Thread: Why God Exists.

Originally Posted by Xei

Matter (or rather, energy; matter can indeed 'disappear') is only observed to be conserved now (and even that is contentious).

Care to elaborate on the part that I bolded?

Oops, I totally forgot what this thread was about. Then again, so have a few people apparently.

Originally Posted by PhilosopherStoned

Care to elaborate on the part that I bolded?

I thought it could be wrong. I was talking about the acceleration of cosmic inflation.

Originally Posted by Xei

I thought it could be wrong. I was talking about the acceleration of cosmic inflation.

Okay. I always forget about that vis-a-vis conservation of energy. Thanks for reminding me. The total energy of the universe is honestly so poorly defined (as is the universe itself) that it's very difficult to think about.

Energy is the "conserved charge" associated with time translation invariance by Noether's Theorem. Consider the case where we don't have time translation invariance. Then we could do one experiment on tuesday and again on friday and get different results. We could then find some way to get free energy. The example I've seen was if gravity was weaker on tuesdays, then we could lift a bunch of water up and let it back down through the rest of the week to power a turbine. We would get more energy out of it than we put in. The logic goes the other way as well so that we can assume either and get the other.

It may well be that time translation invariance fails for the "whole universe". This seems highly likely to me in fact. At any rate, the expansion is thought to be driven by "vacuum energy". So to actually harness it, we would have to find some way to stop some large portion of space from expanding.