For convenience, the argument again:
(1) Whatever begins to exist has a cause.
(2) The universe began to exist.
(3) The universe has a cause.
Today I want to discuss the premises of the argument. Of course, I cannot cover in great detail all the issues involved, but I do want to mention the most important points.
The first premise should be pretty much self-evident to most. Intuition and accumulated life experience tell us that things don't just pop into existence totally uncaused. Believe it or not though, there have been several objections to this premise.
Because of their generally complex and abstract nature, however, I will not cover these objections here. If you are curious, feel free to leave a comment about it and I'll be glad to discuss it there.
The second premise, on the other hand, requires some support. Especially since until very recently (the last sixty years or so) the prevailing view, even among physicists, was that the universe was eternal.
There are a couple of ways to approach this premise: philosophically and scientifically.
Philosophy: There is a very simple philosophical argument that shows, fairly convincingly I think, that the universe is not eternal. Think about it: if it were eternal, then it would contain an infinite series of past events. But it is impossible to traverse an infinite series, so it seems that we could never have arrived at the present moment. Therefore, the universe cannot have an infinite past.
Here's another. An actual infinite is impossible. If the universe were eternal, then it would be an example of an actual infinite. Therefore, it can't be eternal.
But how do we know an actual infinite is impossible? In short, David Hilbert.
Hilbert was a German mathematician responsible for a very interesting (and mind bending) thought experiment. He asks us to imagine a hotel with an infinite number of rooms. Once we have this in our heads, imagine that an infinite number of guests arrive to check in, so that the hotel is now full. But then infinitely more guests arrive, also wanting a room, and so the proprietor of the hotel simply moves every guest in room n to room 2n, thereby freeing up an infinite number of rooms. This could obviously continue indefinitely.
The thought experiment actually gets much more complex than this, but to avoid confusion, let's just say that such a hotel results in clear absurdities (even contradiction) and so is obviously impossible in the real world. It is merely an abstraction meant to help us understand infinite sets. Even Hilbert himself said, "...the infinite is nowhere to be found in reality." 1
But what about the scientific evidence? What has modern cosmology shown us about the beginning of the universe?
A whole lot. In fact, far more than I can even mention here. Suffice it to say that nearly every serious scientist that studies these things today is convinced that the universe had a beginning a finite time ago. I'll give two brief examples.
In 1964, physicists Arno Penzias and Robert Wilson accidentally found the straw that broke the proverbial back of the eternal universe idea. After building a new antenna, they noticed a radio noise that was not accounted for, a noise that would later come to be known as 'cosmic microwave background radiation.' It's basically radiation left over from the initial explosion of the universe, and we find it no matter where in the universe we look. Penzias and Wilson were later awarded the Nobel prize for this finding.
Secondly, physicists predicted that this background radiation, though seemingly constant across the universe, ought to contain slight fluctuations since in order for galaxies to form, the density of the very early universe (what we're looking at with this background radiation) would need to vary in places. And sure enough, upon closer examination, scientists found very small fluctuations in this radiation corresponding to galaxy formation. They also won a Nobel prize.
And I haven't even mentioned such important and persuasive topics as the expansion of the universe, redshift, the 2nd law of thermodynamics, or Einstein's General Theory of Relativity. No other theory even comes close to the Big Bang in explaining all these things.
The universe had a beginning. The logical and inescapable conclusion, then, is that it also had a Cause.
1 From "On the Infinite" in Philosophy of Mathematics, ed. by Benacerraf and Putnam.