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Q & A: cosmic expansion and energy

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Most recent answer: 10/22/2007
Q:
If the universe is always expanding , wouldn’t there be creation of new energy. How can the universe be expanding from the original Big Bang?
- charlie
kalkaska
A:
If there was nothing interesting in empty space itself, then simple expansion would not involve any increase in energy. there would be graual reduction of relative velocities due to gravitation, which would reduce the kinetic energy of some batch of galaxies as seen by one of them. That would be compensated by the gain of gravitational potential energy due to their increased distances. That’s basically a Newtonian picture, but I’m told that a proper General Relativistic calculation also gives the same result.
More interestingly, it looks like ’empty space’ does have something like a ’dark energy’ to it, so that making more space does increase the net energy. Oddly, that drives the expansion to accelerate. You can think of the gravitational potential energy of the interactions of those ’empty’ regions as providing an increasing negative energy, again cancelling the positive increase.

Mike W.

(published on 10/22/2007)

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