Why is it so hard for people to believe that there are some particles that are not interacting with electromagnetism that we haven't detected directly yet? It's not even a precedent, the neutrino is just like that.

I guess the name "dark" matter was a mistake because it implies something weird, when in fact it just means whatever this is, doesn't have electric (or chromo) charge.

You are not to blame for not understanding this, it's just that the analogy for the electric dipole moment coming from a non-spherical 'shape' of the electron is extremely bad. Moreover it's missing the most important reason why we search for EDMs, because the existence of one in an elementary particle would indicate the violation of the time-reversal symmetry (T), which assuming CPT conservation [1] leads to CP violation (Charge conjugation and parity symmetries). CP violation [2] is needed to explain the matter-antimatter asymmetry of the Universe.

A more proper way, in my opinion, to reason about an electric dipole moment is to think in terms of Feynman diagrams. An EDM (or any dipole moment for that matter) is an interaction of the electron with an electromagnetic field, so interaction between an electron and a photon. The most simple such interaction you can imagine is an electron flying in, at one point it absorbs a photon and flies out - that would be the magnetic dipole moment. You can go more complex though - electron flying in, at one point it emits a photon, then the electron interacts with the EM field (absorbing a photon) and then it reabsorbs the photon it has emitted previously. (Note that these analogies are again not perfect as for elementary particles time and space are not the same as in the macro world). Now, it can get even more complicated: If you have an electron it's not really a 100% pure electron. There is always some chance that it transforms for a short time into a quark or neutrino or whatever you can imagine.

When you analyze all such scenarios (electron going into something else, interacting with the EM field and then going back to an electron) some violate CP symmetry, and those contribute to the electric dipole moment. We use that name (dipole moment) as the final result is as if the electron was a ball with some separation between the negative and positive charges and placed into an electric field it experiences some torque. The analogy misses the most important part though, as if it was such a polarized 'ball' it would not violate CP symmetry.

Within the Standard Model the only source of CP violating interactions come from the weak interaction (CKM matrix). These have a very small contribution as the weak interaction is, as the name suggests, very weak. That's why the Standard Model predicts very tiny electric dipole moments. When we are searching for EDMs we are in fact searching for such rare transformations through some new undiscovered particle that violate CP symmetry. If we detect some non-zero EDM that would mean that there is some interaction that is not included in the standard model that violates CP, not that the electron is not a round sphere or a sphere with a bump.

[1] - https://en.wikipedia.org/wiki/CPT_symmetry [2] - https://en.wikipedia.org/wiki/CP_violation

A more proper way, in my opinion, to reason about an electric dipole moment is to think in terms of Feynman diagrams. An EDM (or any dipole moment for that matter) is an interaction of the electron with an electromagnetic field, so interaction between an electron and a photon. The most simple such interaction you can imagine is an electron flying in, at one point it absorbs a photon and flies out - that would be the magnetic dipole moment. You can go more complex though - electron flying in, at one point it emits a photon, then the electron interacts with the EM field (absorbing a photon) and then it reabsorbs the photon it has emitted previously. (Note that these analogies are again not perfect as for elementary particles time and space are not the same as in the macro world). Now, it can get even more complicated: If you have an electron it's not really a 100% pure electron. There is always some chance that it transforms for a short time into a quark or neutrino or whatever you can imagine.

When you analyze all such scenarios (electron going into something else, interacting with the EM field and then going back to an electron) some violate CP symmetry, and those contribute to the electric dipole moment. We use that name (dipole moment) as the final result is as if the electron was a ball with some separation between the negative and positive charges and placed into an electric field it experiences some torque. The analogy misses the most important part though, as if it was such a polarized 'ball' it would not violate CP symmetry.

Within the Standard Model the only source of CP violating interactions come from the weak interaction (CKM matrix). These have a very small contribution as the weak interaction is, as the name suggests, very weak. That's why the Standard Model predicts very tiny electric dipole moments. When we are searching for EDMs we are in fact searching for such rare transformations through some new undiscovered particle that violate CP symmetry. If we detect some non-zero EDM that would mean that there is some interaction that is not included in the standard model that violates CP, not that the electron is not a round sphere or a sphere with a bump.

[1] - https://en.wikipedia.org/wiki/CPT_symmetry [2] - https://en.wikipedia.org/wiki/CP_violation

On a side note, 'ultra cold neutrons' are a super interesting type of matter. Their energy is so low that they can be stored in bottles and are transported through tubes using turbines and mechanical valves.

The usual quote is that for the proton we can reach sensitivities up to 10^-29 (around three orders of magnitude lower than the current nEDM limit), but thats only the statistical sensitivity. The systematic effects that would spoil that come much earlier and this limit is close to science fiction at this point. For example, if you have a magnetic field in the order of attotesla in the region of the storage ring it will dominate the measurement.

Would be happy to answer more edm questions :)

One thing I often see and it seems reiterated here is 'Why do we need more and bigger expensive colliders?'. In general, in the particle physics community right now there isn't much of a push for 'bigger colliders'. Scientists seem to have agreed that the low-energy precision physics frontier might be more fruitful for a fraction of the cost. Even the Mecca of collider physics acknowledges that and have lunched the 'Physics Beyond Colliders' study group https://pbc.web.cern.ch/ Also, there are numerous experiments done at the LHC which are not 'search for new particles'. Yes, the main goal of the LHC was to discover the Higgs boson and the great hopes were that supersymmetry (SUSY) particles will start falling from the sky. Now we know that SUSY is most probably not the way the world works and the efforts are mostly abandoned. Especially by younger physicists in the field.

The other problem that people seem to have is with the current directions in physics which in this blogpost are referred to as 'pseudo-problems' such as: "the baryon asymmetry or the smallness of the cosmological constant". These might not be problems on the same scale as "What the hell is this dark matter??" or "How do we reconcile general relativity with the Standard Model?", but in my opinion it would be a bigger waste of resources to focus all of physics in only the few big questions and leave everything else unexplored. Yes, from a certain point of view you could say that there is no reason that matter and antimatter should be equal in the universe so the baryon asymmetry is not a real problem, but still, there is no explanation yet why everything we see is matter and antimatter is next to non-existent in the Universe.

tl;dr: The money that go to collider physics are not 100% of the money that go into particle physics and generally there are no plans in the community for larger colliders at least in the next 25 years. (the Future Circular Collider has quite a long way to go before its even considered for building)

(also wanted to see my avatar)

https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

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I put my stuff on my blog. Feel free to check it out here: https://physica.dev/art/

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