"A Look to the Heavens"

“How big is the universe? Could it be infinitely large? If the universe has an edge, what is beyond the edge? And if the universe had a beginning, what was going on before that? Our experience of the everyday world does not prepare us to grasp the concept of an infinite universe. And yet, trying to imagine that the cosmos actually has a boundary does not make things any easier.

There is an edge to what we are able to see and could ever possibly see in the universe. Light travels at 300,000 kilometers per second. That's top speed in this universe—nothing can go faster—but it's relatively slow compared to the distances to be traveled. The nearest big galaxy to our Milky Way, the Andromeda galaxy, is two million light-years away. The most distant galaxies we can now see are 10 or 12 billion light-years away. We could never see a galaxy that is farther away in light travel time than the universe is old—an estimated 14 billion or so years. Thus, we are surrounded by a "horizon" that we cannot look beyond—a horizon set by the distance that light can travel over the age of the universe.

This horizon describes the visible universe—a region some 28 billion light years in diameter. But what are the horizons of a civilization that inhabits the most distant galaxies we see? And what about galaxies at the limits of their vision? There is every reason to think that the universe extends a long way beyond the part of the universe we can see. In fact, a variety of observations suggest that our visible patch may be a small fraction—maybe an infinitely small fraction—of the whole universe.

This view of the universe fits with the currently popular idea that the universe began with a vast expansion of size. The idea describes a kind of undirected energy present in the vacuum of space, called scalar fields, that somehow got channeled into a process called "inflation." By conservative estimates, the universe expanded so much during this period that something the size of an atom inflated to the size of a galaxy.

If this grand idea is correct, then the universe is larger than we ever could have imagined. But the question remains: Is there a boundary, and if so, what lies in the voids beyond? The answer, according to some cosmologists, is truly mind-boggling. If the universe sprung forth in this manner, then probably inflation has occurred in other places, perhaps an infinite number of places, beyond our horizon and outside of our time. The implication is that there are other universes, perhaps similar to ours or vastly different, each in its own space and begun in its own time.”

- Brent Tully- http://www.pbs.org/wgbh/nova/universe/howbig.html