4 ms·
The explanation isn't very satisfying to me. If you expand the surface of a sphere, you're still expanding a 2-manifold in 3 dimensions. When you expand the sph
by rcme 4y ago
The explanation isn't very satisfying to me. If you expand the surface of a sphere, you're still expanding a 2-manifold in 3 dimensions. When you expand the sphere, you're expanding into the empty part of 3-space.
- rhn_mk1 4y agoYou can describe any 2d shape using 3 dimensions, just imagine that it's set askew or bent. From the perspective of the inhabitant of such a flatland, it's undetectable and irrelevant. So is it from the perspective of the topology of the shape. Describing the universe's shape is similarly done from within, so we can't see the outside and don't need any "outside" to see that the Universe is expanding. It's a description of how our 3d world is behaving, seen from within, and not relying on any "outside". The word "expand" is not describing the exact same physical phenomenon as what we are used to seeing, because when we expand something, we typically cause it from the outside. That's why it can't be satisfying: it's a similar but different thing.
- galaxyLogic 4y agoRight so the expansion of our 3-D universe would need to be happening into the 4th or more dimensions for the analogue to make sense. But is that really what they are saying that when cosmologists speak of the expansion of the universe they mean it is expanding to the other 3+ (spatial) dimensions?. Note the title of the article "What is our Universe Expanding Into? Is it expanding into the 4th spatial dimension?