Far out cosmology: our universe expands into what? (Introduction)

by David Turell , Saturday, May 27, 2023, 18:11 (544 days ago) @ David Turell

There is nothing beyond us:

https://bigthink.com/starts-with-a-bang/what-universe-expanding-into/?utm_campaign=swab...

"But if the Universe has been expanding for all this time, what is it that the Universe is expanding into? That’s a common question that people have.

“One question comes to mind, just exactly what is the universe expanding into?”

"The short, one-word answer to this question is as pithy as it is unsatisfying: itself. The Universe expands into itself, rather than into any definable “outside” medium. This is another example where the science of General Relativity defies our common experience and intuition, so let’s see if we can help you understand it a little bit better by unpacking the science behind the expanding Universe.

***

"Although, in theory, the Universe could have been either expanding or contracting, expansion is what it turns out it’s actually doing.

***

"A slightly better analogy, therefore, is to consider a fully three-dimensional object that expands: like a ball of raisin bread dough, i.e., bread dough with raisins distributed all throughout it. As the dough leavens, it expands, but the raisins within it don’t. The raisins simply move farther away from one another in all three dimensions. If you’re within a raisin, you see: nearby raisins recede slowly, intermediate-distance raisins receding more rapidly,
and the most distant raisins receding most quickly of all, even though the raisins are actually stationary relative to the expanding dough. If the dough were transparent, it would behave like the fabric of space, while the raisins behave like individual galaxies within the expanding Universe.

***

"It’s that last point, about the dough expanding into “something,” that provides the greatest difficulty in making an analogy with the expanding Universe. Whereas the dough is an object that’s embedded within a larger reality (the full scope of three-dimensional space), the Universe itself is simply all there is. Or, at the very least, all that there needs to be.

"One way to overcome this difficulty is to imagine, instead of a ball of dough (embedded with raisins) in our three-dimensional Universe, is to imagine a three-dimensional Universe that is entirely filled with this raisin-embedded dough.

***

"...there’s no “outside” or “beyond” to the cosmos; it is simply all there is and ever was and ever will be.

"And that’s the biggest thing to wrap your head around. When it comes to the expanding Universe, it isn’t expanding into anything, because there isn’t anything else above, beyond, outside, or before or after space-and-time. All at once, it’s both everything and nothing: everything because it contains all that exists, and nothing because if you take all the matter, radiation, and quanta that exist within it away, it still persists: the nothingness of empty space itself. That’s what the fabric of spacetime is, and that’s why it can’t expand “into” anything: it itself is a fundamental part of our reality.

"That’s why, when you ask, “What is the Universe expanding into?” the best answer we can give is “itself.” The key realization is to stop thinking of the Universe as a thing that evolves in some larger, greater context; it’s perfectly reasonable to think of it as all there is, and to simply recognize that expansion and contraction are properties inherent to space itself."

Comment: our universe is all that exists. We cannot know what is outside, if there is an outside.