functionally faster than light.

[Klaynos]

The answer is "electrodynamics would fail." If you derive Maxwell's equations for electromagnetism, you find that the speed of light is a constant in any reference frame. Remove this restriction and I don't know how you'd solve the equations to get consistent predictions between reference frames.

 

Chapter 12 of Griffiths's Introduction to Electrodynamics is a good primer here.

It's also of note that the spectra of stars agrees with what we would expect assuming Maxwell's equations are true and thus c is invariant.

[swansont]

Unless there's a medium which is approximately at rest to the Earth which light travels through at c, dubbed "aether." Of course Michelson-Morley + SR makes this an ad hoc unnecessary assumption that doesn't generalize well to curved spacetimes. Lorentz Ether Theory is perfectly consistent with SR and Maxwell's Equations, but it's incompatible with much of modern physics.

 

I was assuming that any physics that had been shown wrong (or ad-hoc correction that can't be demonstrated to be right) was to be ignored.

[elfmotat]

I was assuming that any physics that had been shown wrong (or ad-hoc correction that can't be demonstrated to be right) was to be ignored.

 

I'm just trying to get a grip on where the OP's confusion is stemming from. If it's coming from a belief in aether theories, I thought it worthwhile to point out that while they can be perfectly consistent with SR and EM, they are incompatible with much of modern physics.

[swansont]

I'm just trying to get a grip on where the OP's confusion is stemming from. If it's coming from a belief in aether theories, I thought it worthwhile to point out that while they can be perfectly consistent with SR and EM, they are incompatible with much of modern physics.

 

Quite right. That's a myopia that seems to be quite common — embracing a model that solves some specific (perceived) problem but conflicts with a broader scope.

[Didymus]

By criticising the methodology of time dilation experiments, I didn't intend to support aether winds... It was only mentioned because the absence of evidence for that isn't strong evidence for any particular other theory. Just like a evidence against string theory isn't necessarily proof in a particular deity.

So... No one wants to take a crack at the question: Is time dilation caused by relative speed?

Because, this is what the theory states... However because no frame of reference is preferred. Thus object a will see object b's clock so.... SR Dictates that object B will see an equal lag in the clock of object A. Thus, time dilation happens equally between these two objects.

Meanwhile, in the hefele-keating experiment, they took the clock readings, then adjusted for their expectation of the clocks on the jets losing time from SR... not considering that, if SR worked, the clocks on the ground would lose an exactly equal amount of time.

 

one could claim that, since we remained at rest relative to the ground clock, we would not notice the difference... but the pilots of the jets were equally at rest relative to the jet clocks... and they were able to see the clocks from the frame of reference they were in the whole time as the ones who lost time. By definition, the relative motion of object A to object B is equal to the relative motion of object B to object A. If the experiment is to be trusted to prove time dilation, it's only proved that there is either a preferred reference frame (which turns SR upside down) or that relative speed can not be the determining factor (again, turning SR upside down).

Edited March 15, 2013 by Didymus

[Klaynos]

You're frame mixing. When the clocks re brought back together one of them must accelerate which would be a non-inertial reference frame. This is not an effect which can be discussed as part of SR which probably accounts for their modification, it is a GR effect. You really need to compare clocks without causing acceleration so muon decay experiments are an example that jumps to mind.

[swansont]

 

So... No one wants to take a crack at the question: Is time dilation caused by relative speed?

 

That's been answered a few times already. You even acknowledged that you've seen an answer when you chided elfmotat for using velocity instead of speed.

 

 

Because, this is what the theory states... However because no frame of reference is preferred. Thus object a will see object b's clock so.... SR Dictates that object B will see an equal lag in the clock of object A. Thus, time dilation happens equally between these two objects.

 

Meanwhile, in the hefele-keating experiment, they took the clock readings, then adjusted for their expectation of the clocks on the jets losing time from SR... not considering that, if SR worked, the clocks on the ground would lose an exactly equal amount of time.

 

No, that's not correct. The clocks on the ground are not at rest, nor are they in an inertial frame of reference. They are in the same non-inertial frame, so they all tick at the same rate, but there is no symmetry of inertial frames since none of the frames are inertial. The analysis they did is explained in their paper. It's from an inertial frame.

 

one could claim that, since we remained at rest relative to the ground clock, we would not notice the difference... but the pilots of the jets were equally at rest relative to the jet clocks... and they were able to see the clocks from the frame of reference they were in the whole time as the ones who lost time. By definition, the relative motion of object A to object B is equal to the relative motion of object B to object A. If the experiment is to be trusted to prove time dilation, it's only proved that there is either a preferred reference frame (which turns SR upside down) or that relative speed can not be the determining factor (again, turning SR upside down).

 

Again: the frames are not inertial.

[michel123456]

That's been answered a few times already. You even acknowledged that you've seen an answer when you chided elfmotat for using velocity instead of speed.

 

 

No, that's not correct. The clocks on the ground are not at rest, nor are they in an inertial frame of reference. They are in the same non-inertial frame, so they all tick at the same rate, but there is no symmetry of inertial frames since none of the frames are inertial. The analysis they did is explained in their paper. It's from an inertial frame.

 

 

Again: the frames are not inertial.

The clock that remained on the ground is not at rest?

[swansont]

The clock that remained on the ground is not at rest?

Nope. The earth is rotating, and since rotation involves an acceleration, the frame IS distinguishable from an inertial frame, and you need to take this into account in any clock analysis. IOW, you can tell you're rotating. You could e.g. build a Foucault pendulum and see this.

 

From a practical standpoint, in most applications we treat the earth as a rest frame, but that leads to curious effects. The most commonly known one is the Coriolis force. For timekeeping, there is the Sagnac effect. If you move a clock around the world at the equator (or send a timing signal along that path, e.g. with an optical fiber), it will disagree with a clock you left there by just over 200 nanoseconds, with the sign depending on the direction. That's in addition to the speed-dependent term for moving the clock. (The Hafele-Keating experiment doesn't treat the earth as inertial, so it doesn't need/have the Sagnac term in its analysis)

[michel123456]

So the HK experiment is about acceleration.

And IIRC in an accelerated FOR the speed of light differ from C.

Thus, is it correct to invoke the HK experiment in examples where C is constant ?

-------------------

Note:

I learned something today. Thank you.

[Didymus]

woa woa woa... So, the clock on the ground is not an inertial frame because of the rotation of the earth.... but the clocks on the aircraft IS an inertial frame? An object stationary relative to the ground is not inertial, but a plane flying through the atmosphere is?

Would you consider a boat traveling through the water to be inertial (say calm seas and large enough boat that waves aren't a factor, only momentum across the water)? Would you say a car driving across the ground is inertial?

I'm not calling you into question, but I need to make sure I haven't misunderstood... do you actually believe that SR supports the idea that if someone on the earth viewed the clocks on the plane, that they would see the plane's clocks tick slower.... and that the people on the plane would agree that their clocks were ticking slower than the clocks on the ground because they're traveling relative to a non-inertial frame?

Edited March 15, 2013 by Didymus

[swansont]

So the HK experiment is about acceleration.

The H-K analysis is about acceleration.

And IIRC in an accelerated FOR the speed of light differ from C.

Thus, is it correct to invoke the HK experiment in examples where C is constant ?

I don't think anyone invokes H-K as a constancy of speed of light example. It's an example of the effects of relativity.

 

woa woa woa... So, the clock on the ground is not an inertial frame because of the rotation of the earth.... but the clocks on the aircraft IS an inertial frame?

No. I'm not sure how you came to that conclusion. I said "there is no symmetry of inertial frames since none of the frames are inertial" The H-K analysis uses an inertial frame, which is not on the earth or plane. You'd know this if you had read the paper.

 

I'm not calling you into question, but I need to make sure I haven't misunderstood... do you actually believe that SR supports the idea that if someone on the earth viewed the clocks on the plane, that they would see the plane's clocks tick slower.... and that the people on the plane would agree that their clocks were ticking slower than the clocks on the ground because they're traveling relative to a non-inertial frame?

No, I don't, and yes, you have misunderstood. I said "there is no symmetry of inertial frames since none of the frames are inertial"

[Didymus]

K. I'll buy that it's not "symmetry of inertial frames" because of the rotation of the earth. But, this factor affects each frame equally because both are traveling with the orbit of the earth.

 

I'm not going to get distracted from one question by asking the same questions again... but I pointed out the fact that they used an imaginary clock "at the center of the earth" a while back... I have quite specific objections to this.

[swansont]

K. I'll buy that it's not "symmetry of inertial frames" because of the rotation of the earth. But, this factor affects each frame equally because both are traveling with the orbit of the earth.

 

No, because traveling with the rotation is faster and traveling against it is slower, when viewed from the inertial frame they use.

 

I'm not going to get distracted from one question by asking the same questions again...

 

Well, except for "Is time dilation caused by relative speed?" that is. Did you have a point by bringing that up many times?

 

but I pointed out the fact that they used an imaginary clock "at the center of the earth" a while back... I have quite specific objections to this.

 

It's actually "looking down on the north pole from a great distance"

[Didymus]

Whatever convoluted process they use... The end comparison is between the clocks in the plane and the clocks on the ground. The relative speed between the clocks on the plane and any part of the ground is the aircraft's ground speed.

 

Do you have a different source where they state it as a comparison of the planes to an imaginary clock vs. The ground and an imaginary clock? The sources I've seen state that it's a direct reading from the plane vs. The ground clock (adjusted for GR)

[swansont]

Whatever convoluted process they use... The end comparison is between the clocks in the plane and the clocks on the ground. The relative speed between the clocks on the plane and any part of the ground is the aircraft's ground speed.

 

Do you have a different source where they state it as a comparison of the planes to an imaginary clock vs. The ground and an imaginary clock? The sources I've seen state that it's a direct reading from the plane vs. The ground clock (adjusted for GR)

 

Their paper is straightforward in the analysis they did. The comparison used their speed as measured by the inertial observer, that is, the rotation speed of the earth ± the plane's speed, depending on direction of travel, to get the timing effects relative to a ground-based clock. There is no "imaginary clock" in their analysis.

[Didymus]

So, two remaining questions:

 

1-something I've never seen... Did they actually document how the clocks directly compared without adjusting to the inertial frame? Everything I've seen posted was after adjustment.

 

2- why did they account for the earth's rotation, but not it's orbital speed? What makes the rotational speed affect the clocks in a way that the orbital speed does not?

[swansont]

Didymus, on 15 Mar 2013 - 22:20, said:

So, two remaining questions:

 

1-something I've never seen... Did they actually document how the clocks directly compared without adjusting to the inertial frame? Everything I've seen posted was after adjustment.

I'm not sure what you mean by "adjustment". The data in their paper shows the comparisons to the ground clock before and after the flight. Nothing was done to the clock, or to the data.

Didymus, on 15 Mar 2013 - 22:20, said:

 

 

2- why did they account for the earth's rotation, but not it's orbital speed? What makes the rotational speed affect the clocks in a way that the orbital speed does not?

answered

http://www.scienceforums.net/topic/73129-functionally-faster-than-light/page-4#entry733765

 

The orbital motion is, to the level of precision in the experiment, inertial. By using the frame of an observer above the north pole, the speed is zero. The size of the Sagnac term depends on the angular frequency, which is ~365 times smaller for the orbit.

[michel123456]

Their paper is straightforward in the analysis they did. The comparison used their speed as measured by the inertial observer, that is, the rotation speed of the earth ± the plane's speed, depending on direction of travel, to get the timing effects relative to a ground-based clock. There is no "imaginary clock" in their analysis.

http://www.pttimeeting.org/archivemeetings/1971papers/Vol%2003_17.pdf

 

If this is an accurate description of the experiment, as it seems to be, I see no FOR at the North pole looking down from a large distance, I see a comparison of traveling clocks with a set of 15 clocks at rest at the U.S. Naval Observatory. See page 8 of the pdf.

[swansont]

http://www.pttimeeting.org/archivemeetings/1971papers/Vol%2003_17.pdf

 

If this is an accurate description of the experiment, as it seems to be, I see no FOR at the North pole looking down from a large distance, I see a comparison of traveling clocks with a set of 15 clocks at rest at the U.S. Naval Observatory. See page 8 of the pdf.

 

I'm quoting from their theory (predictions) paper in Science. http://siba.unipv.it/fisica/articoli/S/Science1972_%20177_4044_%20166.pdf The development of equation (1) includes this detail, missing in the other paper.

 

The PTTI talk/paper is almost entirely about the data analysis, like the second (observations) Science paper. However, you'll notice he says "rest", including the quotes, when describing the clocks.