Periodically I look at this graph, and I'm like, "holy shit, that is so much Nothing. Wut. Like, they converted it to log-scale so it would fit into my brain and it's still so much Nothing, Jezus Christ."

Eliezer's Dath Ilan verse has this song for people who died before the invention of cryonics:

Even if the stars should die in heaven
Our sins can never be undone
No single death wil be forgiven
When fades at last the last lit sun.
Then in the cold and silent black
As light and matter end
We’ll have ourselves a last look back
And toast an absent friend.

And I find myself wondering "What are the physical limits on 'some sentient computation surviving into the dark era?" Assuming we don't learn anything new about physics, or acausal-trade our way into another universe or whatever, what's the farthest to the right on this timeline you could possibly get, if you goal was to have some computation that, as late as possible, looks around at the universe one last time, comprehends it, and says "yep, still full of infinite blackness. Goodbye, world."

Vaguely relevant things I'm vaguely aware of include:

  1. Something something you can somehow harvest energy from black holes. Does this plausibly get us to the end of the Black Hole Era or is that energy eventually too weaksauce?
  2. Space is, like, really cold (especially when All Has Become Darkness), so any time-capsule robot would face an uphill battle not radiating it's energy into the void.
  3. On long enough timescales, protons (probably?) decay, and... like, your robot would eventually... just... disintegrate?

If anyone knows enough physics to satisfy my random curiosity, uh, I'd appreciate it.

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Sep 16, 2022


Alright, this is kind of a Special Interest, so here's your relevant thought dump.

First up, the image is kind of misleading, in the sense that you can always tack on extra orders of magnitude. You could tack on another thousand orders of magnitude and make it look even longer, or just go "this is 900 OOM's of literally nothing happening, lets clip that off and focus on the interesting part"

Assuming proton decay is a thing (that free protons decay with a ridiculously long half-life)....

ok, I was planning on going "as a ludicrous upper bound, here's the number", but, uh, the completely ludicrous upper bound wound up being a WHOLE LOT longer than I thought. I... I didn't even think it was possible to stall till the evaporation of even a small black hole. But this calculation indicates that if you're aiming solely at living ludicrously long, you can stall about a googol years, enough for even the largest black holes to evaporate, and to get to the end of the black hole era. I'm gonna need to rethink some stuff.

EDIT: rethought some stuff, realized it doesn't change my conclusions from when I last looked into this. The fundamental problem is that, for any remotely realistic numbers, if you're trying to catch the final evaporation of a black hole to harvest its mass-energy, you'll blow a lot more than the amount of mass-energy that you could gain, in order to wait that long.

Final conclusion: If proton decay is a thing, it's definitely not worth waiting to the end of a black hole, you'll want to have things wrapped up far earlier. If proton decay isn't a thing, you'll want to wait till the black hole evaporates to catch that final party and last  kg of mass-energy. If proton decay is a thing and you're willing to blow completely ridiculous cosmic amounts of resources on it, you can last till the late parts of the black hole era.

The rough rationale is as follows. Start with 10x the mass of the largest black holes in the universe, around  solar masses stockpiled. If they're spinning fast enough, you can extract energy from them, assume you can extract all of it (it's over 10 percent, so let's round it up to 100 percent). Assume that proton decay is  years (a high estimate), and that we use the energy at 100 percent efficiency to make matter (also high estimate), you can take out one proton, wait for around a proton decay time, take out the next proton, and so on. Then you can take out around  protons, and each one lasts you around  years, getting around  years (high uncertainty). And, coincidentally, natural Hawing radiation finishes off the black hole of that size in  years, leaving a small margin left over for silly considerations like "maybe the intelligence needs more than one proton to physically implement".

So, not remotely practical, but maybe something like  years would actually be doable? That extra 29 OOM's of wiggle room patches over a lot of sins in this calculation.

But, in terms of what would actually be practical for the far future of humanity, it'd be the strat of "dump as much mass into a fast-spinning black hole as possible. Like, eat the entire Laniakea supercluster complex. Wait a trillion years for the cosmic microwave background radiation to cool to its floor temperature. You'd be in the late Stelliferous era at this point, with a few red dwarfs around, if you didn't dump all the stars in the mega-black-hole already. Set up some infrastructure around the mega-hole, and use the Blandford-Znajek mechanism to convert the mega-hole spin into electrical power. You should be able to get about a gigawatt of power for the next  years to run a whole lotta computation and a little bit of maintanence, and if proton decay is messing with things, chop however many OOM's you need off the time and add those OOM's to the power output. Party for a trillion trillion trillion eons with your super-optimized low-temperature computing infrastructure"

Crucially, these are all virtual beings once you start getting past the stelliferous era, so you can do a whole lot of tricks with subjective time.


Sep 15, 2022


That's an excellent question, pondered by the brightest minds. The great Freeman Dyson proposed a solution dubbed eternal intelligence (Dyson 1979, Reviews of Modern Physics, Volume 51, Issue 3, July 1979, pp.447-460). Basically, some finite amount of matter=energy is stored. As the universe cools over time, energy costs per computation decrease (logarithmically, but forever). After each cooling time period, one can use some fraction of the remaining energy, which will thus never go to zero, leading to eternal consciousness. 

It was later understood that the expansion of the universe is accelerating. If that holds, the concept breaks down, as Dyson admitted. In the far future, any two observers will be separated, making the remaining subjects very lonely. 


Sep 15, 2022


I tried to answer the question here: How to Survive the End of the Universe 

At a cursory glance, this seems slightly differently focused than my question – I'm specifically not asking "how can we survive the end of the universe?", but "how long can we survive into the end of the universe?".

(but still seems good to have a reference to here)

Also, Dark Age will be dominated by Boltzmann brains and it could be harvested by the use of some form of Dust theory.
Well yes, in the sense that the Dark Age is infinitely long and the diagram only shows a finite time span. The first possibility of Boltzmann brains would be - even in the logarithmic scale - so far off the right side that extending the diagram to fit would mean leaving our solar system to read it. But yes, your statement is correct since in this model there would be still an infinitely long time span beyond that.


Sep 15, 2022


I'm not sure that you can get to 10^60 years even if protons don't decay. If they do, then you might not have very much more time than whatever the decay timescale is. It could be that free protons decay while bound ones don't, in which case you might just avoid having any hydrogen or other light elements around.

Assuming you have a galactic mass available to do with as you please and can extract essentially all of its mass-energy, then over 10^60 years you would have a few picowatts available to do all the maintenance that might be required for whatever infrastructure you have. That's a pretty miserly budget for managing structures at a scale that can convert galactic mass to usable energy! It would have to cover all sensors as well as computation and also any work that might need doing from time to time. I would be very surprised if maintenance costs didn't scale along with mass, just because the number of particles enormously expands the state space.

Over these sorts of timescales even the most rigidly bound materials diffuse like a gas due to various quantum processes, but maybe there is some clever way to avoid that and still have them able to perform the desired functions when required.

Anything over these sorts of timescales are going to be very speculative, so this is probably about the best "answer" I can give. In reality, we don't know what happens to matter over 10^30 year timescales even if the cosmological predictions were spot-on.

It sounds like part of the thing here is "you can spend energy/time/effort re-arranging matter into configurations that will survive longer, but you'll pay a bunch of costs trying to optimize for that, and it's not obvious that those costs are worth it."

(i.e. maybe you can arrange a galaxy to survive as long as possible to output "goodbye, world" with minimum viable sentience at the longest possible timeslot, but, like, do you really wanna sacrifice a bajillion possible flourishing lives so that you can print "goodbye, world" at seventy bajillion trillion years instead of 1 bajillion trillion years?")

And, well, that's fair I guess.

Logan Zoellner

Sep 16, 2022


Assuming protons don't decay and that there's no big rip, I feel like you can do obnoxiously large numbers.  Build a clock out of superconductors that consumes 0 power until the top bit flips over (since incrementing a counter is reversible, this should be possible).  Then, when your "alarm" goes off, wake up the sentient being and let it have its last thought.  The limit is now on the number of bits B in your clock.  Assume this is somewhere between 10**67 (number of atoms in the galaxy) and 10**80 (number of atoms in the visible universe).  Your wake-up time is now 2**(10**B).

Ignoring proton decay, don't you still need to deal with entropy and losing energy? Like, you have some energy store to run your final computations, and I'd expect the hard part to be preventing that energy store from leaking out.

1Logan Zoellner2y
Yep, I think this kills it.  I have a sort of argument in my head that nothing can emit energy slower than a black hole due to hawking radiation.


Sep 16, 2022


If there is a way for data structures to survive forever it would be something we couldn't imagine, like three leptons orbiting each other storing data in their precise separation distances, where it would take a godzillion eons to generate a single pixel in an ancient cat picture. 

2 comments, sorted by Click to highlight new comments since: Today at 5:47 PM

Some random observations:

  • What we actually want to optimize is how much subjective time we survive, not surviving as long as possible on the physical timeline.
  • If for some reason we wanted to survive as long as possible on the physical timeline, the best strategy might be storing energy/negentropy harvested during early periods rather than finding ways to harvest remaining energy during late periods.
  • AFAICT, it might be possible to harvest energy without stars or even black holes, by collecting cosmic gas and doing nuclear fusion, or something even better than nuclear fusion (e.g. inducing proton decay or throwing matter into small rapidly evaporating black holes).
  • AFAIK, it's possible that there are bound states of neutrinos held by the weak force, and bound states of such "multi-neutrinos" held by gravity. And, the particles dark matter is made of open even more possibilities. Maybe we can build computers out of this stuff after all protons decay.
  • If our vacuum is only metastable, we might be able to induce some kind of controlled vacuum collapse and escape into the resulting new universe, which opens a bunch of more options.

Related to this questions is this youtube video, which I think you might find very interesting. 

In this video (or perhaps a related one from the same person) they explore the idea of space getting extremely cold at long-times when the cosmic microwave background is much more red-shifted than it is today. In contrast to your idea they actually argue that all that cold is a good thing. A cold computer can run the same calculations with less energy. They go as far as to propose that this hypothetical civilisation will lie dormant until the universe has grown colder, as this allows the rest-mass energy of their black hole to simulate a larger number of virtual people, than they could have simulated had they started in our relatively hot age.