The Final Stretch: Candidate's Day
Are We There Yet?

The Trouble With Physics

Believe it or not, but I've been reading a book on theoretical physics. Yes, really. (You know how there are "cat" people and "dog" people? Well, there are "math" engineers and "physics" engineers. I am a math one. And a dog person. So reading physics amounts to going to the dark side.) It's called "The Trouble with Physics", and it's a fascinating read. It describes, as mentioned in the subtitle, "the rise of string theory, the fall of a science, and what comes next." The reason I find the book fascinating is because the author, Dr. Lee Smolin, who has worked on string theory but has become mildly critical of it, narrates how a mathematical theory who seems deeply flawed and can neither be proved nor disproved in experiments (and won't be in the foreseeable future) has come to sweep the field of theoretical physics, to the extent that young researchers now feel pressured to pursue that line of research, "because it is perceived as the ticket to a professorship at a university. And they are right: in the United States, theorists who pursue approaches to fundamental physics other than string theory have almost no career opportunities. In the last fifteen years, there have been a total of three assistant professors appointed to American universities who work on approaches to quantum gravity other than string theory, and these appointments were all to a single research group. Even as string theory struggles on the scientific side, it has triumphed within the academy." (p.xxii, paperback edition).

The issue, it seems, is that the mathematical theory is too mesmerizing for researchers to admit it leads to ridiculous conclusions in practice. The basic idea appears vaguely reasonable at first: particles should not be viewed as points, but as rubber bands. (Since rubber band theory doesn't exactly sound "sexy", it got renamed string theory.) Alright, maybe at the microscopic level, particles could be string-like rather than point-like. I'll grant them that. Unfortunately, that opens the door to a variety of problems. "After a few years' work, it was found that string theory, as a fundamental theory, could be consistent with special relativity and quantum theory only if several conditions were satisfied. First, the world had to have twenty-five dimensions of space [rather than three]. Second, there had to be a tachyon - a particle that goes faster than light."(p.105) The author deadpans: "The world does not appear to have twenty-five dimensions of space. Why it is that the theory was not just abandoned then and there is one of the great mysteries of science." (ibid.)

Smolin acknowledges that this "reliance on extra dimensions deterred many people from taking string theory seriously before 1984" and that the "tachyons had never been seen; even worse, their presence signaled that the theory was unstable." (ibid.) But some researchers kept forging ahead, and found much of their motivation simply in the fact that the theory was just too "beautiful" to give up on. The word 'beautiful' comes up a lot to describe that framework. For instance: "One of the most beautiful features of the theory [is] a kind of unification of motion and forces." (p.107) Later the number of space dimensions required to make the theory work was reduced from twenty-five to nine, which I guess didn't sound too bad, and enthusiasm for string theory swelled when it was established the theory did not suffer from "a certain dangerous pathology afflicting many unified theories, called an anomaly." (p.114) I'm not going to get into the details of the theory and all the issues it has, but, as my last quote, the following paragraph on p.136 will give you an idea of how ridiculous this all has become (warning - put down that mug and swallow that sip of coffee before you read on): "Later that year, Witten gave the so-far-undefined theory a name. The act of naming it was brilliant: He called it simply M-theory. He didn't want to say what "M" stood for, because the theory did not yet exist. We were invited to fill in the rest of the name by inventing the theory itself." OH MY GOD. THESE PEOPLE ARE CRAZY. 

While the temptation of favoring beautiful theories for the sake of beauty has been pushed to the extreme in physics, it can be found in many other disciplines, including my own, operations research - academics have long had a weakness for elegant formulas and mathematical theorems. Since operations research models a lot of business problems involving customer behavior, it can be hard to formulate and test precisely assumptions regarding, say, people's price sensitivity. Fortunately, in contrast with theoretical physics, we do get access to real-life data, at least if we develop partnerships with industry sponsors - one of the reasons why the National Science Foundation has been pushing toward more collaborative efforts. I for one don't want to become embroiled in a "string theory"-like controversy, although the diversity in operations research applications would make it difficult to enforce conformity the way physics departments have done. At conferences, I have found it less usual (compared to, say, five years ago), at least in the well-attended sessions, to hear results sounding like (and of course this is a caricature): "if pigs could fly and we lived on Mars, this beautiful closed-form formula would hold," (emphasis on 'beautiful'), which might be the one advantage of the National Science Foundation's budget crunch. Universities' pressure on their faculty members to get publications, though, incites researchers to adopt similar frameworks to those already in print; one of the people who have authored that early framework will likely be a reviewer to the newly submitted paper; people often feel a change means their approach was inadequate and interpret this as a personal criticism, which they obviously do not greet with unbridled enthusiasm. But the wide array of problems we can work on guarantees we as engineers will never face a situation as dramatic as theoretical physics, and I am grateful for that.

Comments

Some people argue that Smolin is a mediocre scientist, and that his frustration for not being able to give any relevant contributions to theoretical physics has led him to write that book. Someone who is particularly aggressive towards Smolin is LuboŇ° Motl ( http://en.wikipedia.org/wiki/Lubo%C5%A1_Motl ), a very talented and highly opinionated Czech theoretical physicist who was at Harvard and is now outside institutionalized Science (guess why!). For an example of Lubos' attacks on Smolin, check this out:
http://nige.wordpress.com/2006/08/31/assistant-professor-lubos-motls-disgraceful-attack-on-lee-smolin

Many people seem way too eager to criticize String Theory without knowing anything about it. I think Smolin's views may be too biased. There are many heavy-weight people doing work on String Theory: Ed Witten, Steven Weinberg, Leonard Susskind, Brian Greene, Lisa Randall, etc etc etc. This group is worth its weight in gold. Are they all crazy? I doubt it. String Theory is a work in progress, and I think it would be wise to give it time to mature. As usual, I am against over-generalizations, and I would argue that it's not whether String Theory is good or bad, but which work in String Theory is good or bad. Many extremely smart people have dedicated many years of their lives to String Theory, and I think it's unlikely that we're witnessing collective madness here.

For a good overview of String Theory, Brian Greene's TED talk is truly awesome! :-)
http://www.ted.com/index.php/talks/view/id/251

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