vihren

We do have a pretty substansive evidence that dark matter exists: from the cosmic background radiation, gravitational lensing, galaxy formation simulations, galaxy rotation curves, etc.

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 might like Gattaca if you haven't seen it.

That's purely by convention. It's just that we fist discovered electrons and protons and quarks with their fractional charges came in much later.

How is it fair? You do give the same amount to everyone, but you do not take the same from everyone - you have to take more from those who chose to work. Hence the unfair part.

I'll just paste a comment I had on a different thread because it answers your question as well.

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

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

I cannot find the citation right now, but the p and n EDMs are expected to be close to each other ~1e-32 e.cm. One part is that they are uud and udd and the other thing to consider is that the quarks make up only ~2% of the proton/neutron mass. Most is binding energy and a soup of virtual quarks and gluons and in that regard they are even more similar I think. I am not very familiar how theoreticians calculate the EDM of such complex particles though.

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.

I'm working on the search for the EDM of the muon. Essentially it's much harder to search for the proton EDM than the neutron EDM. All EDM searches rely on a strong electric field applied to the particles. Because neutrons are neutral they are easily stored in some volume for a long time. You cannot so easily store protons because the moment you apply some E-field you start accelerating them. That's why you need to build a large storage ring with magnetic/electric focusing and so on. This brings numerous challenges that you don't have for the neutron. This, combined with the fact that we don't expect much different novel physics for the proton that won't be seen in the neutron has led to the focus on the neutron EDM, while the proton was left behind.

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 :)

Particle physicist here (relatively new to the field). I mostly do not understand the problem of Dr. Hossenfelder and others like her.

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)

Its the momentum that kills you p=mV, not the kinetic energy. So I would guess that mass ia much more important.

That's the issue exactly. Many things can go wrong if you place a lot of radioactive material on top of liquid hydrogen and liquid oxygen tanks.

I have the same problem. I have recently moved to Switzerland and I am so grateful for the culture here. Noise is not tolerated, as it should be.

Yup, definitely second that. With that change I can definitely imagine this as a user option in the settings. Reading is so much easier.

(also wanted to see my avatar)

Some healthy fraction of c seems to be possible with current technology also. If you consider 3% healthy that is.

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

I am a physicist by trade, but recently I started drawing on my Samsung tablet. I'm really enjoying it. For other folks that are doing digital drawing I can recommend that you print out your stuff on canvas with a high-end printer. The feeling of having your work that you can hang on your wall is amazing!

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

Abstract: Understanding the mortality impact of COVID-19 requires not only counting the dead, but analyzing how premature the deaths are. We calculate years of life lost (YLL) across 81 countries due to COVID-19 attributable deaths, and also conduct an analysis based on estimated excess deaths. We find that over 20.5 million years of life have been lost to COVID-19 globally. As of January 6, 2021, YLL in heavily affected countries are 2–9 times the average seasonal influenza; three quarters of the YLL result from deaths in ages below 75 and almost a third from deaths below 55; and men have lost 45% more life years than women. The results confirm the large mortality impact of COVID-19 among the elderly. They also call for heightened awareness in devising policies that protect vulnerable demographics losing the largest number of life-years.

I have tried it on a RPi3 and it is painfully slow. I would not recommend this to anyone.

It is more related to the needed strength of the magnets to keep the particles on track and also the synchrotron radiation. The first issue is that the lower the radius of the circle, the stronger magnetic field is needed because of the increased centrifugal forces. The second issue is that synchrotron radiation leads to loss of energy. It is again proportional to the acceleration perpendicular to the vector of the velocity of the particle [0].

[0] https://en.wikipedia.org/wiki/Synchrotron_radiation

That seems pretty great, but I always have the problem of creating the ASCII art in the first place. Is there a tool to help with that?

Just to add to the cacophony, there is one between Gif-sur-Yvette and Bures-sur-Yvette, Paris area. Its a nice walk for anyone close to the Paris-Saclay research center.

In my workplace qwant is the default SE and I'm sorry to say it, but its awful. Maybe if you search in French it will be a bit better.

I'm using DDG and I'm quite happy about it. Very rarely I switch to google and if I do it usualy to search some location specific things like nearest pharmacy.

This is a very interesting observation if its real. I am from Bulgaria and I am a PhD candidate in physics. Whenever I tell someone that, they always say that its sounds cool and difficult and the next question is: What are you going to work after that? I guess that physics, at least in Bulgaria is not considered as a field that you could work in, more as in something you learn for the sake of knowledge.

Why do you think that in English speaking countries is different than others? I temporarily currently living in France and I do not have many contacts with non scientists, but the ones that asked me what I do all found it cool sounding.

We are not discussing nuclear waste here. It is highly concentrated and disposed of in the end of the fuel cycle. What you should be comparing with is the radioactivity that is released in the environment during the operation of the plant. That is mostly Tritium and isotopes of Xenon, definitely no heavy metals. Tritium is a very low energy beta emitter and is mostly harmless. Xenon is a noble gas and a beta emitter, so again not very harmful.

The WHO guidelines on alpha emitters (all elements you cite that are contained in fly ash) is 1 Bq/l in drinking water. So depending on how and where this ash goes to, you can definitely cause some significant damage with it.

It seems that when they squeeze all possible optimizations, GCC was a bit faster, but for the not so optimized code GCC and rustc seem very comparable.

I have just submitted an article to an Elsevier journal. They have some non-functional web interface so that you can edit the article yourself. My biggest problem was fixing the tables, because they looked really bad after the automated copy editing. There was some text on the interface which said something like "This will not be the final version of the tables", or at least that's how I understood it. Well, I clicked submit and without any real editing from a human on their side the article was published. Now my article, which I have put so much effort in, has messed up tables.

The creator of Sci-Hub is Alexandra Elbakyan and she is from Kazakhstan. According to Wikipedia [0] she spend 1 year working for a Moscow company, but that's it. I wouldn't classify it as a Russian service. There is a nice russian service for paywalled ebooks and articles called LibGen [1]

[0] https://en.wikipedia.org/wiki/Sci-Hub [1] https://en.wikipedia.org/wiki/Library_Genesis