Why would it only expand in one plane not every direction like you’d expect?
Also how is a flat universe even possible? Surely since we live in 3 dimensions the universe needs to be a 3 dimensional shape.
Im probably misunderstanding what physicists are trying to say but that’s why im here.
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‘Flat’ means if you walk in one direction, you won’t eventually loop back to where you started.
‘Spherical’ means that you will eventually loop back to where you started.
As far as we can tell, the universe is not spherical so if you keep walking in one direction you would not expect to loop back to where you started.
If the universe expanded from a single point why are things running into each other. Drop a stone in a pond and the circles expand away from each other, not into each other.
You need to distinguish between the observable universe and the whole universe. Yes the observable universe was a lot smaller but that is just our section of it. The rest of the universe was also part of this process and is not part of that bit we are talking about. So for the whole universe you are not talking about a point, you are possibly talking about something infinite in extent. When the big bang happened it didn’t happen at a point, it happened everywhere in every bit of the universe both in our shrunk down observable section and all the rest too. It is not an explosion from a point, it is all the the points in the early universe all expanded at every point. The place we in now? That expanded. Alpha Centauri? It expanded there too. Everything everywhere expanded, including the parts of the universe we cannot see. At its earliest point there is a singularity and we cannot tell what was going on there but after we have some theories, and every point that existed in the entire universe all expanded.
Sabine talks about a bubble of galaxies in this one which might help a little
[https://youtu.be/bgKiMokFr3o?si=Zsf-x8b2AfWABVYx](https://youtu.be/bgKiMokFr3o?si=Zsf-x8b2AfWABVYx)
Space and time are actually the same thing. Stuff curves space-time in such a way that objects that normally move in a straight line move towards one another. The bigger the object, the more it distorts spacetime and the more it changes the paths of objects moving through spacetime.
But what does spacetime look like when there are no objects nearby? Does that mean there is no curvature? If there isn’t then we say space is flat. If spacetime is curved without any objects then it depends on whether the curvature is like an innie bellybutton or an outie.
We know that the universe is expanding and one explanation for that is that the curvature is like an outie when there are no objects nearby. If the curvature is an outie or flat, then the universe will expand forever. If the curvature is the other way, then the universe will stop expanding one day and gravity will take over causing the objects in the universe to move towards one another until they are in a single point again.
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