The equations of general relativity should predict (although I might be wrong) that in absence of mass the spacetime is everywhere flat. That is, time is the same everywhere. However, I'm not sure about what would happen in total absence of matter, including energy.
Now, I know that this is not actually possible, but I'm taking a very theoretical example. Suppose a universe without mass nor energy. My questions are:
- Does it still make sense to even speak about time? If there is no event to compare, does time still exist, at least from a purely mathematical viewpoint? I'm not asking if it's useful to consider its existence, just if it still exists.
- So, relating to the first question, is the existence of time independent on the existence of matter? Is time actually a physical entity, as much as matter? Does time exist without matter or vice versa?
In short, what is the modern, theoretical definition of time?
Thanks in advance.
EDIT: no, the suggested duplicate does not answer my question. In the scenario of that question, there's still energy, while I'm asking for total absence of matter in all of its forms (it's probably a very stupid question, but I'm stupid as well, so it isn't surprising).
