Re: Twin paradox revisited ll

Dear bill:

"bill" <cosmosco@xxxxxxxxxxxxxxx> wrote in message
news:1185242135.229779.35710@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Jul 23, 11:03 am, "N:dlzc D:aol T:com \(dlzc\)"
<d...@xxxxxxx>
wrote:
....
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?

He can measure and assume he is a "virgin", and
infer that all those changes are "physically
happening". He can make those measurements,
and assume he is a devotee of classical Doppler,
and infer what he sees as much better, but still
not agree with the stay-at-home twin. Or he can
make those measurements, and use relativity, and
determine exactly what the stay-at-home is
measuring for him/herself.

In other words, when he applies his knowledge of
relativity he realises that what appears to be
taking place is nothing more than a visual illusion
created by his rate of travel relatively to the earth
and that the earth is not physically orbiting the sun
at faster or slower rates than it was when he was
on the planet as it appears to be doing?

Look. Relativity allows you to determine from your measurements,
what someone moving relative to you would measure. If the
traveller is moving at 0.866c, he will measure the Earth moving
twice as fast as *his own* clock says it should (taking out
classical Doppler), but infer exactly the right motion for the
twin on Earth.

It is not only that "he can make those
measurements, and use relativity, and determine
exactly *what the stay-at-home is measuring for
him/herself.*" he can also determine exactly what
is *physically* taking place back at the solar system.

Yes, which is "business as usual".

It is not a question of what he is measuring. The
question is what can he do to make sense of it?

Thank you, my point entirely.

....
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.

Not at all. If you were entirely clueless, and
assumed you knew nothing about the physics of
the Sun-Earth system, you would still be able to
make that system work. The mass of the Sun and
Earth would have the same proportion as the stay-
at-home twin woudl say it was, but the total mass
would decrease to make that orbit "work out".

He 'sees' (determines) that the sun's mass has
increased or decreased by a gamma factor of round
30,000 yet is of the belief that this tremendous
variation of the sun's energy output has no affect on
the earth which is still, from his point of view, at the
same distance from the sun?

Yep. Because he would see that the Earth was able to radiate
that energy away, because it too was hotter. See we can look
back and see processes we recognize: spectra of stellar process
with a "gamma" of 5, CMBR radiation with a "gamma" of more than
1000, and we don't assume those stars only output light at those
lower temperatures. It is our clock, and / or our motion that
makes them look cooler, there type Ia supernovae "unfold" more
slowly.

....
So he sees (determines, measures) the planet
moving at *physically impossible* orbital velocities

... physically *possible* ...

The earth orbiting the sun at close to, or beyond (if we
apply the maxium attained GF of 40,000), the speed of
light is 'possible' from the traveler's point of view?

Approaching infinitely fast, faster than could be sustained by a
black hole with which you were held at rest. Because it is an
unadjusted measurement of events impinging on his frame.

but then applies relativity and concludes that the earth
is *not* moving at those velocities *in its own reference
frame*

... in fact is moving no differently than it was when he lived
there.

Thank you, my point precisely.

But you have to know that *your clock is not immune to your
motion*.

The original posting was to the effect that from
the traveler's point of view, the earth *is physically*
moving at those impossible velocities.

Which is both true and false, and ultimately leads to your
confusion.

I'm sorry, but the comment that it is both true and false also
contributes to my confusion.

You keep insisting on "physically" this and "physically" that.
You are moving with some terrible speed. Are you physically
going to be in-system long enough to actually measure any of
these things? Or are you depending on light to carry this
information to you?

Say you make your passage to a nearby point in space, and you
travel at 0.866c. You leave and return in one year by your own
clock, and acceleration times are negligible. We here on Earth
will have you gone for two years. It is not *we* who are
affected, beause we have a whole Universe that will also agree
you were gone for two years.

....
The original posting

... in this context, I thing you mean "the original poster",
or
OP for short ...

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*.

That is incorrect. The values of acceleration are unimportant
*in SR*. And are really outside the scope of SR, except in
some
very limited cases. It is "velocity history", essentially
"how
fast" for "how long" that matters.

I *know* that it is incorrect. I'm referring to what the OP
*wrote*
and my intention is to *show* that this solipsist nonsense *is*
incorrect or more to the point absolute nonsense.

OK.

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.

It *was* reality for him, because that is what he measured.

You wrote that when he applies relativity he concludes that
the earth is *not* moving at those velocities *in its own
reference frame*. For him to then conclude that this is
*reality* is contradicting his own logic.

Reality is measurement, not inference. Perhaps I drop "reality",
and you drop "physical"?

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

I still don't see how you achieve "obliteration". If you mean
"his twin has aged more than him, including the possibility of
death and meeting his own grand-kin", yes.

No, that's *not* what Im talking about. Having accelerated to
almost the maximum attained velocity (at which *instant* the
earth 'is' orbiting the sun at near light speed) he takes his
foot off the gas and 'sees', according to the OP, the earth's
orbital velocity *instantaneously* revert from near light speed
to its more mundane 30K-s (repeat) "at that very instant*!

You are correct, that is nonsense. Acceleration does not provide
that.

Alternatively, his ship is fitted with an anti-gravity device
that
allows him to accelerate at 1,000g. At the very *instant*that
he
pushes down on the accelerator he 'sees' the planet
accelerting toward him at 1,000g.

Knowing that the planet is not fitted with anti-gravity devices
does he conclude that this is *physically* taking place OR
does he - as Confucius suggested - apply his knowledge and
conclude that what *appears* to be taking place is nothing
more than a visual illsion created by *his* relative rate of
travel?

That works for me.

If the traveler is of the opinion that he has not aged
at the slower rate

Nothing in his frame will seem slower to him. Only on
comparison of his clock to the Universe will come surprises.

If he applies the aspect of Einstein's 1918 article that it is
the
twin who has experienced time dilation he must conclude tht
*his* is
the moving clock thus that whilst his clock seems to be ticking
over
at the rate as it was before he left home it is *actually*
ticking
over at a slower rate then the earth clocks, that it is *not*
the
earth clocks that are ticking over at the *faster* rate even
though
this *appears* to be taking place.

That is a problem with relative points of view, and at least the
English language. We once thought of the Earth as the center of
the solar system too, and ornate maths were constructed to allow
that to happen... since my "clock rate" seems normal, it must be
everyone else's that sped up...

but that his twin ages at the faster rate he is denying
Einstein's 1981

He died in 1955, what did you mean?

I apologise for that typo I meant, of course, 1918.

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 twin paradox can be perfomed with 3 clocks (3 people if
you
like), and no acceleration within the period of the experiment
(departure to final arrival). The acceleration is just part
of
the gedanken, and not a requirement (unless you insist on
seeing
the same twin arrive and meet his older twin).

The OP to which my present postings refer only stipulated two
clocks
so it is only adding to the confusion to introduce another
clock. I
prefer to stick to the subject on hand.

OK.

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.

I guess that dpends on what you mean by "obliterate" then.

Destroys, see above.

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

... no, "fast moving" ...

In order to *become* fast moving the electrons *must* have
been *accelerated* or are you implying that the time dilation
effect does *not* take place whilst the particls are being
accelerated?

There is some effect from the stress of being accelerated. But
for the sake of simplicity, how fast they are going at any
instant, describes most of the effect we can experimentally
verify.

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

Compared to the fast moving particle, who can insist *nothing*
changed for him, the Universe ages more rapidly.

However, as you point out, if the traveler (equivalnt to the
fast
moving particle) applies his knowledge as above he should
realise that what appears to be taking place is *not* reality -
that the universe has *not* been made to accelerate to, and
travel, at near light speed.

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.

This is a joke, right?

I certainly *hope* so!

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.

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.

Which is in part incorrect.

It is *totally* incorrect! It is an absolute nonsense.

David A. Smith


.

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