Why in the world would Einstein suggest....

@layman,

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To me it is simply an blatant self-contradiction to claim: (1) That you can never know who is moving

For the life of me I can't see how it's a self-contradiction. In classical relativity it simply doesn't make sense to ask which one is moving

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, and also
(2) That you know which twin is moving (because that would be the one who ages slower)

You have us going around in circles, Lay. By "You" do you mean me

Your phrase "the one who ages slower" also doesn't make sense. Again, A sees B as slower and B sees A as slower

I think the problem is semantic. When a relativist refers to the "twin paradox," he means "apparent paradox"

Am I somehow missing the boat

Con where are you, we needja

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@layman,

BTW I was also puzzled by the apparent lack of symmetry in the aging twins example. I remember referring to an "expert" who explained it by reference to one twin being "accelerated" and the other not. Obviously, unlike uniform motion, acceleration is "observable" by a sense other than vision.

Also, I seem to remember that in Quantum Mechanics, the parameter "motion" becomes somewhat nebulous or irrelevant (perhaps with respect to the concept of non-locality ?) . In any case, the point seems to be that arguing about Einstein's handling of "motion" may be no more useful than arguing about "phlogisten" or "the four elements: earth, air, fire and water"

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@dalehileman,

No, Dale, I don't mean you personally, I mean relativists in general (who claim that it is the travelling twin who will age more slowly--which they are bound to do by the theory, which says moving clocks run slower).

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In classical relativity it simply doesn't make sense to ask which one is moving

So, you (and relativists) assert. But it does make sense, and they implicitly acknowledge this when they concede that it is the travelling twin's clock which will run slower.

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@fresco,

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I remember referring to an "expert" who explained it by reference to one twin being "accelerated" and the other not.

Yeah, Fresco, that (acceleration) is a classical non sequitur employed in an attempt to somehow deny the very real self-contradiction.

It has been proven at high acceleration labs, like Cern, that acceleration has absolutely NO effect on time dilation. It is only the relative speed which makes a difference.

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@layman,

No. I am not talking about the time dilation due to final relative velocity. I am talking about how to distinguish between the twins, the point being that at some stage (even birth) they were "motionless" with respect to each other.

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@dalehileman,

Put another way, Dale, as I have already said in another post.

Each of two observers can, subjectively, assume that they are motionless. No inherent contradiction there, I guess.

But, if they are moving relative to each other, at least one of them MUST be moving.

Therefore, at least one of them is mistaken when he claims he is motionless.

That's why I ask why we would want to base a whole theory on conflicting assumptions, at least one of which must be wrong.

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@fresco,

Quote:

No. I am not talking about the time dilation due to final relative velocity. I am talking about how to distinguish between the twins, the point being that at some stage (even birth) they were "motionless" with respect to each other.

It is a distinction without a difference, Fresco, that's all I'm saying.

It's kinda like saying that the twins are not really identical because one has red hair, and one doesn't. Such a "distinction" has absolutely no bearing on whose clock will run slower.

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@layman,

No. Surely It is the one who experienced an acceleration who ultimately "ages slower". That word "experience" being used in the same sense of Archimedes "body experiencing an upthrust...". Without that asymmetrical physical force/experience there would be no way in deciding which one was "moving faster or slower" i.e. which one should "age faster or slower".

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@fresco,

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No. Surely It is the one who experienced an acceleration who ultimately "ages slower".

Care to explain your basis for making that claim, Fresco? How does acceleration in any way account for slower aging?

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@layman,

I'll give my own answer to that, in the meantime.

(1) if you are accelerated, you are moving.
(2) according to the law of inertia, once you stop accelerating you are STILL moving.
(3) You age slower because you are moving (NOT because you were accelerated, per se--that is just an incidental occurrence).

SRT says that MOVING clocks run slower. If one party ages slower than another it is because he is moving faster, according to SRT itself.

Once again: It has been proven at high acceleration labs, like Cern, that acceleration has absolutely NO effect on time dilation. It is only the relative speed which makes a difference.

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@layman,

You seem to be going round in circles perhaps because you have a block on the complete symmetry of special relativity. The initial scenario for the twins is general relativity and that implies asymmetry. All we need understand is that who is moving"at constant velocity is arbitrary but who was accelerated is not, because that accelerated one is subsequently deemed "the faster" or "the mover" and is seen by the other (through his hypothetical binoculars) as living in slow motion. The "faster mover" of course sees his own pace of life as "normal". (Star Trek has done the whole thing !)
I don't need to justify the aging issue as a function of acceleration, only the asymmetrical difference in identity of the twins as relatively "faster" or "slower".
I don't think I can make it clearer than that,

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@fresco,

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I don't think I can make it clearer than that,

Well, I guess what you're saying will never be "clear" to me then, unfortunately.

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I don't need to justify the aging issue as a function of acceleration, only the asymmetrical difference in identity of the twins as relatively "faster" or "slower".

Ipse dixit, eh? Sorry this "explains" nothing, so far as I can see.

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@layman,

Actually, Fresco, we seem to be agreeing on the basic points, so I'm not sure why you think there's some issue here.

If one party is moving, and one isn't (or isn't moving as fast) then, yes, their circumstances are asymmetrical. One is moving, one isn't.

That's not the problem I'm raising.

I'm simply saying that it is a contradiction to say that you can't tell who's moving. According to the theory itself, it is the one whose clock runs slower.

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@fresco,

Quote:

You seem to be going round in circles perhaps because you have a block on the complete symmetry of special relativity

On the other hand, perhaps you have a block on seeing that the putative "complete symmetry" of SR is self-contradictory.

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@fresco,

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The "faster mover" of course sees his own pace of life as "normal".

That kinda depends, doesn't it? As I said before, I personally "see" myself as moving when I'm riding my motorcycle.

Einstein tells me I MUST assume I'm not moving (if I'm maintaining a steady speed).

But why would I ever assume that? It's not true, and I know it.

Contrary to SR's dictates, I assume that MY, not YOUR, watch is running slower when I'm riding my motorcycle and you're sitting at home.

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@layman,

I am amazed that you don't seem to understand that "what is moving" in the case of relative constant velocity is arbitrary or meaningless. One fundamental departure of Einstein from Newton is the rejection by Einstein of a "fixed" or "absolute" spatial reference frame. In short all reference frames were equivalent. It was consequently physically arbitrary to assert whether the train or the platform was "moving". If you cannot understand that, I don't see how you can understand that the axiom of the constancy of the speed of light with respect to any reference frame gives rise to the time dilatation issues and other phenomena like disagreements about "simultaneity".
I rest my case.

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@fresco,

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I am amazed that you don't seem to understand that "what is moving" in the case of relative constant velocity is arbitrary or meaningless

I understand that this claim is made by relativists.

I also understand that they contradict themselves when they make it.

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I rest my case.

Heh, OK.

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@layman,

If a relativist were to be consistent, when asked which of the two twins ages less, he would have to say:

"Each twin is younger than the other."

Of course they don't say that. They can't. It is inherently self-contradictory.

It also contradicts their own theory, which says that moving clocks run slower (not that all clock move slower than all others not going the same speed).

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@layman,

What contradiction ???
It is merely a restatement of Newtons Laws that "a state of rest" or "uniform motion in a straight line" are physically equivalent and can both be labelled as "inertia".

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@layman,

There is no such thing as a "relativist" in physics. There are only those who understand the difference between special relativity and general relativity which you apparently don't. Relativity in a philosophical sense is another ball game entirely.

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Why in the world would Einstein suggest....

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