This thread will probably get me banished to just purusing from now on on but…
I get the feeling you guys are afraid of the really hard questions. In my thread “4D, yes?”, I tossed it out rather hastily assuming that the intent would carry. I see now the folly of my thinking.
So, I propose a new question. But first (indulge me Manny, I apparently need lay a little more groundwork)…
Sorry, jcgmoi, the raisin bread analogy is close - but this is science.
I should not have thrown in the FTL bit. I just thought that any group who could do 5 pages on marmot killing might have enough imagination left for some serious speculation. Wrong again.
Yes, Phobos, I meant galaxys.
Thanks for the link, CKD, but I think Cecil rushed to judgment. He might have even been (spoken in hushed tones)…gulp…wrong!
I have read Einstein and understand it quite well, thank you.
My Question (thanks for your patience, Manny): Can anyone provide a WORKING (in theory) model of our cosmos, as we understand it, without using a 4th physical dimension?
If the universe is closed, the answer is ‘no’. This is why Carl S. chose the 2D balloon example (otherwise, why not just give a 3D example?). If the universe is open as Chronos points out, we are back to the ‘raisin bread’ problem. Things will look different from the ‘edge’ raisin’s POV than they will from a ‘middle’ raison’s POV.
This question is meant to stimulate thought only, no ill-will or mean-spiritedness intended.
Well, I was with you through the part about the marmots, but I lost my grip when Carl Sagan and the fourth dimension came up, and now I’m out here all alone in the darkness. Guess you’ll just have to carry on without me.
P.S. If you’ll give me a link, I’ll occupy myself while waiting for the roller coaster to come to a complete stop with looking at it and seeing if I can formulate a response to the one question that I did grasp, namely, “Wha’d I do wrong in the other thread, that nobody wants ta talk ta me?”
I just looked up your other thread (4 diminsions, yes?), and I also don’t see why you didn’t post this there. The discussion seems to have been going along fine. If you needed to clarify your question, why not do so there?
As far as your question goes, I think it was answered there. Basically, a fourth dimension is used to make the model easier to visualize, but that doesn’t mean there is actually such a dimension along which you could travel.
I’m sure some mathematical prodigies are capable of maintaining a mental picture of a closed universe in three dimensions, but people like me need to reduce it to the 2D ballon analogy to get it. Since that analogy uses a 2D surface in a 3D world, it seems to imply the universe exists as a 3D surface in a 4D world.
Chronos says that this is not necessarily a true extension of the balloon model, and that you can model the universe in three dimensions. Chronos knows this stuff a heckuva lot better than I, so I’ll trust him on it.
One more thing: The link you commented on was written by Dex, the guy who posted the link (he posts and moderates on the boards as CKDextHavn). He’s a member of the SD Staff, but he isn’t Cecil. He wrote it with the help of Karen (she posts under the name Karen Too) of the Straight Dope Science Advisory Board, a practicing physicist.
Where do you think they went wrong? The column is a perfect description of the concept of dimensions, as far as I can see. Though it was fairly tangential to your question, as CKDextHavn said when he linked it.
O.K. I’ll cop to a few things. It seems I should have clarified this in my OP. Honest mistake. I really thought I had started the confusion by not being clear. I’m learning.
And, D.D.G., I did some soul searching. Maybe I was a little confused by the lack of responses but, hey, this is a free board. I know that. But look at the first response to this post. Asmodean does his best Monty Python “And now for something completely different”.
And I’m sure Chronos is a clever guy I just don’t feel his answer was correct/complete. After all, aren’t we fighting ignorance here? Shouldn’t we dig as deep as we can?
My sincerest apologys to both Cecil and Dex for confusing them.
Dex was answering a question posed by a 12 yr old and did a fine job. Though they may seem the same, I believe (though I could be wrong) the question I was asking was a little more fundamental in nature and
I think it could use a little more investigating, but if you guys don’t think so, hell, I got a gun - where’s them marmots?
They would, if there were any edge raisins. The difference is that the Universe has no edges (it’s likely infinite, but there’s other ways to get away with not having any edges), so nothing’s closer to the edge than anything else.
The best demonstration of the “no center” business unfortunately won’t work over a message board, but you can try it yourself, if you have access to a couple of transparency sheets and a copier. First, draw a bunch of dots on one sheet, randomly arranged. These represent galaxies. Now, make a copy of that sheet onto the other one, but at 9/10 scale. If you then pick a galaxy (the same one on both sheets) and line them up at that galaxy, you’ll see the point of view from that galaxy at two moments of time. No matter what galaxy you pick, it’ll always look like the Universe is expanding uniformly around that galaxy. Try it.
O.K. I did the experiment as you suggested, and guess what? It worked! I was right, you are a clever guy.
BUT, we are still using a 2D model to explain a 3D situation. And there were “edge raisins”. I guess I was still vague in my OP. When I said “our cosmos, as we uderstand it”, I was refering to a 3D model, of the raisin bread kind.
I maintain that if there are no edges , the universe must be closed. And if it is, there must be 4 dimensions. Merely expanding the model you suggested upward (into 3D) doesn’t work if the universe is finite.
And if it is finite, how could it not be closed if there is no edges?
Thanks, Chronos, for your input and time. I would welcome your thoughts on this post.
Why can’t the universe have edges? Seems to me that if you’re in the “no edges” camp, then your belief system includes only one, infinite universe.
But if your belief system includes a universe with edges, then it would also include other universes. Right? So all it boils down to is whether you want to believe in one all-encompassing universe, or lots of little individual universes.
Now tell me this is a vast oversimplification, and tell me exactly how it is oversimplified, because the marmots are gonna want to know, and I’ll have to be able to explain it to them.
If you have edges, then the problem becomes, what’s on the other side? If space extends beyond the edge, then it’s not really an edge. If there’s some sort of barrier, then what is it made of? Or do things just cease to exist when they cross a certain plane? That would cause major problems with physics. Incidentally, there’s still the possibility for other Universes, but we can’t reach them or communicate with them in any way. If we could, then they would be considered part of our own Universe.
There’s a few distinct possibilities for a Universe without edges. Perhaps the simplest is a Universe with spherical geometry: It’s finite and closed, and (possibly) embedded in a higher-dimensional space. Again, the existance or nonexistance of that higher dimension is outside the scope of physics, since all we can see is our regular dimensions. The second possibility is that the Universe is not closed, but is infinite, and therefore still has no edges (actually, there’s two different possibilities that match this, but they’re close enough to the same for our purposes right now). A third possibility is that the Universe is flat (not closed), but that it still “wraps around” on itself in some other way: A two-dimensional example is an Asteroids screen. When an asteroid flies off one “edge” of the screen, it comes back on on the other. The “edges” are arbitrary, though: When you fly your ship around, it always stays in the center of the screen, and what looks like the edges is always the same distance from the observer. A three-dimensional version would be similar, but would use blocks (or some other shape) instead of rectangles.
Yes, the example with the transparancies is finite and two dimensional, but it generalizes very easily. You should be able to picture both sheets extending out infinitely, and if you really wanted to, you could build a three-dimensional model of it with wires and beads, and it’d show the same behavior.
Time (strictly speaking, “duration”) is another dimension, but it’s not the one that we’re discussing here. What darkcool seems to be asking about is another spatial dimension, in which our three spatial dimensions would be curved.
There isn’t really any way to give a definitive answer to this question, because it is a question more about yourself than the universe. You are asking “Is there there some sort of mental representation of the universe which I can imagine, will satisfy me as a suitable representation of the universe, and uses only three spatial dimensions?” This depends on what you accept as a mental representation. Take, for instance, the Earth. One person may travel aroung the Earth, end up where he started, and say “Gee, the Earth must be round. But for a two dimensional urface to be round, it must curve through a third dimension. Therefore, the Earth must exist in a three dimensional universe.” Someone else may say “No, the Earth is perfectly flat. You were simply transported back to where you started.” The first guy would probably say something like “What do mean, ‘somehow transported back to where I started?’ People don’t just jump from one part of the world to another!” These two people have different ideas about what are acceptable mental representations. The second guy accepts the two dimensional model; the first guy doesn’t.
Duck Duck Goose
Why does the absence of edges imply that the univerese is not finite?
well, this definitely should have been kept with the other thread, but anyway…
Chronos has explained things well.
Finding a simple analogy for a complex system is never going to be scientifically satisfying…that’s why mathematics is needed…something which may be too much to get into in a message board…perhaps you may find this link interesting… http://www.astro.ucla.edu/~wright/cosmolog.htm
The simple analogies already mentioned (expanding balloon, rising raisin bread, walking the Earth) are the ones that are used the most often because and they get the idea across pretty well. But it’s just a starting point.
