The WMAP which seems indicates that the universe on a global scale is geometrically flat.
Cervaise - yes, that is what I was trying to say. Language defines and restricts the way we think. Even abstract ideas are expressed in concrete metaphors, borrowed from the physical world around us - and a lot of these are spatial. The unseen physical forces (eg gravity, energy) are not obvious to non-physicists and have not found their way into everyday language, so I suppose we don’t have the range or subtlety of language-tools to manipulate them. But is it just a matter of practice? Glad to hear you are optimistic, but I’m sceptical about whether I’ll ever be able to grasp the idea of infinity. When I try, I get an almost physical sensation of the thought flying along and then crashing into the edge of my brain. But there again, the concept of time, its measurements and limits, is deeply embedded in language and thought, making it pretty tricky to think about in a fresh way.
I’m still confused about what cosmologists think about the “beginning” of the universe. Grey said: “14 billion years ago the universe came into existence”. But MC Master of Ceremonies said: “Current observations show that the universe is probably infinite”. Infinite spacially AND temporally? So when you talk about the Big Bang, are you talking about an original event out of nothing (an effect without a cause, the bit I really don’t get on with) or the beginning of the universe that we can see now- the old universe in a new phase? (The latter makes a lot more sense to me despite problems thinking about infinity)
I assume I am allowed to hijack my own thread…?
This needs explanation because I think it’s the real question being asked by the OP. It is also a bit misleading.
If you want to know what “space” as in “interstellar space” is composed of, that question has been thoroughly answered. However, if you’re asking about space as in “space-time,” that’s another question entirely.
The structure of space time is the key question in cosmology and ultimately in physics itself. The answer is that no one knows what “space” is “composed” of. Space-time clearly has a “structure” and clearly has properties. There is lots of conjecture (I’m a brane fan, myself) as to what it is, but as of yet, nobody knows for sure. On one level, this is equivalent to asking “Why is the universe and its laws this way and not some other way?”
The reason Grey’s quote is misleading is that the universe didn’t expand “into” anything. The universe is expanding but it is expanding because all of space is expanding. This is a hard idea to grasp, but the “space” between you and your computer monitor is expanding at the same rate as the entire universe.[sup]1[/sup] One interpretation of this is that space, whatever it is, is constantly being created.
[sup]1[/sup] This does not mean that your computer monitor is moving away from you. Your computer monitor is bound to you and stays at the same distance. If your computer monitor were not bound to you, it would be getting farther away, just as distant galaxies are.
Here’s the breakdown in atoms per cubic centimeter:
Air - 10 quintillion
Best Man made vacuum - 10,000
Between planets - 10
Between stars 1/2
Between galaxies 1 per 10,000,000 cc
If you’d like to return to philosophy for a moment, Immanuel Kant said that [gross oversimplification] space is the form that the mind imposes on the external world as perceived by the senses, and time is the form imposed on internal perceptions. [/gross oversimplification] Sorry, I can’t toss around his charming jargon (synthetic a priori judgement, transcendant a posteriori apperception) with ease any more. It’s been more than 20 years since I read him.
In case you thought the *physics *is confusing. The metaphysics is even worse.
A good analogy I have always found for thinking about a causeless universe is to use size as an analogy for time. We can have a ball 5cm across and another ball 10 cm across is 5cm bigger. However, you cannot have an object 6cm smaller than a 5cm ball. Its equally meaningless asking why 0 cm is the limit to how small objects can be. It is not that the universe is the beginning of time any more than 0cm is the beginning of size. It is what defines what time/size as.
Try to imagine going north at the North Pole or maybe try to find the end of a circle. There’s just no meaning to “what happened before time zero” when there was no time before time zero anyway.
Now the expansion idea is one where space-time inflated or expanded rapidly. Since space-time is not a signal and carries no information it can expand faster than the speed of light. It seems that the universe experienced a brief inflationary stage that made the geometry flat (Euclidian) and led to the seeding of small ripples in the distribution of matter in the early universe. These seeds seem to be what allowed the initial hydrogen atoms to gravitationally collapse. You see if they were uniformly distributed there would be no region of slightly higher density to trigger star formation.