- Whatever begins to exist has a cause
- The universe began to exist
- Therefore, the universe has a cause
Skeptics, however, take issue with the second premise. They argue that the universe could be past eternal, i.e. that it never had a beginning, but this view seems to run counter to the standard Big Bang model of cosmology which states that the universe exploded into being from a single point about 14 billion years ago.
One of the most prominent cosmologists in the field is a physicist named Alexander Vilenkin, who, along with Alan Guth and Arvinde Borde, developed the Borde, Guth, Vilenkin theorem which asserts, among other things that any universe that has the characteristics that ours does, had a beginning. Vilenkin writes about the implications of this theorem in an interesting piece here.
The passages most relevant to the second premise of the above argument are these:
Inflation [of the universe] cannot be eternal and must have some sort of a beginning.Nevertheless, Vilenkin sees a problem with the first premise. He asserts that it's possible for a universe to pop into existence out of nothing:
[T]he universe could not have existed for an infinite amount of time before the onset of inflation.
This leads immediately to the conclusion that a cyclic universe cannot be past-eternal.
The answer to the question, “Did the universe have a beginning?” is, “It probably did.” We have no viable models of an eternal universe. The BGV theorem gives us reason to believe that such models simply cannot be constructed.
If all the conserved numbers of a closed universe are equal to zero, then there is nothing to prevent such a universe from being spontaneously created out of nothing. And according to quantum mechanics, any process which is not strictly forbidden by the conservation laws will happen with some probability.Two things: Vilenkin is not saying that the universe actually did begin causelessly out of "nothing," but rather that quantum theory can't rule it out.
...No cause is needed for the quantum creation of the universe.
The theory of quantum creation is no more than a speculative hypothesis. It is unclear how, or whether, it can be tested observationally. It is nonetheless the first attempt to formulate the problem of cosmic origin and to address it in a quantitative way.
Secondly, Vilenkin employs a metaphysically problematic concept of "nothing." He seems to be saying that the pre-creational state could have been a physical system of zero energy out of which the universe could have arisen uncaused. This state he defines as "nothing," but a physical state of any sort is surely not nothing. It may have no material substance and the positive and negative energies may total zero or there may be no energy at all, but if it's a physical state it's not nothing. We may have difficulty comprehending it and describing it, but at least we can say that it is something. Nothing means "not anything," and what Vilenkin describes does not fit that definition.
In any event he closes his paper with these thoughts:
When physicists or theologians ask me about the BGV theorem, I am happy to oblige. But my own view is that the theorem does not tell us anything about the existence of God. A deep mystery remains. The laws of physics that describe the quantum creation of the universe also describe its evolution. This seems to suggest that they have some independent existence.Well, with due respect to Professor Vilenkin, a good beginning to addressing the mystery can be found in the argument at the top of this post.
What exactly this means, we don’t know.
And why are these laws the ones we have? Why not other laws? We have no way to begin to address this mystery.