Time symmetry → energy conservation

17:12getting really weird and really beautiful at the same time, right? It's like getting weird. [laughter] Um in in any case, let's let's talk about Okay, so so we've talked about symmetries, right? and like the laws that are laws are going to be the same no matter what I do. >> Yes. >> Okay. Both both in a classical sense >> and and we we've just touched upon the quantum quantum sense of things, right? Um so let's talk about something that does break symmetry cuz not every trans transformation is going to preserve the laws of physics. For example, if you do a change of scale, right? Suppose I make my experiment and it's like you know 1 m by 1 meter or whatever and then I just

17:53like increase the the size of my experiment. Am I going to get the same physics? The answer is no. Because nature does have a fundamental scale, right? There are such things as atoms and those atoms are about 10us 10 m big like one angstrom, right? So to make my thingy bigger, I need to use more atoms and that's going to change the physics of my apparatus. So the physics of scale of stretching and squishing is not a symmetry of the universe because there is a fundamental scale. The other way when I was saying like you know the the the symmetry of time there's no t equals z. I guess there is when it comes to the big bang when it but when it comes to experiments that I do in the lab there's

18:34no t equals z >> in the perception of the way we understand and see the universe. It's a little bit of a different context. Yeah, that's a little bit of in cosmology there's a little bit of a different context, right? There is such a thing as t equals 0. But in in the scale of like experiments that I want to do in the lab, there isn't. There's no x equals 0, y equals 0. There's no like origin for the universe. So I can shift my