This week we're asking the most fundamental question of faith: how do we know God exists? If you say that you believe in God and that's good enough for you, atheists will counter that they don't believe in God and that's good enough for them. And they're right--if all we have is our subjective opinion that God is real, we don't have much of a foundation to build on.

The most popular response to our question is to ask how there can be a creation without a Creator. (This argument is known to theologians and philosophers as the "cosmological argument for God's existence," reasoning from the "cosmos" or world.) You say that the universe began as a Big Bang--I ask where the Big Bang came from. I say that life began as a cell floating in a pool of water--you ask who or what made the water. Since you and I populate a world where every effect has a prior cause, it's easy to think that the world came from somewhere or Someone. This "First Cause" (to use Aristotle's term) we can call "God."

Unfortunately for those of us who like to use this approach, it doesn't really prove as much as we wish it would. For instance, scientists tell us that our universe is running down (restating the Second Law of Thermodynamics). Some day all energy will be converted to matter and everything will collapse on itself. Not today or tomorrow, but perhaps 10 to the 150th power (that's a 1 followed by 150 zeroes) years in the future. Your Christmas plans are probably safe.

These cheery optimists call this delightful day "heat death" and say that it will convert the entire universe into a single "black hole" (restating the Third Law of Thermodynamics). Atheists then ask: Who's to say that this is not how the Big Bang started? Maybe the previous universe collapsed and then blew up creating the present one. No God required.

Yet another way to look at the universe is to suggest that history moves as a circle rather than a line, with a succession of Big Bangs. Skeptics cannot prove these theories to be right, of course. But we can't prove that they're wrong.

The Bible obviously says that God made the universe, and predicts that he will turn history into eternity one day (2 Peter 3:10; Revelation 21:1-5). But it would be impossible to prove these claims unless we and the person we want to convince were both present at the beginning of time. Using God's word to prove God's existence is probably the dictionary definition of circular reasoning. So let's move on tomorrow