The usual analogy to describe the geometry of spacetime is an expanding balloon. The surface is 2-D, closed, warped in a 3rd dimension, inaccessible to the balloonists. However, the ballon has a center - in the 3rd dimension.
Now, extend this picture to our expanding 3-D universe; can we compute the 'radius', the distance to the center, in the 4th space dimension? Analogous to the balloon model, it should be the same for all observers.
And that would educe a circumference, would it not?
-- Rich
No Center
Also see Ned Wright's Cosmology Tutorial
WMAP: Foundations of the Big Bang theory
WMAP: Tests of Big Bang Cosmology
Yep, and the answer is 42 astronomical cubits.
Dave.
I thought the universe was infinite. What are we in? A fish bowl?
It might be that if one could go far enough, the last bit of big bang material could be surpassed and then there's nothingness or perhaps other big bangs (other universes?). The universe could be just like a pile of fire crackers tossed in the air. Then there's the big crunch theory. So, some places could be crunching and some banging.
Lots of things resonate.. The universe could be just another bell. Bang...crunch...bang...crunch... Boing...boing..boing...like a rubber ball.
D from BC myrealaddress(at)comic(dot)com British Columbia Canada
Considering the universe as a sphere it certainly should have a center. However considering gravity, expansion and other things we don't know about yet things might not be as we thought they were ;)
Maybe we can't exist outside the visable universe. Or it's just as any ordinary space. But VERY empty :-)
Now if it would be possible to travel outside the visable universe. There's something interesting to discover.
Correction; the internal and external volumes (and the center of course) are inaccessible, the surface is all that's accessible.
Sure, why not? The yardstick will be the path of a photon from the Big Bang to your eye (in the 5-dimensional space in which our expanding 4D universe is expanding) and that path will resemble an Archimedean spiral. However it will be slightly altered by such things as Cosmic Inflation early on, when the expansion rate increased greatly for a while.
Yeah, but we can never see but a small bit of it.
Mark L. Fergerson
Dear RichD:
Representing space.
... Time.
The "Big Bang".
the "raisin bread" model..
I believe the "distance" has been calculated to be 14.5 Gy (may have moved again).
... at any given *now*, with the usual synchronization problems.
Not a unique circumference, since there is no guarantee this Universe is hyperspherical. Might be a dang torus.
David A. Smith
I think that the point is that the universe looks as if it is between
13.6 and 13.8 billion year oldso you can't get anyplace that further from us than 13.8 billion ight years, and no place further away that that can get to us, so that we can say anything useful about more remote areas, and they can't affect us.
In that sense, we do live in a gold-fish bowl (albeit it a rather large one).
-- Bill Sloman, Nijmegen
It appears (at least from our perspective) to be finite in age, which tends to lead one to suspect that it could also be finite in extent. Note that I said "could"; there are different choices for the geometry of space that could make it open or closed, and the parameters that determine this geometry, as measured so far, seem to be frustratingly close to the critical deciding values so that it's not obvious.
Can you travel far enough on the surface of a balloon to "surpass" all the balloon material and reach a void?
Except that in the case of the universe there's no pre-existing 'air' for the explosions to occur in; there's no space outside the universe, and current theory says that all of spacetime grew out of the Big Bang. TO retrun to the balloon analogy (which has its limitations), for an expanding balloon surface, there's no uber-balloon-surface that the balloon surface is expanding on. The balloon surface itself is all there is.
People have looked for evidence that we can see the same bit of space from two different directions, and not found any, which doesn't prove anything much.
My understanding was that the smart money was on the 4-D equivalent of the saddle-shaped geometry, but I can't remember why.
-- Bill Sloman, Nijmegen
It appears that the universe is finite but doesn't have a boundary in all 4 dimensions. You need to consider the 5th dimension to be able to say that there is something we could call a center.
I would argue that the universe must be finite for the following reason: Consider the location and speed of just one electron. This information must be stored somehow. From quantum mechanics we know that there is a limit on the resolution. From Einstein we know that the speed has an upper limit. The only remaining number that could be infinite is the position in an infinite universe. If this was the case, the number of bits would be infinite. From Shannon, we know that it takes energy for each bit that you store. From Einstein, we know that this energy would have mass. From this, I claim that an electron in an infinite universe would have infinite mass.
Nice crack pot theory. Huh?
How does that work? 6 x 9 x 1 Astronomical Cubits? 6 x 3 x 3 AC?
The radius of the universe is infinite, the diameter is finite.
No Center
Also see Ned Wright's Cosmology Tutorial
WMAP: Foundations of the Big Bang theory
WMAP: Tests of Big Bang Cosmology
No. The outside of a black hole's event horizon has a finite diameter implied pole to pole. The inside diameter is infinite, passing through the center singularity. Think "tardis" but with a roomier interior.
Tell us how to locate paired interior poles of an event horizon.
-- Uncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2
I recall a video where there is a boundary where we don't see stuff because the light hasn't reached us yet. Invisible stuff due to distances so great it makes the speed of light seem retarded. A new big bang could have happened elsewhere but so far away..we won't see the light for billions of years. Unprovable at the moment. However, it's nice to imagine stuff like that. It's much better than being lobotomized by a religion and just say 'God Did It. End of story Duhhhh..whatever you say boss..'
D from BC myrealaddress(at)comic(dot)com British Columbia Canada
Kandor.
Cheers! Rich
Finite in age?? We just see old light.. We can't see the new light. We have to wait for the light to reach us. Blackness could mean the light hasn't reached us yet. Distances >>> Speed of light
I tend to avoid egocentric 'we are special' idea's. Idea's like: Earth at the center of the solar system. A single creator. A personal universe with boundaries.
Isn't that balloon analogy seem stuck on 2 dimensions? The choices are: Curved forward. Curved backward. Curved left. Curved right. There's no up and down.
The void would be whenever there's no contact with the balloon.
That's deep.
D from BC myrealaddress(at)comic(dot)com British Columbia Canada
When the measured velocities of the distant galaxies are plotted and tracked backwards in time they all appear to end up 'here' some 13.7 billion years ago. Or, put in a slightly different way, everything we can see seems to have been all in one place some 13.7 billion years ago. That
*includes* the stuff beyond our current horizon, which was carried away from us at rates exceeding the speed of light in space during the expansion phase known as the inflation era.Sure. The idea that there is no special place in our universe is fundamental to the Big Bang theory. Any observer located anywhere (except in pathological places like inside a black hole!) would see essentially the same picture and deduce the same model. That is to say, every observer sees himself as being exactly at the center of the expansion. In this regard, everyone can actually be justified in claiming that they're at the center of their own universe!
Yes, exactly. The point is to allow one to explore the requisite concepts in a geometry that is familiar to our our common sense. It's harder to picture in our minds eye a three dimensional 'surface' plus time curved in a fourth spatial dimension. Hence the reliance on simpler two dimensional surfaces for putposes of illustration.
Which can't happen if there's no up and down, right?
Since the 4th dimension is time, by your reasoning the distance to the centre is 13.7 billion years, give or take.
-- Dirk http://www.transcendence.me.uk/ - Transcendence UK http://www.theconsensus.org/ - A UK political party http://www.onetribe.me.uk/wordpress/?cat=5 - Our podcasts on weird stuff
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