Quote:
Originally posted by NismoDrifts
Well, blackness is lack of light...............sure theres stuff out there, its just too far for the light to reach at the time, so we see black, and, how does something 3-dimensional curve in on itself? not saying youre wrong or anything, im just really interested by this stuff
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Good call on the blackness.
The universe is not necessarily three dimensional. It may only look that way from our very narrow perspective. I think MBTN's 'ribbon' is an idea that came out of string theory, which posits that there are something like 15 dimensions. If you look at a sheet of paper pefectly on edge, it looks like a line. If it were fixed in front of your eyes like that for a long time - you'd probably believe it was a line. But it's not, it's a plane, you just have to get a new perspective to see it. We haven't quite figured out how to get a new perspective to see the dimensions proposed by string theory, but lots of smart folks are working on it.
But, even if it is three dimensional, it can curve in on itself if
space itself is curved. One of the older and still quite useful theories that comes out of general relatitivity (i.e. space is curved by gravity) is that the universe is
finite in size, but has
no edge. If I get in a rocketship and fly as straight as I can for a very
very long time, I'll end up exactly where I started.
Consequently, no matter where I am, I can look around and convince myself that I'm at the exact center of the universe! (And no, that's not because I have a big ego
)
Picture a big sphere - this contains all the matter and energy in the universe (which is finite since the sphere is finite). Now, imagine that if you headed out of one point on the edge of the sphere, you would instantly be transported to the diametrically opposite point where you would now be entering the sphere.
This is just like the old video game Asteroids, where when your ship went off one edge of the screen it immediately reappeared on the opposite edge, still traveling in the same direction. You have a two dimensional screen which is a distorted representation of the surface of a three dimensional toroid (doughnut shape) -- but note that everything happens within just two dimensions; there is no third dimension in Asteroids, but it's quite useful to picture the ship traveling on the
surface of a three dimensional object.
That's very similar to how the universe space is curved. It's only got three dimensions, but if you picture it as a sphere - when you exit one side, you come right back in the opposite side. We have a three dimensional universe that is a distorted representaion of some four dimensional object. If you could picture four dimensions, you could picture it easily (but you probably can't...
). So just like Asteroids with only two dimensions, there are only three dimensions in the universe, and it's just useful to picture us traveling on the surface of a four dimensional object.
It may take a little head scratching, but if you think about it, no matter which way you look, it always appears that you are in the center...
Upshot - the universe is
finite and has
no edges because space is curved. You simply can not ask the question "What's beyond the edge?" - it simply has no meaning in this universe.
Of course, this is all based on a specific interpretations of General Relativity resulting in a spherical or toroidal topology for the universe. There is no absolute consensus on this, and many experiments recently have been pointing towards a local hyperbolic geometry of space, and perhaps an overall hyperbolic topology as well (which would be an infinite universe). We'll see...
Cool stuff eh? :smoker2:
PS> Here's a good article:
http://www.sciam.com/1999/0499issue/0499weeks.html