Why in the world would Einstein suggest... 2

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Following upon a dead thread:
http://able2know.org/topic/265997-1

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@Olivier5,

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Note that it is almost identical to SR except for the hypothesis of a unmoving aether. It includes time dilatation and length contraction, etc.

Yeah, imagine that. I wonder how Al happened to come across the exact same mathematical transformations that Lorentz had published years ago? As even the basic articles I have referred you to show, there no requirement of an "aether." Today they just use the CMB for the preferred reference frame for cosmological purposes.

If it says the same thing as SR, why do you prefer it to SR?

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The only real difference in these theories is between (1) postulating the nonsensical, paradox-generating "relativity of simultaneity" (see my first post, for starters) and (2)postulating absolute simultaneity, which eliminates all paradoxes and predicts things (such as the net accumulated time differences in the Hafele-Keating experiment) which SR doesn't (and happens to be right).

That condradicts something you posted above from wiki, about the two theories having the same mathematics and empiric consequences.

Why clinch on simultaneity? It's not even an intuitive notion. If there's no need for it, why fetish it?

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Type: Question • Score: 2 • Views: 10,913 • Replies: 188

For a pre-relativity overview of the problems linked to simultaneity, one may wish to read the chapter called The Measure of Time, in Henri Poincarré's Valeur de la Science (1911). The thesis is summed up in its conclusion:

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To conclude: We have not a direct intuition of simultaneity, nor of the equality of two durations. If we think we have this intuition, this is an illusion. We replace it by the aid of certain rules which we apply almost always without taking count of them.

But what is the nature of these rules? No general rule, no rigorous rule; a multitude of little rules applicable to each particular case.

These rules are not imposed upon us and we might amuse ourselves in inventing others; but they could not be cast aside without greatly complicating the enunciation of the laws of physics, mechanics and astronomy.

We therefore choose these rules, not because they are true, but because they are the most convenient, and we may recapitulate them as follows: "The simultaneity of two events, or the order of their succession, the equality of two durations, are to be so defined that the enunciation of the natural laws may be as simple as possible. In other words, all these rules, all these definitions are only the fruit of an unconscious opportunism."

http://en.m.wikisource.org/wiki/The_Measure_of_Time

The reasonning remain valid.

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@Olivier5,

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If it says the same thing as SR, why do you prefer it to SR?

It doesn't say the "same thing." I'll come back to this.

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That condradicts something you posted above from wiki, about the two theories having the same mathematics and empiric consequences.

That's only true, if at all, in any one case comparison. However, the Hafele-Keating experiment involved 3 clocks as follows:

1. A clock at a naval station in Maryland,
2. A clock on a plane which took off from there and flew west, and
3. A clock on a plane which took off from there and flew east.

The planes flew at the same speeds, altititudes, etc. SR says the speed of light is constant, regardless of the motion of either the emitter or receiver of the light, that all time dilation is "reciprocal," etc.

If, using SR, and using the naval station as your chosen frame of reference, you calculate the time differences you would predict that each clock on the planes would slow down by an equal amount, relative to the "stationary" clock at the naval station. If you used either other plane as your chosen frame of reference, you would get different (conflicting) answers.

The absolute differences in accumulated elapsed time were measured, after the flights were completed. As it turned out, the plane flying west showed the least elapsed time, the "stationary" clock at the naval station was "in the middle" and showed more time elapsed than the westbound plane, and the eastbound plane showed the least time elapsed. Translated this would mean the eastbound clock moved the slowest and the westbound the fastest, amongst the three.

There was one, and only one, frame of reference which could be used which would accurately predict the amount of time that elapsed on each clock, and that was a non-rotating earth-centered inertial frame of reference. Using such a preferred frame requires you to posit absolute simultaneity, with all differences in time being slowed more or less WHEN compared to the "master clock" at the ECI.

Enough for one post.

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@layman,

As I see it, if one cannot tell those two theories apart empirically, then the difference between them is metaphysical at best.

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@Olivier5,

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The reasonning remain valid.

Poincaire was a conventionalist when it came to definitions and such, , but, applying his reasoning, as you stated it, then LR, not SR, would fill satisfy that criterion. As far as I know, Poincaire never accepted SR and instead preferred LR.

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@layman,

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Using such a preferred frame requires you to posit absolute simultaneity, with all differences in time being slowed more or less WHEN compared to the "master clock" at the ECI.

Why that? There is no master clock in that experiment, just three rotating clocks.

One rotates at the speed of earth's rotation (the earth-bound clock).
One rotates slowlier than the earth-bound clock because it flies counter earth rotation, ie westbound.
One flies ahead of earth rotation, eastward, therefore it rotates faster than the earth-bound clock.

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@Olivier5,

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As I see it, if one cannot tell those two theories apart empirically, then the difference between them is metaphysical at best.

That has been said by others, but I disagree for several reasons. First of all, each has different implications for what happens, and how it happens, in the rest of the universe (I have cited authoritative claims in support of this position elsewhere in this thread).

As an example. Like Mach said, you can get exactly the same predictions of planetary movement whether you use a heliocentric or geocentric frame of reference. But that is NOT to say the make equal sense or are "equally likely."

If the earth is not rotating, for example, then the distance stars would have to be travelling at immense speeds to circle the earth once every 24 hours--a speed many times more than the speed of light. There is nothing per se "illogical" or per se "impossible" about this, but we would have to rewrite virtually every aspect of our physics books to accommodate it.

So, that's one point: reaching the same prediction does not mean that the theories are "just the same" or "different only on metaphysical grounds."

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@Olivier5,

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Why that? There is no master clock in that experiment, just three rotating clocks

As I said, you can only make correct predictions from ONE (preferred) frame of reference (the ECI). It is that frame's clock which is deemed to be "motionless" and "correct."

The clock reading themselves remain completely unchanged by this, of course. It just a question of what theory will accurately PREDICT what those changes will be.

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@Olivier5,

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Why clinch on simultaneity? It's not even an intuitive notion.

Whether or not "simultaneity" is an "intuitive notion" may depend on how you define it.

But the notion of (just as one example among millions that could be chosen) of whether you are (still) moving, relative to the earth, after having been accelerated down the tracks on a train and then reaching a steady speed, it quite intuitive. NOBODY thinks that they are motionless on that train while the earth moves "backwards." Nobody, whether they "feel" their motion or not.

As a matter of physics, the law of inertial would also tell them they MUST (still) be moving, even though their motion is now uniform. SR assumes that the opposite is true, ignoring the law of inertia and all common sense (such as that it takes a constant consumption of fuel to keep the train moving and that there is no apparent "force" which is causing the entire earth to move while you remain motionless).

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. If there's no need for it, why fetish it?

There is a need for it. Both SR and LR need a notion of simultaneity. SR's notion is that it is "relative." LR's notion is that it is "absolute."

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@layman,

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SR says the speed of light is constant, regardless of the motion of either the emitter or receiver of the light, that all time dilation is "reciprocal," etc.

Just about everyone, including every physicist, but excluding Parados, agrees that each clock does NOT run slower than the other. No one really needs an experiment to "prove" this. It follows from elementary logic alone.

So, as a matter of both logic and verified empirical fact, time dilation is NOT "reciprocal," as SR claims. LR does NOT hold that it is reciprocal (strange as that may seem to some devotees of SR). On the contrary, it says that it is NOT reciprocal. So do logic and the Hafele-Keating experiment (not to even mention the GPS). What a coincidence, eh?

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@layman,

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Just about everyone, including every physicist

I really have no basis for saying this, I suppose. What I really mean is "every reputable physicist that I have ever seen render an opinion on the topic." That would include Einstein himself. That said, I would guess that there are in fact some physicists who believe otherwise. But they would not be theoretical physicists. Just run-of-the-mill physicists who specialize in experiments, work at Coca Cola, or whatever.

As I recall, Max claimed to be a physicist. But he also claimed that Lorentz's theory of relative motion had been "proven false," so....

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@layman,

Pointcarré was a radical thinker. I should read more by him, i like his take on intuition.

BTW, The Measure of Time was written in 1898 as a stand alone article, before being bound with other articles in a book in 1911. Therefore it is indeed pre-relativist. That's why it does not mention Einstein.

Pointcarré contributed to SR by helping Lorentz develop his equations, and pointing at time dilatation as being a profound intuition rather than just a computation device. Apparently he was pissed off that Einstein did not acknowledge his debt to him.

I learnt something in this discussion: that relativity had many fathers, and that Einstein's contribution was smaller than I thought.

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@layman,

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time dilation is NOT "reciprocal," as SR claims.

SR does not claim that it is. You got that wrong.

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@Olivier5,

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SR does not claim that it is. You got that wrong.

Really? Then it's not SR, is it? It's LR without that.

What DOES it claim, do you think?

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@layman,

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As I said, you can only make correct predictions from ONE (preferred) frame of reference (the ECI). It is that frame's clock which is deemed to be "motionless" and "correct."

Not at all, it's just a convenient frame to use, nothing more. You could use any inertial frame and find the same result. Eg a frame centered on the sun would work just as well.

In fact, a frame centered on the earth center of mass is NOT really inertial because of the sun's attraction. But for the short duration of the experiment (a few hours), such a frame can be considered inertial as an approximation because the earth center of mass trajectory is almost in straight line for that duration.

We've been through the same idea about the Michelson Morlet, where an apparatus placed on the earth surface (in a lab) formed the frame of reference. It could be taken as inertial only because the experiment lasts a few milliseconds, during which any point at earth surface can be seen as moving in straight line at constant speed, as a good enough approximation.

The main problem with SR as I see it is precisely that there is no such thing as a purely inertial object in the universe, and thus that no frame of reference anchored onto a physical object is ever inertial, in SR sense of the word. Thus SR can only be used to describes what happens during very short time-frames, short enough for an object to behave inertially, as an approximation.

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@Olivier5,

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...pointing at time dilatation as being a profound intuition rather than just a computation device.

You use the term "time dilation" here, but what you are referring to is Lorentz use of the concept of "local time." Lorentz developed this as a strictly mathematical shortcut, and said that, while it had no physical meaning (was not related to "reality') it was a very useful mathematical tool. It saved a lot of time in doing calculations, which was no small thing back then when there were no electronic calculators to do all the work. Every calculation back then had to be done the old-fashioned way--with pen and paper.

Like Lorentz, Poincare never accepted "local time" as being "real" in any sense. He saw the usefulness of it, and said it created a concept of SUBJECTIVE relativity, but he never took the relativity to be more than that (subjective, not objective).

Al stole Lorentz's concept of "local time" and said (in positivistic fashion) that it WAS time. Poincare always rejected this view, and never adopted SR over LR. It makes no sense to claim that it is objectively "real" as Al did. In my view, it remains what it always was, according to Lorentz, Poincare, and many others: simply a useful mathematical tool without any correspondence to actual reality.

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@Olivier5,

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You could use any inertial frame and find the same result. Eg a frame centered on the sun would work just as well.

This is wrong. If you wanted to change "sun's frame" to the barycenter of the solar/planetary system then you would have a point, if you were doing non-terrestrial calculations for motions within the solar system. But, again, you are using a lorentizan theory of relative motion when you do that (as all astronomers do--they don't use SR for those calculations).

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@Olivier5,

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In fact, a frame centered on the earth center of mass is NOT really inertial because of the sun's attraction.

What does being "inertial" have to do with it? That is only a concern for Einstein, not LR. LR works with respect to ALL frames, not just inertial ones.

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@layman,

You got that wrong.

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@layman,

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What does being "inertial" have to do with it

It simplifies the calculations quite a lot. That's what frames of reference are made for: simple calculation. In this regard, the distinction between inertial and non-inertial frames is central to all mechanics, including Newton's, because all inertial frames are equivalent to describe any motion. Therefore choosing a frame is a matter of opportunism, the question being: what inertial or quasi-inertial frame of reference can we pick that will lead to the easiest computation? In the case of the Hafele-Keating experiment, a frame centred on the earth was determine to be the easiest one to use. One centred on the sun (or the solar system center of mass, to be precise) would work too but makes the computation much more complicated.

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