Author: dabacon

I have often heard it describe that to be a great philospher, one must grab ahold of a single idea, put on blinders to all opposing thoughts, and then run with it. This is not to accuse all philosophers of such maniacal tunnel vision, but there certainly is at least a grain of truth in this idea. And it is certain the one part of philosophy as practiced by philosophers which drives physicists absolutely nuts!
Why all of the sudden philosophy bashing? Well I just finished reading A World Without Time: The Forgotten Legacy of Gödel and Einstein by Palle Yourgrau. From the title you would guess that this book is a discussion solely of the friendship between Einstein and Gödel, but really the book is a vigorous argument that Gödel should be taken seriously as an important philosopher. In particular Yourgrau believes that Gödel’s work in general relativity and his argument “against time” have been overlooked by philosophers as is of great importance. The book, therefore, will be of more interest to those familiar with Kant and Wittgenstein than to those who are interested in the logic and the physics that Gödel and Einstein are usually associated with.
Now back to philosophers going overboard in one direction. Here I think that Yourgrau is so zealous in his defense of Gödel as a philosopher that he misinterprets the reason why physicists argue against the relevance of Gödel’s universe. Gödel’s universe is a cosmological solution to the equations of general relativity in which the universe is rotating. Interesting in this solution to the equations of general relativity there exist closed timelike curves. Now I won’t get into the reasons why Gödel is interested in this universe and I don’t object to the use of this universe in philosophical discussions about the nature of time, but I think that Yourgrau’s characterization of physicist’s reaction to solutions to Einstein’s equations with closed timelike curves isn’t quite right. In particular he bluntly dismisses the chronology protection conjecture as totally adhoc. Or, in his words

Just as David Hilbert tried at first to avoid the consequences of the incompleteness theorem by inventing a new rule of logical inference out of whole cloth, so too the relativistic establishment, in the person of Stephen Hawking, tried to get around the embarrassing consequences introduced by the Gödel universe. If the annoying Gödel universe was consistent with the laws of general relativity, why not change the laws? Hawking thus introduced what he called the “chronology protection conjecture” (though a better name would have been the “anti-Gödel amendment”), which proposed a modification of general relativity whose primary goal was to rule out the possibility of world models like Gödel’s, with their awkward chronologies premitting closed temporal loops and causal chains with no beginning. Despite having, as Russell noted in a different context, all the advantages of theft over honest toil, Hawking’s chronology protection conjecture has won few adherents, its ad hoc character betraying iteself.

This characterization of the chronology protection conjecture seems to me very misleading. Why? Because the chronology protection conjecture isn’t just an “add-on” to general relativity: it is the conjecture that general relativity when combined with the other laws of physics does not allow for closed timelike curves. This is different from arguing, as Yourgrau later does, that the objection is simply that Gödel’s universe is not our universe: it is arguing that the more complete laws of physics disallow closed timelike curves. Of course, if your blinders are on, like a good philosoher, then perhaps this distinction is not important. But as a physicist, where there is more than just general relativity to consider, the chronology protection conjecture is a different sort of statement and has considerable evidence in favor of it (and I think most phyisicsts don’t have much of a problem with the chronology protection conjecture, in constrast to Yourgrau who thinks that most people have a problem with it.)
So read “A World Without Time…” with your “physicist” or “scientist” mode shut off and you will be fine. Is it actually possible to turn off these modes? Only if you were a literature major like me 😉