David Albert on the (non)-time reversal invariance of classical electromagnetic theory (contd.)

0:00 Are you not seeing an electromagnetic field? Well, I thought, I'm not sure what the rules are here. I thought that we were trying to represent electromagnetic phenomena. And the idea is that when we're representing electromagnetic phenomena, and we're looking at these histories, and we're not told in advance, whether we're seeing the initial movie or the movie run backwards, we see certain patterns in absolutely all cases. We see this relation between the tangent line and displacement, and that's what we're calling the electromagnetic field. We aren't told in advance which movies we're looking at, and we aren't given the opportunity to say I have one rule for the first kind of movie and another rule for the second kind of movie. it's a basic fact of life that this relation is observed when you're preaching to the conversion. I think I basically, yeah, not basically, I agree with everything you said. I think I want to make one little point and that is I think if you want to see in the simplest way what the problem is here, David's approach, which I think is simply carrying a certain naive realism about physical quantities, which takes place in quantum theory all the time, and carrying it to classical physics. By naive realism, I mean being a naive realist about convenient mathematical representation for physical quantities rather than instead of paying attention to the actual geometrical nature of the quantities themselves. Now, the role of the magnetic field, what kind of thing it is, and just think about non-relativistic electromagnetism. It's a mapping from velocity vectors to forces. That's the kind of geometrical object it is. Therefore, if under time reversal, velocities change and you want to keep the mapping the same, the representation of it in terms of the magnetic field has to get reversed. In other words, the most direct, simple equation to see what that B must change is to write down the defining equation for B,

2:30 namely force equals QB cross B. And that's just... And I guess the only thing I would criticize in your talk is simply that while you emphasize that in the relativistic case, you don't include the force equation and the non-relativistic equations. I didn't consider the decomposition of the F equal M-A law. If we decompose that... That will all come out, I agree, but in the simple non-relativistic presentation, you simply ignored the force law, which I think it really, that's the simplest way to see that the kind of thing B is is such that it has to reverse them. Just think about means. It really isn't important for present purposes. I have some difficulty to understand what one means by non-relativistic production. I think of it as a relativistic theory that in the 19th century was superimposed on a classical space-time background. It's very hard to get a grip. It's an unstable hybrid, and that instability historically gave birth I just want to object, because I just did it. Well, you can object in line, Rob. We'll get in line. I had a tiny question about your transparency of the preliminary responses going one, two, and three. The second one was that you were saying there that we can always get rid of the magnetic field, important can it be. But that surely can only be in the case of when we have a single charge in inertial motion. If we have two charges in relative motion, we can never get rid of the magnetic field by any force transformation. What I was thinking of was this. One can characterize the field at any one time in terms of its electric and magnetic components, or one can characterize it in terms of its electric components as determined relative to a whole bunch of different observers. In particular, one can characterize it relative to an observer who's co-moving with a particle. We will see only an electric field and magnetic components as that. So what I was thinking of is rather than thinking about what happens to E and D with respect to one frame, just characterize it in terms of E relative to different frames, it satisfied

5:00 David Alpert that in every case E should be kept intact. E has determined relative to all these different observers should be kept intact, and that is a constraint so strong that it fully determines what happens to the people. Okay, maybe one last question. Bill is next and then a rock can take David outside and they can fight and then if somebody is still standing, you can answer. I was just thinking about it. We'll do something very early. Or we'll do it by the way. I'm just hopeless. I'm just point of clarification of what you were saying about Albert, and maybe you already answered it, but this notion of separate oncological substances, perhaps you already refuted that. Is that his primary metaphysical motivation? Because if it is, it goes against the entire evolution of physics. I think of Wigner in a new paper on group theory and how x and t and how geometrically speaking, if you look at relativity groups and certain mathematical objects, the implication is they mutually couple and transform into each other, which doesn't imply any kind of pluralism of substances. If anything, you have a pluralism of aspects. In other words, we don't interpret X and T as separate substances. It almost sounds like a medieval scholasticism. I mean, I think of X and T as purely different aspects that mutually transform it. Maybe you're ready. I don't know that I've addressed that, but I don't really have a good sense that I understand the background intuitions that David Halbert has it in the future. Maybe somebody else can speak to that. I did want to direct attention to one thing, which is perhaps separable from some of these other issues. It was my impression, once again, indeed just lie their picture. And if one did have that picture, if one were able to bracket how one gets to the field, but just think of them as lying once and for all within the field, then perhaps it wouldn't be surprising if they'd be left intact when they reach out with the . So, do you want to?

7:30 You're sure? Yes, please. My question doesn't concern your main thesis, but something you discussed early in your talk concerning David Albrecht, he had a principle under what circumstances would the reversal of quantities be minus the quantity at a reverse time. And it seems to me one way of getting hold of this, it won't give you all the answers you want, but it will be very, very useful for the kinematical variables, is to go to quantum mechanics and make use of machines, treatment of use of the primitivity theorem to get the structure of the variables, the quantitatical structure of the observables, the relationship among the position observables, the velocity of momentum observables, the generator of the time translations the angular momentum and when one gets these relations on mechanically the instantaneous state is not going to be the quantum state at a time no no no commitment to whether being as part of the instantaneous state or not, you will get some information about the quantum mechanical analog of these algebraic relations among the observable and the quantum state. And that will give you everything you said about the way in which angular momentum observables, spin observables, draw and transform. Give you all those answers unequivocally. And you've got this quantum mechanically, then you go to the classicalism. I don't think it will then give you all the answers you want to concern the electromagnetic field of the charge current, but it will give you something. And it would be a way of examining David Alvarez.

10:00 I find that point to be very ingenious. And as we talked about yesterday, one certainly can. As was discussed yesterday, one can characterize these basic magnitudes in terms of characteristic transformation by the machine of the primitivity theorem to have these magnitudes. A very powerful machine theorem, too. Well, I think we should thank David again. We'll reconvene in quarter of.