# How is the universe unbounded?

1. Feb 12, 2012

### homeylova223

I mean look at a triangle or a square or even a sphere kind of has something outside of it. Even a circle does.

2. Feb 12, 2012

### Simon Bridge

http://www.math.brown.edu/~banchoff/STG/ma8/papers/leckstein/Cosmo/properties.html
It may at first seem strange to speak of a space which is both unbounded and finite, but we shall see that many such shapes exist. Consider a spherical Flatland. A Flatlander can travel forever and never fall off the edge of the universe, even though this Flatland has a finite area. In the next section, we will encounter analogous shapes for our space.

3. Feb 13, 2012

### bapowell

Consider the 2D surface of the Earth. It is unbounded. And importantly, there need not be a 3rd dimension within which to immerse the sphere: the 2D spherical surface can be defined in 2D.

4. Feb 14, 2012

### arashbh

referring to math ..
when something has a limit at infinity so there must be a boundary somewhere..
there is a theory that we actually are living in a black whole , in fact the whole big-bang process was a birth of a black whole which clearly defines the existent of parallel universes
i really fascinated by that idea it COOL

5. Feb 14, 2012

### Staff: Mentor

The idea that we might be inside a black hole is fascinating to some, but it is not the current view of the standard model. There are a lot of things that a theory based only on math can show. It is important to understand that just because the math in one "theory" shows it is possible does not mean that it actually is. Believe it if you want, but I won't be holding my breath.

6. Feb 15, 2012

### arashbh

well, so far thats the only thing i consider the most sensible. you see Hawking's argument of a divine creator might not be 100 percent true... we got so much more to go through to judge whether theres one or not.. if hes right then we're pretty much done with this world and we just popped to this universe period, i think we're bounded, we should be bounded otherwise what math says is basically wrong, math always have worked and will work ..

7. Feb 15, 2012

### Staff: Mentor

You can believe what you want. As for one thing being more sensible than another, I don't think anyone can argue that at this point in time. Also, I don't see why an unbounded universe would make math wrong.

8. Feb 15, 2012

### arashbh

your totally right. arguing for make a certain point is just a waste of time, keeping all possibilities in mind though gives us a clue to proceed. if we assume the universe is bounded just like math proving the otherwise will be our job, its always been this way!
the most obvious example for continuity and limitless is two parallel lines right? they don't exist, we cannot reach that point( the END ) but it is there..thats what im thinking

9. Feb 15, 2012

### Simon Bridge

... in Euclidean geometry, parallel lines will not intersect. However, in real space they do.

An unbounded universe is as good mathematically as a bounded one, and has a better fit with observation.
Making claims about the math without actually learning the math is not a good idea.

Your question has been answered - we cannot help it if you do not like of believe the answers. The truth is often uncomfortable.

10. Feb 15, 2012

### arashbh

i agree with you .. im completely aware that being in Calculus BC is just not enough to making claims about these stuff ..
and how could you be that sure about the truth?
im willing to believe the truth that's why im here,so why would i be uncomfortable with it?

11. Feb 15, 2012

### Simon Bridge

That is what scientific method is all about.
You check your ideas against the Universe.
But it is not an on/off thing - the methods allow you to work out how confident you can be in a particular answer.

Since you are interested in these things, you should take the next opportunity to take a 101 level philosophy of science paper. At least read some online papers on the subject.
If you get stuck on any of the topics, we can help. But did you even do the course in the link I gave you?

12. Feb 15, 2012

### arashbh

thats exactly what im saying , you check your ideas and take the best one !
the BB idea has become a bit old it used to be the best idea!.. there are strong possibilities that this event is a cosmic cycle it never stops and it never starts ! if its true then the universe is a very strange place!

13. Feb 15, 2012

### bapowell

The standard big bang model is still the best and most parsimonious fit to cosmological data.

14. Feb 15, 2012

### arashbh

i meant the BB being a start point might not be true..as Prof. Kaku explains it
i did happen but it wasnt the first time

15. Feb 15, 2012

### phinds

Kaku talks about wildly speculative ideas as though they were fact, including such unproven and currently unsupported speculation as this. He used to be a real physicist but he is now a popularizer of the worst sort.

16. Feb 15, 2012

### bapowell

Yes, and I think we're all in agreement, but that specific question might not be answerable even in principle with cosmological observations. The standard big bang model certainly doesn't address it.

And Phinds -- I couldn't agree more with your appraisal of Kaku.

17. Feb 15, 2012

### arashbh

hopefully everybody is saying the same thing ..
Kaku's blog called "big think" is a great futuristic place !

18. Feb 15, 2012

### Spourk

Check out some of these videos from A Google Search for Hyperspheres

It's a little easier to understand what they are talking about when they discuss the shape of the universe.

19. Feb 20, 2012

### alphachapmtl

look at the integers:
... -2 -1 0 1 2 ...