5 ms·

Things still happen in heat death because of quantum mechanics and fluctuations. Time still has a meaning, but it may lose its arrow if microscopic quantum inte

• pixl97 3y ago
  https://en.wikipedia.org/wiki/Conformal_cyclic_cosmology https://en.wikipedia.org/wiki/Conformal_cyclic_cosmology If everything but what exists at the quantum level then CCC is a possibility.
  • meroes 3y ago
    I’m petty sure this is loosely agreed by Susskind except CCC is a more specific version. Entire bubble universes have a chance to fluctuate out of any patch of spacetime. (Colemann-Delucca process or something). That fractal nature of spacetime is appealed to by Susskind in the video.
• passion__desire 3y ago
  Sean Carroll disagrees wrt Boltzmann brains will dominate the class of observers. https://youtu.be/nqQrGk7Vzd4?t=2614 https://youtu.be/nqQrGk7Vzd4?t=2614
  • meroes 3y ago
    That’s because he disagrees with mainstream cosmology models in a different way than Susskind. Susskind takes the cosmology of our bubble universe as more settled, but addendums a huge inflationary multiverse on top. I’m pretty sure Carroll disagrees with the cosmology model of our bubble universe, and uses that to rule out BB’s dominating instead. Susskind’s says BB’s dominate any single universe over time, but not the multiverse as a whole.
• benlivengood 3y ago
  There's also the branches of our multiverse where we simply don't experience heat death due to being on the unlikely side of the 2nd law of thermodynamics. Infinite simulations in those branches could account for a lot of "normal" experience. I haven't done the math but it seems intuitively like a simulation that keeps running in 10^-M branches (effectively quantum immortality) due to avoidance of entropy increase are more frequent than the 10^-N occurrence of boltzman brains where N>>M.
  • red75prime 3y ago
    Given that decoherence is not perfect, I'd expect those branches to lack the "normal" macroscopic structure and maybe the time arrow as they interfere with each other.
• raattgift 3y ago
  > BB's really are a problem to modern physics/cosmology No, they really aren't. They have never been observed. They are incompatible with present-day observations, and so as far as we can tell probably they have never existed in the history of our observable universe. They thus are a diagnostic on approaches to cosmology which have conditions favourable to BBs in approximately present times (or in the past), essentially killing any theory that does not suppress them. They also imperil some theories of the far future which rely on fluctuation theory to produce a whole new universe (some decay-of-false-vacuum models, for instance). Very short lived and spatially tiny low-entropy configurations are enormously enormously ENORMOUSLY more likely than large low-entropy configuration that persist. Boltzmann brains describe a very short lived (much less than seconds) fluctuation into a very low entropy configuration, and are thus much more likely than a fluctuation producing Boltzmann being who can survive in outer space for at least minutes, let alone a galaxy in which a thinking being evolved and personally experienced many years of life, or a universe with many such galaxies. This also means that because of the scale and history of the universe that we have direct experience of, one cannot safely draw a physical-theory parallel between our universe's projected high-entropy far future and our low-entropy past more distant than the dense low-entropy phases about which we have evidence (from the surface of last scattering to baryon species and abundances, ...). Multiverses are not needed in this analysis, and don't really help one way or another. If you figure out how some other space in a multiverse configuration interacts with ours (and prove it experimentally or observationally), you will have mostly just changed our understanding of our universe and its (quasi-)local physics, particularly thermodynamics.
  • meroes 3y ago
    Just because whole new universes might fluctuate from spacetime patches, doesn't mean the non-fluctuating patches wont be in heat death forever in the far future. In so far as we can talk about multiple universes in such a picture, "ours" will be in heat death and some daughter spacetimes will not be for some duration. To say we can't predict more than 14b.y. in to the future seems at odds with most theoreticians and I've seen many predict much further with mainstream theories. For BBs, yes the "tiny" ones will be exponentially more likely. But it seems like the 'medium to large' BBs in the heat death spacetimes will outnumber natural observers still, unless there are more spacetimes out of heat death comparatively. Some kind of measure of pre-heat death spacetimes vs far-into heat death spacetimes is needed to theoretically match our observation of no BBs. This is a multiverse. A certain kind of multiverse does this, one where the odds to fluctuate new universes is high enough to outpace the ones in terminal heat death. I mean, we talk about inflation with little hope of the verification you talk about in your last paragraph. This is barely anything beyond inflation, it just sets the proper measure/odds among all the details to match observations. To say it does nothing, what of Susskind's video then? I'm just paraphrasing him. Carroll and Susskind both find it useful to talk of BB's, and use them to weigh on which theories to accept. That's all I was saying. Whether one has actually existed, don't know. Inflation might be so pervasive it makes BBs infinitesimal.