Smolin, Arkani-Hamed, and Randall at APS: my recollections(adsbygoogle = window.adsbygoogle || []).push({});

These recollections are probably substantially inaccurate in the details and should be treated with caution. I am not a court recorder.

Lee Smolin gave a clear explanation of the recent work on the Bilson-Thompson trinion braid model. The part I remember most was that quarks etc. are topological invariants. Those with one or two crossings are trivial or reducible so the model is based on those with three irreducible crossings. I think he said that they were causal, but not local. Also, that they were local in the braid, but not local in spacetime. At one point he speculated that if the crossings were of the order of the Planck length, and the “moves” happened every Planck time, you could estimate the spread of a newly formed object through the background braid or weave and come up with a very rapid spread.

At the end of the presentation, I shot my hand up real quick and got to ask the first question. I said I was really curious about the photon and graviton, but would ask an easier question. Since the model has quarks, what do the gluons look like? Smolin replied that they were already working on that and thought that it would involve braids with more than three crossings. He pointed out that there are an infinite number of possible braids with higher numbers of irreducible crossings and suggested that this could take care of all the gauge bosons. (In answering a later question, he also suggested this as a means of getting the second and third generation of standard model particles) . He then mentioned a few more points about the gauge group and gauge bosons that mostly went over my head. He concluded by saying again that they were working on it, and expected to have results out soon. I think I asked a better question than I realized. Several of the later questions also focused on the gauge groups or gauge bosons. Of course, the most exciting part is that they expect to have more results soon.

Nima Arkani-Hamed covered a lot of ground in his talk. I will try to relate two or three highlights:

The first is a joke. Nima compared particle physics and cosmology to a boy and a girl. Then he said it was a very lopsided relationship. Particle physics gave and gave. (Neutrinos, Neutralinos, Axions. Big Bang Nucleosynthesis. Inflation). But Cosmology never paid any attention. She never gave anything back. But now, finally, she hasgiven something back. Nima shows a sketch of a girl hitting a boy over the head with a big hammer, labeled Lambda. Unfortunately, he says, cosmology is hitting us in the head with this incredible value of lambda.

He went on to say that of course we should check for quintessence or other scalar fields and measure the Hubble parameter as a function of time, etc., but that as far as he was concerned, theorists should assume that it really was lambda, an Einstein type cosmological constant, until proved otherwise. He was quite emphatic about this point.

(This surprised me, but what do I know about string theory or cosmology)

He then went on to discuss split supersymmetry. He pointed out that making the fermions relatively light and the bosons relatively heavy preserves the successes of supersymmetry and gets rid of most of its problems. He also pointed out that split supersymmetry is a rather strange and very unlikely theory from an apriori viewpoint.

He pointed out that if siandard simple supersymmetry were real, therb are many low mass manifestations we should have already seen, which have been diligently searched for but not found. In effect, he pretty strongly predicted we won't see standard supersymmetry, if I understood what he was saying.

He then went on to discuss the notorious landscape. He said that if it exists at all, the landscape is real, although perhaps very far away. He said there is no known way to see it, but also no proof that it is impossible to see it. (I hope I am remembering this part correctly). He also indicated that the landscape was in some sense an unusual or unexpected idea, but that it was supported by things other than theory such as the observation of inflation and the Weinberg prediction of the magnitude of the cosmological constant. He then suggested that if we see split supersymmetry, a very unusual theory, it is another support for the idea that a huge landscape exists, and that we are in one of its more unusual corners.

(Me speaking: I greatly enjoyed the joke, and of it all, I was most impressed by the low energy evidence suggesting that we will not see standard supersymmetry. I hadn't really grasped the importance of this before.)

Lisa Randle gave an evening public talk on her book Warped Passages. The Texas schools had brought in a lot of junior high school students. (I had heard this talk before in Washington and also brought my 14 year old daughter to hear her speak). After the talk, Lisa was grilled by the 9th graders (and some of their teachers) while the professional physicists, many of whom were there, kept silent. A local sponsor gave a free copy of Lisa's book to every student who asked a really good question. Lisa was very good at thinking on her feet and answering every question in an easy to understand, but still technically correct way. Mini black holes were asked about. Lisa said they were a possibility, but basically de-emphasized them. When asked what might be seen at LHC that would support her theories, she mentioned Kaluza-Klein towers.

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# Smolin, Arkani-Hamed, and Randall at APS: my recollections

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