I always thought that the standard model as a set of equations (a model) that fits observed data, without venturing far into “why this model is the governing pr

I always thought that the standard model as a set of equations (a model) that fits observed data, without venturing far into “why this model is the governing principle for our universe”. That is, it is not able to explain things like “why an electron comes with two heavier varieties”. To explain that I need to explain symmetry breaking. Consider a pencil. The equations for a balanced pencil are completely symmetric with the point of symmetry being balanced on its tip. However an actual pencil is never to be found balanced on its tip it is always lying on a side. Therefore a perfectly symmetric theory may describe a real world situation which is not in the least symmetric. The Standard Model is exactly such a theory. It is in principle completely symmetric, and there is no particular reason in it why an electron would weigh less than a proton rather than more. However it posits a number of free parameters, whose actual values are set by fields, which are therefore fixed throughout the observable universe. Each field is carried by a particle. And we've found all of those particles for the Standard Model, thereby confirming the existence of the fields. And our measurements of the properties of those particles reveals the values of the free parameters, and our theory gets better. How many parameters? As https://en.wikipedia.org/wiki/Mathematical_formulation_of_the_Standard_Model#Free_parameters https://en.wikipedia.org/wiki/Mathematical_formulation_of_th... says, the traditional Standard Model has 19 parameters which we've measured. Thus while the theory itself says nothing about why the electron would have 2 heavier varieties, it does say that there should be 3 varieties on that particle, and the measured parameter values say what the masses are very precisely. Proposals to include the complexities of the neutrino add another 7 parameters which we've so far not managed to measure. But we're working on it.