Re: Grandfather Clocks and Relativity

David wrote:
On Sun, 28 Jan 2007 08:58:59 -0500, jem <jem@xxxxxxx> wrote:


David wrote:


On Sat, 27 Jan 2007 09:16:53 -0500, jem <xxx@xxxxxxx> wrote:



David wrote:


On Fri, 26 Jan 2007 09:45:33 -0500, jem <xxx@xxxxxxx> wrote:




David wrote:



On Fri, 26 Jan 2007 14:06:43 +0100, "harry"
<harald.vanlintelButNotThis@xxxxxxx> wrote:





"David" <dseppala@xxxxxxxxxxxxx> wrote in message news:s4ujr2pniq8kdevl96rif1hfat0ld1jkbg@xxxxxxxxxx




Einstein said ideal clocks in different inertial frames run at
different rates, but this does not apply to pendulum clocks.
Einstein's notions of time and space must apply to all clocks. How
was the exception for pendulum clocks resolved?
Thanks,
David Seppala

He explained it himself in the footnote:

http://www.fourmilab.ch/etexts/einstein/specrel/www/#foot172

Harald


Hi Harald,
Your link is to the paper where he said pendulum clocks must be
excluded: "Not a pendulum-clock, which is physically a system to which
the Earth belongs. This case had to be excluded." The situation wasn't addressed there.
David




What do you think an "ideal clock" is?

I used the term "ideal" in the sense that we all know that every
timing mechanism is subject to many physical variables - temperature,
electrical variations, wear, manufacturing tolerances, etc to name a
few.

Ideal instruments are abstractions - hypothetical devices that exactly reproduce the values of specific variables in specific physical models. However, models don't necessarily presume that instruments are unaffected by peripheral factors (e.g. temperature, etc.). For example, in ether models, the tick mechanisms of ideal clocks are presumed to be precisely adjusted as the clocks pass through a ubiquitous ether. Relativity, OTOH, presumes that the motion of clocks has no effect on their tick mechanisms, a presumption that's clearly violated in the case of pendulum clocks.

I meant "ideal" in the sense that I'm not asking variations


caused by those types of physical parameters, but rather a clock's
operation in inertial reference frames and its operation when
accelerated, but still working properly.
When I posted my question about twins being the same age at a
point in space and time but having a constant relative velocity V, and
one twin then accelerating into the other's inertial frame,
responder's like Dirk said that the clocks (meaning time) are simply
reset.

According to Relativity, the time that's observed on a clock as it moves past a particular location will be the same as the time that would show on the clock if it were instantaneously decelerated at that location. IOW, the deceleration itself has no effect.

That made no sense to me since a twin cannot reset his age


like we can change the hands on a clock or the numerals on an LED
display.

It's not resetting the twin's age, but resetting a stationary clock to reflect the twin's age as the twin passes by it.

The posting I was referring starts out with the two identical twins
passing each other with velocity V. When they pass, they are the same
age, clocks read the same, etc. As they separate, per Einstein, each
twin is aging at a slower rate than the other twin.

Hardly. According to Relativity, the overall motion of things has no effect whatsoever on the rates at which they age. In fact, it's not even correct to say that, per Einstein, each twin is /measured/ to be aging at a slower rate than the other twin, since there are also measuring procedures that will show faster (or equal) aging rates.

When they are

separated by some distance L, one of the twins accelerates into the
other twin's inertial frame. When he is in this new inertial frame he
measures the age of the twin that hasn't gone through any
acceleration. He finds that this twin, instead of being younger, is
now older. The non-acclerating twin gained this age when the other
twin underwent the acceleration. As you stated, at the particular
location where the twin accelerated, no one could measure any
significant change in his clock readings or age. So what caused the
non-accelerating twin to age during the acceleration of the other
twin?

What "causes" the sizes of distant objects to increase as they're approached?

The pre-acceleration age determination was based on one measurement procedure (i.e. from the twin's pre-acceleration perspective), and the post-acceleration age determination was based on a different measurement procedure (i.e. from the twin's post-acceleration perspective). IOW, the aging was "caused" by a shift in perspective.

Dirk says good grief you simply reset clocks. That doesn't

make sense to me.
I understand that the non-accelarating twin's age as determined by
the twin that undergoes the acceleration is determined based on
Einstein's equations prior to the twin accelerating. After the
acceleration, the age computed by those equations has to be "reset".
My question is what measurement does the acclerating twin make that
shows the non-accelerating twin did not age at the same rate he has
always been aging?

Immediately before the acceleration, the accelerating twin (Ta) determined (via measurement) that the non-accelerating twin (Tn) was younger, and immediately after the acceleration, Ta determined (via measurement) that Tn was older. That pair of determinations /is/ a measurement which shows that Tn (was measured to have) aged at a different rate (relative to Ta and from Ta's perspective) during the acceleration.

The accelerating twin (Ta) did not determine the age of the
non-accelerating twin (Tn) via measurement. He determined it via a
combination of measurement and theory.

Ta determined Tn's age strictly by measurement (e.g. by asking a co-moving assistant what the twin's age was when the twin passed by), and *we* used the theory to find out what that measurement was.

If he were to apply these same
concepts to distances, he would find that star positions changed by
huge distances during his acceleration. Of course he knows that is
non-sensical.

Yes, Virginia, in an Einsteinian world, time and distance /measurements/ really do change during acceleration, just as in a Galilean world, size /measurements/ really do change during motion. And these effects, which are attributable to shifting perspective, are certainly not nonsensical.

What I don't follow is why can't this accelerating twin
make any measurements on his own to determine the age and aging of the
other twin.

Of course he can. He can make all sorts of measurements to determine those things, but all he can do "on his own" is look and listen.

He can definitely determine his own age and the readings
of his clocks, etc. Why must he conclude that the distance to the
other twin is a major factor in how much the other twin's age changed
during the acceleration (other than its a consequence of Einstein's
theory)?

Measurements aren't consequences of theories - theories are consequences of measurements. The world works the way the world works. Why it works that way is a senseless question.


David

If the accelerating twin accepts the notion that his twin (or any
object) that moves at a constant rate ages at a constant rate,

In Relativity, every object ages at the same (assumed constant) rate as every other object.

Unlike in the Galilean world, in the Einsteinian world it's not necessary for two clocks to tick at different rates in order to accumulate different amounts of time.

then

the accelerating twin must either conclude that the way he determined
the non-accelerating twin's age must be wrong or during the
acceleration something happened to the "time" - that is aging and
ticking of clocks of the accelerting twin (his own self).

No, he concludes that any age changes that are measured during the acceleration are arbitrary, since the pre-acceleration age of the non-accelerating twin could only be assigned arbitrarily.

Yet no one

in the local vicinity of the accelerating twin can measure such a
change, nor does the accelerating twin measure any significant change
in the local clocks.
Thanks David


And in that posting, the twin that accelerates has to


conclude that the twin who remained at a constant velocity, who didn't
undergo any acceleration, who didn't do anything different, suddenly
has aged at a much faster rate during the acceleration of the other
twin, and his clocks ticked much faster, and used more energy,
although no one can make any measurement of such an occurence.

Of course it can be measured. If the tick rate of clock1 is measured to be slower than tick rate of clock2 prior to some event (e.g. the instantaneous deceleration of clock2), and if clock1's tick rate is measured to be the same as clock2's subsequent to that event, then relative to clock2's tick rate, clock1's tick rate has been measured to increase.



So I'm trying to understand what is the physical source that
confirms that this actually happens,

The SPR FAQ contains a long list of experiments that confirm the predictions of Relativity, but don't look for any with human twins and their clocks racing by each other at relativistic speeds.

instead of concluding that if you


don't see why it happens, you will be called an idiot, a troll, dumber
than a can of paint, etc because Einstein's equations say it must -

What Relativity says is generally taken to be true of Nature because most currently feasible tests of that model have been conducted, and (so far) none of the results of those tests have been confirmed to deviate significantly from the model's predictions.



although he also says that we cannot establish a local time between
these two twins even when they are at the same point in time and
space.

I don't know what it means to "establish a local time between these two twins".





David

.

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