0

I read in several sources that matter, dark matter & dark energy contributes 5%, 26% and 69% of the known universe. Also, I read in a slide deck about Big Bang theory on nobelprize.org that total energy in the universe is not conserved. Then how does universe generates new energy to propel infinite expansion?

Qmechanic
  • 201,751
WeShall
  • 109
  • A very good question....... although we don't know about the infinite bit –  Jul 12 '16 at 20:59
  • I think, I should be more careful using the term 'infinite' – WeShall Jul 12 '16 at 21:17
  • We don't yet know what exactly is causing the expansion, look up Wikipedia about dark energy –  Jul 12 '16 at 21:23
  • Universe by definition includes everything, including any known/unknown sources of energy. Therefore, it must not be creating any new energy, it must be just re-distributing it. Dark matter, and dark energy are just hypothesis to fill the in-explainable. – kpv Jul 12 '16 at 21:25
  • Wikipedia says dark energy is the inherent energy of vacuum. That's agreeable. But this energy is doing work. Everywhere. Within the celestial structures and interstellar space. So if there is a source to it, it has to be everywhere. #JustMyThoughts – WeShall Jul 12 '16 at 21:48
  • There are lots of answers to this question on this site. Look them up. @tparker's answer is exactly true, but there's other arguments. One way of thinking, not really covariantly, is that that energy goes towards doing work by expanding the universe and creating negative potential energy. In this view the total energy is actually zero. But potential energy is also not a general relativity entity, so at best what GR can do is show some pseudo-Tensors that seem to, Ina non-covariant way, conserve energy. – Bob Bee Jul 13 '16 at 00:38
  • Related: http://physics.stackexchange.com/q/2838/2451 and links therein. – Qmechanic Jul 13 '16 at 01:54
  • I even liked this answers: http://physics.stackexchange.com/questions/1327/hubbles-law-and-conservation-of-energy?rq=1 – WeShall Jul 22 '16 at 19:48

1 Answers1

1

The reason that energy is usually conserved in most contexts is that Noether's theorem guarantees that energy is conserved in systems with time translational invariance. But the metric of the universe as a whole is (approximately) the Friedmann–Lemaître–Robertson–Walker metric, which does not have time translational invariance (more precisely, there does not exist a timelike Killing field corresponding to conservation of energy). So there's no reason to expect that energy would be conserved in this context. There's no specific "source" of the new energy.

tparker
  • 47,418