# Freeman Dyson: Advanced intelligences thinking in an expanding universe [closed]

I dont know if this is the correct place to ask this, because is highly speculative and maybe even hard scifi. But... I think is less speculative than the many worlds interpretation of QM or many aspects of string theory :D and not so a big deal, just a little idea. What follows is from a new interview with Freeman Dyson:

It’s this idea that you talked about a while ago that potentially intelligent beings may be capable of thinking an infinite number of thoughts in an open expanding universe. Do you know which proposal I’m talking about?

Yes well, of course in those days when I wrote that, about thirty years ago, everybody then believed that the universe is expanding linearly with a constant velocity of a given object.

And now we know that the universe is accelerating – that’s the discovery of the last ten years – and in an accelerated universe everything is different so that whole discussion, in fact, is now wrong. I don’t think we know enough about the accelerating universe to go over it and see how it’s changed.

Are you saying that due to the idea that the universe is accelerating it potentially changes your idea about how we think and the capability of thinking?

Yes. In a very drastic way. It’s bad news if we really are accelerating all the time in the future.*

Why the accelerating universe changes the possibility of this evolved thinking? I think its an interesting cross-field discussion mixing physics, computer science and philosophy. If some of us discuss Boltzmann Brains, Quantum Computing universe and "Fermi paradox, this is not different.

## closed as primarily opinion-based by Dvij Mankad, sammy gerbil, Kyle Kanos, Jon Custer, Cosmas ZachosJul 11 '18 at 13:26

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

• It's a great chat room question, but I think it will be closed as opinion based. – user198207 Jun 30 '18 at 20:09
• @Countto10: It is not an opinion based. The original paper by F. Dyson (1979), Time without end: Physics and biology in an open universe. Reviews of Modern Physics, 51(3), 447, proposed a concrete strategy for the intelligent life to achieve "infinite number of thoughts" (a notion with a clear thermodynamical meaning) in an expanding universe. This question asks how accelerated expansion invalidates the strategy. – A.V.S. Jun 30 '18 at 20:31
• Ok, put that in the post, in case of comment rot, but because you have "what do you think?" And "discussion", these are off topic, in my opinion:). Best of luck with it, see what the consensus is. – user198207 Jun 30 '18 at 20:39
• I'm fairly certain that we can show objectively that if the dark energy represents a Einsteinian cosmological constant (which I believe is treated as the least hypothesis by many people), then the optimistic conclusion of Dyson's paper is rendered null and void. – dmckee Jun 30 '18 at 22:24
• Ive edited that "what do you think?" , but of course I'm not talking about opinions without rational and empirical based arguments. As mentioned above, Dyson presented the idea in a valid format in his 1979 paper, and this question is 100% related to that. – Juan Manuel Jones Volonté Jun 30 '18 at 23:55

Physical eschatology is the field of exploring the long term future of the universe using known physics. While much of it deals with just inanimate contents there has been a fair bit of interest in what role life and intelligence could play: intelligent creatures can engineer conditions that are unlikely to happen spontaneously on their own but can unfold into long-term changes. Researchers typically look at necessary conditions for life and intelligence such as information processing and memory storage. If you cannot do those things, then life will run out.

The big issue in an accelerating universe is that it has event horizons. There exist a distance (about 4.9 Gpc right now) beyond which we cannot affect or reach any matter. Galaxies beyond this horizon cannot be reached even by light we send. The reason is that the expansion will move them away from us faster than we can move to catch up with them. As the universe becomes older more and more of the matter will disappear out of reach.

This implies that any civilisation will only be able to gather a finite amount of mass-energy, and it will tend to separate into smaller gravitationally bound "island universes".

Another important effect of this acceleration is the existence of a horizon radiation. This is somewhat like Hawking radiation or Unruh radiation, and means that the background temperature of the universe will never go below $\approx 10^{-29}$ K. Right now the CMB is far hotter, but in a few trillion years the horizon radiation will dominate (this is why I have suggested it is rational for computation-hungry civilisations to aestivate until this era).

Together these effects pose a serious limitation of future intelligent life. Since error correction is an irreversible thermodynamic operation it has an entropy cost $k_B T \ln(2)$ (the Landauer principle). This is proportional to temperature. This means that to remove errors (which always occur at some finite rate, if only by quantum tunnelling) it has to pay a constant price in energy (or some other source of negentropy). But it only has a finite amount of stuff! Hence it will either run out of stuff, or have to accept randomisation of stored memories over time which means it will eventually start looping into Poincare recurrence.

Reversible and quantum computation that do not have any entropy costs just mean that much more computation can be done, not that it can go on indefinitely, since they also have to do some error correction from time to time.

So these considerations appear to put a finite (but possibly every large) limit on the future computations that can be done by any creatures in the universe and how long they might survive. There are of course other problems like proton decay that might limit things further, but I think the event horizon + horizon radiation + Landauer principle places the firmest constraint here.

The question is whether there are any loopholes here - maybe the dark energy is not constant and horizons eventually disappear, maybe we are badly wrong about Unruh radiation, maybe there are hyperturing computation - but so far there is no evidence of any of that.

• Thanks for the answer, very informative. So we need error correction and it consumes energy, thats a central point to me. But in that case, the civilization can still evolve computing new things, because each new isle universe starts with different "thoughts". Those spread civilizations cant communicate with each other, but they can compute in novel ways. What can stop this? – Juan Manuel Jones Volonté Jul 1 '18 at 21:07
• @JuanManuelJonesVolonté - The island universes will not be able to communicate with each other, since the gulfs between them expand faster than signals can cross them. – Anders Sandberg Jul 1 '18 at 21:18
• Yes, of course. What I say is that those island universes could compute outputs previously unknown to others, so each one can go out of resources and errors will randomize their information, but overall, novel computations will never stop. – Juan Manuel Jones Volonté Jul 2 '18 at 0:55