- #106
Chalnoth
Science Advisor
- 6,197
- 449
Pretty sure that is fundamentally impossible.jay.yoon314 said:I think the universe is infinite in space and time, but finite in energy and mass.
Pretty sure that is fundamentally impossible.jay.yoon314 said:I think the universe is infinite in space and time, but finite in energy and mass.
jay.yoon314 said:However, if the metric expansion of space involves the conversion of space-time into mass-energy specifically in the form of dark energy, then my claim cannot stand. But this would involve having to define an additional conservation law between not only energy and mass, but between mass-energy and space-time, and there isn't a shadow of a hope for that to work.
phinds said:Possibly I am misunderstanding what you are saying here, but it seems to imply that you believe in conservation of energy on cosmological scales, but there is no such thing.
jay.yoon314 said:If there is indeed no such thing, at what scale does the law of conservation of mass-energy break down? It breaks down neither at the atomic nor at the level of the galaxy. If it breaks down at the level of the observable universe as a whole, shouldn't this breakdown be observed at the level of the galaxy (or galaxy clusters?)?
A conservation law that is so general cannot go from being obeyed in all instances at all scales that are smaller than some arbitrary scale, but then transition abruptly into there being existing "no such thing" as you said. In any case, the burden of proof is on your part. We both agree that there is a possibility that the universe's properties at the cosmological scale are different, even in extremely surprising ways, from the universe at smaller scales. But this doesn't eliminate the fact that such differences need to be quantified, or precisely stated. How is saying that there is no such thing as a conservation of energy on cosmological scales any different, in its radicalism, than me saying that there is a finite amount of mass-energy? At least, in my view, the law of conservation of mass-energy is obeyed, which is not at all a triviality.
phinds said:Unfortunately I'm not knowledgeable enought to explain it adequately, but it has been discussed numerous times here on the forum and I assure you it is true, however non-intuitive it is. I too found it quite disagreeable when I first heard it. I suggest a forum search if you want a decent explanation.
jay.yoon314 said:If there is indeed no such thing, at what scale does the law of conservation of mass-energy break down? It breaks down neither at the atomic nor at the level of the galaxy. If it breaks down at the level of the observable universe as a whole, shouldn't this breakdown be observed at the level of the galaxy (or galaxy clusters?)?
It breaks down the moment that the expansion of the universe becomes a non-negligible component to the behavior of the system. For smaller systems, you can define energy in such a way that it is conserved.jay.yoon314 said:If there is indeed no such thing, at what scale does the law of conservation of mass-energy break down?
What you don't seem to be getting is that this fact is derived directly from physics we observe here in our own solar system. First of all, energy conservation is now understood to not be a fundamental fact of nature, but instead a consequence of a particular sort of symmetry. In fact, all conservation laws are now understood to be consequences of symmetry.jay.yoon314 said:In any case, the burden of proof is on your part. We both agree that there is a possibility that the universe's properties at the cosmological scale are different, even in extremely surprising ways, from the universe at smaller scales.
jobigoud said:It would seem that you guys do not use the accepted definition for the word "universe".
Universe: The totality of everything that exists.
It cannot be in something, or located. It is everything.
bill alsept said:Compared to solar systems, galaxies, clusters and super clusters we can call everything else the universe only because we are inside of it. But that doesn't mean there are not many other universes just like it all lined up forever. I believe they use to call the Milky Way the universe.
phinds said:Yes, and they used to call the Earth flat. What's your point? Previous ignorance should require current ignorance?
You don't get to decide what you want the definition to be even though you seem to think you can.