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Decades-Long Quest Reveals Details of the Proton’s Inner Antimatter (quantamagazine.org)
260 points by theafh 46 days ago | hide | past | favorite | 73 comments

Once again I am impressed with Wolchover's consistently great writing. I think I could call myself a fan at this point.

There's no bullshit. There's no more glossing over details than needed. The key finding is explained in as close to a layman's terms as you can get, given it's deep physics, yet with some human elements to it. And both sides of any debate are given a chance to give their side of the story.

Science writing will never please everyone, but this has exactly the level of detail I enjoy.

I'm so pleased it doesn't start with stuff like "It was a windy autumn afternoon in Geneva in 1991, and Carlo Broggini had no idea, as he sipped his coffee, that the results he was about to see on his computer would turn the physics world upside down"

You forgot to use "whimsical", "flabbergasted" and "discombobulated" ;)

The moment you think it's going to start,

"Carlo Broggini grew up in the lazy suburbs of..."

Quality of her articles - depth, precision, explanation power - rivals those of Martin Gardner, which is admittedly a high bar. I don't know anybody else today coming close.

Not to deep into this topic, but Sabine Hossenfelder, both providing a critical insight and depth+precision is also something to consider as an outsider to physics. See backreaction.blogspot.com. Hits my sweet spot between maths, physics and layman guidance.

Hossenfelder is not that much of an outsider, she publishes respectable papers and is supported by many physicists, and she agrees with essentially every part of the present consensus.

I think "to consider as an outsider to physics" here means "for people who are outsiders to physics to consider".

Came here to comment on the great article, great to see I'm not alone.

I completely agree. I find her writing very straightforward to understand.

also agree, great stuff

This was excellent. Substantial enough that it didn’t feel superficial to me having taken a class in quantum mechanics. But still approachable enough for someone who only took that one class and didn’t major in the subjects.

The next two decades of nuclear science are going to be extremely exciting as the next-generation electron-ion collider is built and comes online in the US. Since electrons are not composite particles, electron colliders allow us to probe nuclei much more precisely than protons, neutrons, and other baryonic particles do. It's going to like going from a VHF tuner on a CRT to an 8K AR experience.

What's different between the new collider being built in the US and HERA?

Great question! The biggest difference is luminosity. The proposed collider, eRHIC (electron Relativistic Heavy Ion Collider), will generate 100-1000x more collisions per second than HERA.

Second, eRHIC will generate ion beams as well a proton beams. This is a key distinction as protons and neutrons are modified by being inside a nucleus so their internal quark distributions are modified as well. These differences will shed light on some of the key properties of the strong nuclear force.

Third, the detectors and collider will be designed to probe further down into the low-energy tail of the sea quark distribution than HERA and other previous e-p colliders did. This will include designing the beam and detector to allow for very forward instruments which would measure small deflections due to extremely low-energy particles.

Ah interesting! Thanks for answering. The question came from looking up electron-ion colliders on wikipedia and noticing that one had already been built. So was curious as to what had changed. Thanks again.

The way we study the nucleus is kind of funny: Throwing stuff at it and seeing the distribution pattern of how it bounces off or breaks out pieces.

It's like if Oumuamua[1] was thrown at us and some giant gas cloud entity that wanted to see if we had planets by measuring the trajectory anomalies as it came out. Or if meteor showers were to probe atmospheres.

Alright, back to work.

1. https://www.theatlantic.com/science/archive/2017/11/interste...

"It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you." - Rutherford

I was suspicious about this quote as I thought tissue paper wasn't invented [1] when Rutherford said that but apparently Rutherford said this retrospectively in 1936; not in 1909.

[1] Kleenex introduced the facial tissue in 1924

Tissue paper in the UK isn't for cleaning but rather a type of paper https://en.wikipedia.org/wiki/Tissue_paper (usually used in arts and crafts)

Among the applications of tissue paper listed at your link, are toilet tissue, facial tissue, and paper towels.

It also mentions "household towels" which doesn't make sense to me, surely they don't mean what I am used to.

In my area of the US, however, "tissue paper" out of context doesn't imply any of those, I don't think, rather it's the stuff used to wrap gifts or maybe to crumple up to pad them in a box. The stuff is also crumpled and put in new shoes, for instance.

It doesn't strike me as that odd to call toilet paper and facial tissues "tissue paper" although I don't think it's common; however calling paper towels or other towels "tissue paper" seems strange.

Considering the more-established meaning of “tissue”, using for any paper seems a bit odd.

As an neophyte in QM, my mind boggles of the extraordinary energetic nature of these particles, and that this happens on a universe scale level, with laws of nature governing the same response everywhere.

Also how many different levels of scale there are, from giant structures in space, to our solar system, to our human experience, to cells, atoms, quarks and I wonder if there are more such levels down to the planck scale.

i would bet there are more levels we are not currently aware of. could also be a fractal.

Thermodynamics dictates that energy will spread out into all available degrees of freedom equally. If there were extra DOFs, they would either have to be frozen out at human-reachable temperatures, or inaccessible due to not interacting with anything, or else they would appear to us in the form of mysteriously disappearing heat.

Unfreezing new DOFs at high energy densities is the modus operandi of accelerators like the LHC. Everything that happens there can be seen as doing that for different purposes.

Quantum mechanics puts even more constraints on unknown degrees of freedom, because information leakage into ancillary systems has observable effects on interference patterns.

Action quantization (colloquially "planck scale") suggests limits on how small these things can get (very small size = very high momentum, which is not observed).

Assuming are understanding of physics is correct at the plank scale. We already have 2 different theories of physics that are not completely consistent with each other, and we have no empirical evidence of anything near the planck scale.

But electrons are considered to be point particles, so they would have infinite momentum in this case?

No. They are vibrations of the electron field. There are no point particles in the standard model.

σ_x * σ_p ⩾ ħ/2

The product of the uncertainty in each is always at least some constant. They can still be point-like without you knowing where they are; and also knowing exactly where they are regardless of if they are point-like or extended means there is no defined momentum rather than it is defined as infinite.

That said: (a) you can’t pick a number from the set of Reals with a continuous uniform distribution, so I guess you can’t ever have perfect knowledge of the location ever even in principle, and (b) I’m self taught so likely only have a half-understanding.

“Point particle” is an approximation that doesn’t accurately predict reality. It only works at large actions.

Classical is R^3, quantum is R^3 -> C. (Sort of; this glosses over a lot.) Objects don’t really have a concrete location; they have complex-valued distributions.

I'm pretty sure electrons are not considered point particles?

Pretty sure they are. They’re leptons, and elemental (within the confines of the Standard Model, at least).

Something being a lepton has nothing to do with whether it's a point particle.

Pontryagin duality of position/momentum (which comes from both QM and Relativity, depending on your perspective) rules out the physical existence of point particles. It would require infinite momentum to have zero extent.

The truth of all meditations .. there is only up, and down, The rising and falling of transient phenomena ... it seems to be sentient, too! To think, thought is so deeply rooted; matter giving form to matter ... sweat, tears, sadness and joy ... so interlinked with the lowest forms of the blocks that make us all up!

Truly awe inspiring on a grand scale. Its no wonder the ancient greeks attributed gravity to Aphrodite‘s magic .. i honestly find it so fitting; its love all the way down!

Since the “SeaQuest” is from circa 2000, surely it is a reference to the TV show SeaQuest DSV, which aired on NBC from 1993-1996.


There are some fun episodes but the show is not very good and has not aged well.

Man, that sent me down a nostalgia rabbit hole. I really liked the first season of that show, then it sucked, then it got canceled. And now I find out Jonathan Brandis killed himself 17 years ago and I didn't even realize, and apparently he dated Tatyana Ali all the way back then? And now I guess I need to go watch the Fresh Prince reunion and pretend I'm a kid again, but that's just gonna make me sad because Uncle Phil is dead now, and wait a second? Uncle Phil was both War Machine in the old Iron Man cartoon and he was Shredder! How the heck did I never know that?

There was also a seaquest game for the 2600. I don't know how well it's aged.

sealab 2021 is where its at

> Planned future experiments will help researchers choose between the two pictures. But whichever model is right,

I would expect neither model is "right", and instead each is better at capturing slightly different aspects of the true behavior.

Yeah this is one of those articles that reminds me that we almost certainly have no idea what is going on. Not to say we dont have good descriptive models.

The standard model has always felt like a piecemeal built contraption begging for a Maxwell type figure to come along and straighten it all out for us.

I call it the modern Ptolematic system.

It's incredible how something that's both so small and everywhere is so difficult to understand. Fascinating read.

These systems do have a feel of cellular automatons. Questions like: why every proton is exactly the same? how particles interact? why are these clouds of particles? have much neater answers, if there is a correspondence of a "stable pattern" to a "particle".


There are other particles made of quarks (generally called hadrons). Those with and odd number of quarks are called baryons. Mesons are those that have an equal number of quarks and anti-quarks.

"All" protons we see are the same because the exotic configurations decay. (While protons are not yet known to decay.)

Scott Aaronson gave some issues with it being cellular automata even with threads connecting them (search "Bell Inequality" https://arxiv.org/pdf/quant-ph/0206089.pdf), so Wolfram has moved on to graph automata things due to, if I am remembering right, someone figuring out efficient approximations of determining graph isomorphisms and it making evocative pictures with some simple transform models, and also it solving the Bell's Inequality no-go problem.

"We learn in school that a proton is a bundle of three elementary particles called quarks..." - do kids learn this in school nowadays? Because I don't remember learning that in school.

so... could a "subatomic centrifuge" of sorts be built to separate the quarks and antiquarks (using energy of course to pull them apart)?

Would antimatter make a good energy storage medium?

You cannot separate quarks and antiquarks. The force that holds them together increases, rather than decreases, the further apart you pull them, until the energy in that field is so strong it can spontaneously convert to matter in the form of a new quark and antiquark to bind to the now-separated old quark and antiquark.

I've read that description before, and it always makes me feel like there must be a lay-appreciable way to describe those two modes that would provide more insight.

There's a certain tension between the idea that something is composed of parts, yet it can't be separated. How is that fundamentally different from composite things which can be separated?

That's a rhetorical question; I just mean there ought to be a more satisfying way of describing the dichotomy.

Perhaps it can be described without math per se but in terms of visualizable fields?

picture a rubber band, lying in a circle, on a table

left half band is red rubber

right half is blue

as you stretch the rubber band, it resists more and more

when you pull hard enough, it breaks on the red/blue divide. a new red/blue half spontaneously appears for each.

now you have two rubber bands

I've heard that sort of thing before.

My point is, that when you consider that sort of explanation, and let's suppose it vaguely seems to make intuitive sense, then what about the things/particles that don't act like that?

If the explanation of "A" doesn't distinguish between "A" and "not A" then it isn't in fact an explanation.

You can't pull apart quark pairs because the energy involved is so large it will create new quarks to pair up with the ones you're separating.

Antimatter would make a great energy storage medium, if we could create it efficiently and in bulk.

Antimatter is a pretty poor energy storage (or spaceship fuel), because annihilation produces high-energy electromagnetic radiation which is hard to handle or put to any productive use. It just pierces matter and carries the energy away.

It's the ultimate in energy density, though.

Unless antimatter is stored within some medium. Wikipedia mentions a few exotic particles, one of them is a pair of electron and positron revolving around each other.

On the other hand, we tamed nuclear fission, which is also pretty hard to handle. So I am optimistic that we'll sort something out when the time is right

It would be great if (a) you could safely prevent it from releasing its energy when you don't want it to (KABOOM!), and (b) you could efficiently capture and use the energy it releases, which is going to consist largely of gamma rays.

Now where did I leave that dilithium?

CERN manages to safely capture antiprotons and move them around

I can safely move around three eggs at a time, moving 3e9 eggs at a time is slightly more difficult.

A container ship loaded up with packaged eggs in containers could move 3e9 eggs.



Sure, but not nearly enough for practical energy storage and retrieval.

>> You can't pull apart quark pairs because the energy involved is so large it will create new quarks to pair up with the ones you're separating.

What if baryons are electrostatic black holes? No quark can escape. Any infalling particle would slow down and never cross the event horizon as far as an outside observer could tell. Stuff like that...

> What if baryons are electrostatic black holes?

They can't be the equivalent of black holes because things can escape from them in nuclear reactions.

Do we know that things get inside them?

What would the predicted diameter be?

> Do we know that things get inside them?

Of course. Experimentalists have been shooting electrons and muons and other things inside hadrons since the 1960s (hence the "Decades-Long Quest" in the title of the article). That's how we gained pretty much all of our knowledge of the internal structure of hadrons and how the current theory of QCD was developed.

> What would the predicted diameter be?

A hadron is roughly a femtometer (10^-15 meters) in diameter.

Quarks cannot be separated. See https://en.wikipedia.org/wiki/Color_confinement

I haven't been downvoted here for a while, so let me annoy HN a bit. In the standard physics model, quarks are inseparable because the magic force that binds them only grows when you try to pull quarks apart. Don't ask why, the magic force just has this property. Occultism, on the other hand, sees each proton composed of 9 particles that are held together by a stream of something like electricity (they call it "fohat") that pierces each particle thru its axis. Pulling any of the particles aside would be quite a feat, however it's trivial to choke that electricity stream to let all 9 particles free. This hypothesis is unfalsifiable with today's tech.

That's interesting that atoms have tiny fragments of antimatter inside them. That implies that some day it might be possible to build an engine that runs on extracting this energy. Space drive, any one?

"Has" is not exactly the right word to use. A closer analogy might be that momentum flows through both matter and antimatter quantum fields as it traverses between particles. It's more of a current than a charge. If you "froze" it and cut out a slice of the space between two particles, you wouldn't find anything there any more than you'd find electricity inside a slice of a cut power cable.

I agree that it is super interesting but... empty space also has ephemeral fragments of antimatter in it. We can’t extract energy from it.

There is already gobsmacking amounts of energy available to us in the atomic nucleus in the strong force, and we’ve been working for ~70 years to extract it (via fusion).

Iirc, in a conversation with Feynman, Wheeler speculated that positrons may be hiding inside protons and that's why we don't see many positrons around.

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