Perhaps cosmology really is a branch of particle physics. For, according to one idea that has progressed over the ten years or so all the way from being thought of as completely crazy to the near- respectability of being regarded merely as outrageous, the universe and everything in it may be no more and no less, than one of those vacuum fluctuations that allow collection of particles to burst forth out of nothing, live for a while, and then be reabsorbed into the vacuum. The idea ties in very closely with the possibility that the universe may be gravitationally closed.
A universe that is born in the fireball of a Big Bang, expands for a time and then contracts back into a fireball and disappears, is a vacuum fluctuation, but on a very grand scale.
If the universe is exactly balanced on the gravitational edge between indefinite expansion and ultimate re collapse, then the negative gravitational energy of the universe must precisely cancel out the positive mass energy of all the matter in it.
A closed universe has zero energy overall, and it not so difficult to make something with zero energy overall out of a vacuum fluctuation, even if it is a rather neat trick to make all the bits expand away from one another and allow, temporarily, for all the interesting variety we see about us.
The original idea can be traced back to Boltzmann, the nineteenth century physicist who was one of the founders of modern thermodynamics and statistical mechanics. Boltzmann speculated that since the universe ought to be in thermodynamic equilibrium, but manifestly is not, present appearance might be the result of a temporary deviation from equilibrium, allowed by the statistical rules provided equilibrium is maintained, on average, in the long term. The chances of such a fluctuation occurring on the scale of the visible universe are tiny, but if the universe existed in a steady state for infinite time then there would be a virtual certainty of something of the kind of happening eventually, and since only a deviation from equilibrium would live to exist, it comes as no surprise that we should be here during a rare departure of the universe from equilibrium.
Edward pointed out at the time if the universe has net energy zero and the amount of time it is allowed to exist. He said he did not claim that universes like ours frequently, merely that the expected frequency is not zero. The logic of the situation dictates, however, that observers always find themselves in universes capable of generating life, and such universes are large.
If the business of physics is ever finished, the world will be a much less interesting place in which to live, which is why I am happy to leave you with loose ends, tantalizing hints, and the prospect of more stories yet to be told, each one as intriguing as the story of cat.
We have to find a new view of the world that has to agree with everything that is known, but disagrees in its predictions somewhere, otherwise it is not interesting.
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