Why in the world would Einstein suggest....

@fresco,

Your first link makes the very point I have been making, and which you have been disputing. It says:

Quote:

Moving clocks go slower, and so do the clocks of the moving twin.

Wasn't your claim that such a statement was "meaningless" and incapable of being determined?

He is talking about "moving clocks," and is attributing the moving clock to the travelling twin here.

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@layman,

Read the whole thing. The statement is meaningless if they never meet in a common reference frame in which the non-inertial twin can be compared with the inertial one. For each, the other appears to be " moving slower". That appearance is exactly equivalent to Brits imagining Australians are walking "upside down" and vice versa. Its about relative points of view.

The key section deals with the resolution of the apparent paradox. "Common sense" simply does not apply to an understanding of "space-time".

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@layman,

One of your links also refers to the effect of acceleration on time dilation:

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[It] is not that clocks run especially slowly during the acceleration phase - that's not what is behind the twin's age difference...

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@fresco,

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Surely It is the one who experienced an acceleration who ultimately "ages slower"

Brings up an interesting q though, Fres, one that has long puzzled me. Once I accelerate away from Earth, you and everyone else on earth not in motion see my clock stopped. Of course using my telescope at the rear window of my ship, I see your clocks stopped also

Yet having circumnavigated the universe in just a few seconds my time, returning to my starting point from the other direction I find you're long gone, died of old age maybe millions of years ago; maybe the planet is gone too

Yet that seems a violation of Albert. If our relative velocity is near c, to me your clock should have been stopped too. One controversial answer I've heard: Yes it's the guy who accelerates whose clock stops. But why

Another possibility (To be sure, sheer wild guesswork on my part): Your clock is not stopped throughout my journey but somehow as a result of the "curvature" of space, even though I find myself passing nearby objects at near c in effect I am slowing relative to you, allowing you to age with respect to me

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@fresco,

Quote:

Read the whole thing. The statement is meaningless if they never meet in a common reference frame

It there any place where your link says it is meaningless?

Many examples of the "twin paradox" have been expounded upon which do NOT involve any acceleration or return to earth. That doesn't change the predictions of SR one iota.

The predictions of SR are NOT premised upon the ability to compare clocks, side by side. That is merely a positivistic philosophical concern, a la Mach.

Fresco, despite your earlier acknowledgment that positivism (logical empiricism) has been refuted, you seem to routinely adopt and advocate positivist premises and arguments.

These types of claims, unfortunately, seem to be quite prevalent in discussion of SR, due to the heavy reliance on positivism by SR apologists in its formative years.

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@dalehileman,

Dale, I'm afraid I don't quite understand the exact question you are posing. But with respect to this:

Quote:

One controversial answer I've heard: Yes it's the guy who accelerates whose clock stops. But why

As I have already stated in other posts, acceleration is irrelevant to time dilation (except in an indirect way, because accelation can cause an increased speed--although a decrease in speed is also "acceleration," technically speaking):

Quote:

The clock hypothesis is an assumption in special relativity. It states that the rate of a clock doesn't depend on its acceleration but only on its instantaneous velocity.... it has become a standard assumption and is usually included in the axioms of special relativity, especially in the light of experimental verification up to very high accelerations in particle accelerators.

Source: http://en.wikipedia.org/wiki/Clock_hypothesis

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@layman,

Of course there is "reading", and "reading with clouded spectacles".
If you don't understand basic Einstein about "disagreement about simultaneity", you don't have a cat in hell's chance of understanding much else to do with clocks. You are like the Brit who thinks the Aussies really are upside down.

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@fresco,

Quote:

If you don't understand basic Einstein about "disagreement about simultaneity", you don't have a cat in hell's chance of understanding much else to do with clocks. You are like the Brit who thinks the Aussies really are upside down.

Care to explain or elaborate upon your statement in any way, Fresco, or is this just one more pontific pronouncement of yours?

Let's suppose (contrary to your assumption) that I DO understand what Al was trying to say about "relative simultaneity." That was, after all, the very subject I brought up in my initial post here. Now what? Do you have any more to say on the topic?

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@layman,

An analogy similar to Al's "passenger on a train who insists he's motionless" explanation of "relative simultaneity" can be seen in a lightning vs thunder scenario.

A guy who is right next to a lightning-struck cloud will both see the lightning and hear the thunderclap simultaneously.

On the other hand, a guy a few miles away will see the lightning, but not hear the thunder for maybe 10 to 15 seconds later.

Do physicists then say that the thunder was generated at two distinct times because subjective observers heard the thunder at different times? Of course not.

They simply explain why the second observer heard the thunder later. They do NOT say that he is "correct" when he claims the lightning and thunder were "not simultaneous."

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@fresco,

Fresco, I'm afraid you strike me as being very long on ad hominem insinuations and very short on any type of explicatory exposition.

What's up with that?

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@layman,

Quote:

As I have already stated in other posts, acceleration is irrelevant to time dilation

Yea Lay, I understand, and thanks for the link. I presume you mean, then, contrary to classical relativity that after my takeoff it's me who's "really" moving not you

So don't you require a "stationary" ref of some sort, but isn't that contrary to Al's theory; and so are you asserting that he's wrong

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@layman,

Another illustration involving "appearance" versus "reality" has been invoked which involves the following perspectival differences.

Two guys, each 6' tall are standing face to face talking to each other. Then they say goodbye and start walking away from each other.

Thereafter, each time either one of them looks back at the other, each one has the "visual impression" that the other guy is getting smaller and smaller.

So what? Does this mean that neither guy is 6' tall anymore? Of course not. Who (other than relativists, maybe) would claim otherwise?

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@layman,

So Lay are you saying that my view of your stopped clock is illusory

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@dalehileman,

Quote:

Yea Lay, I understand, and thanks for the link. I presume you mean, then, contrary to classical relativity that after my takeoff it's me who's "really" moving not you

Yeah, Dale, that would be my contention (and it is supported by all the observable facts).

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So don't you require a "stationary" ref of some sort, but isn't that contrary to Al's theory; and so are you asserting that he's wrong

Well, Dale, there are a number of issues involved here, and I have made a lot of comments addressed to those issues.

As I have noted, for example, the proposition that "you can never tell who's moving" is NOT a part of the mathematical foundations of SR. On the contrary, the mathematic formula gives you a clear method of determining who's moving.

The "you can never tell who's moving" proposition is NOT a scientific statement. It is a philosophical one espoused by positivists, after the fact.

So in that sense it is NOT part of Al's theory, per se. In fact, it was Al himself who originally noted that a travelling organism would age slower than stationary companions he left behind.

For him to even make such a claim presupposes that you can tell "who's moving."

I'm not sure if that responds to your question about what is "contrary to Al's theory," though. Does it, or is your question something else?

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@dalehileman,

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So Lay are you saying that my view of your stopped clock is illusory

No, Dale, I'm not saying that at all. Time dilation is real, not just some illusion. However, time dilation is NOT "reciprocal." It is only the faster-moving object whose time slows down (not both).

I made a post on page 6 which starts out like this: "SR works something like this:"

I don't know if you've read that, Dale, but that basically encapsulates what I'm trying to say.

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@dalehileman,

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So don't you require a "stationary" ref of some sort, but isn't that contrary to Al's theory; and so are you asserting that he's wrong

Dale, as I noted very early in this thread, contrary to what some claim, SR calculations ALWAYS incorporate a "preferred" (motionless) frame of reference. According to SR, that preferred frame is always the "one you are in."

Without some sort of preferred frame, no calculations would even be possible.

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@layman,

The problem, as I see it, (and as I have repeatedly said in this thread) is that, while this methodology can work out just fine from a math perspective on a "case by case" basis, it is wholly unsatisfactory from any "comprehensive" standpoint.

(1) we have two observers, in relative motion to each other
(2) In SR each is compelled to insist that he is motionless, and it is only "the other guy" who is moving.

But they cannot BOTH be motionless. If they were, there would be no "relative motion" between them.

So at least one on them MUST be wrong when he insists he is motionless.

Nonetheless, many relativists want to somehow claim that "each is correct." Or, perhaps alternately, "no one is correct, there can be no correct answer to the question of which one is actually moving." But this is an impossible task to succeed at, while still being logically consistent. You have to give them credit for "trying," though, I guess.

Furthermore, it contradicts the basic conclusions of the Lorentz transformation which say that the moving clock (and ONLY the moving clock) slows down

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@fresco,

Quote:

The key section deals with the resolution of the apparent paradox.

I take it that you're referring to this section:

Quote:

We have here an apparent contradiction: how can both statements be true? How can my own clocks be slower than those of the other space station, and the other station's clocks slower than mine?...In Einstein's theory, there is a definition of simultaneity that employs light signals going back and forth (cf. The definition of "now"). However, simultaneity thus defined is relative. Observers that are in motion relative to each other (and that employ Einstein's definition of simultaneity) will generally end up with different results....This insight allows relativity to escape the apparent contradiction that one and the same clock is both slower and faster than another clock

This deserves some comment, I guess.

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@layman,

1. Einstein has his own *special* definition of simultaneity, eh? I addressed this is my very first post, and several times since then.

That's the "definition" he explicated when he said a guy on a train, who insisted he wasn't moving, would come to a different conclusion about what was simultaneous than he would if he acknowledged his motion. Al knows that the guy's moving, and Al uses this knowledge to explain exactly where the train passenger goes wrong.

But, rather than simply correct the woefully mistaken assumptions the poor soul is making, Al elevates those misperceptions to the status of "truth." Solipsism gone wild.

2. This author says " Observers that are in motion relative to each other (and that employ Einstein's definition of simultaneity) will generally end up with different results." To his credit, he was careful to include the parenthetical portion ("and that employ Einstein's definition of simultaneity"). But what if you don't "employ" that definition like Hefele & Keating didn't? Hmmm? What then? Who would employ it? Who would take the illusions of a fool (the train passenger who denies that he's moving) and treat them as gospel truth?

Certainly not the designers of the GPS system. No engineer I ever heard of designed a car based on the assumption that it doesn't need to move, because all places in the country will come to it, so long as it is inertial (which it is, if it's motionless).

3. This author says "This insight allows relativity to escape the apparent contradiction that one and the same clock is both slower and faster than another clock." Insight? He calls that special definition an "insight?" I don't, I call it a definition, one which I deem to be extremely poor. Al is free, of course, to take the color black and call it "blue," if he wants. But, so what? What's "blue" to him is still black to virtually everyone else on the planet. But at least he would have his own *special* definition, eh?

4. The author asks: "How can my own clocks be slower than those of the other space station, and the other station's clocks slower than mine?" The answer to that is actually rather simple. They AREN'T. SR says that the moving clock, and ONLY the moving clock, runs slower.

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http://www.dummies.com/how-to/content/einsteins-special-relativity.html

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Why in the world would Einstein suggest....

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