I have studied high school physics but only have a pop-sci kind of understanding of ideas like Noether's theorem so go easy.
As far as I know, Noether's theorem simply states that any kind symmetry of a physical system is accompanied by a particular conserved quantity.
The normal example of this is that if we consider a system to be time symmetric (the laws that govern the system are the same at all points in time), then energy conservation emerges. There are, however, supposed to be examples of systems where energy is not conserved, implying that the laws that govern the system isn't symmetric.
My problem is with this idea that laws are not symmetric over time. What does this really mean? Does this mean that the laws literally change over time? Is it not a very basic assumption for the study of physics that the laws that govern the universe never change? If we found systems where laws changed, how could we ever study the laws?
I believe that my confusion here is down to a misunderstanding of what it means for a system to be time symmetric but maybe it's something else. Thanks for any answers.