Re: Twin paradox revisited ll


"bill" <cosmosco@xxxxxxxxxxxxxxx> wrote in message news:1184981064.527191.20310@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
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:

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.

This is the crux of the problem. The problem we have is that the
English language has evolved to describe things we see in
normal life. It turns out that, when high speeds are involved,
things are very different and we do not have words to adequately
describe what happens. Thus, is the current context, words
like 'really' and 'physically' do not have any useful meaning.

In everyday life, if I say something 'really' or 'physically'
happens, there is no need to explain what I mean; everybody
knows.

So, what can we do to come to any form of agreement?

Firstly, we can state the facts that are undisputed and
explicable without ambiguity in the English language. For
example, we agree that on his return, the traveller has
aged less then the inertial twin. We can also agree that
in the inertial frame of any twin nothing unusual happens.

Secondly, we can state what we expect the results of any
measurement will be. For example, during the cruise phase,
if either twin measures the clock of the other they will
measure it to be running slower than their own. This
statement applies to any and every sensible method of
measurement. In other words, there are no sensible
measurements whatsoever that do not show the results
described above. Is this real? How real do you want?
It is as real as the fact your head hurts when you hit it.

Thirdly, we can try to come up with forms of words which
describe the situation You might say that the mutual slowing
of clocks is a consequence of measurement in the world
in which we live. This would be acceptable to most
physicists. A more personal view is that physics is all
about measurement, so the slowing is real, but here I am using
'real' in a specific way to mean 'as measured'. I would not
use the word in this context without explaining what I meant
by it.

We can also use analogies to explain what we mean or
talk only in mathematical language. As Daryl has suggested
the more ways you have of looking at the subject the better
your understanding will be.


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.
We are simply down to the meaning of words - see above.


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?

Yes. It least I would in his position.


You need to define 'physically'.

That the traveler destroys all life on the planet.

By that definition, there is no change on Earth 'physically'.


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.

No he does not believe that. Although he measures time to have
slowed down on Earth, all the laws of physics are also transformed
in such a way that life goes on as usual. It is never the case in
SR that one observer measures a different final outcome
from another. Are you familiar with the 'pole and barn' paradox.

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.

I agree that all experimental results require interpretation but
the interpretations used in SR are no different from those used
in Newtonian physics. If you use light to measure some distant
event you must make allowance for its transit time, for example.
This is perfectly normal, indeed not to do so would be an
obvious error.

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.

Over the whole journey the HK experiment does just that. When the
two clocks meet, one shows more elapsed time than the other. We
obviously cannot ask the clocks what they believe but we have to
take it that each clock measures time. In other words, if you fancifully
asked each clock what had happened during its journey it would
say 'I measured time to pass as normal, I therefore presume that the
other clock has run fast/slow while we have been separated'. Or
to put it another way, you tell me which clock in the HKX told the
right time.


--
Martin Hogbin





.

Relevant Pages

  • Re: Models. predictions, physicallity, and observations
    ... considering a broader "reality" than this. ... That said, Physics ... what is it that caused a clock to have lost ... measurement itself - "physicality" is demonstrated by changes in the ...
    (sci.physics)
  • Re: Models. predictions, physicallity, and observations
    ... considering a broader "reality" than this. ... That said, Physics ... what is it that caused a clock to have lost ... measurement itself - "physicality" is demonstrated by changes in the ...
    (sci.astro)
  • Re: Models. predictions, physicallity, and observations
    ... considering a broader "reality" than this. ... That said, Physics ... what is it that caused a clock to have lost ... measurement itself - "physicality" is demonstrated by changes in the ...
    (sci.physics.relativity)
  • Re: Twin paradox revisited ll
    ... If there is no objective way to tell, it is not physics just ... *not* physics but is just the personal feelings of the traveller. ... :> because we are on the Earth. ... :>> that the inertial clock ticks over at the slower rate on the basis ...
    (sci.physics.relativity)
  • Re: Twin paradox revisited ll
    ... In your opinion - the results of the Hafele-Keating experiment cannot ... examples of *your* comment that "a clock made to travel on a circular ... But this is what physics is about. ... *not* physics but is just the personal feelings of the traveller. ...
    (sci.physics.relativity)