How can spacetime be 'flat' if we can move around in

The same way a piece of paper is flat if you bend it along a direction. If you try and bend it along two directions (which you can't) it won't be flat no more. The only way to distort the paper is to draw a fat person. The mass will cause the paper to curve and thus gravity will be observed as a residual effect.

>>8730138
Well, it is a bit unintuitive but once you understand why the earth is flat then you can extrapolate that same logic for why the entire universe is flat.

Spacetime isn't flat, it's just conceptualizing 3 dimensional curvature is difficult for many

>>8730149
wtf?

>>8730138
flat as in it doesn't curve back into itself

flat as in, as long as there is no mass distorting the spacetime light will go in a straight line forever

>>8730178
spacetime is definitely flat

>>8730138
>>8730172
>>8730178
>>8730196
>>8730226
>>8730369

Ever seen a picture of multiple galaxies? The spirals of the galaxies are not all facing the same direction.
Spacetime ain't flat

General relativity is sort of based on the idea that the universe is locally flat. This is similar to walking outside and the ground being flat but we know we're on a sphere. I believe the universe appears flat almost everywhere but it isn't perfectly flat at all points.

As for what happens at the edge I'm not sure if anyone knows, but it could be similar to the earth again. We can move forever but we know the earth is finite

>>8730521
>if evolution is true then why are there still monkeys?

>>8730138
Space-time is not flat!! Space-time is a net but Einstein's theory is a simplification of the reality. He also was aware of that, but just considering space-time flat makes calculus so complex..considering space-time flat is so stupid and prove that people don't really read and understood Einstein's thought.

>>8730521
I think it's more accurate to say space time is 3d but can decay (via gravity) into 2d/flat space. Much the same way our 3d universe is a holographic projection in a 4d universe.

>>8730521
>I don't know what topology is but will opine on the subject anyways

brainlets plz go

>>8730521

A cube to a four dimensional observer is as a square is to a 3 dimensional observer.

If you take a square drawn on a paper and bend the paper, from the square's perspective in the 2d 'universe' of the paper, it remains a square. The bend exists beyond the 2d plane and in the third dimension.

Similarly, imagine a cube sitting in a 3d volume, contained in a four dimensional space. No matter how you warp the 3d space, twisting or bending, the cube will remain unaware, because the bending and twisting are happening in a dimension apart from the 3 it exists in.

Weather or not the universe we live in is flat is not a question of how matter is arranged in it, it is a question pertaining to the fundamental shape of our 3d universe in 4d space.

If the universe is 'flat' in four dimensions then from our perspective it would appear to be an infinite 3d volume of space in all directions. If the universe is curved, it can either be enclosed or hyperbolic. An enclosed universe curves into a sphere in four dimensions. Similarly to a 2d plane wrapped into a sphere, going in a straight line will eventually curve you all the way back around to your starting point. The universes volume would thus be finite but unbound, there would be no 'edge' or wall, it would just loop if you were to go far enough. A hyperbolic universe is more interesting, it's a scenario in which instead of curving 'down' into a sphere, it curves 'up' into a strange manifold with strange properties. For example, if you were to draw two straight lines of equal length from an origin at 90 degrees, the hypotenuse of the triangle would be longer than sqrt2, and the longer the two starting lines, the more the hypotenuse would outgrow the other lines. In hyperbolic space, a circle has a circumference much larger than 2pi*radius, because space is 'bigger' the farther from the origin (whatever point of view you consider) you get.