Equivalence of Clocks in Gravitational Fields: A Thought Experiment

[yogi]

I was trying to get a free look at the paper cited by Eugene - and came across this - very pertinent to this thread and recent posts regarding clocks on discs - see pages around 11 -14 - somewhere in that range

arXiv.org > physics > arXiv:physics/0008012v1

 

[meopemuk]

I was trying to get a free look at the paper cited by Eugene - and came across this - very pertinent to this thread and recent posts regarding clocks on discs - see pages around 11 -14 - somewhere in that range

arXiv.org > physics > arXiv:physics/0008012v1

Thanks, yogi,

There is even more interesting (experimental) stuff on pages 31-36.

Eugene.

 

[Ich]

very pertinent to this thread

Extremely pertinent to this thread, as the authors suffer from the

same misconception as you suffer.

Starting with

If one keeps on maintaining that in general relativity
‘clocks measure proper time’ one is faced with the following questions.
How clocks are sensitive to the metric? Why all clocks are sensitive
to the metric in the same way? Usually, we try to understand how
an instrument (in this case a clock) measures something or it can
be influenced by something: this methodological rule should not be
violated.

(Not the clocks are influenced by the metric, they do just fine in measuring what they are supposed to, namely time. Not even time is influenced by the metric, it is part of it.
they exhibit a fundamental lack of understanding, e.g.

Hafele and Keating’s experiment cannot be considered as a practical
realization of the clock paradox, because the clock paradox requires that at
least a fraction of the journey of the traveling clock be an inertial motion
or - as in the case of Bailey et al. experiment - an accelerated (circular)
motion during which, however, the acceleration does not influence the clock.

From where did they get that requirement?
or

For instance,
since the lifetime of muons does not depend on acceleration and,
therefore, from gravitational potential, it may be argued that two muons -
based clocks should read the same after a Hafele - Keating trip of one of
them

'and, therefore, from gravitational potential' is the author's own imagination. No such claim is supported by the sources they quote.
Instead of fortifying you own views with the help of dubious papers, why don't you simply calculate clocks on a spinning disk yourself? All you need is basic SR and how it deals with aberration (transversal doppler effect). You will find that the asymmetry arises quite naturally, contrary to Bonizzoni's claims. If you get stuck, here's the place to find help.
There's also a neat proof that clocks at the same diameter exhibit no frequency shift in MTW, using only coordinate-free geometry.

 

[Ich]

[double post]

 

[pervect]

(Not the clocks are influenced by the metric, they do just fine in measuring what they are supposed to, namely time. Not even time is influenced by the metric, it is part of it.

Exactly. The arguments of the paper are basically philosophical, and said arguments when viewed with a different philosphy somewhat naive and even silly.

The philosophy which basically blows these arguments out of the water is one of the simplest possible philosophies - it is no more and no less to assume that whatever it is that clocks measure represents "reality".

The metric, then, does not represent "reality". The metric describes how reality is "mapped", i.e. the function of the metric is to turn the underlying "reality" of time, which is assumed to be what clocks actually measure, into coordinates, which are human constructs. As constructs, like labels on a map, coordinates are not "real" (at least not on any fundamental level) they are just convenient labels.

why don't you simply calculate clocks on a spinning disk yourself?

Good advice - while some benefit can sometimes be gained from philosophical discussions, in my experience actually sitting down and calculating things and coming up with thought experiments which make testable predictions is one of the better ways to avoid some of the pitfalls of philosophy. (The usual philosophical pitfall is the endless loop problem, where discussions go on forever.)