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by isaachier
2813 days ago
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I used to be a bit interested in astrophysics, so I can't vouch 100% for this being accurate, but it's my understanding: The universe isn't the penny, it's the balloon. Physicists believe we are living on the surface of a hypersphere. One important consequence of this idea is that the big bang didn't occur at a specific point in our 3D space, but at the center of the sphere. Furthermore, the concept of a balloon expanding vs. deflating is a bit of a misconception. The argument used to be that whether or not the balloon is expanding, depending on the rate of the expansion, gravity could eventually win out and cause the matter to collapse back together (big crunch scenario). The problem with that theory is that we now know that galaxies are speeding away from us at a growing speed that (not sure the exact details, probably based on red shift in light from nearby galaxies). So the idea of gravity winning out was not based on evidence, just one of a number of possibilities, but the evidence proved it wrong beyond a doubt. |
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The analogy isn't perfect though. I don't think it's quite right that cosmologists believe we are living on the surface of an expanding hypersphere; that would imply that the expansion of the universe had a real spatial center somewhere in a large extra dimension, just as the inflating surface of a balloon has a real spatial center in the balloon's three dimensional interior, inaccessible to observers that can only probe the surface.
That the universe has a real, albeit extra-dimensional spatial center isn't a mainstream idea, but there are theorists exploring the possibility that the universe exists on the surface of a brane in a higher dimensional 'bulk', and that the big bang resulted from a collision between branes in that higher dimensional space [1].
There might be some utility in thinking of the universe as an inflating hypersphere whose radius corresponds to time, rather than to an additional spatial dimension. In that analogy, the center of the hypersphere (or balloon) would represent a point in time, rather than a point in higher-dimensional space. The surface of the hypersphere (corresponding to the space of our universe) would appear to expand the further an observer was from the temporal 'center', which would be equivalent to the big bang. There is a consensus among cosmologists that the big bang appears to be a special point in time, if not in space.
[1] https://en.wikipedia.org/wiki/Brane_cosmology