Possible evidence of black holes from a different universe

Here is the paper link: https://arxiv.org/pdf/1808.01740.pdf

It's fairly short. But it proposes a really interesting question. What happens at the heat death of the universe? If it ends up as a bunch of black holes slowly evaporating from Hawking radiation you're left with just photons and gravitons.

And then if that is what happen, did it happen before the big bang and so could we see evidence of it in the cosmic background radiation. (Sort of a peek at the initial conditions for a very complex differential equation).

The result through a bit of hand waving seems to be perhaps. Clearly more work to be done to follow up but a really interesting approach to the question. I just assume/accepted that anything that happened before the big bang could not possibly have impacted our current universe.

Variations in the CMB is a lovely sub grift in the cosmology ecosystem. I only know from former peers back from grad school who went into that area, so take my take with a grain of salt of course. This is (yet another) "explanation" of variations but of course it isn't convincing, many other things could explain different variations in the CMB hence why it's a furtile area for particle physicists to grind for publications.