Home > posts > Kill every rooster that doesn’t lay eggs : comments on Loeb’s “Theoretical Physics is Pointless without Experimental Tests”

Kill every rooster that doesn’t lay eggs : comments on Loeb’s “Theoretical Physics is Pointless without Experimental Tests”

August 13, 2018

Abraham Loeb, professor of Astronomy at Harvard University, recently published an op-ed in Scientific American critiquing theoretical physics (Loeb 2018). I’m confused who the audience is when it’s published in Scientific American. I’m afraid that my pharmacist will get a few wrong impressions about what theoretical physicists are doing these days from the article, but I will ignore audience questions and assume that it was addressed really to theoretical physicists with a plea to reflect on what we are doing.

In that sense I am very happy that he wrote it. One’s views should be expressed openly, where we have a chance to reflect on what we agree with and what we disagree with, improving our own vision and behavior as a community of what it means to be a good theoretical physicist. My criticisms and agreements below are in that spirit.

There is no “new culture”

To begin, I question the claim that there is “a new culture of doing theoretical physics without the need for experimental verification.” As I see it, there is nothing new under the sun. For a hundred years there have been theoretical physicists attached closely to the details of past, current and future experiments. That exists today too, in spades. To give an example close to Loeb’s interests, hundreds of theorists are working on experimental ideas to search for dark matter, which also has some prior experimental support (galaxy rotation curves, CMB, etc.) and justification that was understood in part because of original theoretical work.

Loeb would probably not disagree with the above statement on the existence of vast numbers of theorists working closely with experiment firmly in mind, and would probably say that when he said “new culture” he is referring really to a “new subculture” that is allowed to thrive doing theoretical physics without the need for experimental verification. If that was meant, the word “subculture” should have been used in the actual writing. Surely anybody who is not within theoretical physics will read the “culture” statement as declaring a sea change in the theory world, and be alarmed that nobody cares about experiment any more in the theory community, which of course would be a very wrong impression.

Second, it is not “new” that there exists a thriving subculture of theoretical physicists who do not pay close attention to experiment. This has been going on for as long as theoretical physics (or theoretical anything) has existed. It’s part of the meaning of “theoretical” that there should be some of that. Since time immemorial theoreticians have explored the more speculative and developed more mathematical foundation work. Not only is it ok to have such people, but they are needed. Should we have told Von Neumann to fold up his notebook and be quiet because he was recasting quantum mechanics in a more elegant mathematical language that had little to do with identify new experimental signatures? No. His work has greatly aided our understanding and use of quantum mechanics today. Should we have told all physicists who began careful study of group theory and topology more than a hundred years ago, “Shut it down! I don’t see any experiments listed in your notebooks, just a bunch of so-called ‘elegant’ mathematics!”? No. The value of foundational mathematical work to systematize more efficiently our hard-gained knowledge, which in turn then leads to new insights and deeper understanding, should not be dismissed.

Einstein was simply wrong, with no grand lesson to learn

Loeb continues the argument by criticizing Einstein for having several wrong ideas, including not believing in the existence of gravitational waves, and seems to be arguing that thought experiments are therefore bad and misleading, and we have to glue ourselves to experiment or we go off the rails. First, Einstein didn’t screw up on gravitational waves because of a thought experiment. He just hadn’t sorted out gauge dependence issues properly, and made technical blunders. In other words, he failed briefly at being a good theoretical physicist. That simple. Others had it figured out and believed in gravitational waves at that time even, including Infeld and Robertson, who appears to have mostly convinced the older Einstein of his errors (Kennefick 2005). The field of gravitational wave physics was born out of theoretical physics despite Einstein’s bumbling, and the field matured over time because of this long-ago and continuing theory work, whose experimental detection prospects were considered very dim for many decades.

“Galilean Oath” ignores diversity of skill sets

Pressing further the central importance of experiment, Loeb suggests that theoretical physicists should take a “Galilean Oath”, in which “they agree to gauge the value of theoretical conjectures in physics based on how well they are tested by experiments within their lifetime.” I understand the motivation for this statement, and am sympathetic to the pressures it intends to apply to our thinking. However, it probably would be a bad policy. Should Hawking have buried his work because he couldn’t think of a way to test radiation from a black hole? No. Should Higgs have buried his work because he personally couldn’t think of a way to experimentally test for a propagating scalar field predicted by the theory? No.

My biggest concern about the Loeb article is its lack of acknowledgement of the long and fractured time arc behind many great experimental discoveries. In many cases it starts with a set of T-people making clever ideas about how the universe is organized, and a different set of P-people who figure out how those ideas can be tested, and yet a different set of E-people who figure out how to construct the experiments and carry them out. Each group typically is incapable of doing the work of another group. Sometimes there are individuals who can do both T and P work, or both P and E work, but I can’t think of anybody since Enrico Fermi who could do two of these categories extremely well, at the level needed for the greatest breakthroughs in science. Going from T to P to E takes a lot of development at each stage, and a lot of time to hand off the baton from one stage to another. The more than half-century story behind the Higgs boson discovery is an illustration of this very long and fractured time arc (Wells 2018). Having a T person, who is highly valued, take the “Galilean Oath”, is like telling a rooster on the farm that he too must lay eggs.

Showing off intellectual power

I think the most important point in Loeb’s article is contained in the sentence: “Given our academic reward system of grades, promotions and prizes, we sometimes forget that physics is a learning experience about nature rather than an arena for demonstrating our intellectual power.” There is much in this sentence that I like. Let me try to explain exactly how I agree with it.

In Geneva I was acquainted with a titan of industry, who worked in areas ranging widely from commodities trading to the manufacture of machines. He also had a lot of interest in physics and CERN and he had employed some individuals leaving CERN for industry. At the time I knew a good graduating theory PhD student who was interested in going into industry and I talked to him about whether there was a position for him. He made a very interesting statement, which I paraphrase here: “You theoretical physicists are all about big brains, but I’m all about working hands. I need my employees to see essential things and get them done, not spend forever perfecting amazing ideas that won’t work. If you think he can understand the difference, I’ll take a look at his CV.”

Loeb’s statement gets at the heart of this very same issue the industrialist brought up. As a field we reward people more for the wild and interesting speculative leaps with suspect empirical impact that demonstrates a brilliant ray of intellectual power (big brains) than we do people who, for example, carefully and reliably work through a hard, but needed three-loop calculation (working hands), which by the way also takes big brains but is not respected as such. This reward system could hurt science if the imbalance grows. Loeb may feel that the imbalance is large enough now that it is hurting science, and it is worthwhile considering that possibility.

Along these lines, years ago when I was interviewing for a faculty position at a prestigious university, a distinguished professor said, “We are much more interested in hiring a theorist who has a chance to show up in the New York Times for brilliant new theory work, than somebody who is guaranteed to be useful for experiment.” I was young and just took his words for granted that there was a real and legitimate choice they had to make between these two incompatible possibilities. I now know to be much more skeptical of such dichotomies. A particularly compelling example of no dichotomy existing is the inspiring story of theoretical physicist Kip Thorne and his role in the discovery of gravitational waves, which resulted in a Nobel Prize last year. I think Loeb is trying to tell us that we must not stop supporting and encouraging the up and coming Kip Thorne’s in theoretical physics — working hands with the single-minded doggedness to simply learn more about nature. Can’t argue with that.

Kennefick, D (2005). Einstein versus the Physical Review, Physics Today 58, 43.

Loeb, A. (2018). Theoretical Physics is Pointless without Experimental Tests. Sci Am

Wells, J.D. (2018). Beyond the Hypothesis: theory’s role in the genesis, opposition, and pursuit of the Higgs boson. Stud.Hist.Phil.Mod.Phys. 62, 36.

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