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https://arxiv.org/abs/1404.1207

I have some questions in regard to this paper. If I am not mistaken it is akin to Alexander Vilenkin's proposed cosmological model that has the Universe begin to exist from a quantum nucleation event.

  1. What is a "small true vacuum bubble" and "metastable false vacuum"? I am having a hard time finding out and the closest I've came is that they are sectors of space. Does this mean they exist in spacetime or they require spacetime to exist?

  2. What is created exactly in this paper? Is spacetime created? That is to say, the paper stars from a system of no space and no time and ends up with a system that has spacetime? The paper states that "once a small true vacuum bubble is created by quantum fluctuations of the metastable false vacuum" but if the false vacuum is a sector of space that means space (and time?) already exists in this paper.

  3. What is meant by "spontaneous"? Are the quantum fluctuations really not caused ? I have heard someone say that either wave-function collapse (in collapse theories) or some hidden variable (in non-collapse theories) produces these fluctuations. The only thing there is debate about is whether the causation is deterministic or not.

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I can answer point 1 of your question but will have to leave points 2 and 3 to people with more knowledge.

The seminal paper about bubbles (sections IV and VI of the paper you referenced) is https://journals.aps.org/prd/abstract/10.1103/PhysRevD.15.2929. The basic idea is that two different vacuum states are possible, one of which is of higher energy than the other (see attached picture). quartic potential with small asymmetry added In the simple picture all of spacetime is in the false vacuum (the one of higher energy) and quantum mechanics allows tunneling to the true vacuum. Because this is quantum mechanical the bubbles start off very small but quickly expand at approximately the speed of light. Consequently after a long time all of the false vacuum will have been converted to true vacuum.

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  • $\begingroup$ But aren't vacuums a sector of space ? How can a vacuum exist where there is no space and no time ? $\endgroup$ – momo666 Aug 4 '17 at 21:04
  • $\begingroup$ Vaccua can only exist where there is spacetime. In this case there are simply regions with different values of the field potential. This isn't tunneling quantum tunneling from one place to another, it is just the field changing value. $\endgroup$ – Tom Clarke Sep 20 '17 at 12:49

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