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zero_call comments on Open Thread: July 2010 - Less Wrong
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Is there a principled reason to worry about being in a simulation but not worry about being a Boltzmann brain?
Here are very similar arguments:
If posthumans run ancestor simulations, most of the people in the actual world with your subjective experiences will be sims.
If two beings exist in one world and have the same subjective experiences, your probability that you are one should equal your probability that you are the other.
Therefore, if posthumans run ancestor simulations, you are probably a sim.
vs.
If our current model of cosmology is correct, most of the beings in the history of the universe with your subjective experiences will be Boltzmann brains.
If two beings exist in one world and have the same subjective experiences, your probability that you are one should equal your probability that you are the other.
Therefore, if our current model of cosmology is correct, you are probably a Boltzmann brain.
Expanding your evidence from your present experiences to all the experiences you've had doesn't help. There will still be lots more Boltzmann brains that last for as long as you've had experiences, having experiences just like yours. Most plausible ways of expanding your evidence have similar effects.
I suppose you could try arguing that the Boltzmann brain scenario, but not simulation scenario, is self-defeating. In the Boltzmann scenario, your reasons for accepting the theory (results of various experiments, etc) are no good, since none of it really happened. In the simulation scenario, you really did see those results, all the results were just realized in a funny sort of way that you didn't expect. It would be nice if the relevance of this argument were better spelled out and cashed out in a plausible Bayesian principle.
edited for format
Is there really a cosmology that says that most beings with my subjective experiences are Boltzmann brains? It seems to me that in a finite universe, most beings will not be Boltzmann brains. And in an infinite universe, it's not clear what "most" means.
I gathered this from a talk by Sean Carroll that I attended, and it was supposed to be a consequence of the standard picture. All the Boltzmann brains come up in the way distant future, after thermal equilibrium, as random fluctuations. Carroll regarded this as a defect of the normal approach, and used this as a launching point to speculate about a different model.
I wish I had a more precise reference, but this isn't my area and I only heard this one talk. But I think this issue is discussed in his book From Eternity to Here. Here's a blogpost that, I believe, faithfully summarizes the relevant part of the talk. The normal solution to Boltzmann brains is to add a past hypothesis. Here is the key part where the post discusses the benefits and shortcomings of this approach:
The years there are missing some carats. Should be 10^100 and 10^10^120.
Oh I see. I... I'd forgotten about the future.
Link to talk.
This is always hard with infinities. But I think it can be a mistake to worry about this too much.
A rough way of making the point would be this. Pick a freaking huge number of years, like 3^^^3. Look at our universe after it has been around for that many years. You can be pretty damn sure that most of the beings with evidence like yours are Botlzmann brains on the model in question.