[MikeS]

In an earlier post in this thread I wrote.

"Imagine a hypothetical sealed box with a divider.  There are different gasses in the two compartments.  The box is chilled to absolute zero and the divider 'magically' removed.  The gases do not mix but the arrow of time is still there as we know that when the temperature rises the gases will mix.  At absolute zero, entropy is at a maximum and time has stood still.  An input of energy is necessary for the gases to mix.  Or to put it another way without an input of energy there can be no further increase in entropy.  Entropy being the main arrow of time.

We may not be able to demonstrate the arrow of time without motion but we are certainly aware of it."

A photon is its own antiparticle and one way of demonstrating that is in a variation of the above experiment.   Antimatter and matter might be gravitationally repulsive.  The Jury is still out on that one. 

Imagine a hypothetical universe much the same as ours but with time flowing backwards relative to us (forward relative to itself).  The same experiment will have the same result despite the different relative directions of the arrow of time.  The experiment shows that the photon is its own antiparticle and does not carry the arrow of time.  In other words 'energy' in the form of photons is necessary to cause change but the direction of the arrow comes via gravity from 'mass' whether it be matter or antimatter . 

This shows the distinct separation of the 'arrow' of time from the 'time dilation factor' (the passage of time).

[syhprum]

There has been a further development in timekeeping with what might be called a Neutron clock


https://newsroom.unsw.edu.au/news/science/nuclear-clock-may-keep-time-universe

[MikeS]

There has been a further development in timekeeping with what might be called a Neutron clock


https://newsroom.unsw.edu.au/news/science/nuclear-clock-may-keep-time-universe

Thanks syphrum
quote from the article

"Because the neutron is held so tightly to the nucleus, its oscillation rate is almost completely unaffected by any external perturbations, unlike those of an atomic clock’s electrons, which are much more loosely bound."

Very interesting but what are the implications for this?

If the clock is "almost completely unaffected by any external perturbations" what does this mean.
If the clock were completely unaffected by any external perturbations then presumably it could not synchronise itself with 'local' time.  It would show the same 'time dilation factor' anywhere in the universe including the EH of a black hole.  Presumably therefore the words "almost completely" are very significant.  "Almost completely" allows the clock to be influenced by whatever it is that synchronises the clock to the time dilation factor of local time.  (Personally I believe that to be essentially gravity)

[syhprum]

The idea of a Neutron orbiting a nucleus seems very strange to me I did not know such a thing could exist, I did not think a Neutron could exist for long outside a nucleus and cannot imagine how it is held in orbit.