# Is the universe infinite? [duplicate]

Is the universe infinite? Or is it finite?

If it is infinite,it's very difficult to imagine an endless space(though not impossible).

But if it's finite, the idea that we can't go beyond a certain space just creeps me out.

So, what is it actually?

## marked as duplicate by John Rennie, Colin McFaul, Ali, user10851, Qmechanic♦Jul 12 '14 at 12:48

• We don't know the answer yet, and on some level we're not even completely certain the questionable answerable. It would sure be neat if someone figured it out though. – David H Jul 12 '14 at 4:27
• possible duplicate of Is the universe finite or infinite? – alemi Jul 12 '14 at 4:30
• @Sayans25 That said, there is a wealth of partial results on the conditions for / implications of a finite/infinite universe. See en.m.wikipedia.org/wiki/Shape_of_the_Universe#Global_geometry – David H Jul 12 '14 at 4:38

You can relate observational measurements to this question by making an assumption. Namely, if we assume that the cosmological principle holds, then the curvature of the universe that we have measured from our earthly vantage point is true throughout the universe. This allows to extrapolate our measurement of the local curvature so as to make predictions about the global shape of the universe. If the curvature is $\Omega > 1$, then the universe's spatial shape can be thought of as the equivalent of the surface of a sphere in 4-D Minkowski space. In this case it is finite. If we have $\Omega < 1$ then it has a hyperbolic shape, making it infinite. If $\Omega = 1$ then it is flat, also making it infinite. I won't go into the subtleties of discussing the shape of the universe in cases where curvature is not constant or not necessarily the same in all directions, suffice it to say that things can get more intricate than this simple 3-way scenario. Current observations don't actually allow us to distinguish between these 3 scenarios as we currently roughly measure $\Omega = 1 \pm 0.01$. This value that is very close to flatness is speculated to be due to inflation, but that is another topic for another time.