What exactly is the Universe? Is it finite and if so why? If the Universe is expanding, what is it expanding into? How much of the Universe is made of “dark matter”? Is it possible that there are stars and galaxies that are so far from us that there light has never and will never reach us? Any help gratefully appreciated.
Hijack! Not really, though. Kinda, I guess. Anyway, I was wondering if someone (i doubt it) knows what color there is beyond the universe. I mean, it can’t be black, there isn’t any matter to make it black. I suppose it doesn’t have any color, it just is.Unless you have taken some way advanced science course, you probably won’t know the answer to my question.
The universe is that matter which exists on the surface of some 4-dimensional solid. It’s expanding into something which is totally beyond our ability to observe or experience, so anything said about it is pure conjecture. The universe appears to be of finite volume, so all light will reach the earth eventually; however, it may be quite some time after the human race has passed on.
It seems unlikely that we can ever know anything about what’s outside of our universe. There may be matter out there, or there may not be. It might be filled with gumbo, for all we can ever know. So there’s no way to determine what color it might be.
You sure? AFAIK, there’s no evidence one way or the other that space is embedded in a 4-dimensional figure; how you view it is I suppose a matter of perception, but in any event, we have pretty good reason to believe that there are only three relevant spatial dimensions, so it doesn’t really matter.
Oh god, now THERE’S a scary thought. If true, whatever made the universe has no taste. 
Got me. That’s what I thought I’d been hearing, but I could be wrong.
The universe is a figment of its own imagination, which didn’t exist until it existed, prior to which there weren’t any days in which you could have said that it didn’t.
The universe, mistakenly described as having been created in an event known as the Big Bang, is an event known as the Big Bang, which is the only event which has ever occurred, and has no prior cause.
And you are it.
The universe is just a sophisticated simulation or mathematical model, it’s not real at all.
Are we living in a simulated universe?
Douglas Adams, from The Restaurant at the End of the Universe
ultrafitter wrote:
“It seems unlikely that we can ever know anything about what’s outside of our universe.”
There can be nothing “outside” the universe. By definition, the universe is everything that there it is.
When I’ve seen philosophers speak of this, they use the word “Universe” to mean the totality of existence, and “universe” to mean our little corner of it. I was using the word in the second sense.
Insider, I think the scope of your question is a bit beyond the scope of this message board. You might want to try reading some books. Go to your library and do a subject search for “cosmology.”
I also found some good stuff doing a Google search for cosmology faq.
I should have realized that, ultrafitter.
Sorry if I came across as a pedantic know-it-all.
No prob.
As I understand it the universe is infinite and finite at the same time. It was likened by Stephen Hawking to the surface of a sphere. It has a finite size but you can walk around it forever and never find the end. The universe is finite since current cosmological models have the Big Bang as the beginning. Starting from a VERY small size the universe grew to its present day size and is still growing. Given that the universe had a beginning and that it grows over time it cannot, by definition, be infinite (even if it grows forever as is the current thinking).
The universe is expanding but it isn’t expanding ‘into’ anything. There is no ‘outside’. There is just the universe. If there really is an ‘outside’ then any guess is as good as another. You may think ultrafilter was being silly about Gumbo being outside the universe but it is truly as good an answer as anything else if you try to speculate what would be there. It is absolutely beyond our ability to measure or know in any way shape or form.
For dark matter it is speculated that as much as 90% of the universe is made of the stuff. Don’t ask me what it is since I don’t know…nobody knows yet.
I believe that some light from other galaxies may never reach us although I’m not positive. I seem to remember a brain teaser that asked why the night sky isn’t bright white…the theory being that if you travelled long enough in any given direction you’d eventually hit a star. Therefore the night sky should be bright white and not black at night. I think the answer to this was that the universe is expanding near (or at) light speed so some (most) light will never reach the earth. I think I may have some of this part of the answer wrong though so I’ll have to doublecheck or wait for someone around here to pick up the pieces.
[nitpick]It would be better to say that it’s finite but unbounded.[/nitpick]
I’ve always understood it this way: Time is the fourth dimension.
Think of it like this. Any event in space can be located with three coordinates…X, Y & Z. So, I could say, relative to me, that my wife dropped a glass 2 miles west, 1 mile north and 200 feet below me (I’m in an office building). Those are the X, Y and Z coordinates of that event relative to me. But if you think about it we are still missing a piece. When did she drop the glass? We now have a fourth coordinate to define that event. My wife dropped a glass 2 miles west, 1 mile north and 200 feet below me at 8:45 a.m. CST.
Chronos once explained to me how this actually relates in a spatial sense but I didn’t really quite grasp it. I’ll have to look around for the post but I think it was something like take a 3-D cube, move it for 3 seconds, connect all the points and you have a (4-D) hypercube. Maybe Chronos will come along and clear up this point as well.
Universe is the sum total of all there is. Asking what color is on the outside is like asking what flavor of dogfood do poodles like who are not in the set of all poodles that have ever existed. It’s just plain nonsense and unanswerable.
The Universe isn’t just about matter, neither. Space, time, energy: those are all the stuff the universe is made out of too. In fact the concept of nothing that is to more precisely say a vacuum is also a member of things that exist within the universe. What do things look like outside the universe? It’s not something we can even begin to conjecture.
The universe is the gravitational field.
Without mass/energy and its associated gravitational field there would be no universe.
Yes, time is the fourth dimension. What ultrafilter and I are discussing is the idea of our three spatial dimensions as the surface of an object with four spatial dimensions; I’m not even sure that whether this is actually true or not can be answered, but there should be no confusion about time being a separate dimension from the fourth spatial dimension in which our three spatial dimensions are imbedded.
In other words, think of the balloon analogy. To locate any given point, we need, as you said, 4 pieces of information. To locate a point on the surface of the balloon, though, we only need 3 (say, latitude, longitude, and time). The extra spatial dimension that we’re talking about would be distance from the center of the balloon, and it’s the higher dimensional analog of that dimension we’re discussing.