Time in a Steady-State Quantum System

[LarryS]

Suppose we are given an arbitrary multi-particle quantum system whose state function / probability density does not change with time. Given, Einstein’s definition of time, that “time is what a clock measures”, is it possible to build a “clock” within such a system? More generally, does time have any meaning in such a system? Thanks in advance.

 

[dmtr]

Suppose we are given an arbitrary multi-particle quantum system whose state function / probability density does not change with time. Given, Einstein’s definition of time, that “time is what a clock measures”, is it possible to build a “clock” within such a system? More generally, does time have any meaning in such a system? Thanks in advance.

IMO: I think it is possible to build "clock" within such a system, it also seems to me that this clock would stand still for an observer completely decoupled from the system.

I can think of several examples of such decouplings that vary (or stop) the unitary time evolution:
1) Quantum Zeno effect. See. [http://qserver.usc.edu/group/wp-content/uploads/2007/02/pra690323142004.pdf]
2) An observer in the accelerated reference frame (consider the system left behind the event horizon)

Here is a lengthy [and unresolved] discussion on the same subject. https://www.physicsforums.com/showthread.php?t=351259