I'm not someone who has even tried to study GR, but from what I have gathered over time...The empty FRW-universe with curvature parameter k=−1 and expanding linearly is well known. Also that it is mathematically equivalent (after a coordinate transformation) with the Milne universe which also expands linearly.
Yes, and deSitter discovered that redshifts would exist in his Static universe but....with no matter!. I'm sure he was just simplifying GR to get on a path to a better model. But he was able to show that a static universe could have increasing redshifts with distance in a static universe. Einstein's own model was fine with matter but he could not figure out how redshifts would work in what all knew was the actual universe - a static one. Lemaitre solved both their problems with expansion.... in the empty universe the densities are zero and thus k has no defined value.
This opens a whole host of interesting questions one may ask, but if your point is that dark matter and/or energy could explain "nothing" then this is theoretically impossible.Do we know that our "nothing" is not simply brought about by dark whatever, taking up the space vacated by mass?
I take your point. Perhaps I had in mind the possibility of something still unknown, its purpose' to abhor a vacuum. Not at all scientific - a philosophical flight into fancy for which I apologise to anyone taking it too seriously.This opens a whole host of interesting questions one may ask, but if your point is that dark matter and/or energy could explain "nothing" then this is theoretically impossible.
Isn't the effect of dark energy supposed to be visible in observable space?, that is the expansion of the universe.
No actually this is really interesting because I never considered dark energy, vacuum or pressure for these kinds of questions.Perhaps I had in mind the possibility of something still unknown, its purpose' to abhor a vacuum.
Sorry I can't refer to anything. It just came out of my philosophically flighty senile left hemisphere. If you find anything, I'd be grateful if you would inform meNo actually this is really interesting because I never considered dark energy, vacuum or pressure for these kinds of questions.
A vacuum, dark energy, dark matter, nothing etc. may have something in common or related, I think I'll read more about this stuff only for the purpose to understand more.
That is more of a Philosopher's approach than a Physicist's approach. But, I respect that.The belief that nothing exists outside "our" universe is akin to believing the world is flat. We have such a limited view of space, time and matter, making every thing fit into a very small space. What are we turning into? We as a species or we as this universe? Is the universe expanding, or are the tentacles that make up the spiral arms coagulating? The distance between the spiral arms create greater distances leaving a even greater void between galactic arms. We may not be able to traverse the space between arms, but can travel down the corridors that make each galactic tentacle which may stretch from the galactic core to the outer rim of the universe. Once at the outer rim of the universe we shall find infinity where an infinite number of independent universes exists. Time has no beginning, and time will have no end. As galaxies merger into larger one, so shall universes have and do merge. Did this universe begin with a bang, or did it begin with a merger of a smaller universe? Are there such things as Universal Clusters? Are there such things as Dwarf Universes? Are we now in the process of merging with yet another universe? Are we alone in the cosmic realm of space, or just a thread in the fabric of life? Time, space and matter are infinite, this universe is finite.
That's a good point, if the Universe is totality, there is nothing outside it. Thanks for that, CatIG, you ask: "what proof do I have that the Universe has nothing outside it? "
I would suggest that proof is not an issue. If, as you eloquently explain, Universe is totality, then the definition alone "does the job".
Sorry, wrong word, we are expanding into "nothing.""We are expanding into nowhere". This is ambiguous (unfortunately).
1. not in or to any place; not anywhere.
In context, not anywhere, no place to expand into, .would mean nowhere outside the Universe, confirming the idea that the Universe is all there is
2. no place. "there was nowhere for her to sit"This sort of overlaps with 1. but can also mean (as in example), there is somewhere but it is occupied - this does not really translate into the Universe context.
In the article, I see the common mistake, IMO, of what happens when wild imagination can be considered to be physics. I commented on it in that thread.
Yes, and we, and our sister galaxies, are "floating" in space, so we see the results of what is truly expanding. And, the galaxies themselves aren't expanding since their local gravity is far stronger than the juice behind the expansion.Actually, the Universe is not expanding, it is the space that is. So, a better one would be "space is expanding into something devoid of space."
It's indeed hard to semantically describe something that doen't exist. Isn't it?IG, this is getting into semantic difficulties, isn't it? Are you not including space as part of the Universe?
Also "something devoid of space" surely be non-existant, and therefore cannot be expanded into?