# Are black holes trapdoors to the center of the universe? [closed]

Correct me if i'm wrong here, but if you consider the analogy of inflating balloon when explaining the universe expansion, then the center of the universe lies within the center of the inflating balloon and outside our space and time, so our own 3d universe is analog to the surface of the expanding balloon. Does that mean the black holes push the space towards the center? Mass lying on the surface of the balloon is bending the space (surface), in our case as it tries to return to its previous state at the t=0, much like the ball that is picked up and dropped to fall back down on the ground. It resists the expansion of the universe as it pushes inwards (has "weight") towards the center of the "expanding balloon" that we call universe, so the expansion of the universe is a sort of measurement from t=0 to today since anything that is about to happen still hasn't, and the mass hinders the expansion and causes things to fall down and slows time (and thus the expansion). In the case of black holes it is said the time stops completely, thus expansion stops because the black holes infinitely curve the space around them. Than it would mean it bends the surface all the way back to ground zero, or the center, where t=0, or maybe they just stop the expansion and there is no way to use them to "travel back in time"? Hopefully someone can explain if it works this way or not.

## closed as unclear what you're asking by Brandon Enright, Neuneck, user10851, Kyle Oman, DanuMay 24 '14 at 6:23

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• – John Rennie May 24 '14 at 6:05

Correct me if i'm wrong here, but if you consider the analogy of inflating baloon when explaining the universe expansion, then the center of the universe lies within the center of the inflating baloon

You're wrong here. In the balloon analogy, the universe is a 2-D surface - a 2-D sphere, not a 3-D ball - that is expanding.

A sphere has no privileged center. The point in the embedding space from which all the points on the 2-D surface are equidistant is not within the surface - not within the sphere - and thus, is not a physical point within the universe in this analogy.

See, for example, this Where is the centre of the universe? for further reading:

When thinking about the balloon analogy you must remember that. . .

• The 2-dimensional surface of the balloon is analogous to the 3 dimensions of space.
• The 3-dimensional space in which the balloon is embedded is not analogous to any higher dimensional physical space.
• The centre of the balloon does not correspond to anything physical.
• The universe may be finite in size and growing like the surface of an expanding balloon, but it could also be infinite.
• Galaxies move apart like points on the expanding balloon, but the galaxies themselves do not expand because they are gravitationally
bound.

In the inflating balloon analogy, as you said in your question, you are supposed to imagine that the universe is the surface of the balloon. So any candidate "center of the universe" had better be on that surface as well, and as you can observe there is no such center. The point of the analogy is so you can see how it can be that space (in this case the surface of the balloon) can expand without there being a 'center' from which it expanded from. But it is not intended to go beyond that. The universe is not (as far as we know) like a balloon in any other way. We don't imagine that it should be possible to go off in one direction and then come back to where you were like you would if you circumnavigated the balloon, for example.

The analogy of the rubber sheet with balls on it bending space time is also an analogy, but space time is not (necessarily) bending in some higher dimensional space like the rubber sheet. So you shouldn't imagine that you can poke into the 'balloon' and find your way inside something. So the answer to your question is: no.

• thank you for the info. I immagined the area between the center point of expansion and the surface (our universe) as some sort of "witchspace" outside our normal space and time, where the volume changes depending on the point of time in history of the universe. If our space is growing and aging, what do physicists believe is beyond our space and time? Is time travel at all possible in the wildest theories? Did past happen never to be reached again? – rambo May 25 '14 at 20:54