[Physics] Clock time vs. common sense time

[Doug Marett]

Hi Ilja,

    Your last remarks about clocks are not what I would expect a
subvantivalist would say - I would have expected the defense to be that,
for example, in a gravitational potential my head and feet are progressing
into the future at different rates (as would be verified by accurate enough
clocks) but because the difference in time between them is so slight, it is
imperceptible, and thereby, not noticed. You, on the other hand, argue that
the clocks would be in the same present, and would remain in the same
present, that they just differ in readings, which is what I have been
saying all along. : ) But if that is true, then subvantivalism is dead, and
4D space time is just a fiction. And I can say that, because, as a
Positivist and Presentist, I have free will, and my choices are
unencumbered by an overbearing future!

Doug

On Wed, Oct 26, 2016 at 7:32 AM, Ilja Schmelzer <
ilja.schmelzer at googlemail.com> wrote:

> 2016-10-26 12:00 GMT+02:00, physics-request at tuks.nl <
> physics-request at tuks.nl>:
> > But this is very telling - because the earth rotational clock (or any
> > rotating frame of reference, such as a spinning disk rotating past a
> light)
> > can be constructed as a clock such that it obeys exactly your definition
> of
> > "a working clock."
>
> Any time-like coordinate would do it.
>
> Or, in other words, to be a "working clock" in the usual meaning of
> measuring common sense time, the clock would have to measure some
> time-like coordinate.  This is a necessary condition.
>
> Unfortunately, it is not sufficient.  There are many imaginable
> time-like coordinates, but there is only one time.  And GR does not
> have any idea what could distinguish true time from all the other
> time-like coordinates.   So it choses the positivist variant of "we
> have no way to identify true time", which is "true (absolute) time
> does not exist".
>
> > But this statement renders "time" to be effectively meaningless, it is "a
> > number on a clock" ; this is not what Einstein actually meant - the clock
> > readings have "meaning" in the theory of relativity - because they refer
> to
> > the speed of real processes in nature.
>
> And I do not say it is meaningless.  It, indeed, defines a lot of
> interesting things.  In particular how we age ourselves. Because the
> processes in our body are also some sort of clock - even if only a
> very inaccurate one.
>
> > So we can't render the clock
> > readings as meaningless - in fact because the theory does attribute
> > physical meaning in this way, it is inherently testable. You can't just
> say
> > "what can't be measured doesn't exist."
>
> Nobody says the clock readings are meaningless.  I say that they don't
> measure
> common sense time.  They measure clock time.  Which is something important,
> and, in particular, a good approximation in everyday life for common sense
> time,
> but which is nonetheless something different.
>
> What I say is that GR has no way to distinguish true time from any of
> the many other imaginable time-like coordinates. And that it makes,
> therefore, testable predictions only about clock time, not about true
> time.
>
> > If relativity is a true scientific
> > theory, then all of its assumptions have to be testable (Popper)
>
> More accurate, please.  A scientific theory should be able to make
> testable predictions.  More testable predictions means higher value of
> that scientific theory.
>
> But there is no claim at all that all statements, or all assumptions
> of a scientific theory have to be testable.
>
> > we have no other
> > choice but to conclude that when an atomic clock says it is in the
> future,
> > it is actually in the present - this should be a big problem for the
> theory
> > of relativity,
>
> Sorry, but this makes no sense. No clock says, never, that it is in
> some future.  Everything is always in the present.  If you have two
> clocks, and they show different times, you usually have no way to say
> which of them is correct.  And even if you have, the wrong clock is
> not "telling it is in the future",  but simply makes a different
> (wrong) claim about the time now.  And it is certainly not a problem
> for a theory, if it predicts that, say, some clocks go slower under
> some special circumstances, like extreme temperature or pressure or
> whatever.
>
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