# Thread: boundaries of the universe

1. This always troubled me. The universe is expanding, but what is it expanding into? Is there a true boundary or is the universe continuous? If you traveled in one direction would you eventually end up where you started?

2.

3. It's not expanding into anything or anywhere. The universe is all there is. There's just more space.

4. ok so what would happen if you traveled in one direction at the speed of light for eternity? Wouldn't you reach the end of the universe?

5. No, given that the universe is expanding faster than light, you'd travel for all eternity.

6. wait i thought that once something travels faster than the speed of light, time slows down for it. That would mean the fastest expanding points of the universe haven't even expanded yet from our viewpoint.

7. There's nothing moving through space with a velocity greater than light. What a recession velocity greater than light means is that there is so much new space being created that light will never succeed in crossing the ever increasing distance.

8. Originally Posted by TAMB0
This always troubled me. The universe is expanding, but what is it expanding into? Is there a true boundary or is the universe continuous? If you traveled in one direction would you eventually end up where you started?
It is just expanding, it is due to dark energy. Some regions of the universe are believed to be expanding more so than others. One theory as to where this ends is called 'the big rip' in which eventually the universe will expand so much that star systems will be torn apart, stars, planets, molecules, atoms, quarks etc. Ending up where one started implies a spherical shape, from observation the universe appears to be flat:

http://en.wikipedia.org/wiki/Shape_of_the_Universe

wait i thought that once something travels faster than the speed of light, time slows down for it. That would mean the fastest expanding points of the universe haven't even expanded yet from our viewpoint.
If something goes faster than light it can go backwards in time, so the theory goes. This is evident in black holes where space itself can move and any object moving with that space can apparently be moving faster than light. Space beyond the photon sphere of a black hole for instance is said to be 'falling' faster than light so that light can never catch up.

Interesting fact, a stream of galaxies are moving away from where they are supposed to be due to what is called the 'dark flow', an interesting effect of something that is outside our visible universe but in our past light cone.

Dark flow - Wikipedia, the free encyclopedia

9. good stuff guys. thanks for the info

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