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"We're probably not in the center of the universe" The way I understood things, there is no center of the universe. Or equivalently, all points in the universe

by cryptoz 15y ago

"We're probably not in the center of the universe" The way I understood things, there is no center of the universe. Or equivalently, all points in the universe have a view such that it appears that you are in the center of the universe. The universe is spacetime itself, and the idea of a center requires an idea of space outside of spacetime, no?

jessriedel 15y ago
Nobody knows what the topology of the universe is, nor, contrary to this animation, does anyone have a reliable estimate for the size of the universe (as opposed to just the observable universe). It might be infinite, or it might be just slightly larger than the observable universe. But yes, all current models of the universe are homogeneous; no point is more central than any other point. It doesn't have to be this way, but it's the simplest assumption.
- victork2 15y ago
  "Yes and no". The universe is not homogeneous on a large scale, there are filaments of galaxies and everything but yes the idea of the center of the universe does not correspond to anything. The Big Bang from current models happened everywhere and the expansions comes from the fact that the very "fabric" of the universe expands. But there are some awesome implications of an infinite universe, take a look here if you are interested: http://en.wikipedia.org/wiki/Multiverse#Level_I:_Beyond_our_cosmological_horizon http://en.wikipedia.org/wiki/Multiverse#Level_I:_Beyond_our_...
  - jessriedel 15y ago
    In the sense of matter distribution, the universe isn't homogeneous on small scales either. But that's not what is meant in the context of a cosmological model. The global spacetime is modeled with a FLRW metric, whose key property is homogeneity and isotropy.
  - lutorm 15y ago
    On very large scales, the Universe does seem to be isotropic and homogenous, just like the assumption in the models is.
dedward 15y ago
If the laws of physics as we understand them hold true, then by definition we (or any other observer anywhere) are at the centre of the universe they see, insomuch as the further away we look, the further back in time we look, in all directions, back to the beginning... or something along those lines. Unless we find we can circumvent the rules we know now, or that they don't hold true, anything outside our light-cone, outside our observable universe by definition cannot be shown to exist.

by cryptoz 15y ago

jessriedel 15y ago

Nobody knows what the topology of the universe is, nor, contrary to this animation, does anyone have a reliable estimate for the size of the universe (as opposed to just the observable universe). It might be infinite, or it might be just slightly larger than the observable universe. But yes, all current models of the universe are homogeneous; no point is more central than any other point. It doesn't have to be this way, but it's the simplest assumption.

victork2 15y ago
"Yes and no". The universe is not homogeneous on a large scale, there are filaments of galaxies and everything but yes the idea of the center of the universe does not correspond to anything. The Big Bang from current models happened everywhere and the expansions comes from the fact that the very "fabric" of the universe expands. But there are some awesome implications of an infinite universe, take a look here if you are interested: http://en.wikipedia.org/wiki/Multiverse#Level_I:_Beyond_our_cosmological_horizon http://en.wikipedia.org/wiki/Multiverse#Level_I:_Beyond_our_...
- jessriedel 15y ago
  In the sense of matter distribution, the universe isn't homogeneous on small scales either. But that's not what is meant in the context of a cosmological model. The global spacetime is modeled with a FLRW metric, whose key property is homogeneity and isotropy.
- lutorm 15y ago
  On very large scales, the Universe does seem to be isotropic and homogenous, just like the assumption in the models is.

dedward 15y ago

If the laws of physics as we understand them hold true, then by definition we (or any other observer anywhere) are at the centre of the universe they see, insomuch as the further away we look, the further back in time we look, in all directions, back to the beginning... or something along those lines. Unless we find we can circumvent the rules we know now, or that they don't hold true, anything outside our light-cone, outside our observable universe by definition cannot be shown to exist.