Theoretical Particle Physicist and Cosmologist; Victor Weisskopf Distinguished University Professor, University of Michigan; Author, Supersymmetry and Beyond
The Facility Whose Data May Help Formulate And Test Ideas About A Final Theory Of Our Universe Is Now Working

The most interesting recent physics news is that the Large Hadron Collider (LHC) at the European laboratory CERN, in Geneva, Switzerland, is finally working at its highest ever design energy and intensity. Why that is so important is because it may at last allow the discovery of new particles (superpartners), which would allow scientifically formulating and testing a final theory underlying the physical universe.

As Max Planck immediately recognized when he discovered quantum theory over a century ago, the equations of the final theory should be expressed in terms of universal constants of nature such as Newton’s gravitational constant G, Einstein’s universal speed of light c, and Planck’s constant h. The natural size of a universe is then tiny, about 10-33 cm, and the natural lifetime about 10-43 seconds, far from the sizes of our world. Physicists need to explain why our world is large and old and cold and dark. Quantum theory provides the opportunity to connect the Planck scales with our scales, our world and our physical laws, because in quantum theory, virtual particles of all masses enter the equations and mix scales.

But that only works if the underlying theory is what is called a supersymmetric one, with our familiar particles such as quarks and electrons and force mediating bosons (gluons, and W and Z bosons of the electroweak interactions) each having a superpartner particle (squarks, selectrons, gluinos, etc.). In collisions at LHC the higher energy of the colliding particles turns into the masses of previously unknown particles via Einstein’s E=mc2.

The theory did not tell us how massive the superpartners should be. Naively there were arguments they should not be too heavy (“naturalness”), so they could be searched for with enthusiasm at every higher energy that became accessible, but so far they have not been found. In the past decade or so string- and M-theories have been better understood, and now provide clues to how heavy the superpartners should be. String-theories and M-theories differ technically in ways not important for us here. To be mathematically consistent, and part of a quantum theory of gravity and the other forces, they must have 9 or 10 space dimensions (and one time dimension). To predict superpartner masses, they must be projected onto our world with three space dimensions, and there are known techniques to do that.

The bottom line is that well-motivated string/M-theories do indeed predict that the Large Hadron Collider run (Run II) that started in late 2015, and is planned to move ahead strongly in early 2016, should be able to produce and detect some superpartners, thus opening the door to the Planck scale world, and promoting study of a final theory to testable science. The news that the LHC works at its full energy and intensity, and hopefully can accumulate data for several years, is a strong candidate for the most important scientific news of recent years.