which might be a good thing in that the neutrino mass is a "missing part of the standard model" as opposed to "possible physics beyond the standard model". The neutrino mass term could explain dark matter, dark energy and the matter-antimatter asymmetry
whereas a Higgs Factory or top factory seems likely to be a big disappointment because all the evidence we have is that the Higgs field is as simple as it could possibly be and a top factory might end up just verifying that complex calculations people did 40 years ago (by the time the machine comes up) were right.
Muon colliders are a possible path to a Higgs factory or top factory but the path to a muon accelerator that can revolutionize precise neutrino physics is much shorter and I think more rewarding.
Notably neutrino physics is win-win. Either the right-handed neutrino exists as a heavy particle and is very likely to be the darkon or the neutrino is a Majorana fermion (is its own antiparticle) which is certainly a weird and interesting result. Contrast that to all the other poorly motivated darkon candidates such as sparticles, axions, etc.
I remember reading a lot of papers about muon accelerators about 20 years ago, they have been a big research topic in the US and Japan because we didn't have CERN.
My initial gut reaction was that the authors were ignoring the obvious solution of simply putting the ring below ground level and setting up maintenance walkways above the ring instead of next to it.
Then I realised the the Earth is spherical and that it doesn’t matter how deep you put this thing, the beam will come out somewhere, even if it needs to go through a thousand kilometres of regolith to get there.
So there could be some random patch of grazing land somewhere in another country that’s dangerous to go near whenever the experiment is running.
PS: I solved the funding problem! Just tell the military about this new unstoppable death ray that can kill anyone even through the planet. [Disclaimer: death will be a decade from now due to cancer. Victim must remain stationary for one year. Construction work is required to retarget beam.]
> they could produce enough neutrinos to be dangerous
Dangerous in the sense of "ionizing radiation" or in the sense of "this will overturn careers"? Getting killed by neutrinos sounds like a freak accident from a sci-fi story.
> Most of the ionization energy dose deposited in a person
will come from interactions in the soil and other objects
in the person’s vicinity rather than from the more direct
process of neutrinos interacting inside a person. At TeV
energy scales, much less than one percent of the energy flux
from the daughters of such interactions will be absorbed in
the relatively small amount of matter contained in a person,
with the rest passing beyond the person.
If you're looking to get bit by a radioactive spider, spiders living down range of such a collider might be a decent place to start.
With high-energy particles the showers made when the particles hit something can be more dangerous than the original particles.
For instance if you are building a space colony there is an optimal thickness for the biological shield: most high energy particles blast right through you and if you have too much shielding there are too many opportunities for a particle to explode a nucleus in the shield and multiply the number of radioactive particles dramatically. Off the top of the head I'd say about six feet of soil is about right, but you don't do better with 60 feet or anything reasonable until you are talking multiple kilometers (maybe of vacuum or air space) that give shower muons time to decay.
Speaking of muons, it is an easy experiment often used in physics education to measure the the lifetime of cosmic ray muons produced in showers.
If a muon gets slowed down by matter you see a pulse of radiation, then you see a pulse of radiation a few microseconds later when the particle decays. If you measure the time gap in two-pulse events you can get the half-life. It was a popular experiment in Cornell's 510 lab for grad students who weren't particularly interested in doing experiments because it was so easy.
"near" is a relative term that isn't specific enough to get an idea of how dangerous something is.
It's dangerous to be near hydrogen sulfide. It's dangerous to be near a primed hand grenade. It's dangerous to be near an artillery shell impact. It's dangerous to be near a drunk driver. It's dangerous to be near an active battlefield or even near a war.
But they are all different nears.
When you say its dangerous to be near the plane of the collision, are we talking 1m, 10m, 100m, 1000m, etc? Are there dangerous byproducts created that might kill you even after the event itself? That's useful information. A general "don't be near" isn't really helpful.
My reading is that "in the plane" literally means in the plane, +- a couple or tens of meters, depending. The paper is concerned with effects on the earth's surface, in an aircraft or orbit the duration of exposure and lack of stuff for neutrinos to run into probably means it's less of a concern. To put a number on it, they give examples of accelerators buried at 300 meters which would create a radiation hazard at a radius of 62 kilometers where the plane exits the surface (assuming earth is spherical).
As far as the danger, the paper estimates up to a few mSv/year if you hung out in the wrong place all the time. You definitely wouldn't want to have a town in the way of that, but it's not an immediate danger on an individual level. The danger would be greater/more concentrated if there were straight segments in the accelerator, or if it was closer to the surface (smaller circle of intersection).
"My reading is that "in the plane" literally means in the plane, +- a couple or tens of meters, depending."
What wad said was so vague as to be practically useless.
"...they give examples of accelerators buried at 300 meters which would create a radiation hazard at a radius of 62 kilometers"
Again, this is overly vague and unhelpful. As I replied to LegitShady, no specific mention is made about the type of radiation dangers or how long radiation would be expected to linger in soils etc.
Well said. I was annoyed by the lack of specific information for exactly the reasons you mentioned
More specific estimates of safe distances versus collider power would be helpful, same too about the nature and type of radioactive byproducts in soil (what elements would be expected to become radioactive along with their half-lifes, etc.).
Sometimes I think it ought to compulsory for scientists to study philosophy—at least its parts that deal with logic, language and semantics.
Philosophy defines near —like good— as a 'simple notion' that cannot be subdivided into simpler terms. The word needs qualifiers/quantifiers (figures, distances, amounts) for it to be useful—info that the paper was overly vague about or omitted to specify.
It's not their number so much as their energy. The cross section for energetic neutrinos interacting with matter scales as energy squared, if I recall correctly. These neutrinos have cross sections too low to shield, but too high to ignore.
Interestingly, that may actually make the collider-produced neutrinos less dangerous than those from a supernova. I'm not sure how it translates to other types of radiation, but at least for neutron radiation (e.g. cosmic rays) the amount of energy one would absorb peaks and then falls off at higher energies. Not harmless though, just slightly less dangerous.
Neutrino cross sections increase with energy, so these are much more dangerous than from a supernova. Note that when they do interact, much or all of the energy of the neutrino manifests in a form that can then interact further, so the more energetic neutrino also creates more secondary radiation when it does interact.
There was a discussion two months ago (https://news.ycombinator.com/item?id=39271472) about a paper on using neutrino beams to destroy nuclear weapons, which showed that neutrinos can be dangerous.
I’m doing a PhD in quantitative field, not stupid by any means. But people doing physics seem out of this world to me. I feel like they’re just orders of magnitude smarter. It’s a shame the field seems a bit stagnant now. I hope they find a way to advance the knowledge without planet-scale accelerators. There should be a feasible and elegant compact solution.
> They do have insane pattern recognition skills when it comes to models. Good mathematicians also have this.
The skills physicists and mathematicians build aren't very comparable.
Physicists has the more complex equations and models, probably most complex of any field since physicists often invent new math to model things. Quantum field theory is insanely complicated math wise with infinite number of infinite integrals, mathematicians has still not figured out how to formalize that.
Mathematicians focuses much less on modeling and equations so they aren't as good at that, instead they are much better at formal proofs and theorems. The skills are very different and doesn't translate well.
Or in other words, physicists are experts at making complex math tools to model things. Mathematicians are experts at verifying tools that exists. Those two skills has less overlap than you might think.
I wouldn't be so dismissive of the overlap. A friend of mine has a math PhD and got a 32 on the Putnam each time he took it, which if you're familiar is proof he's no joke when it comes to math skills. He spent his career as a quant on wall street modeling economic relationships because it paid a lot more than staying pure math.
Interesting way to look at it. Your description of what physicists are experts at matches my math PhD pretty closely. I focused on mathematical modeling. I now work with a bunch of physicists, so I guess that checks out.
Yeah, if you work on the applied side of math it can be very similar to what people do in physics. But I was thinking more about pure math.
Edit: I think the main difference there is that in applied math they still prove that the models are mathematically correct. In physics they just show that the model align with experiments and skip math formalism.
I was with you on the generalities, but oh do theoretical physics suffer from math envy when it comes to formalism. Basically since the invention of quantum mechanics, has physics been dominated by “proofs” and “theorems” like the physical world is assumed to be axiomatically defined by Heisenberg’s and Pauli’s principles, and everything else is just maths.
No small part of the stagnation I sense in physics today stems from too deep a faith in the ultimate truth of the mathematical models we call theories. It doesn’t help the fact that we rely on Taylor expansions and perturbation methods for most experimental predictions.
The Higgs hunt and the passivity of the (experimental) physicists in challenging this stupid theory-driven search for new physics is emblematic of this era.
If only math was seen as a modeling language and not somehow truth/consistency itself, physics would be much better off.
Yeah, I saw that as well, met some professors in grad school that started talking about physics in terms of axioms and proofs instead of experimental results and models. At that point I lost interest and just went with math instead, if it is going to be math anyway why not go with the real thing.
> Physicists has the more complex equations and models
This isn't really the case. In general in any class of mathematical objects, the physically realizable ones are the most tame. Physical realizability is a huge constraint that typically dramatically simplifies problems.
> Quantum field theory is insanely complicated math wise with infinite number of infinite integrals, mathematicians has still not figured out how to formalize that.
My understanding was that the issue is that QFT as used by physicists is known to be mathematically inconsistent. For example, see Haag's theorem [0]. As Wikipedia puts it "there does not exist a well-defined interaction picture for QFT, which implies that perturbation theory of QFT, which underlies the entire Feynman diagram method, is fundamentally ill-defined."
So the problem is not that we don't know how to formalize it, it's that what physicists are doing is known to be wrong. So we need some better argument for why it sometimes seems to work under the conditions it does. And that's arguably more about getting the physics right than it is about math.
This is something that happens in general: physicists will often use tools or arguments that are known not to be correct despite the fact that they work well in practice.
I think in general, that's a good thing. Physicists need to be able to brainstorm ideas in a way that is unconstrained by needing to formally prove them. In this process they might find something that works 60% of the time. Then someone will refine it to work 80% of the time, etc. But at the end of the day, the tools do have to be mathematically consistent for them to actually describe the physics, unless we live in a mathematically inconsistent universe.
So the characterization I'd give is that physicists are generally better at modeling, but also less constrained by the need to be correct.
> Mathematicians are experts at verifying tools that exists. Those two skills has less overlap than you might think.
This part is reversed IMO. Mathematicians created nearly every major tool used by physics since the history of humanity. Occasionally physicists will run ahead and come up with an idea that is lacking in tools, and they'll turn to mathematicians as the tool experts for help. Like, for example, Einstein did when trying to formulate relativity. More rarely, they'll come up with a novel tool like Feynman diagrams without knowing why they work, and then the mathematicians will be called in as the experts to sort things out.
And of course it is true that physicists will come up with ideas like the Ads/CFT correspondence that arise from physical considerations. It's also true that the problems of physics can inspire new mathematics simply because they're new and interesting problems.
> Mathematicians created nearly every major tool used by physics since the history of humanity
Calculus was created by a physicist who didn't even bother it since he just published the resulting physics, Fourier analysis was created by a physicist etc. Mathematicians first and foremost formalizes things after they were created, they don't create many useful tools to begin with. Very few fundamental tools were made first by mathematicians.
They often call physicists/polymaths mathematicians after it happened since they published a lot of math, but they did the physics/natural first at the time. The formalist mathematicians we see today weren't even a thing 150 years ago, the useful tools developed by formalist mathematicians is basically zero, the new useful tools physics used the past 100 years were done by themselves.
For example, generalized functions where done by physicists, mathematicians scoffed at it saying it is inconsistent as you said here, but then after over 100 years apparently it all worked out just and the physicists were right that you can work with functions that are defined by their properties when integrated instead of their values. The same will happen to QFT, it isn't wrong to work with infinities its just that mathematicians aren't good enough to figure out how to formalize such tools but such tools working with infinities works.
I have studied both theoretical physics and pure mathematics at a graduate level and published in both, I have a fair idea how the fields works. Rarely formalizing a tool can open up for more usages of it, but that is about it.
> Calculus was created by a physicist who didn't even bother it since he just published the resulting physics
Calculus was discovered by a number of people. I'm assuming you're thinking of Newton, who was a professor of mathematics and whose advisor was a mathematician. Remember the fundamental theorem of calculus had been proven by mathematicians Gregory and Barrow (Newton's advisor) before Newton, not to mention the work of people like Fibonacci. Calculus as we know it today was mainly developed by the mathematician Leibniz independently of Newton.
> Fourier analysis was created by a physicist etc
Joseph Fourier was a mathematician whose advisor was mathematician Joseph-Louis Lagrange whom he succeeded at ENS.
> Mathematicians first and foremost formalizes things after they were created, they don't create many useful tools to begin with. Very few fundamental tools were made first by mathematicians.
This is wildly wrong and contrary to history.
> They often call physicists/polymaths mathematicians after it happened since they published a lot of math
The people I'm calling mathematicians, like Newton and Fourier, are people who trained in mathematics and had mathematical advisors. What other definition do you want of a mathematician other than one who does math, studied math, is employed to do and teach math, and whose advisor was a mathematician?
For example, while Wikipedia calls Fourier a mathematician and physicist, Britannica just calls him a mathematician. Britannica does mention that he was also an Egyptologist but never calls him a physicist.
> generalized functions where done by physicists
Distributions have been used by mathematicians since the 19th century. I'm aware of no examples of physicists claiming priority. Physicists do often use them incorrectly, for example a lot of physicists view the Dirac delta "function" as a function despite the fact that no functions have those properties. They sometimes confuse that, as you seem to do, with thinking that mathematicians don't understand what generalized functions are about.
Footnote: Haag's theorem only invalidates naive perturbative approximation. But that's not what physicists actually use; they use it for motivation and then switch to a renormalized perturbative approximation, which is compatible with Haag's theorem.
Your point stands though: mathematicians are indeed able to cope with path integrals. But several of the models -- qed, Higgs, electroweak, basically everything but qcd -- used in particle theory suffer from a fatal flaw, the Landau pole. They can only exist as incomplete approximations to something else.
>So we need some better argument for why it sometimes seems to work under the conditions it does. And that's arguably more about getting the physics right than it is about math.
Douglas adams solved it though, he understands why this flawed physics seems to work -- 6x9 = 42
not all physics is particle physics! gravitational-wave physics, for just one example, is not the least bit stagnant! and soft matter physics is amazingly fertile ground right now...
Yes, there's quantum computers and information with fundamental tests of quantum mechanics, condensed matter with superconductors, soft Condensed matter in Biophysics with dna and protein folding, computational physics that underpins huge swaths of theoretical chemistry. There's many many other fields of physics, each with dozens of exciting projects going on right now.
Particle physics/cosmology is closest in some sense to "fundamental physics". Its also, as i understand, the most competitive field in physics right now with the highest achieving theoretical mathematician people (i.e. the super geniuses) but that's also an effect of the slowly drying funding making the field more selective. It's by no means the only field in physics and there are extremely intelligent and hard working people in all fields of physics doing high impact, world changing research because they love it.
I will also add, as an academic who works closely with hundreds of physicists, that although they are indeed typically smarter in one dimension, they are also considerably dumber than your average person in others. It turns out life is all about tradeoffs!
I don't think it has anything to do with "smart/dumb", so much as how much time you think about those problems. Academics in esoteric disciplines are just far removed from many common, every day problems that they seem to lack common sense. They wouldn't have an issue acquiring that understanding if they had comparable experiences as others.
Sean Carroll has some good talks on this. Basically there's two frontiers: intensity and sensitivity.
With intensity going past LHC is looking very difficult but not necessarily impossible. There's been advances in compact linear accelerators that look promising.
With sensitivity we're got a lot of untapped potential to observe high energy particles/physics produced by nature.
I don't mean to trivialize the difficulties but there's reasons to be optimistic about us learning new physics in the coming decades.
Building more colliders isn't what I would call a revolution, more like status quo. What would be a revolution is if a series of scientifically sound (tabletop) experiments started advancing the field.
If such tabletop experiments were possible, then surely the particle physicists who use these colliders would be building them? As far as I can see, they're requesting colliders because to the best of their knowledge, colliders are necessary.
A muon collider would be revolutionary in the sense that it would open up a new energy range for lepton collisions. It would also be a technological marvel.
It's not that simple. There are many smaller scale experiments in HEP, all kind of dark matter detectors among them. Colliders are irreplaceable in a sense that we do not know how to get higher energies without them, but it's unclear for me that just getting higher energies is enough.
Energy scales for new physics can be enormous for all we know, I do not see any reason to expect that new physics hides "around the corner" (in a 1.5 orders of magnitude FCC or muon collider could give us). Muon collider is at least looking in a different place, and it's definitely more interesting than FCC for me, but I'm still not 100% sure it is the right thing to do, given the limited resources.
Those colliders need more research, but are possible (like wakefield accelerators). The physicists who want these colliders probably aren't interested in this kind of research though, so they push for classic collider designs they already know how to build.
I agree that muon colliders are a better investment than something like the Future Circular Collider though, it's an area that hasn't been as thoroughly explored.
- "Decaying muons also radiate energetic neutrinos, creating a novel radiation safety challenge. Shooting horizontally from the collider ring, these elusive particles would zip through the earth and emerge dozens of kilometers away."
I understand you have neutrinos leaking from the entire collider ring, along all the tangent rays? That fills out an entire geometric plane!
Maybe the collider is the basis of a neutrino transmitter.
The purpose of this study was to inspect the possibility of using neutrinos for communications for military submarines ... Because neutrinos are nearly unaffected by matter, a neutrino beam could traverse directly through the earth from the transmission site to the submarine. A directional beam would allow confidential information to be passed only to the intended recipient. Neutrino communications would also be totally jam-proof. As an additional benefit, a neutrino message could be received in the deepest of waters, leaving a submarine less vulnerable to enemy attacks. -- https://www.physics.ucla.edu/~hauser/neutrino_communication_paper/siljah_mod.htm
But the conclusion isn't optimistic about the receiver.
A muon storage ring with straight sections would produce powerful beams in the direction of the straight sections when the muons decay which would produce orders of magnitude higher flux than existing accelerator neutrino experiments not to mention a highly collimated beam.
(I am still amused by the superluminal neutrino flap because (a) it wasn't the first case where people thought they saw superluminal neutrinos, I remember seeing an experiment at Los Alamos Lab where curve fitting the neutrino mass was giving an imaginary (superluminal) number in the 1990s, and (b) it sounds so much like something out of https://en.wikipedia.org/wiki/Steins;Gate)
The OPERA experiment does show that if your equipment was calibrated properly you could possibly get a high data rate from turning your source on and off rapidly, however, I don't think you can turn a muon storage ring on and off.
- "however, I don't think you can turn a muon storage ring on and off."
What if you had two storage rings whose straight sections were at slightly different angles, and a switch bridging them? Populate one ring for "on", move muons to the alternate ring for "off".
I have a question. Doesn't observing some signal require interacting with it? And wouldn't most interaction sufficient to gain a high fidelity signal modify the underlying particles in some way that might destroy the message? How, if we can retrieve the message in the beam with accuracy, do we not simultaneously gain the technology to disrupt the beam? Isn't jamming just loud and sophisticated form of communication? If we can communicate, how are we not simultaneously able to jam?
Neutrinos are directional. Any jamming would come from a different direction.
The jammer can't match the direction - as the submarine moves the direction of the source changes in a predictable way, the jammer would change in a different way.
Think of it as a tiny light bulb blinking as you walk in a circle around it. Doesn't matter where you put the jamming light bulb it won't be in the center of your circle like the source light bulb is.
It might be worth considering just how much other physics could be done with these resources. Improve education and experimentation for many other investigations instead. There is still much to learn about fluid dynamics, the chemistry of water, alternative plastics, and many other open questions. The vast amounts of resources poured into exotic reactors could educate many more physicists, launch many more satellites, and operate many more laboratories. Moving forward with very large projects may effectively starve out other investigations that might ultimately have far more practical applications. In some ways this proposal seems more like a lack of imagination than a positive surplus of imagination.
I'd say that the "missing" neutrino mass term and the identity of the dark matter particle (quite likely a neutrino) are two of the most interesting problems in physics and I'm afraid that Team LHC's interest in (I think boring) Higgs and Top factories could crowd out investment in the much more interesting area of neutrino physics the way that you say.
The good news is that going down the muon accelerator route you probably need to build a neutrino factory to validate the technology long before you can build those other things.
TFA: The P5 report calls for R&D on a muon collider, stating, “This is our muon shot.”
That just doesn't have the same ring to it as "moon shot". I hope they do not continue using this phrase. It doesn't have the same gravitas nor is it awe inspiring. I highly doubt it help earn funding. In fact, it leaves me with a negative charge.
I assume this will cost billions in government funding to create, which begs the question: What is the benefit to the ordinary person here? What kind of scientific discoveries could be unlocked? New devices that could be made? How would it improve society?
The record energy reported last year was 5.36 TeV per nucleon pair [1]. That sounds like a lot until you remember that a nucleon is a bag of quarks held together by gluons. Having two of these things collide spends the per-nucleon energy on all of them, and produces a magnificent mess of strongly interacting particles which is very hard to analyze.
So when the posted article says,
muons are fundamental particles that put all their energy into a collision, enabling a muon collider to compete with a hadron collider running at 10 times the energy. So the muon collider could be much smaller and, hence, cheaper. A 10-TeV muon collider could be had for $18 billion, advocates estimate.
it actually understates the case for a muon collider. It is not just more efficient, it's also cleaner, since muons, like electrons, don't do strong interactions.
just one more accelerator bro. just one slightly larger accelerator than the one we just got online. we can revolutinize physics with just one more accelerator bro
> A muon collider could be much smaller and cheaper than a functionally equivalent proton collider, advocates say. It could fit on the 2750-hectare campus of the United States’s dedicated particle physics lab, Fermi National Accelerator Laboratory (Fermilab), enabling the U.S. to reclaim the lead in the continuing competition for the highest energy collider. Most important, younger physicists say, it might be built sooner than a more conventional competitor, perhaps in as few as 25 years. “If you want you can add 10 years to that, that’s still a lot better than when I’m dead,” Holmes says.
:) When I made the joke I was thinking about energy levels and theoretical physicists'/string theorists insistence that we're just a bit more energy away from evidence of the grand unified theory
Also we haven't built a collider that's even close to the collision energies of the SSC, which was cancelled mid-construction over 30 years ago. We're still playing catch-up.
I feel like this sort of research cannot be good in either direction: it seems like a waste of money and resources for society to fund this and other abstract things which can only lead to amusing mathematical models that will have zero impact on society, which is a bad thing because we have very real problems. But, if it DOES lead anywhere, the technology could be devastating and we're probably too stupid to use it. Seems pointless to me.
https://accelconf.web.cern.ch/p99/PAPERS/WEBR6.PDF
which might be a good thing in that the neutrino mass is a "missing part of the standard model" as opposed to "possible physics beyond the standard model". The neutrino mass term could explain dark matter, dark energy and the matter-antimatter asymmetry
https://arxiv.org/abs/1303.6912
whereas a Higgs Factory or top factory seems likely to be a big disappointment because all the evidence we have is that the Higgs field is as simple as it could possibly be and a top factory might end up just verifying that complex calculations people did 40 years ago (by the time the machine comes up) were right.
Muon colliders are a possible path to a Higgs factory or top factory but the path to a muon accelerator that can revolutionize precise neutrino physics is much shorter and I think more rewarding.
Notably neutrino physics is win-win. Either the right-handed neutrino exists as a heavy particle and is very likely to be the darkon or the neutrino is a Majorana fermion (is its own antiparticle) which is certainly a weird and interesting result. Contrast that to all the other poorly motivated darkon candidates such as sparticles, axions, etc.
I remember reading a lot of papers about muon accelerators about 20 years ago, they have been a big research topic in the US and Japan because we didn't have CERN.