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kelly0303
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Why for some systems (such as the electron or neutron) the presence of an electric dipole moment (EDM) implies time reversal violation, while for others, such as water molecule, this is not the case? Thank you!
I am not sure I understand. What does the structure has to do with this? A neutron can be though of a dumbbell, with positive charge at one end and negative at the other (of course the separation is very small, hence why the EDM was not observed experimentally yet). How does the "L" shape of water doesn't violate CP, but the dumbbell shape of neutron does?mfb said:A water molecule has an ordered structure in space ("L"-shaped, oxygen at the center). Neutrons and electrons do not.
Only from very weak effects from CP violation. Otherwise it wouldn't have that shape. Don't take illustrations with quarks too literal.kelly0303 said:A neutron can be though of a dumbbell, with positive charge at one end and negative at the other (of course the separation is very small, hence why the EDM was not observed experimentally yet).
Well it's the CP violation the main reason I am asking this question. I know it is due to the weak interactions, but if it wasn't for the weak interaction I wouldn't have asked this questions (and same applies to the electron, so I am not sure what do you mean by quarks illustration). But again, I am not sure why does the shape of the molecule matters. I can take 2 non-conducting hemispheres, having opposite charge and stick them together. I would get a dipole moment without violating parity. I can have almost any shape I want and still get a dipole moment. But these won't violate CP and I am not sure I understand why.mfb said:Only from very weak effects from CP violation. Otherwise it wouldn't have that shape. Don't take illustrations with quarks too literal.
Chemical bonds have binding angles. Quarks in hadrons don't have fixed positions.
They will still have some dipole moment from CP violation but it will be completely negligible compared to the dipole moment from the structure. Something the neutron doesn't have because it doesn't have a structure.kelly0303 said:But these won't violate CP and I am not sure I understand why.
Yes. My question is, why doesn't the dipole moment not coming from the weak interaction violate CP? I am sure that doing the math and applying the C and P operators for a given system will show that, but I am looking for some more physics insight. For example, I imagine T violation implies that running the movie of an experiment forward and backward, will look differently. So for some reason if I film the electric dipole of a water molecule and run the movie backward I can't tell the difference. But if I do the same with an electron, I would be able. I am not sure why. Thank you!mfb said:They will still have some dipole moment from CP violation but it will be completely negligible compared to the dipole moment from the structure. Something the neutron doesn't have because it doesn't have a structure.
I am thinking about the answers, I just don't understand. What I understood so far is that water can have an electric dipole without violating CP because it is L-shaped. But I don't understand the physical reason as to why the shape of the molecule (or any object I would build, as mentioned above) would not violate CP, while the neutron does violate CP by having an EDM. Thank you!Vanadium 50 said:You're not thinking about the answers you are getting. You are reacting to them.
How do I know? Because only a few minutes pass between an answer and your reaction that you don't understand. There hasn't been enough time for you to think things through. You would be much better served by thinking about the responses you are getting and if you need a follow up to ask something focused and well-posed rather than just shotgunning questions back as fast as you can. You are much, much more likely to reach understanding that way.
EDM, or Electric Dipole Moment, is a measure of the separation of positive and negative charges within a molecule. Time Reversal is a fundamental symmetry in physics that states that the laws of physics should be the same whether time is moving forward or backward.
EDM and Time Reversal are important concepts in physics because they help us understand the fundamental laws of the universe. They also play a crucial role in the study of quantum mechanics and the behavior of subatomic particles.
EDM and Time Reversal are related because the presence of an EDM in a particle violates the Time Reversal symmetry. This means that the laws of physics are not the same when time is moving forward versus when it is moving backward.
The violation of EDM and Time Reversal symmetry has significant implications for our understanding of the universe. It could potentially lead to a better understanding of the origin of matter and antimatter, and shed light on the existence of dark matter.
EDM and Time Reversal are studied through experiments involving high-energy particle collisions and precision measurements of subatomic particles. These experiments help scientists to test the predictions of theoretical models and search for deviations that could indicate a violation of these fundamental symmetries.