As the galaxies rush apart....?

Question

A theory that explains the scale and boundlessness of the universe states that if you could manage to travel through the universe in a straight line that you will eventually end up right where you began...If that's true then wouldn't that mean the the galaxies that are rushing away from us eventually come back around the other side and the light would be blue-shifted?? but everything I've heard says they are all red-shifted.

Any ideas would be helpful or even filling me in on something i'm missing would be great.

Answer 1

The theory that suggests if you go far enough in one direction you will return to your starting point makes 3 dimensional space the surface of an expanding 4 dimensional sphere.  The analogy is the surface of a balloon: space is the surface (minus one dimension), and as the balloon gets larger the galaxies fly apart.  Therefore, if going in one direction you return to your starting place, the universe will still be much larger than when you started.  BTW the 4th dimension in this theory is time, which makes the analogy more confusion but it fits with Einstein's theory of relativity concerning 4 dimensional space-time geometry.

Regarding additional details, the nearest things we can see are pretty close to 13.7 billion light years away, but there is no reason galaxies can't exist well beyond that.  Based on the expansion rate of the universe, we should in fact be able to see about 15 billion light years until the expansion of space exceeds the speed of light.  The last sentence holds a clue: there is nothing about relativity theory that prevents space itself from expanding faster than light.  Matter or energy travelling through space, however, is limited to light speed.

Answer 2

Nothing travels fast enough to do this.  You'd have to exceed light speed.

Eventually a galaxy may seem to recede at more than the speed of light.  However, the galaxy is not moving that fast.  The apparent speed comes from the expansion of space itself.

Imagine space expands (just a made up example) 1 foot for every million miles in space per year.  When you are separated by 12 billion light years that one-foot adds up over and over again giving things very far out the appearance of receding faster than the speed of light despite nothing actually moving that fast.

Answer 3

It is not just galaxies moving apart, space itself is expanding. Scientists usually say it is like a rubber balloon with spots painted on it. As you blow up the balloon, the spots get farther apart. The spots are like the galaxies and the rubber the balloon is made from is the space. But don't take it too literally, because that rubber is a 2D surface curved in 3D space, where the universe is 3D space curved in a higher dimension we can't see. But we can describe it mathematically.

Answer 4

In theory, you're right. In practice, you may be talking about your neighbour going around the world to get to you, which is a long way. If the world expands, then they may never get there. This is what happens in space.

Also, they will not occur blueshifted, because the distance the long way around a sphere is also increasing, just like the distance the short way round, as the sphere expands. So photons which take the long way round to the Earth will be "streched" by the expansion even more.

Good question...

Mike

edit- eelfins above me says that the 4d geometry of curved space is 3 space and one time, I am not certain but would question this- flat space would have 4D spacetime as well. Wouldn't it be a spacially 4D hypersphere (so the surface of a baloon becomes a volume of the universe, finite but not bounded), and then the "5th" dimension is time? Just wondering. Thanks.

Answer 5

MY FRIEND,

SPACE IS DARK MATTER. IT MOVES LIKE THE OCEAN CURRENTS. NOTHING IN SPACE IS STRAIGHT DUE TO BLACK HOLES. THEY GATHER TIME AND SPACE.

OUR UNIVERSE IS SPECIAL. LINKS TO THE FIRST BANG AND THE SECOND BANG OR BACKDRAFT.

THAT'S WHY THE BIBLE SAID . THE DARKNESS HAD TROUBLE WITH THE LIGHT.