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Is it though? It is my understanding that the quantum fluctuations that give rise to BBs will still exist, even after (and specially after) the evaporation of b

Is it though? It is my understanding that the quantum fluctuations that give rise to BBs will still exist, even after (and specially after) the evaporation of black holes (perhaps assuming no Big Rip).

JohnMakin 1y ago
It's just a joke but the average number of years for a spontaneous quantum fluctuation to produce a boltzmann brain was calculated at something like 10^500 years. You're right that the processes involved would still remain barring some kind of big rip event.
- squigz 1y ago
  Does this mean such an event could produce, say, an entire universe? If so, does this theoretically mean that a cyclic universe is possible in this way, and that if one were to go far enough - impossibly, unfathomably far - you might find the remnants of other universes?
  - immibis 1y ago
    The theory of Boltzmann brains is that you're way more likely to get just a brain (including false memories of a planet earth and a whole visibile universe around it), than to get a brain, a planet earth, and a whole visible universe around it. So the chance that any of that is real, given that a brain exists to perceive it, is infinitesimal. We are probably just floating human brains that popped into the vastness of space three microseconds ago, complete with false memories of the distant past. To dispel a misconception: They're not some hypothetical type of brain that exists as pure quantum fluctuations (though those are even more likely). Boltzmann was talking about the probability of actual flesh-and-blood human brains arising spontaneously out of the vacuum.
    - simonh 1y ago
      Wouldn’t the vast majority of those be incoherent broken messes, of various levels of inconsistency? Only a teeny tiny fraction would be coherent. So the expected experience fir any arbitrary Boltzmann brain would be all over the place.
x1000 1y ago
Not a physicist, but I see it this way too. My understanding of Boltzmann brains is that they are a theoretical consequence of infinite time and space in a universe with random quantum fluctuations. And that those random fluctuations would still be present in an otherwise empty universe. So then this article has no bearing on the Boltzmann brain thought experiment or its ramifications.
layer8 1y ago
They may not actually happen: https://arxiv.org/abs/1505.02780 https://arxiv.org/abs/1505.02780

JohnMakin 1y ago

It's just a joke but the average number of years for a spontaneous quantum fluctuation to produce a boltzmann brain was calculated at something like 10^500 years. You're right that the processes involved would still remain barring some kind of big rip event.

squigz 1y ago
Does this mean such an event could produce, say, an entire universe? If so, does this theoretically mean that a cyclic universe is possible in this way, and that if one were to go far enough - impossibly, unfathomably far - you might find the remnants of other universes?
- immibis 1y ago
  The theory of Boltzmann brains is that you're way more likely to get just a brain (including false memories of a planet earth and a whole visibile universe around it), than to get a brain, a planet earth, and a whole visible universe around it. So the chance that any of that is real, given that a brain exists to perceive it, is infinitesimal. We are probably just floating human brains that popped into the vastness of space three microseconds ago, complete with false memories of the distant past. To dispel a misconception: They're not some hypothetical type of brain that exists as pure quantum fluctuations (though those are even more likely). Boltzmann was talking about the probability of actual flesh-and-blood human brains arising spontaneously out of the vacuum.
  - simonh 1y ago
    Wouldn’t the vast majority of those be incoherent broken messes, of various levels of inconsistency? Only a teeny tiny fraction would be coherent. So the expected experience fir any arbitrary Boltzmann brain would be all over the place.

x1000 1y ago

Not a physicist, but I see it this way too. My understanding of Boltzmann brains is that they are a theoretical consequence of infinite time and space in a universe with random quantum fluctuations. And that those random fluctuations would still be present in an otherwise empty universe. So then this article has no bearing on the Boltzmann brain thought experiment or its ramifications.

layer8 1y ago

They may not actually happen: https://arxiv.org/abs/1505.02780 https://arxiv.org/abs/1505.02780