New interpretations suggest the "heat death" hypothesis might not hold (2023)

Practically stars are mostly burned out in another 50 billion years and radioisotopes that produce a heat gradient will also be mostly decayed by then. Eventually good tidal energy situations like

https://en.wikipedia.org/wiki/Tidal_heating_of_Io

will end as well since this kind of situation changes the orbits. So energy for life and usable thermal gradients will disappear even if entropy will continue to increase for a long time -- for instance, black holes will be slowly inspiralling and crashing into each other resulting in huge entropy increases on paper.

I've had plans for a sci-fi book I plan to never write that takes place in the ultra far future. The chapters' numbers would be the time dilation scale in a base 10 logarithm. The book would be made up of a series of short stories told from the point of view of a "time coast guard" rescuing idiots who refuse to time dilate from their creaking space hulks.

A later (set?) of chapters might just be in the 90+ scale; at that regime the characters can flit around the universe in the notional blink of an eye, even though their nanoships' velocity is only a few km/s. In my mind it'd be just a nuts-and-bolts 30's-style hard boiled detective story; but, set in the year 10^110.

Oh! Oh! And Charlie Stross would write this book for me, and it'd be a series.