mhansen:
Then what’s on the other side of the “space boundary?” Isn’t that kinda like “walking off the edge of the earth?”
Seriously though, I know space is still expanding, but I was always curious as to what is on the other side of that line where space “ends”…
Mike
I’m going to try and copy the relevant bits from Fr. Stanley Jaki’s “Why The Question: Is There A God?” that hopefully will answer your question:
“If the number of stars is infinite and their distribution is fairly uniform in space, then from any point in space a ray of starlight would reach the eye. Therefore at at any of its points the sky would shine as the surface of the sun and all the time. Paradoxically, this is not the case. The sun occupies but a small area of the day sky and the total amount of starlight visible at night is a small fraction of the light of the full moon. Dark indeed is the sky at night and seems to bespeak cosmic finitude.”
The point here is that if the universe is infinite, than the infinite light from infinite numbers of stars should be lighting our nights and days. Problem being, they don’t! Wilhelm Olbers (a nineteeth-century German physician-astronomer) offered the partial absorption of light through an “ether” as a solution, however, this proved false thermodynamically: and so we’re stuck with the paradox of dark nights.
Dr. Jaki goes into a very brief history of how various physicists such as Lord Kelvin tried to cope with this paradox—in Lord Kelvin’s argument, “our Milky Way was taken to be the principal part of the visible stellar realm. Therefore, so went the argument, negligible was all that starlight that reached us from even an astonishingly large cosmic space beyond the MIlky Way.” However, it’s not possible to escape the “paradox posed by infinite spaces stretching beyond the Milky Way, full of other light-emitting stars or galaxies.” In short, it could not be denied that at least a minute portion of that light had to reach earth: the multiplication of any small quantity (however negligible) with infinity, could only yield an infinite quantity. Therefore, we ought to have no dark nights if the universe were infinite: we do, and so it can be shown that the universe is NOT infinite. Nor could the infinite be comprehended by physicists anyway: the physicist must measure in order to reach physical truth, but there is no way to measure an infinite extension.
However, as you point out, the idea of a finite universe comes with the idea of boundaries; that is, that one could sit at the “edge” of such a universe. This idea, though, only justifies an infinite universe in an abstract way through finite lenses, as though we can truly comprehend infinity. We can’t. One can’t realize, for example, an actual infinite quantity: any quantity will be a number, which can only be finite because any number is finite. One solution is to represent space as a kind of “saddle”, as others here have mentioned: it has a special curvature and is very thin at times. This means that the universe must be a very specific thing, but anytime one is faced with a very specific thing, you’re stuck with the metaphysical question: why this very specific thing and not something else?
Here’s Fr. Jaki: “Therefore to eliminate the absurd possibility that one might reach the edge of the universe and, sitting down there, swing one’s feet beyond it, that finite quantity of matter had to be cast into a four-dimensional manifold, in which no straight line is permissible. There all permissible lines of motion resemble a curve. Therefore no body can move to the edge of the material universe, and much less beyond it…” “It is clear that such a cosmological model is something very specific. Therefore it poses, as does any other specific thing, the question: why such and not something else?”
Hope that helps.
Whew!
