Twin Paradox exhumed still again

Dale, I said the same thing in the other thread which you were participating in, but I'll say it again here.

Relativists want to say "there is no paradox."

In my view, they are correct, but not for the reasons they say. For that matter, different people will have different ideas of what the alleged "paradox" even is.

There is no paradox, simply a contradiction, brought on by relativists themselves.

It is contradictory to simultaneously claim both that:

(a) all frames are equally valid, that no one can be preferred over another, and that "therefore" (I put that it scare quotes because it doesn't even follow) that there is "no way to know who is moving, relative to another"

AND, also

(b) We (relativists) subscribe to and propound a theory that gives you a way to tell who's moving.

With respect to this part, you can note that it is almost universally acknowledged in the twin example that it is the earth bound twin who is older and the travelling twin who is younger. It doesn't matter what they might otherwise say about how the travelling twin would "see" the earth twin's clock. As a matter of theory (and fact, given experiments) they concede that he is the one moving. If he thinks otherwise, he is simply wrong, they say (in effect). So the two frames are not"equally valid."

No one ends up claiming that "each clock is slower than the other" or that "each is correct." Yet, that's what they want to also maintain, in most contexts.

Hence it is a contradiction. But not a "paradox."

Thank you Lay for the summary, which seems to suggest either that (1) acceleration is the culprit or (2) there's a "stationary ref"

I'm not sure just what the difference is but I'm hoping to hear a resolution from one quarter or another, perhaps couched in brief sentences of short words arranged in the usual order, language suitable to your Average Clod (me)

I'm just using these definitions, which come from Merriam Webster:

1. Paradox: "something (such as a situation) that is made up of two opposite things and that seems impossible but is actually true or possible" (there are alternate definitons there also--some of which would also apply)

http://www.merriam-webster.com/dictionary/paradox

2. Contradiction: "a difference or disagreement between two things which means that both cannot be true."


The relativists are saying two opposing things (a contradction) but each is not "actually true or possible" (which would make the contradiction a "paradox," if it were the case).

Dale, I don't know if you're implying that anything I'm saying is incomprehensible to you, but, if you are, I would be happy to try to rephrase it, if I know what it is you don't understand.

I don't think it's an "either/or" thing, and I'm not sure what you mean by "culprit."

1. It has been repeatedly demonstrated that acceleration, per se, does NOT have any effect on time dilation. As I cited in the other thread, wiki says the "clock hypothesis" has now been incorporated as an additional "axiom" of SR.

That said, acceleration can lead to an increased speed, and, for that reas0n, could be seen as a factor which creates or contributes to time dilation. But it does not, in itself, cause or contribute to the time dilation. Only the difference in speed does that.

2. As I have also said elsewhere, for all practical purposes there is ALWAYS a "stationary reference" in every SR calculation. It is always the one you're in. For the earth twin, it is his frame, for the travelling twin it is his frame.

But,and here's the same contradiction re-appearing,: they cannot BOTH be "at rest."

If they both assume/claim/assert that THEY (not the other guy) are "at rest," then at least one of them MUST be wrong. To say otherwise is merely a contradiction, not a paradox.

I believe our differences if any are largely semantical. You seem to be saying that to resolve the Twin Paradox there must be a "stationary" or a "preferred" ref, one of four possibilities rolling around in my ancient mind

Taking what I've said so far one step further:

As between the two frames in question, the earth-bound twin frame is the "preferred one," according to SR itself. It is only from his frame that you discern the "truth." He calculates that he will be older than the traveler. He is correct (according to SR).

On the other hand, to the extent that the travelling twin assumes or asserts that he is "at rest" during the inertial portion of his flight, then, to that extent, he is simply wrong (again, according to SR, itself).

Whether there is one, universally applicable, frame which is "absolutely motionless" is a separate question. Many theoreticians say there must be (and therefore is) such a frame, whether detectable or not.

Yes, I've never quite managed to understand why it's "preferred." If it's our visible Universe for instance zooming through a much larger void so that when I leave I am coming to a standstill, I find it very hard to believe that we'll be the same age when you next see me

I guess we're repeating a whole lot but thanks anyhow Lay. Maybe this time we'll attract somebody with a fifth

When you ask "why" something is the case, you could be asking many different things.

This may not be (and probably isn't) the answer to the question you're asking, but:

In simple terms, SR says a "moving" clock will slow down. That is because SR adopts Lorentz's transformations (which Lorentz developed to explain why things appear the way they do IF there is an absolute standard of motionlessness).

Therefore, if you know which of two clocks run (or ran) slower, you also know who was moving (as between the two). Likewise, if you know which one is moving, then you will know which clock is "really" running slower.

Again, this is simply a question of relative motion. To say that one object is moving "faster than" another, is not the same as saying it is running at an exact speed of (for example) 100,000 mph relative to an object that is "absolutely" motionless.