Re: Clock synch


"Tom Roberts" <tjroberts137@xxxxxxxxxxxxx> schreef in bericht
news:j_PDg.6702$1f6.2244@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Nicolaas Vroom wrote:

And accordingly to you what Rat described is not a physical effect ?

Typo. This should have been Ray (d'Inverno)

The phrase "physical effect" is HIGHLY ambiguous, which is why I said
precisely what I meant. d'Inverno is NOT describing a clock whose
intrinsic tick rate has physically changed, he is describing a measurement
of a clock's rate by an observer in another frame, as I described earlier
in this thread.


Suppose there are two Observers A and B at the same position P1
which both have identical clocks and which initially show the same value.
How would you call the effect, that, if Observer A stays at home
and Observer B moves from P1 to P2 and back to P1,
that when they meet,
they realize that the two clocks show a different value ?

Those two observers follow different paths through spacetime, and their
path lengths are different. For a timelike observer, elapsed proper time
corresponds to the path length, so it is no surprise that their clocks
display different values when they rejoin, because clocks simply indicate
their elapsed proper times. <shrug>


What is wrong by calling that a physical effect ?

It depends on what you mean by the phrase. If you mean "their clocks
ticked at different rates" then it is wrong; if you mean "their clocks
experienced different elapsed proper time" then it is correct.

Ray also writes the following:
"However an experiment has been performed where an atomic clock
was flown round the world and then compared with an identical clock
left back on the ground. The travelling clock was found on return to be
running slow by precisely the amount predicted by time dilation"

My interpretation is that from the point of view an Observer at rest
a moving clock ticks slower.

And is this time dilation ?

No.
Yes

It is different path length over different paths (here timelike paths, so
elapsed proper time corresponds to the path length).
Yes

Nicolaas Vroom


.

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