A simple question:-

Is it possible to talk of or define space and time in an empty universe,that is, in an universe devoid of matter?

 

I was thinking about time and realised that every-time we talk of time, it is w.r.t to some periodic phenomenon and hence there in nothing like absolute time. But,what if there is nothing to give rise to any kind of periodic phenomenon? What if there is no matter and energy? Then we can't talk of decay clocks or cycle clocks or any kind of clocks.Right? Will that mean that there will be no time? Same will apply to space also. Will space-time exist in an universe devoid of matter? In such an universe there will be nothing to observe or measure space-time and as per relativity, these entities are not independent of measurement. Is it even possible to define an universe without matter/energy? So,what do you people think?

Space is not devoid of matter/energy. There is what is called the zero-point energy, and particle/antiparticle pairs briefly pop into existence and annihilate everywhere.

No doubt that space is never devoid of matter/energy, but can it be used to measure time or space? Is it possible to talk of time just on the basis of zero point energy? Does this vacuum energy give rise to arrow of time or concept of time?

 

Thanks in advance.

It kind of seems like he is trying to say that you cannot have a reference frame without matter. Devoid of matter, all references to time are constant.