Saturday, October 10, 2015

Quote Of The Day: William Lane Craig Is Wrong On Cosmic Time

William Lane Craig really doesn't like the B-theory of time, also known as eternalism. He's written whole books and essays trying to debunk it and to promote the A-theory of time, also known as presentism. The reason why is clear. Craig's favorite go-to argument for god's existence is the kalam cosmological argument, and it presupposes the A-theory of time. In fact, on the B-theory, the argument is useless. So Craig has spent many calories trying as hard as he can to make the case for the A-theory. One of them is this notion that "cosmic time" allows us to have an objective reference frame, which is ruled out under special relativity which says that all reference frames are subjective. It's even convinced another atheist blogger at one point that the relativity of simultaneity doesn't imply a block universe and the eternalism that describes it. But this is wrong, as physicist Aron Wall writes on his blog:

Now it is true that on some specially nice spacetimes, there is a naturally nice choice of time coordinate. For example in an FRW expanding universe, there is a "cosmic time" coordinate which tracks the overall size (the "redshift factor") of the universe. Some philosophers, such as St. William Lane Craig, have suggested that God's "time" might simply be this "cosmic time".

But this is a misunderstanding of the physics of our universe. The FRW metric is a just an approximation to reality. It describes a universe which is completely uniform (the same in everywhere) and isotropic (the same in every direction). This is a very good approximation on large distance scales (billions of light years), but on shorter distance scales (e.g. the solar system, or the milky way, or your living room) you may have noticed that matter is not distributed uniformly. It comes in clumps, and each of these clumps has a gravitational field which distorts the spacetime metric, making the FRW metric no longer correct. On a lumpy spacetime, the notion of "cosmic time" is not well-defined.

Aron Wall is a physicist and a devout Christian, so he certainly doesn't have a theological ax to grind here.

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