Yeah, if we get to the point where humans (or whatever our evolutionary progeny are can't imagine it'd be anything resembling humans today) are still around when that starts happening at 10^28 years which is ~10^17 years from now I'll consider that a job extremely well done as a species/civilization.

10^28 years is ~10^17 years from now? I think you either typoed or your math is faulty...

I just messed up the math. It should be 10^19. Either way it'd be an unqualified success.

I still think you're incorrect. If we're at 10^13 years, then 10^28 minus 10^13 is, essentially, 10^28 years from now.

> Either way it'd be an unqualified success.

Certainly. I'm just picking nits on the math.

Oh wow yeah. Well too late to edit the original now. My math mistake shall live on.

Even if you count proton decay as a reasonable mechanism of ageing (which it probably isn't, given that proton decay has never been observed), there is no reason to assume that you can't replace parts with decayed protons with new parts. Humans aren't closed systems.

If protons decay, they don't come back -- the whole reason why the Standard Model lacks proton decay is in how it treats conservation of quark number, since there is no path for a proton's components to a lower-energy state. If that part of the Standard Model is not exactly correct, protons may decay, and the final products will generally be useless for structure-building (e.g. a Georgi-Glashow model proton decays into a pair of gammas and a positron, and it is not energetically favourable for an "anti-decay" back into a proton to occur).

That is, when the protons are gone, so is chemistry, electronics, and so forth.

Of course lots of protons -- likely the vast majority of them -- will end up in stellar collapse remnants anyway, and in the black hole cases you're also not getting the protons back, whether or not they would eventually have decayed. The rest will be in an extremely tenuous gas and dust far outside the black-hole-dominated remnants of no-longer-star-forming galaxies, and most of that will be neutral hydrogen (and in that case if the proton decays, the residual positive charge will annihilate the electron, so all you have left is light flashing off in several random directions).

"Mining" for new components in the extreme future looks like a losing proposition even without proton decay; with proton decay, you run out of usable material all the sooner.

Running out of food is different from aging. Eventually everything dies as the universe dies, but I don't think it is meaningful to call that aging.

I was replying to:

> no reason to assume that you can't replace parts with decayed protons with new parts

with reasons.