Edd111@aol.com writes:
> I recall, at one of the senior associate meetings in Palo Alto,someone
> mentioned the possibility of a metastable universe, in which, anytime, but
> far more probably billions of years in the future, the universe could undergo
> a phase shift, in which all matter (visible and dark), in fact, the entire
> structure of the universe would be forever altered. Of course, all life
> would be instantaneously- gone!
>
> The question I ask, is this metastability something that most scientists
> believe in, or is it very much a minority theory. And if it 'can happen
> anytime', due to the limiting speed of light, will it be forever impossible
> to know if the universe is phase shifting, even as we speak?
It is a speculative possibility, based on the ideas of false vacua. In the older models of inflation the universe got stuck in a "metastable false vacuum state", an unstable phase of the vacuum with nonzero energy density. During this period inflation occured and the universe expanded tremendously, but eventually the false vacuum decayed into a real vacuum, slowing the expansion and releasing a lot of energy. More modern models do not have a metastable false vacuum but rather a flat potential for the vacuum state (like x^4-x^2 near zero), but the principle is similar ( see http://www.damtp.cam.ac.uk/user/hawking/open.html for a talk by Hawking on inflation).
But what if the universe is not in a true vacuum state but a false vacuum? Then the vacuum could randomly decay one day, releasing its energy and likely making the fields defining particle masses and properties change. The decay would spread with the speed of light, and our world would be utterly wrecked. A bit like when you change the rules of a Cellular Automaton when a simulation is running.
It is not a very likely danger (if it could happen with a high probability it would have happened by now), but it is one of those boojums in cosmology to keep one awake in the middle of the night.
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