“As the universe itself is a closed entity” - This was recently stated on SD message boards. Wait a minute… Doesn’t the universe go on forever? Eventually would a ‘spaceship’ just hit a wall as the end of the universe? I know it is expanding, but what is it expanding into? There can’t be just an ‘end’ to the universe. I’m sure this has been debated before but I can’t find anything with searches. My basic question is: Does the universe, as we know it, go on forever?
You can easily argue that the Universe, by definition, comprises all that is. So, it is a closed entity. Not a very useful statement.
As far as “forever” - currently accepted models say maybe. Since the universe is currently expanding at nearly the speed of light, you could never get to the edge to test whether or not there was a wall. Even if you did I suppose you’d be doing something like creating new space as you went along. Eventually the mass of the universe may or may not prove more powerful than its kinetic energy, and it will or will not begin collapsing. If this happened your spaceship would be pulled in by the tug of gravity. Its not exactly that there would be a wall holding you back, but simply the gravity of the universe.
Of course, another useful way of looking at these things is that gravity is not a force “pulling” things, but a force shaping space-time. So one way to think about it could be that gravity constructs “walls”.
The important thing to remember is that all of these concepts are simply models. They don’t describe reality so much as they help us understand it so that we can make predictions.
So…uhm, whatever. Read the Hawking books if you really want to get started on this.
Which universe are you talking about?
We know first of all that the universe is finite in time. It has an age. Since the speed of light is the top speed it also has a finite extent. If I start from where I am and travel outward I can travel forever and still be in our universe by definition.
However, if I start at another point out a considerable distance away I can trace out a different area of space and time. Even though the two starting points agree that either point is in the other’s “universe” there are places that you can get to starting at the second point that I can’t get to starting at the first place. By definition those places could be said to be “outside” of my universe.
However, this is all semantics for the most part. Cosmologist deal with these issues by talking about particle horizons (how far we can see) and event horizons (how far we will see) in order to define different extents of the “universe”. By definition, though, does the universe comprise all there is or just all that interacts with itself? There isn’t a simple a) or b) answer to this questions. It is really more of a “how do I feel today?” type question than anything else.
Unsatisfying, maybe, but it’s the best we can do.
“You can easily argue that the Universe, by definition, comprises all that is”
I think the Universe is anything that can be observed.
This question does not have a clear answer. See My Post
It really is just semantics, and not particularly useful. But this explains what I mean:
universe
n 1: everything that exists anywhere; “they study the evolution of the universe”; “the biggest tree in existence” [syn: existence, nature, creation, world, cosmos, macrocosm] 2: the whole collection of existing things [syn: cosmos] 3: (statistics) the entire aggregation of items from which samples can be drawn; “it is an estimate of the mean of the population” [syn: population] 4: everything stated or assumed in a given discussion [syn: universe of discourse]
Source: WordNet ® 1.6, © 1997 Princeton University
http://www.dictionary.com/search?q=universe
Above definitions of The Universe do not take into account theories of multiple universes.