On Jan 13, 11:31 pm, archytas <[email protected]> wrote: > The sum of energy in the universe is often considered as zero.
I haven't studied physics since I was at school, but this looks odd, especially in view of relativistic mass-energy equivalence. In support of it, all I can recall is that a potential energy field is only defined up to an arbitrary constant, which can therefore be chosen to make the integral of potential energy equal to zero. However, even supposing that to be correct (it leaves undefined what the potential energy field is, and over what manifold it is being integrated, e.g. is it mass-energy being integrated over all space- time, or what?), it doesn't seem to imply that energy (or mass-energy) has no absolute physical reality, any more than the use of an arbitrary (Fahrenheit or Centigrade) scale for temperature proves that there is no absolute zero. Against it, a quick Google yields this assertion: http://www.advancedphysics.org/forum/showthread.php?t=6997 "To give a partial answer, the current best estimate of the total mass- energy (just the energy due to mass) of the universe is around 2 x 10^69 Joules (see http://www.answers.com/topic/orders-of-magnitude-energy for example). " This reference (obtained from that last URL) would appear authoritative, at least to me: http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980211b.html
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