4 ms·

OK, I think I appreciate the issue: “multiverse” is overloaded. When people talk about the many worlds of quantum mechanics, or alternate histories, they’re ta

by evanb 4y ago

OK, I think I appreciate the issue: “multiverse” is overloaded. When people talk about the many worlds of quantum mechanics, or alternate histories, they’re talking about the terms in the path integral sum. But multiverse can also mean, separately, at least two additional things. First, different bubble universes that may be a part of cosmology. Second, alternate quantum field theories (with different actions, or fundamental parameters, or different gauge groups, or whatever). The standard quantum-mechanical path integral is a sum over histories / a many-world theory in the sense that the different histories / parts of the wave function can be detected via interference experiments. Other meanings of multiverse are speculative (though maybe a cosmologist will come and tell me that bubble universes are a direct prediction of inflationary cosmology and are not optional either).

skissane 4y ago
> When people talk about the many worlds of quantum mechanics, or alternate histories, they’re talking about the terms in the path integral sum. Hugh Everett's original "many worlds" theory wasn't just "talking about the terms in the path integral sum" – he saw all the "worlds" as "real" in exactly the same sense that the actual experimental results are "real". Everett believed in "quantum immortality", which only makes sense if you interpret the worlds in a much more literal sense than mere "terms in the path integral sum" suggests. By contrast, even though Feynman calls the paths "real", it isn't clear if he means them to be "as real" as the actual experimental results they are used to predict. People who reinterpret many-worlds as just "terms in the path integral sum" are cutting the theory down to be something far less metaphysically grandiose than its originator intended. To quote Max Tegmark: > Atheist or not, Everett firmly believed that his many-worlds theory guaranteed him immortality: His consciousness, he argued, is bound at each branching to follow whatever path does not lead to death —and so on ad infinitum. (Sadly, Everett's daughter Liz, in her later suicide note, said she was going to a parallel universe to be with her father. [149a]) https://space.mit.edu/home/tegmark/everett/everett.html https://space.mit.edu/home/tegmark/everett/everett.html
- peteradio 4y ago
  Sadly? You presume she is not actually living in a parallel universe!
  - skissane 4y ago
    I realise you are being somewhat flippant, but it is still sad, because (among other reasons) it appears that Liz Everett misunderstood her father's theory. If the theory of quantum immortality is true, then while from our perspective, Hugh Everett died from a heart attack in 1982, from his own perspective, he's living on in some other branch of the multiverse in which he somehow survived that heart attack. Similarly, while from our perspective, his daughter Liz died from suicide in 1996, from her own perspective, she's living on in some other branch of the multiverse in which she somehow survived that suicide attempt. Indeed, if the theory is true, then no matter how many times 1996 Liz tries to commit suicide, from her own viewpoint she will never succeed – but she never gets to see her father again either – he's living on in a different branch of the multiverse from her, one which diverged from hers all the way back in 1982. And even that other Liz, whose father didn't die in 1982, is doomed to eventually watch her father die, and her father to watch her die, even as both go on living forever, trapped in different branches. Quantum immortality promises us a somewhat bleak afterlife in which we all live forever, but none of us ever get to see each other again. Eternal loneliness is our universal doom. The only way in which she actually could see her father again, would be if quantum immortality is false, but some other afterlife theory is true instead.
    - GoblinSlayer 4y ago
      For him to survive his survival has to be the part of the wave function, otherwise he doesn't survive, and the form of wave function isn't wishful.
- skissane 4y ago
  > To quote Max Tegmark: Correction: that's on Tegmark's website, but it isn't Tegmark's words. It is authored by Eugene Shikhovtsev, edited by Kenneth W. Ford

by evanb 4y ago

skissane 4y ago

> When people talk about the many worlds of quantum mechanics, or alternate histories, they’re talking about the terms in the path integral sum. Hugh Everett's original "many worlds" theory wasn't just "talking about the terms in the path integral sum" – he saw all the "worlds" as "real" in exactly the same sense that the actual experimental results are "real". Everett believed in "quantum immortality", which only makes sense if you interpret the worlds in a much more literal sense than mere "terms in the path integral sum" suggests. By contrast, even though Feynman calls the paths "real", it isn't clear if he means them to be "as real" as the actual experimental results they are used to predict. People who reinterpret many-worlds as just "terms in the path integral sum" are cutting the theory down to be something far less metaphysically grandiose than its originator intended. To quote Max Tegmark: > Atheist or not, Everett firmly believed that his many-worlds theory guaranteed him immortality: His consciousness, he argued, is bound at each branching to follow whatever path does not lead to death —and so on ad infinitum. (Sadly, Everett's daughter Liz, in her later suicide note, said she was going to a parallel universe to be with her father. [149a]) https://space.mit.edu/home/tegmark/everett/everett.html https://space.mit.edu/home/tegmark/everett/everett.html

peteradio 4y ago
Sadly? You presume she is not actually living in a parallel universe!
- skissane 4y ago
  I realise you are being somewhat flippant, but it is still sad, because (among other reasons) it appears that Liz Everett misunderstood her father's theory. If the theory of quantum immortality is true, then while from our perspective, Hugh Everett died from a heart attack in 1982, from his own perspective, he's living on in some other branch of the multiverse in which he somehow survived that heart attack. Similarly, while from our perspective, his daughter Liz died from suicide in 1996, from her own perspective, she's living on in some other branch of the multiverse in which she somehow survived that suicide attempt. Indeed, if the theory is true, then no matter how many times 1996 Liz tries to commit suicide, from her own viewpoint she will never succeed – but she never gets to see her father again either – he's living on in a different branch of the multiverse from her, one which diverged from hers all the way back in 1982. And even that other Liz, whose father didn't die in 1982, is doomed to eventually watch her father die, and her father to watch her die, even as both go on living forever, trapped in different branches. Quantum immortality promises us a somewhat bleak afterlife in which we all live forever, but none of us ever get to see each other again. Eternal loneliness is our universal doom. The only way in which she actually could see her father again, would be if quantum immortality is false, but some other afterlife theory is true instead.
  - GoblinSlayer 4y ago
    For him to survive his survival has to be the part of the wave function, otherwise he doesn't survive, and the form of wave function isn't wishful.
skissane 4y ago
> To quote Max Tegmark: Correction: that's on Tegmark's website, but it isn't Tegmark's words. It is authored by Eugene Shikhovtsev, edited by Kenneth W. Ford