Physicist Xavier Bekaert on angular momentum, quantum tops, and supergravity
What does it mean to have a spin equal to one half? What is the missing piece in the Standard model? How can we understand fundamental particles better? These and other questions are addressed and answered by Associate professor of Physics and researcher at the Laboratory of Mathematics and Theoretical Physics at the University of Tours Xavier Bekaert.
Maybe the best way to imagine elementary particles is what scientists sometimes call ‘quantum tops’ – ‘tops’ meaning the things that children make turn around themselves. And in a sense, depending on what we mean by ‘quantum’, elementary particles are some sort of infinitely small quantum tops.
The Higgs boson is the only particle that has a spin equal to zero – which means that it can turn around itself, you can make any angle around it and it still looks the same.
‘Higher-spin gravity’ is the name that we give to the generalized theory of gravity – so not only spin 2, but higher, not only the graviton, but other particles of spin greater than 2, but which are massless. This theory is supposed to be a very exotic extension of general relativity, which still remains very mysterious – we have some equations, but we don’t even have all equations.