Far out cosmology: why no GUTS? (Introduction)

by David Turell , Wednesday, May 04, 2016, 19:49 (2907 days ago) @ David Turell

This article describes the history of the standard model, and explains why there is no grand unified model. Gravity is one of the outliers':-http://www.symmetrymagazine.org/article/a-gut-feeling-about-physics-"While that Standard Model is a very good description of the subatomic world, some important aspects—such as particle masses—come out of experiments rather than theory.-“'If you write down the Standard Model, quite frankly it's a mess,” says John Ellis, a particle physicist at King's College London. “You've got a whole bunch of parameters, and they all look arbitrary. You can't convince me that's the final theory!”-"The hunt was on to create a grand unified theory, or GUT, that would elegantly explain how the universe works by linking three of the four known forces together. Physicists first linked the electromagnetic force, which dictates the structure of atoms and the behavior of light, and the weak nuclear force, which underlies how particles decay.-"But they didn't want to stop there. Scientists began working to link this electroweak theory with the strong force, which binds quarks together into things like the protons and neutrons in our atoms. (The fourth force that we know, gravity, doesn't have a complete working quantum theory, so it's relegated to the realm of Theories of Everything, or ToEs.)-***-"GUTs also predicted that protons should decay into lighter particles. There was just one problem: Experiments didn't see that decay.-"GUTs predicted that all quarks could potentially change into lighter particles, including the quarks making up protons. In fact, GUTs said that protons would be unstable over a period much longer than the lifetime of the universe. To maximize the chances of seeing that rare proton decay, physicists needed to build detectors with a lot of atoms.-"However, the first Kamiokande experiment in Japan didn't detect any proton decays, which meant a proton lifetime longer than that predicted by the simplest GUT theory. More complicated GUTs emerged with longer predicted proton lifetimes - and more complicated interactions and additional particles.-***-"Most modern GUTs mix in supersymmetry (SUSY), a way of thinking about the structure of space-time that has profound implications for particle physics. SUSY uses extra interactions to adjust the strength of the three forces in the Standard Model so that they meet at a very high energy known as the GUT scale.-“'Supersymmetry gives more particles that are involved via virtual quantum effects in the decay of the proton,” says JoAnne Hewett, a physicist at the Department of Energy's SLAC National Accelerator Laboratory. That extends the predicted lifetime of the proton beyond what previous experiments were able to test. Yet SUSY-based GUTs also have some problems.-
***-"Hewett agrees that GUTs aren't dead yet.-“'I firmly believe that an observation of proton decay would affect how every person would think about the world,” she says. “Everybody can understand that we're made out of protons and ‘Oh wow! They decay.'”-"Upcoming experiments like the proposed Hyper-K in Japan and the Deep Underground Neutrino Experiment in the United States will probe proton decay to greater precision than ever. Seeing a proton decay will tell us something about the unification of the forces of nature and whether we ultimately can trust our GUTs."-Comment: Gravity and quantum theory don't fit. Look at article to read more and see diagrams, but they are still trying. Note empirical data is necessary for all theories.