Thought Experiment: What Lies Beyond the Furthest Object in Space?

[Amazed]

If there is space and a distance between an imagined furthest object away from earth and the next closest object toward Earth, then what is on the other side of that furthest object?

Is there also space and a distance surrounding that furthest object and 'stretching out', for lack of a better term, in a line from Earth directly outwards and/or in all directions, or could there be something else there?

If there could be something else, then what could that possibly be?

 

[Ibix]

Our current best models suggest that the universe is more or less the same everywhere, and it is either infinite in extent or a "closed" geometry like the surface of a sphere where a straight line eventually wraps round on itself (but it would have to be very large in that case). There's no edge in either case. There are always roughly as many galaxies visible in front of you as behind you, wherever you are, so there's no furthest away object in the sense you mean.

(If the universe is closed then there is a furthest away object just like there's a furthest away point from you on the surface of the Earth but, just like that Earthly furthest away point, there would be nothing particularly special to see if you reached that furthest cosmological point. Just more of the same, only getting closer to home again.)

 

[Amazed]

Our current best models suggest that the universe is more or less the same everywhere, and it is either infinite in extent or a "closed" geometry like the surface of a sphere where a straight line eventually wraps round on itself (but it would have to be very large in that case).

I have imagined that same scenario also before reading about it, but a straight line on the surface of a sphere implies that that line would be on the 'outside' of the Universe, which is part of the reason why I proposed the thought experiment here.

There's no edge in either case.

I have heard this claim before also. But if something, like a line, is on the surface, again this implies or infers it being on 'the outside' and not within the Universe.

There are always roughly as many galaxies visible in front of you as behind you, wherever you are, so there's no furthest away object in the sense you mean.

Does this mean that the Universe is infinite spatially?
If no, then why not?

(If the universe is closed then there is a furthest away object just like there's a furthest away point from you on the surface of the Earth but, just like that Earthly furthest away point, there would be nothing particularly special to see if you reached that furthest cosmological point. Just more of the same.)

So, if the Universe is closed, then what could this 'surface' possibly be made out?

Now, what you have said and suggested here I have heard of and read multiple times already. Thank you. So, would you like to answer the questions I asked in the thought experiment above instead?

 

[Ibix]

a straight line on the surface of a sphere implies that that line would be on the 'outside' of the Universe,

No, in this model the surface of the ball is the universe. It's 2d, and there is no "inside" or "outside" the surface except when people try to draw it. The full model is a 3-sphere, which has the same geometry as the surface of a 4d ball.

Does this mean that the Universe is infinite spatially?

It means that the universe is the same everywhere, which means that there are no "special" points like edges or corners. That leaves a flat infinite space, or an infinite space of constant negative curvature (a hyperbolic surface that has no Euclidean embedding but looks a bit like a saddle when people try to draw it), or a space of constant positive curvature (a 3-sphere). So it's either infinite or closed, as I said.

So, if the Universe is closed, then what could this 'surface' possibly be made out?

The surface is the universe. It's made of whatever the universe is made of. GR simply says "spacetime". Most candidates for better theories propose something for what spacetime is, but we don't know which (if any) of our theories is right.

So, would you like to answer the questions I asked in the thought experiment above instead?

Your questions appear to be predicated on you misunderstanding what you've read - you seem to be taking the "spherical universe" to be the interior of a 3d ball rather than the surface of a 4d ball. There is no spatial edge to the universe in any of our models, infinite or finite.

You can manually insert an edge to the model of our universe. What happens there depends on the rules you invent for how it behaves. This is common in numerical simulations of GR spacetimes, which usually only model a finite patch of the universe. In such cases, the region outside the simulation will be being ignored (i.e. treated as having no content or effect on the interior, which is fine for modelling isolated systems like solar systems), and stuff reaching it from within the simulation will simply fall off the edge of the map. There is no evidence of such an edge in reality.

 

[Ibix]

Just a note on terminology: topologically, the Earth is a ball and its surface is a sphere. You can study a sphere without assuming the extra dimensions needed for the ball of which it could be the surface.

A perhaps more familiar example is in some computer games, notably the classic Asteroids game, where you can leave one edge of the screen and appear on the opposite one. The play area is topologically a cylinder (if the sides are connected) or torus (if the top and bottom are connected also). But there is nothing "inside" or "outside" the cylinder/torus. Only the 2d surface exists.

Similarly, the universe (if closed) is a 3-sphere. But it doesn't have to be associated with a ball - that is, it does not have to have an "interior" and/or "exterior" region around it. The reality is that there is no evidence of an interior or exterior, just the surface, so there is not one in our models.

 

[martinbn]

Just to add that a line on the sphere is a great circle, so it is entirely on the surface. In case you are picturing a line in space that is just touching the sphere and is on the ouside of it.

 

[Baluncore]

If there is space and a distance between an imagined furthest object away from earth and the next closest object toward Earth, then what is on the other side of that furthest object?

A recursive paradox, or the back of your own head.

 

[Amazed]

Just a note on terminology: topologically, the Earth is a ball and its surface is a sphere. You can study a sphere without assuming the extra dimensions needed for the ball of which it could be the surface.

A perhaps more familiar example is in some computer games, notably the classic Asteroids game, where you can leave one edge of the screen and appear on the opposite one. The play area is topologically a cylinder (if the sides are connected) or torus (if the top and bottom are connected also). But there is nothing "inside" or "outside" the cylinder/torus. Only the 2d surface exists.

Similarly, the universe (if closed) is a 3-sphere. But it doesn't have to be associated with a ball - that is, it does not have to have an "interior" and/or "exterior" region around it. The reality is that there is no evidence of an interior or exterior, just the surface, so there is not one in our models.

Although what really happens and occurs contradicts this made-up model completely.

 

[Amazed]

Just to add that a line on the sphere is a great circle, so it is entirely on the surface. In case you are picturing a line in space that is just touching the sphere and is on the ouside of it.

I thought the word 'on' in relation to 'on the sphere' or 'on the surface' implied being on one side of or literally on top of the surface and/or sphere, but maybe what you mean by 'a line' is that it is the sphere or is the surface of the sphere itself.

 

[Amazed]

A recursive paradox, or the back of your own head.

If this is what you concluded when you thought about the thought experiment, then okay.

 

[berkeman]

Thread is closed for Moderation.

 

[berkeman]

After the cleanup of an insulting post by the OP, this thread will remain closed. The OP has accumulated a number of infractions for various rule violations, and is no long with us.

Thank you to all who were trying to help them with their questions in this thread. It's unfortunate that they were not willing to accept that help.