It is certainly hard to imagine a universe that extends without limit in every direction, or a universe without a beginning or end. It is equally difficult to imagine a finite universe; what is beyond the edge? Or a beginning or end in time; how can something come from nothing? how can what is cease to be?
The problems are so intractable philosophically that their resolution has generally been left to the theologians, which from a philosophical (or scientific) perspective offers no solution at all. Giordano Bruno was burned at the stake for proposing a philosophical resolution (an infinite universe) that offended theology.
An escape from befuddlement is provided by Einstein's theory of general relativity, which -- for example -- can describe a finite universe without a boundary, as the "two-dimensional" surface of a sphere is finite and without an edge. Unfortunately, multi-dimensional curved space-time is so counterintuitive that it is difficult to get one's head around it without mastery of the mathematics. Given a choice between the ancient myths of your local preacher and the obtuse mathematics of the physics professor, it's not hard to guess what most folks will opt for.
I have just received for review a new book by physics professor Chad Orzel called How To Teach Relativity To Your Dog. It's a fun romp, and clever pedagogy, but I can't imagine it making the best seller list, much less displacing Heaven Is For Real from first place.
Meanwhile, I'm reading a meditation on infinity by physics professor Anthony Aguirre, in a collection of essays called Future Science. He discusses contemporary cosmological theories based on general relativity, and in particular the rehabilitation of the idea of an infinite and eternal universe, or, more precisely, that our universe might be just one of an infinity of infinite universes. He writes in conclusion:
What seems clear, however, is that infinity can no longer be safely ignored; beautifully constructed, empirically supported, self-consistent theories have brought infinity from idle curiosity to central player in contemporary cosmology. And if correct, the worldview these theories represent constitutes a perspective shift unlike any other: in comparison to the universe, we would be not just small but strictly zero.Well, I can't imagine many folks racing to embrace that conclusion.
Oh, but wait. Aguirre adds one final sentence:
Yet here we are, contemplating -- if not quite understanding -- it all.