| From: Daniel Johnson | 4/05/99
13:49:58 |
| Subject: Universe and Infinity | post id:
9523 |
| Dr Karl, Your
program on JJJ has intriged me for years and brought me back to a
more attentive and interested level than I had been for a while.
(love the talk back show). My girlfriend and I have been having a running argument (discussion) which we have not been able to solve due to a lack of real understanding of some of the fuzzier physics, the breadth of the subject and perhaps a touch of mutual stubbornness. My question began as a discussion on the universe. My girlfriend (Virginia) believes that the Universe is infinite! I however believe that it is not infinite, but just very, very large. I go on to argue (to limited effect most of the time) that infinity cannot exist except at a theoretical level. The universe for all intents and purposes is infinite, but not actually so. The discussion continues on for awhile then takes the form as follows : the universe (ours) is expanding (we both agree on this). If this is the case I argue that it must have an edge, and by having an edge it is finite in its size. She argues that that which it is expanding into should also be counted and thus it is infinite. I argue (so I know this is convoluted) that what the universe (I am only talking for convenience about a single universe as once we develop an agreeable theory about one universe we can apply it to the other finite or infinite number of universes - depending on your position in the discussion) is expanding into is nothing and as it has no presence, no matter, no energy, and nothing even remotely quantifiable - nothing is nothing! Nothing can not be measured, thus it can not be included in a debate about infinity. Perhaps the only thing that can be infinite is nothing. But that in itself is a paradox because if you cannot measure any part of it then rather than being infinite (the nothing that is) it is .....nothing. So in a rather long winded way I ask (the above was to provide a context for our discussion and any comments you may consider relevant would be appreciated) is :- 1) Does infinity exist in reality or is it just a theoretical abstraction. Allowing for a second the possibility that infinity might exist 2) Are there an infinite number of other universes out there (somewhere) - perhaps passing energy via whiteholes and blackholes - or just a very, very large number of universes. Thanks. I realise that you would get a lot of (e)mail but I don't often take the time to nut out the logic of such an intangible argument and would be thrilled if you were able to respond in some form. If you are (I tremble in anticipation with the possibilities) going to give a tentative answer over the radio please let me know in some way what day as I am rarely able to listen to the whole show (work puts such restrictions on my JJJ listening). Thank you again and keep up the good work. You are an inspiration to a generation of kids (and not so kids). Dan | |
| From: Dave Martin | 4/05/99
14:34:49 |
| Subject: re: Universe and Infinity | post id:
9528 |
| From what I understand (very
little), it is possible that the universe is finite but unbounded. It has
a finite size but no edges. The way this works is a bit like a circle in 2 dimensions - the line is of a finite length but has no start or end point. In 3d a torus (donut) is a similar concept - finite volume but a line starting anywhere on it's surface will never meet an edge. A sphere also has this property. The apropriate 4d (or higher) shape for the universe is beyond my ability to viaualise. In any case defining the edge of the universe is problamatic as there is nothing outside the universe. I don't meen a vacuum here I mean NOTHING. As the universe expands, spacetime expands with it. The universe is everything so it really can't have an edge. I'm sure one of the avatars can explain this much more clearly then I can. | |
| From: Yoda Oz | 4/05/99
16:10:31 |
| Subject: re: Universe and Infinity | post id:
9551 |
| I have a theory and some people
might back me up on this: (by the way I thought of this theory when I was
in primary school long before I heard anybody else talk about
it.) I reckon that if you travel in one direction you'll end up at where you started again. I have another theory where because the universe is expanding, and I think it is expanding at the speed of light, no one will ever be able to catch up to the "boundary" of the universe, and because telescopes are used by light, we will never be able to catch up with our telescopes either. Really, it is like the universe is running away from something. Someday, the universe will expand to a point and the begin to contract. It will keep contracting until it sucks itself in causing another 'big bang'. Get that india! Yoda Oz (Copywrite 1999) | |
| From: James Richmond (Avatar) | 5/05/99
11:40:06 |
| Subject: re: Universe and Infinity | post id:
9662 |
| Daniel said: My question began as a discussion on the universe. My girlfriend (Virginia) believes that the Universe is infinite! I however believe that it is not infinite, but just very, very large. I go on to argue (to limited effect most of the time) that infinity cannot exist except at a theoretical level. The universe for all intents and purposes is infinite, but not actually so. There is a philosophical debate over whether anything can actually be infinite. Philosophers make a subtle distinction between the potentially infinite and the actually infinite. Some say the actually infinite doesn't exist. Like all good philosophical questions, there is no definite answer to this. Maybe it does, maybe it doesn't. Physicists, being a bit more pragmatic, don't really worry too much about subtle distinctions. They simply treat infinity as if it actually exists. Mathematical models of the universe distinguish between two types of universe, infinite and finite. Our observations haven't yet made it clear which model best fits our actual universe. However, ignoring a possible anti-gravity force (which may be dangerous, given recent observations), the eventual fate of the universe is closely related to whether or not it is infinite (as opposed to just very big). If it is finite it will eventually recollapse to a "big crunch" or "gnab gib". If it is infinite, it will expand forever. The discussion continues on for awhile then takes the form as follows : the universe (ours) is expanding (we both agree on this). If this is the case I argue that it must have an edge, and by having an edge it is finite in its size. She argues that that which it is expanding into should also be counted and thus it is infinite. Whether the universe has an edge is a separate question from whether it is infinite (see below). The universe is not "expanding into" anything. This is because the expansion is not the usual type of expansion of something in space, but rather an expansion of space itself. If the universe is finite, there is nothing "outside" to expand into - the space just expands. If it is infinite, it's even easier to see that there is no "outside" - again, the space just expands. Are there an infinite number of other universes out there (somewhere) - perhaps passing energy via whiteholes and blackholes - or just a very, very large number of universes. If there are other universes, there is no way we can know anything about them, since we're kinda stuck in our own one. We can't see inside a black hole without going inside, and nothing comes out of a black hole, so if black holes link to other universes we can't know about that, either. There is no evidence that white holes exist at all. ---- Yoda said: I reckon that if you travel in one direction you'll end up at where you started again. This is true if the universe is finite and unbounded (has no edges). If it is finite and unbounded, the space must "wrap around" somehow. A well-worn analogy is the surface of the Earth, which is unbounded but has finite area. If you set off in a straight line, you eventually end up back where you started, and you can't "fall off the edge". JR | |