GRAVITY PROBLEMS -- off topic from {Falsifying a young Universe}

I don't have a pointer to the equations on the Web. You might want to look at Re: Gravitational Energy Conservation, or do a Google groups search on "total energy of the universe" with Baez as author. There's a hand-waving argument that I recently posted in another thread.There's some reason for assigning potential energy (which can be measured relative to any position) the value 0 when everything is an infinite distance apart. If you do that, and you already know that the act of separating things increases gravitational potential energy (becasue the potential energy is the force times the distance between them), it follows that the gravitational potential energy of the Universe that we see is negative. In fact, it's not terrifically different, as such things go, from the negative of the amount of other positive energy we see ... and maybe they're exactly equal in magnitude but opposite in sign, and exactly cancel each other out. Maybe. Yup. If the energy of the Universe is indeed exactly (or really really close to exactly zero) then the entire Universe might be a quantum fluctuation, allowed to be so long-lived because its energy is so low. This is a serious theory. We're probably fairly far away from refuting or corroborating it.

Oh, and from Is Energy Conserved in General Relativity?:

quote:

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We will not delve into definitions of energy in general relativity such as the Hamiltonian (amusingly, the energy of a closed universe always works out to zero according to this definition), various kinds of energy one hopes to obtain by "deparametrizing" Einstein's equations, or "quasilocal energy". There's quite a bit to say about this sort of thing! Indeed, the issue of energy in general relativity has a lot to do with the notorious "problem of time" in quantum gravity. . . but that's another can of worms.

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