One interesting argument against the heat death is that in this case the most probable observers will be Boltzmann brains, but in the universes with “cutoff” (that is the end like 20 billion years from now), real observer should dominate.
That doesn’t sound like it would work in UDT or similar decision theories. Maybe in Heat Death world there’s one me and a thousand Boltzmann brains with other observations (as per the linked post), and in Big Rip world there’s only the one me. If I’m standing outside the universe trying to decide what response to the observation that I’m me would have the best consequences, why shouldn’t I just ignore the Boltzmann brains? (This is just re-arguing the controversy of how anthropics works, I guess, but considered by itself this argument seems strong to me.)
Yes, it is a good point that based on UDT one could ignore BBs.
But it looks like that cosmologists try to use the type of experiences that an observer has to deduce either he is BB or not. Cosmologists assume that BB has very random experience, and that their current experience is not very random. (I find both claims weak.) They conclude that as their current observations are not random, they are not BBs, and thus BBs are not dominating type of the observers. There are several flaws in this logic, one of of them is that a BB can’t make a coherent conclusions if its experiences are random or not.
Also, even if there are worlds, with Big Rip and another with Heat Death with many BBs, SIA favors the heat death world.
However, some BBs could last longer than just one observer-moment and they could have time to think about the type of experience they have. Such BBs more likely to find themselves in the empty universe than in the one full of stars. Also, interesting thing is that some BBs could appear even in Big Rip scenarios by the process called “nucleation”, where they jump out of cosmological horizon of the accelerating universe.
So, my point is that the idea of the heat death of the universe is getting more alternatives after the discovery of the dark energy, and there are some new arguments against it like the ones based on BBs. All this is not enough to conclude now which form of the end on the universe is more probable.
How so? I looked on the web for a defense of Big Rip being more plausible than heat death but couldn’t immediately find it.
One interesting argument against the heat death is that in this case the most probable observers will be Boltzmann brains, but in the universes with “cutoff” (that is the end like 20 billion years from now), real observer should dominate.
That doesn’t sound like it would work in UDT or similar decision theories. Maybe in Heat Death world there’s one me and a thousand Boltzmann brains with other observations (as per the linked post), and in Big Rip world there’s only the one me. If I’m standing outside the universe trying to decide what response to the observation that I’m me would have the best consequences, why shouldn’t I just ignore the Boltzmann brains? (This is just re-arguing the controversy of how anthropics works, I guess, but considered by itself this argument seems strong to me.)
Yes, it is a good point that based on UDT one could ignore BBs.
But it looks like that cosmologists try to use the type of experiences that an observer has to deduce either he is BB or not. Cosmologists assume that BB has very random experience, and that their current experience is not very random. (I find both claims weak.) They conclude that as their current observations are not random, they are not BBs, and thus BBs are not dominating type of the observers. There are several flaws in this logic, one of of them is that a BB can’t make a coherent conclusions if its experiences are random or not.
Also, even if there are worlds, with Big Rip and another with Heat Death with many BBs, SIA favors the heat death world.
However, some BBs could last longer than just one observer-moment and they could have time to think about the type of experience they have. Such BBs more likely to find themselves in the empty universe than in the one full of stars. Also, interesting thing is that some BBs could appear even in Big Rip scenarios by the process called “nucleation”, where they jump out of cosmological horizon of the accelerating universe.
So, my point is that the idea of the heat death of the universe is getting more alternatives after the discovery of the dark energy, and there are some new arguments against it like the ones based on BBs. All this is not enough to conclude now which form of the end on the universe is more probable.