Update April 2019: The key theory Dr Sandberg puts forward for why aliens may delay their activities has been strongly disputed in a new paper, which claims it is based on an incorrect understanding of the physics of computation.
It seems tremendously wasteful to have stars shining. When you think about the sheer amount of energy they’re releasing, that seems like it’s a total waste. Except that it’s about 0.5 percent of the mass energy that gets converted into light and heat. The rest is just getting into heavy nuclei. If you can convert mass into energy, you might actually not care too much about stopping stars. If the process of turning off stars is more costly than 0.5% of the total mass energy, then you will not be doing it.
The universe is so vast, yet we don’t see any alien civilizations. If they exist, where are they? Oxford University’s Anders Sandberg has an original answer: they’re ‘sleeping’, and for a very compelling reason.
Because of the thermodynamics of computation, the colder it gets, the more computations you can do. The universe is getting exponentially colder as it expands, and as the universe cools, one Joule of energy gets worth more and more. If they wait long enough this can become a 10,000,000,000,000,000,000,000,000,000,000x gain. So, if a civilization wanted to maximize its ability to perform computations – its best option might be to lie in wait for trillions of years.
Why would a civilization want to maximise the number of computations they can do? Because conscious minds are probably generated by computation, so doing twice as many computations is like living twice as long, in subjective time. Waiting will allow them to generate vastly more science, art, pleasure, or almost anything else they are likely to care about.
But there’s no point waking up to find another civilization has taken over and used up the universe’s energy. So they’ll need some sort of monitoring to protect their resources from potential competitors like us.
It’s plausible that this civilization would want to keep the universe’s matter concentrated, so that each part would be in reach of the other parts, even after the universe’s expansion. But that would mean changing the trajectory of galaxies during this dormant period. That we don’t see anything like that makes it more likely that these aliens have local outposts throughout the universe, and we wouldn’t notice them until we broke their rules. But breaking their rules might be our last action as a species.
This ‘aestivation hypothesis’ is the invention of Dr Sandberg, a Senior Research Fellow at the Future of Humanity Institute at Oxford University, where he looks at low-probability, high-impact risks, predicting the capabilities of future technologies and very long-range futures for humanity.
In this incredibly fun conversation we cover this and other possible explanations to the Fermi paradox, as well as questions like:
- Should we want optimists or pessimists working on our most important problems?
- How should we reason about low probability, high impact risks?
- Would a galactic civilization want to stop the stars from burning?
- What would be the best strategy for exploring and colonising the universe?
- How can you stay coordinated when you’re spread across different galaxies?
- What should humanity decide to do with its future?
If you enjoy this episode, make sure to check out part two where we talk to Anders about dictators living forever, the annual risk of nuclear war, solar flares, and more.
The 80,000 Hours podcast is produced by Keiran Harris.