4 ms·

what is 'pretty much the same', and what are the 'fairly good reasons'?

by platz 5y ago

wizzwizz4 5y ago
“Pretty much the same” is “has stars and planets like we do, ignoring the solar system which might be weird”. The “fairly good reasons” are that that assumption has allowed us to develop a very good understanding of physics – good even by standards that don't make that assumption. If an assumption is a good one, it's probably a true one… at least, the others have been, and I assume we can generalise from them.
- platz 5y ago
  Inflation is the leading cosmological theory. If that is true, all our observations are descended from a pinpoint region of space that contained everything we can observe now. We don't have any means to judge whether the parameters of space are the same or different in regions that have always been causally separated from us. Be more comfortable with saying "I (We) don't know".
  - wizzwizz4 5y ago
    Most physicists agree.
  - stan_rogers 5y ago
    For the things we can observe to be the way they are, the furthest things that can be observed by the furthest things we can observe must be more or less the same as well, and so on.
    - platz 5y ago
      This is a bad inference
      - wizzwizz4 5y ago
        Yet that kind of inference seems to generally work.
SamBam 5y ago
Well, the current understanding is 1. The universe was created by the big bang, which created all the energy and matter in an instant. In the first few moments, this soup of energy and matter was near-uniform, but tiny imbalances caused matter to start clumping up into larger clumps. 2. Fast-forward 14 billion years, and those tiny imbalances and the resulting forces appear to have distributed the matter (including dark matter) into a fairly even, consistent structure across the entire universe, with galaxies mostly collecting together in clumps separated by huge filaments (see e.g. [1]). Our own galaxy seems to be in a bit of a void between some of these clumps. So that's our understanding of how the universe came to be, and how it came to be the way it is now. It seems that things are, as I said, "pretty much the same" no matter how far out you go, and this has an explanatory reason: the near-uniformity of the matter and energy created by the big bang. You're saying that it could be that, somewhere, outside the reaches of our telescopes, things are totally different. But we have no theories of how that could possibly have come to be, given our assumption #1 above. It just doesn't seem plausible, given our understanding of the big bang, that somewhere on the "other side" of the universe there's, say, nothing at all. Or a pure carbon crystal the size of our own observable universe. Or a Library of Babel. You're free to say "well, scientists don't know that there isn't," yes, of course, but without some kind of explanatory hypothesis, it makes far more sense to go with the data and theories we have. 1. https://www.space.com/37191-we-live-in-a-cosmic-void.html https://www.space.com/37191-we-live-in-a-cosmic-void.html
- platz 5y ago
  > this soup of energy and matter was near-uniform We can only infer this in the region that we can see in the CMB, which is a small region when re-wound back to the instant after the BB. What you are suggesting is that this uniformity was infinite in all directions, which is not what we're able to infer given the data we have so far. Are you even familiar with the idea of the multiverse or bubble nucleation.

what is 'pretty much the same', and what are the 'fairly good reasons'?

by platz 5y ago

what is 'pretty much the same', and what are the 'fairly good reasons'?

“Pretty much the same” is “has stars and planets like we do, ignoring the solar system which might be weird”. The “fairly good reasons” are that that assumption has allowed us to develop a very good understanding of physics – good even by standards that don't make that assumption. If an assumption is a good one, it's probably a true one… at least, the others have been, and I assume we can generalise from them.

platz 5y ago
Inflation is the leading cosmological theory. If that is true, all our observations are descended from a pinpoint region of space that contained everything we can observe now. We don't have any means to judge whether the parameters of space are the same or different in regions that have always been causally separated from us. Be more comfortable with saying "I (We) don't know".
- wizzwizz4 5y ago
  Most physicists agree.
- stan_rogers 5y ago
  For the things we can observe to be the way they are, the furthest things that can be observed by the furthest things we can observe must be more or less the same as well, and so on.
  - platz 5y ago
    This is a bad inference
    - wizzwizz4 5y ago
      Yet that kind of inference seems to generally work.

SamBam 5y ago

Well, the current understanding is 1. The universe was created by the big bang, which created all the energy and matter in an instant. In the first few moments, this soup of energy and matter was near-uniform, but tiny imbalances caused matter to start clumping up into larger clumps. 2. Fast-forward 14 billion years, and those tiny imbalances and the resulting forces appear to have distributed the matter (including dark matter) into a fairly even, consistent structure across the entire universe, with galaxies mostly collecting together in clumps separated by huge filaments (see e.g. [1]). Our own galaxy seems to be in a bit of a void between some of these clumps. So that's our understanding of how the universe came to be, and how it came to be the way it is now. It seems that things are, as I said, "pretty much the same" no matter how far out you go, and this has an explanatory reason: the near-uniformity of the matter and energy created by the big bang. You're saying that it could be that, somewhere, outside the reaches of our telescopes, things are totally different. But we have no theories of how that could possibly have come to be, given our assumption #1 above. It just doesn't seem plausible, given our understanding of the big bang, that somewhere on the "other side" of the universe there's, say, nothing at all. Or a pure carbon crystal the size of our own observable universe. Or a Library of Babel. You're free to say "well, scientists don't know that there isn't," yes, of course, but without some kind of explanatory hypothesis, it makes far more sense to go with the data and theories we have. 1. https://www.space.com/37191-we-live-in-a-cosmic-void.html https://www.space.com/37191-we-live-in-a-cosmic-void.html

platz 5y ago
> this soup of energy and matter was near-uniform We can only infer this in the region that we can see in the CMB, which is a small region when re-wound back to the instant after the BB. What you are suggesting is that this uniformity was infinite in all directions, which is not what we're able to infer given the data we have so far. Are you even familiar with the idea of the multiverse or bubble nucleation.