Re: Twin paradox revisited ll

On Jul 20, 7:11 pm, "Martin Hogbin" <goatREMOVETHIS...@xxxxxxxxxx>
wrote:
"bill" <cosmo...@xxxxxxxxxxxxxxx> wrote in messagenews:1184887231.899046.188560@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Jul 19, 6:42 pm, "Martin Hogbin" <goatREMOVETHIS...@xxxxxxxxxx>
wrote:
"bill" <cosmo...@xxxxxxxxxxxxxxx> wrote in messagenews:1184810766.298641.95760@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Jul 18, 2:57 am, stevendaryl3...@xxxxxxxxx (Daryl McCullough)
wrote:

So you apparently agree with the decade old posting that the stay at
home twin physically ages at the faster rate ('ages the most') rather
than it is the traveler who ages at the slower rate.

Could you explain what the difference is between those two
scenarios? How could we tell?

The difference is that according to the original posting the stay at
home physically ages at the faster rate and although as you correctly
point out there is no way that we can tell which twin physically aged
at the different rate - from the traveler's point of view the earth
could be orbiting the sun at close to the speed of light then at the
very instant that he takes his foot off the gas pedal that orbital
velocity instantly changes from close to 300,000K-s to 30K-s.

In your opinion - does the traveler *really* believe that this
*physically* takes place?

That is really two questions. On the basis of the best
measurements he can make, and allowing for all effects
that he can think of, the traveller calculates that the other
twin's clock is running more slowly than his own during the
cruise phase. I such circumstances I would believe that this is
what is 'really' happening. Would you come to the same
conclusion?

No I would not. I cannot accept that the traveler *really* believes
that the earth is orbiting the sun at around 1m-s nor do I believe
that this is what would 'really' be happening.

During the acceleration the situation is much more
complicated but the answer is essentially the same.

As regards whether it is 'physically' happening, I cannot
answer this question unless you define exactly what you
mean 'physically'.

By 'physically' I mean the concept that the earth is 'really' orbiting
the sun at 1m-s as distinct from 'apparently' as determined by the
traveller.

It has nothing whatsoever to do with what *we*, as stay at home
observers observers, think but what is claimed the *traveler*
determines is reality.

Yes, for the traveller.

So he *really* believs that the earth is *physicaly* orbiting the sun
at 1m-s?

What we can tell is that, when the two twins meet up, the travelling
twin has aged less than the earthbound twin.

One could argue that inertial clocks run as quickly as possible
and that the best way of describing what has happened is
to say that the non-inertial (travelling) twin's clock has been
slowed down.

Other than what one 'could argue' I fully agree with those comments
but I cannot agree, as expressed above, that the stay at home
*physically* ages at the faster rate thus that the traveler could
obliterate all life on earth by taking his foot off the gas pedal.

You need to define 'physically'.

That the traveler destroys all life on the planet. When he returns
home he learns - hopefully - that this has not *physically* taken
place.

The fact that the traveler finds on his return that everything is
'normal' back here - that life continues - should indicate to him that
the earth had *not* been orbiting the sun at near light speed, that
what he saw or determined was nothing more than a visual illusion
generated by his rate of travel.

No, it indicates that the passage of time is not universal. Of course,
on his return, the traveller will be aware that, from the earthbound
twin's point of view, nothing unusual has happened.

Having 'believed' that all life on the planet has been obliterated it
would not only be 'from the earthbound twin's point of view, nothing
unusual has happened' but also from the *traveler's* point of view.

The bit you have not grasped is that the passage of time is not
universal. This is very counterintuitive but it is the inescapable
conclusion of experiment.

Or rather, in the *interpretations* of those experiments. As far as I
am aware there has been no experiment which proved that from the
traveler's point of view it is his twin that ages at the faster rate
than himself.

Bill


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