Archive for April, 2010


Against the B-Theory of Time

April 4, 2010

There are two competing theories of time: they are named creatively the “A-Theory” and “B-Theory”.  For an introduction, see this article at Wikipedia.  Very briefly, the A-Theory of time affirms that the past and future are not as real as the present, that is, time passes.  The B-Theory of time affirms that past, present, and future are all equally real.

If the B-Theory of time is true, then this is a good rebuttal to the Kalam Cosmological Argument (KCA).  The KCA takes as one of its premises that the universe began to exist.  But this statement doesn’t make much sense on the B-Theory of time.  That is because on the B-Theory, nothing really “begins to exist”, because “begins” is a meaningless concept.  For how could something come into being if past, present, and future are all equally real?

But surely this is a strange concept, right?  It’s strongly counterintuitive, so much so that I’m persuaded it’s false.  Here’s an argument (not exactly original) to that effect:

The “Suicidal” Son
1. If B-theory is true and special and general relativity are true, then time travel is possible.
2. If time travel is possible, then it is possible for you to kill your father before you were born.
3. It is not possible for you to kill your father before you were born.
4. Therefore, time travel is not possible.
5. Therefore, either B-theory is false or special and general relativity are false (or, of course, they are both false).

1, 2, and 3 are the premises to the argument, 4 and 5 are the conclusions.  5 is a disjunction that asks the reader to give up either the B-Theory of time or scientific theories that are very well-tested.

In premise #1, time travel is supported by general relativity if we live in a universe with closed time-like curves.  Also in premise #1, we can assume certain space-time topologies within the special relativity framework to allow for time travel.  Also of course, in premise #1 we are granting for the sake of argument that the past is equally real as the present.

Luke Muehlhauser is blogging a series summarizing the KCA, wherein he articulates the premises to the KCA and arguments supporting them.  Within the series he is withholding judgment on the argument, although at several points on his blog he has hinted at the fact that he doesn’t think the conclusion of the KCA is true at least partly because he doesn’t think the A-Theory is true.  I imagine many others who aren’t persuaded by the KCA use the B-Theory as a sort of escape hatch too.  So for all you B-Theorists out there, what do you think of this argument?