Heh, i wonder what the mean free space between blackholes is?
Now, given that in quadrillions of quadrillions of years all black holes will evaporate and potentially even protons decay there could be a time in the universe where everything is mass less radiation.
I agree OP misspoke, but are we sure the time axis has no upper bound? Or that it doesn’t loop back round on itself? Or that it even exists meaningfully as an axis?
Wut. No there's not? Specifically for spacetime it's obvious to see that's not correct because the time axis has no upper bound.