Thus we come to our first conclusion: a civilization can freely erase bits without forgoing larger future rewards up until the point when all accessible bounded resources are jointly thermalized.
They don’t mention black holes specifically, but my interpretation of this is that a civilization can first dump waste heat into a large black hole, and then later when the CMB temperature drops below that of the black hole, reverse course to use Hawking radiation of the black hole as energy source and CMB as heat sink.
If we only consider thermodynamics (and ignore how technologically feasible this is), I think this should net you the same amount of total computation over time, but allow you to do a lot of it earlier.
I don’t think you can feasibly use the Hawking radiation of large black holes as an energy source in our universe (even if you are patient).
My understanding is that larger black holes decay over ~10100 years. I did a botec a while ago and found that you maybe get 1 flop every 1030 years or so on average if we assume perfect efficiency and very few bit erasures in our reversible computing approach (I think I assumed about 1 bit erasure per 1010 or something?). I don’t think you can maintain a mega structure around a large black hole capable of harvesting this energy which also can survive this little energy. (I think quantum phenomena will decay your structure way too quickly.)
In that case, don’t dump waste heat into black holes so large that it’s impossible to use them as eventual energy sources. Instead dump waste heat into medium sized black holes, which can feasibly be used as eventual energy sources.
I think the size might have to be pretty precise to get this right (I think decay duration is cubic in mass), so they’d probably need to be engineered to have a particular size. (E.g. add mass to a small black hole until it hits the right size.)
But, yeah, with this constraint, I think it can maybe work. (I don’t know the decay duration for the smallest naturally occurring black holes. But as long as this is sufficient low, the proposal works.)
From Bennett et el’s reply to the aestivation paper:
They don’t mention black holes specifically, but my interpretation of this is that a civilization can first dump waste heat into a large black hole, and then later when the CMB temperature drops below that of the black hole, reverse course to use Hawking radiation of the black hole as energy source and CMB as heat sink.
If we only consider thermodynamics (and ignore how technologically feasible this is), I think this should net you the same amount of total computation over time, but allow you to do a lot of it earlier.
I don’t think you can feasibly use the Hawking radiation of large black holes as an energy source in our universe (even if you are patient).
My understanding is that larger black holes decay over ~10100 years. I did a botec a while ago and found that you maybe get 1 flop every 1030 years or so on average if we assume perfect efficiency and very few bit erasures in our reversible computing approach (I think I assumed about 1 bit erasure per 1010 or something?). I don’t think you can maintain a mega structure around a large black hole capable of harvesting this energy which also can survive this little energy. (I think quantum phenomena will decay your structure way too quickly.)
In that case, don’t dump waste heat into black holes so large that it’s impossible to use them as eventual energy sources. Instead dump waste heat into medium sized black holes, which can feasibly be used as eventual energy sources.
I think the size might have to be pretty precise to get this right (I think decay duration is cubic in mass), so they’d probably need to be engineered to have a particular size. (E.g. add mass to a small black hole until it hits the right size.)
But, yeah, with this constraint, I think it can maybe work. (I don’t know the decay duration for the smallest naturally occurring black holes. But as long as this is sufficient low, the proposal works.)