Where are we heading?

Every summer the IAS in Princeton runs a program for graduate students and postdocs called “Prospects in Theoretical Physics”. It’s going on now, with this year’s topic LHC Physics. Much of the program is devoted to the important but complex technical issues of extracting physics from LHC data. Things began though with a talk on Where are we heading? from Nati Seiberg designed to explain to students how they should think about the significance of the LHC results and where they were taking the field.

Most of the talk was about the hierarchy problem and “naturalness”, with the forward-looking conclusion the same one that Seiberg’s colleague Arkani-Hamed has been aggressively pushing: the main significance of LHC results will be telling us that the world is either “natural” (likely by discovering SUSY) or “unnatural” (in which case there’s a multiverse and it’s hopeless to even try to predict SM parameters). Given the negative results about SUSY so far, this conclusion pretty much means that the students at the IAS are being told that the LHC results mean it’s the multiverse, and they shouldn’t even think about trying to figure out where the SM comes from since that’s a lost cause. The talk ends with the upbeat claim that this is a “win-win situation”: reaching the conclusion that the LHC has shown we can’t learn more about where the SM came from will be a great scientific advance and “The future will be very exciting!”. Seiberg does at one point make an interesting comment that indicates that he’s not completely on-board with this conclusion. He notes that there’s a “strange coincidence” that theorists are making this theoretical argument about the necessity of giving up at just exactly the same time in our history that we have run out of technological ability to explore shorter distances. A “strange coincidence” indeed…

For more conventional wisdom along these lines, see Naturally Unnatural from Philip Gibbs, which also argues that what we are learning from the LHC is that we must give up and embrace the multiverse.

Frank Wilczek has just made available on his web-site a new paper on Multiversality. It has the usual arguments for the multiverse, although unlikes Seiberg/Arkani-Hamed he doesn’t try to claim that this is an exciting positive development, closing with a “lamentation”:

I don’t see any realistic prospect that anthropic or statistical selection arguments – applied to a single sample! – will ever lead to anything comparable in intellectual depth or numerical precision to the greatest and most characteristic achievements of theoretical physics and astrophysics…

there will be fewer accessible features of the physical world for fundamental theory to target. One sees these trends, for example, in the almost total disconnect between the subject matter of hep-th and hep-ex.

and a “warning

There is a danger that selection effects will be invoked prematurely or inappropriately, and choke off the search for deeper more consequential explanations of observed phenomena. To put it crudely, theorists can be tempted to think along the lines “If people as clever as us haven’t explained it, that’s because it can’t be explained – it’s just an accident.”

He does see possibilities for understanding more about the SM in two places, the SUSY GUT unification of couplings and axions as an explanation of the smallness of the QCD theta parameter. The last part of the paper is about axion cosmology and anthropics. Wilczek has written about the stories of the 1981 origin of the SUSY GUT unification argument and the 1975 birth of the axion. It’s striking that we’re 32 and 38 years later without any idea whether these ideas explain anything. A depressing possible answer to “Where are we heading?” would be an endless future of multiverse mania, with a short canonical list of ancient, but accepted ideas about fundamental theory (SUSY Guts, string theory, axions) that can never be tested.