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.

The orbit of planets in our solar system have hinted at missing matter several times -- one time it lead to the discovery of a new planet (Uranus or Neptune, IIRC); one time it lead to the discovery of General Relativity.

Until we either detect dark matter/energy, or develop a theory that accurately predicts the behaviour we're attributing to dark matter we cannot say one way or the other which is the correct approach.

It could also be that we are not accurately modelling EM/SR/GR effects at a large scale, such as how they are warped by the different stars orbiting the arms of the galaxies. Or that when we extend QED/QCD to accelerating reference frames (general relativity) that dark matter won't be needed, just like how QED was formulated by extending electromagnetism/QM to special relativity (non-accelerating reference frames).

a new type of matter is a modification to our theories

"Until we either detect dark matter/energy, or develop a theory that accurately predicts the behaviour we're attributing to dark matter we cannot say one way or the other which is the correct approach."

"We" the general public isn't in the business of saying one way or the other is the correct approach, and scientists aren't, either. Scientists conduct experiments and propose theories in whatever lines of inquiry interest them, subject to the constraints of getting somebody to pay for it. Many scientists have been interested in refining the theory of Dark Matter and subjecting those refinements to experimental tests, partly because the theory has withstood and only grown stronger by those refinements and tests. That's a success by any measure, and that success is partly why public funding agencies have been willing to pay for it. Like anybody else, they try to pick winners.

It could also be that we are not accurately modelling EM/SR/GR effects at a large scale, such as how they are warped by the different stars orbiting the arms of the galaxies. Or that when we extend QED/QCD to accelerating reference frames (general relativity) that dark matter won't be needed, just like how QED was formulated by extending electromagnetism/QM to special relativity (non-accelerating reference frames).

It could be. Anything's possible.

But we are not very well educated so yeah, they will doubt it for no good reason other than "it doesn't feel right"

That's a bit of an exaggeration, don't you think?

"But we are not very well educated so yeah, they will doubt it for no good reason other than "it doesn't feel right"

That's also an exaggeration. Laypersons are under no more obligation to understand the details of the scientific professions than scientists are to understand the details of, say, the legal profession. A healthy skepticism within the general public is harmless and even helpful if it maintains an interest in science. I would just gently urge people not to veer from skepticism into dogmatism.

I mean...those are pretty good reasons. If a particular theory successfully predicts more out of "a lot" of observations than any other competing theory does, and is a smaller departure from "a lot" of existing theory than any other competing theory is, would you choose to spend your career researching those competing theories?

How about: a just and civil economic system is one where the more utility I produce the higher quality of life I can achieve?

This is very different from what you implied (being punished for creating value). Taxes and UBI aren't in opposition to this. It still rewards production and those that create value. It also recognizes that hard work isn't always valuable (digging a tunnel with a spoon is harder than with heavy machinery. But the latter provides more value). Maybe we should frame things this way instead. Progressive taxes do not result in situations where a raise in pay causes a decrease in take-home money. It does instead address the issue that money is sticky and the mere existence of capital passively generates capital (which actually means you generate wealth without doing work). Fine at certain levels but clearly can get out of control (generate wealth for retirement vs generational/perpetual wealth where your children end up wealthier than you passively).

Sorry about the cost of your bathroom addition though.

That's to say that functional courts and a state that acts as the only legitimate applicator of force tends to be a lot better for the rich, and those too fall (or themselves turn on the rich, too) when they stray too far from the line.

Not the right framing, but not far off. It depends where you set the threshold and how much you extract. Remember that money is a resource where positive feedback loops exist: "you have to have money to make money", "the first million is the hardest", or "passive income." We can think of money as sticky and attractive. Momentum matters. Also remember that a capitalist market relies on competition and money to be fluid and constantly exchanged. Transactions are not zero-sum, but many times result in a positive value. This is even true in a pure fair transaction and without considering external costs like taxes.

tldr: there are sources and sinks in the economy and this is conditioned on the value in the previous time-step. Capitalism works well when value is continually exchanged: meaning sinks are bad.

Once we consider these things, "fair" gets more complicated. One can argue that it isn't fair that wealth begets wealth. That certain goods have an economic value that is not being captured by the evaluations, and are often difficult to put price tags on (e.g. air quality). Tragedy of the commons is quite real. One can also argue that it isn't "fair" that the system does not optimize for societies and instead optimizes individuals. Fair is difficult to define and none of this is as easy as it appears on the surface. Both pro and anti-UBI people make these mistakes. I'm not attacking a particular side but rather suggesting this isn't as straight forward as you have characterized.

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

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 :)

Ah, that makes sense! I thought neutrons were hard to store because they were neutral and go right through things, but I guess cold neutrons can be stored (at least until they decay into protons).

Is it expected that pEDM ~= nEDM, since they are uud and udd?

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.

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)

As to SUSY, while it is good if young post docs are avoiding it, that does not mean it has gone away (not if PRD table of contents is any indicator). It will take a long time for that paper mill to end, likely with the retirement/death of current researchers or sooner if funding agencies finally come to their senses.

I don't think she is suggesting there should be no efforts in some of the other areas you have mentioned, just that there needs to be a reassessment of how much effort and money should continued to be funneled in those directions.

Also: what makes you say a linear collider would be a better investment?

    X_p0 = X of the pedestrian before collision
    X_c0 = X of the car before collision
    X_p1 = X of the pedestrian after the collision
    X_c1 = X of the car after the collision
    m_ = mass
    v_ = velocity
    a_ = acceleration
    t = time

    //conservation of momentum:
    m_p * v_p0 + m_c * v_c0 = m_p * v_p1 + m_c * v_c1
    m_p * (v_p0 - v_p1) = m_c * (v_c1 - v_c0)
    v_p1 - v_p0 = m_c * (v_c0 - v_c1) / m_p

    // a = delta v / t
    a = (v_p1 - v_p0)/t = m_c * (v_c0 - v_c1) / (m_p * t)