Re: Twin paradox revisited ll

On Jul 21, 11:53 am, "N:dlzc D:aol T:com \(dlzc\)" <d...@xxxxxxx>
wrote:
Dear bill:

"bill" <cosmo...@xxxxxxxxxxxxxxx> wrote in message

news:1184981064.527191.20310@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

On Jul 20, 7:11 pm, "Martin Hogbin"
<goatREMOVETHIS...@xxxxxxxxxx>
wrote:
...
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.

It is not about "believe" but about "measure".

On the basis that 'observation creates reality' - that what one
'measures' (or 'observes' or 'determines') *is* reality why would a
person - who *believes* that observation creates reality - having
determined something then insist that he does not believe what he is
seeing?

You can go
outbound fast enough that you could see the Earth take millions
of years to orbit the Sun once. But it will move like a bat out
of h*ll on your return journey.

And aren't those observations (determinations) nothing more than
visual illusions generated by the red shift and blue shift of the
light from the planet?

The original posting was that because the astronaut sees the light
from earth as being intensely blue shifted he then believes
(determines) that his twin is physically aging at a faster rate than
he is.

My question is - on the basis that the astronaut sees 'the earth take
millions of years to orbit the sun once' does he truly believe that
whilst he is moving away from us that the earth's orbital velocity
*physically* reduces to a mere 1K-s and, as he returns and sees it
moving 'like a bat out of h*ll' does he really believe (determine)
that the earth's rate of travel has increased to an impossible near
light speed?

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.

One expects that the Earth really could care less how fast the
traveller is moving.

My point exactly.

But relativity is about what you measure, and what you can
correctly infer about what another frame might measure (based on
your own measurements).

So if you measure that the earth is orbiting the sun at 1K-s are you
of the opinion that it is *physically* orbiting at that velocity?

If it was, it would be pulled into the sun.

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 *physically*
orbiting the sun at 1m-s?

If that is what he measures *in his own frame*. If he forgets to
use relativity to calculate how fast the Earthlings would
calculate it was moving.

So he sees (determines, measures) the planet moving at *physically
impossible* orbital velocities but then applies relativity and
concludes that the earth is *not* moving at those velocities *in its
own reference frame* ergo he must realise that what he *sees* is
nothing more than a visual illusion created by his relative rate of
travel.

The original posting was to the effect that from the traveler's point
of view, the earth *is physically* moving at those impossible
velocities. My argument was that the traveler would *presumably* have
some sort of education *in* physics including relativity thus that he
should, as Confucius suggested, *apply* (not forget) that knowledge.

Some of the postings in this discussion imply that the traveler is
*incapable* of applying knowledge and makes his decisions on the basis
of a purely solipsist, philosophical attitude.

The Galilean 'Principle of Relativity insists that the traveller
cannot know if his ship is moving with uniform velocity or is at rest
*without reference to an external point* i.e. he cannot *see* the
universe 'rushing past him' at near light speed.

The original posting insisted that the faster aging rate of the earth
twin *only* takes place during acceleration following turn around and
that it does *not* apply when the ship stops accelerating. In other
words, at the very instant that the traveler takes his foot of the gas
the earth's rate of travel around the sun reverts from near light
speed to 30K-s *intantaneously*.

The traveler must *know* that this cannot possibly occur in reality
thus must conclude that what he *saw* (or measured or determined) was
*not* reality either in his reference frame or the earth's reference
frame.

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.

It physically *has* taken place. And the traveller had squat to
do with the stay-at-home aging, only to do with his own "lack" of
aging... with his "gas pedal".


Are you suggesting that the traveler returns, given the respective
factors, that he actually finds that all life on the planet *has* been
obliterated?

If the traveler is of the opinion that he has not aged at the slower
rate but that his twin ages at the faster rate he is denying
Einstein's 1981 insistence that it is the clock (the twin) who
experiences the force of acceleration which is the one that
*physically* ticks over (ages more slowly).

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.

Except that the traveller is younger thant eh stay-at-home.

Irrelevant to the specific topic , merely a reiteration.

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.

Yes, exactly that has been experimentally determined. Slow
particles with short lifespans age more rapidly than faster ones.
And it has nothing to do with "accleration" or "accelerators" or
"magnetic fields" or "new and unexplained physics".

Those experiments have shown that accelerated particles age more
slowly than slower moving particles but they do *not* prove that the
latter, and the universe, ages more rapidly.

The concept that the stationary particle ages at a faster rate than
the accelerated particle should be sufficient for physicists to stop
all of those experiments which cause them to age at a faster rate than
would otherwise occur.

The length of a journey between any two points depends on the
path you take. This applies equally well if the "points" are
elapsed time on a clock, and relative motion provides the
different path between start and end of journey.

David A. Smith

That has nothing to do with the original posting which insisted that
the stay at home twin physically ages at the faster rate and *only*
during the traveler's period of acceleration following turn around.

.

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