-clocks will return a symmetrical result.

but if there is any motion of the array through space..one of the light-clocks will return an asymmetrical result.

another example would be if the array was placed on your train.

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Originally Posted by madman
Relmuis

i'm talking about one reference frame....with basically an L shaped arrangement of the 2 light-clocks...in a manner similar to Lisa/Ligo.

if there is no motion...both light-clocks will return a symmetrical result.

but if there is any motion of the array through space..one of the light-clocks will return an asymmetrical result.

another example would be if the array was placed on your train.
If they have an asymmetrical result, it means the photons do not return to the origin at the same time, so a stream of photons should show a phase shift and interfere - i.e. a Michelson interferometer. But we don't see this when we do the experiment, so how do you reach this conclusion?

8. the conclusion is taken directly from the results of the light-clocks seen in the example gifs i posted.

we agreed that, if given a set velocity, eg: @0.5C.

a perpendicular one would return a symmetric result.
(1.155+1.155=2.31)

and one angled at 90dg would give an asymmetric result.
(2+0.67=2.67))

and again...both would return a symmetric result if stationary.
(1+1=2)
(1+1=2)

and yes...that's what i was wondering about, if combined into an L-shaped detector, they would be like a michelson-morley interferometer....and should detect absolute motion (motion against einstein's "stationary space"?)

but again, as you've pointed out, the result of michelson and morleys' experiment was a negative for this type of test.
Last edited by madman; 2005-Dec-19 at 03:55 AM.

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Originally Posted by madman
the conclusion is taken directly from the results of the light-clocks seen in the example gifs i posted.

we agreed that, if given a set velocity, eg: @0.5C.

a perpendicular one would return a symmetric result.
(1.155+1.155=2.31)

and one angled at 90dg would give an asymmetric result.
(2+0.67=2.67))
I've already explained why this analysis is incorrect. You have neglected to account for the length contraction present in the second case.

10. swansont (on the round-trip of a 90dg angled light-clock's time, being equal to a perpendicular one)
It does if you do it correctly. The other observer sees the lengths contracted by 0.866: 2.67 * 0.866 = 2.31

swansont
Of course there is an "other" observer - there is one at rest with respect to the clock, and one that is moving with respect to the clock (or sees the clock moving with respect to him). There is no time dilation within a single reference frame, it is always in one frame compared to another.

The person at rest sees one unit of time between the forward and backward transits of the photon, separated by a distance L. The person who sees the clock moving does not see the forward motion take 2 units, because the distance is not 2L, it is 2L/gamma because of length contraction. Similarly, the backward motion is not .67L - you need to divide by gamma there as well. Once you do that (i.e. properly apply relativity) then the round-trip times are equal for any orientation of the clock.

The reason you must "tick-tock" is because of the asymmetry that you have introduced, and I explained above. You have to do an apples-to-apples comparison of the elapsed time.

i disagree with:

"There is no time dilation within a single reference frame, it is always in one frame compared to another."

i have shown that time dilation is an inherent effect due only to velocity.

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swansont
Of course there is an "other" observer
where was this "other observer" in michelson'morley's experiment? (see bold text above).

and how did they "move with respect to the clock"?

...so as to ensure that they observed the lorentz contraction?

11. Michelson-Morely was not a test of Relativity, not a test of time dilation. It was simply a test of the non-variance of c.

If there were such a thing as "absolute" rest, that is, if the speed of light were only constant relative to some absolute definition of 0 velocity, then M-M would have detected that. Not because of the asymmetry of the individual trips, but because the total round-trip time would be different for the perpendicular pulse than for the parallel pulse.

Madman: Under SR, the non-symmetry of the parallel light clock is only going be real when the clock is in motion relative to the observer (and it will be real regardless of whether it's the clock or the observer who is moving). When the clock and observer are stationary relative to each other, the two legs of the trip are symmetrical.

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Originally Posted by madman
i disagree with:

"There is no time dilation within a single reference frame, it is always in one frame compared to another."

i have shown that time dilation is an inherent effect due only to velocity.
You don't have a velocity unless you have a second frame of reference. Velocity is always measure with respect to something.

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One way to see this is to imagine the X-T-plane tiled with congruent parallelograms, which represent the frame of reference of an observer in uniform motion (i.e. an inertial frame of reference). That is; if the motion is in the X-direction. Adding the Y- (or perpendicular) direction creates a X-Y-T-solid tiled into congruent parallelepipeds, which are the rectangular prisms on the earlier parallelograms. The sides of the parallelograms are Nicholas' units of time and space (one second, and 300,000 km, for example).

For Percival, the parallelograms are squares. But for Nicholas, they are not. Their diagonals, however, must always be slanted 45 degrees to the horizontal (they are the possible trajectories of light rays). And in both frames the unit cell must have unit surface.

Anyone will probably agree that with these restrictions the sides of Nicholas' parallelograms will both be larger (by the same amount) than the sides of Percival's squares. Which means that, to Percival, Nicholas will have his time unit and space untit dilated by the same amount. They are, in other words, rhombs.

But to Nicholas, it is vice versa. His co&#246;rdinate axes follow the sides of his rhombs, making them look like squares. And to him, Percival's squares look like rhombs.

The situation is symmetrical.

Now as to the parallel versus perpendicular beam of light. The parallel one follows first the long diagonal of a rhomb, and then (after being reflected) the short one of the next higher one. Whereas the perpendicular one follows first the diagonal of a rectangle, and then the other diagonal of the next higher one. If they start in the same corner of a unit parallelepiped, they will end up in the same corner of a parallelepiped two units further into the future. Starting at the same point of time, they return in the same (later) point of time. Therefore, they have taken the same time to travel.
Last edited by Relmuis; 2005-Dec-19 at 04:05 PM.

14. SeanF
Michelson-Morely was not a test of Relativity, not a test of time dilation. It was simply a test of the non-variance of c.
i agree with that...but an inference that can be made is that light would always interact with (or intercept) matter at a fixed RELATIVE velocity of C...and to always do that regardless of the velocity of the matter?

is that what we are to assume from the concept of "constancy of the speed of light"?
otherwise...in what way does it remain constant? (see the next quote).

If there were such a thing as "absolute" rest, that is, if the speed of light were only constant relative to some absolute definition of 0 velocity,..
the gifs i posted show that both light and matter must move relative to a fixed coordinate frame...which i take as being einstein's "stationary space".

this relative motion of light and matter against a fixed coordinate frame must occur if we are to get the correct results for time dilation.

space can't warp and speed can't alter...otherwise they will skew the result.

...then M-M would have detected that. Not because of the asymmetry of the individual trips, but because the total round-trip time would be different for the perpendicular pulse than for the parallel pulse.
yes...that's what i was saying....and i tallied the results of the round trips for you.

if there is no velocity, both will return a symmetrical result.
(1+1=2) clock 1
(1+1=2) clock 2

@0.5C
(1.155+1.155=2.31) clock 1
(2+0.67=2.67) clock 2

the fact that the clocks in the 2nd case differ on their individual results, shows there is motion (the 2 stationary clocks do not differ from each other).

some questions.

is it not then just the sidereal effect that clj4 mentioned on another thread?
why did miller-dayton detect this..and not michelson-morley?

Madman: Under SR, the non-symmetry of the parallel light clock is only going be real when the clock is in motion relative to the observer (and it will be real regardless of whether it's the clock or the observer who is moving).
no...it will be real due to it's non perpendicular angle to the direction of travel.

When the clock and observer are stationary relative to each other, the two legs of the trip are symmetrical.
no...when a light-clock by itself is either stationary....or moving perpendicularly to the direction of motion...the legs will be symmetrical.

15. Originally Posted by swansont
You don't have a velocity unless you have a second frame of reference. Velocity is always measure with respect to something.

"relative velocity of objects" requires 2 "objects" to reference against each other.

"absolute velocity" itself is relative to coordinate space.

16. Originally Posted by madman
"relative velocity of objects" requires 2 "objects" to reference against each other.

"absolute velocity" itself is relative to coordinate space.
And how are these coordinates in coordinate space marked?

Is there some way that I can dip into space itself periodically and obtain these coordinates so that I may determine my "absolute velocity"?

17. Celestial Mechanic

that's the reason for the detector that i described.

but the question i was asking was:

if this is the same setup as what michelson-morley used (and they were not applying the lorentz contraction)...how did they get a null result?

shouldn't they have detected the sidereal effect?

or a doppler motion from the earth or solar system?

18. Originally Posted by madman
this relative motion of light and matter against a fixed coordinate frame must occur if we are to get the correct results for time dilation.
No. The time dilation occurs because there is no fixed coordinate frame. If there were a fixed coordinate frame, then you would actually be able to measure the different velocities of light. You wouldn't have time dilation, you'd have a variable (relative) light speed.

Originally Posted by madman
if there is no velocity, both will return a symmetrical result.
(1+1=2) clock 1
(1+1=2) clock 2

@0.5C
(1.155+1.155=2.31) clock 1
(2+0.67=2.67) clock 2

the fact that the clocks in the 2nd case differ on their individual results, shows there is motion (the 2 stationary clocks do not differ from each other).
And the Michelson-Morely experiment would have detected that round-trip difference if there were one. It didn't, because there isn't. And that means there's no fixed coordinate frame (either that, or the Earth is motionless relative to the fixed coordinate frame).

19. SeanF
If there were a fixed coordinate frame, then you would actually be able to measure the different velocities of light.
no..the absolute velocity of light remains the same.

we would measure alterations in frequency by altering our relative velocity (this is the light based version derived from the doppler shift effects of sound).

this would cause a relative difference of velocities.

You wouldn't have time dilation, you'd have a variable (relative) light speed.
you would still have time dilation..because it is due to the relative speed of the light and the matter.

light requires time to travel from mirror to mirror.

the light clock motion causes the distance between emission point and detection point to alter....therefore creating an altered transmission time...or "inherent physical time dilation".

(either that, or the Earth is motionless relative to the fixed coordinate frame).
YES

this is what appears to be the result of their experiment.

why didn't they detect the sidereal motion?

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and to cover another point.

i think there are 2 effects involved in these exercises....but they are mixed together and need to be separated.

one is the RELATIVE effects.

which is how multiple "frames" may comprehend each other.

this is due to the finite speed of light...and becomes important when relative velocities approach C.

this is from whence the effects of lorentzian contractions et al are derived....as these effects are all observer based phenomena....relying on transmission from one frame to another.

this is what parts of your arguments are based on.

********************

the other effect is the "inherent physical states"...and how they also are affected by eg: motion...and the finite speed of light.

these inherent states do not rely upon observers.

this is what my arguments are based on.

20. Originally Posted by madman
no..the absolute velocity of light remains the same.

we would measure alterations in frequency by altering our relative velocity (this is the light based version derived from the doppler shift effects of sound).

this would cause a relative difference of velocities.
That's what I meant. That relative difference of velocities would be detectable. See my next comments...

Originally Posted by madman
you would still have time dilation..because it is due to the relative speed of the light and the matter.

light requires time to travel from mirror to mirror.

the light clock motion causes the distance between emission point and detection point to alter....therefore creating an altered transmission time...or "inherent physical time dilation".
No, that's not the same thing. In your "fixed coordinate frame" universe, you could set up two identical light clocks perpendicular to each other and they would tick at different rates. One person could sit in front of those two clocks with absolutely no relative motion between them and watch one clock tick faster than the other. Then rotate the entire apparatus 90 degrees and watch the fast clock become slow.

That's not time dilation, it's just two clocks ticking at different rates. And it's exactly what Michelson-Morely was designed to detect but didn't.

Originally Posted by madman
why didn't they detect the sidereal motion?
I don't think the M-M device was sensitive enough to detect it. They were trying to detect the Earth's movement through space. The sidereal motion is the Earth's rotation around its axis.

21. SeanF
No, that's not the same thing. In your "fixed coordinate frame" universe, you could set up two identical light clocks perpendicular to each other and they would tick at different rates. One person could sit in front of those two clocks with absolutely no relative motion between them and watch one clock tick faster than the other. Then rotate the entire apparatus 90 degrees and watch the fast clock become slow.
exactly....that is how you would then find your vector.

when a light-clock is aligned perpendicularly to the direction of travel it produces the shortest round trip possible...and the parallel light-clock would produce the longest round trip possible.

the real vector lies along the axis of the longest round trip.

That's not time dilation, it's just two clocks ticking at different rates. And it's exactly what Michelson-Morely was designed to detect but didn't.
it is...and it's also (as everybody agrees) at odds with the result from michelson and morley.

I don't think the M-M device was sensitive enough to detect it. They were trying to detect the Earth's movement through space. The sidereal motion is the Earth's rotation around its axis.

then why didn't they detect "the Earth's movement through space"?

we know the earth is travelling around the sun...and the sun around the galaxy..etc.

22. Originally Posted by madman
it is...and it's also (as everybody agrees) at odds with the result from michelson and morley.
So experimentation has shown the "fixed coordinate frame" theory to be false. Why are we still talking about it?

Originally Posted by madman
then why didn't the detect it?
As has been said, the sidereal effect is a rotational effect and is too small to be detected by the M-M equipment.

Originally Posted by madman
we know the earth is travelling around the sun...and the sun around the galaxy..etc.
Yes, we do, but there is no "fixed coordinate frame" that the earth is traveling through and so there is no way for M-M (or any other experimentation) to detect that motion. It's relative, not absolute.

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Originally Posted by SeanF
And the Michelson-Morely experiment would have detected that round-trip difference if there were one. It didn't, because there isn't. And that means there's no fixed coordinate frame (either that, or the Earth is motionless relative to the fixed coordinate frame).
And we know we aren't stationary because of stellar aberration. So, we conclude that there is no fixed frame.

24. Madman, you seem to be hung up on the idea that time dilation has something to do with how light travels faster against your direction of travel than with it. The whole pooint of SR and the constant c is that however you are moving (inertially) light will always travel at c relative to you. If you are going to deny that then you are not saying anything at all about relativity other than that one of its postulates is incorrect. In doing so you are disregarding all the experiments (including the MM one) that back this postulate as well as the Maxwell equations for electromagnetism which actually imply this postulate.

It sounds to me like you have thought about how a light clock appears to a relatively moving observer and then intuited that this is how ones own light clock would look if one were moving with it. That intuition is at odds with SR. You can only see light taking longer in one direction than the other in your light clock if you are moving relative to it (and not at 90 degrees).

It doesn't matter how many gifs you construct of your misunderstanding, or how many times you assert that there is an inherent time dilation due to ones absolute motion, it still ain't SR.

25. To reiterate: The 2.67 result you're toting is incorrect - you've failed to take length contraction into account. When you do so, you'll get the result of 2.31 regardless of how you orient the clock.

If you're looking at a light clock moving relative to yourself (or the "coordinate space", which is equivalent), SR predicts that you'll observe:
* Time dilation
* Length contraction
* Simultaneity changes

When the clock is perpendicular to the direction of travel, it just so happens that length contraction and simultaneity changes will be zero, but this is a very special case. Any other orientation of the experiment will cause them to appear, and unless you account for their effects your derivation is not in agreement with SR.

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Quite right. And I pointed this out in post number 124, where I showed algebraically that the perpendicular signal takes the same time as the parallel signal. The last sentence of this post refers to the Lorentz-Fitzgerald Contraction of the parallel arm of the apparatus.

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in all mainstream versions of time dilation that i've read about, the operation revolves around determining gamma.
Why don't you read the standard explanation on the classical way of determining time dilation? This should explain away all your misconceptions.

http://www.wbabin.net/sfarti/sfarti9.pdf

this version seems more complete:

http://www.mrelativity.net/Papers/29...orSTR_IS_1.pdf

28. what i'd like to know is, why do we have the gamma formula to begin with?

it is based on a perpendicular light clock...which is an impossibility to maintain in reality.

where would you find a real example of a light clock that is always oriented perpendicular to the direction of travel? (apart from a demo)..so that you would ever consider using the gamma formula in the first place?

all physical bodies would be an amalgam of "light-clocks" oriented at random angles.

the range of these angles will be from perpendicular to parallel...and a mean (or sum) would be 45dg.

so why don't we have one all-encompassing formula based on something like 45dg?...that is always applied without exception?

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Originally Posted by madman
what i'd like to know is, why do we have the gamma formula to begin with?

it is based on a perpendicular light clock

No, it's not. It's just that the light-clock is a straightforward example. We have the formula because Einstein derived it and published it in 1905. IIRC, with no perpendicular light-clock.

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This is one reason, the other reason can be found in the description of the Ives Stilwell experiment where the ions fly in many different directions. Actually , the magic thing about the IS experiment is that they managed to separate the transverse effect in the context of the ions flying mostly at zero degree angle!

You need to read both the 1905 paper and the IS description I gave you above.

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