Are there more than 3 generations of particles in the Standard Model? Updated 2024-12-15 +Created 1970-01-01
PHYS 485 Lecture 5: Standard Model and Feynman Diagrams by Roger Moore (2016)
Source. www.youtube.com/watch?v=AKtN6ajjSQo&t=1474 gives an argument why there might only be 3 generations of particles.A suggested at Physics from Symmetry by Jakob Schwichtenberg (2015) chapter 3.9 "Elementary particles", it appears that in the Standard Model, the behaviour of each particle can be uniquely defined by the following five numbers:
E.g. for the electron we have:
- mass:
- spin: 1/2
- electric charge:
- weak charge: -1/2
- color charge: 0
Once you specify these properties, you could in theory just pluck them into the Standard Model Lagrangian and you could simulate what happens.
Setting new random values for those properties would also allow us to create new particles. It appears unknown why we only see the particles that we do, and why they have the values of properties they have.
Initially light was though of as a wave because it experienced interference as shown by experiments such as:
But then, some key experiments also start suggesting that light is made up of discrete packets:and in the understanding of the 2020 Standard Model the photon is one of the elementary particles.
- Compton scattering, also suggests that photons carry momentum
- photoelectric effect
- single photon production and detection experiments
This duality is fully described mathematically by quantum electrodynamics, where the photon is modelled as a quantized excitation of the photon field.
Initially there were mathematical reasons why people suspected that all boson needed to have 0 mass as is the case for photons a gluons, see Goldstone's theorem.
So people started theorizing some hack that would fix up the equations, and they came up with the higgs mechanism.
Can be contrasted with baryons as mentioned at baryon vs meson vs lepton.