# Something’s Up In Switzerland: Explaining The B Meson News From The Large Hadron Collider

Particle physics is a field of extremes. Scales always have 10really big number associated. Some results from the Large Hadron Collider Beauty (LHCb) experiment have recently been reported that are statistically significant, and they may have profound implications for the Standard Model, but it might also just be a numbers anomaly, and we won’t get to find out for a while. Let’s dive into the basics of quantum particles, in case your elementary school education is a little rusty.

It all starts when one particle loves another particle very much and they are attracted to each other, but then things move too fast, and all of a sudden they’re going in circles in opposite directions, and then they break up catastrophically…

## The Standard Model

In the 1970s physicists started coalescing around a thing called the Standard Model, which is similar to the Periodic Table of Elements, but at a much smaller scale. It describes the particles that make up the protons, neutrons, and electrons (which in turn make up atoms), and the forces that act on them. The Standard Model has held up to most experiments so far, but the one earlier this year may throw a small wrench in that.

The Standard Model reuses a lot of pre-existing words in confusing ways, so let’s break it down a little bit from (relatively) large to small.

• A molecule is made of atoms.
• An atom is made of protons and neutrons surrounded by electrons.
• Protons and neutrons are called composite particles because they’re made of smaller elementary particles.
• Protons and neutrons are made of combinations of quarks. There are other composite particles, and in general these particles made up of combinations of quarks are called hadrons.
• There are 6 different types of quarks, named: up/down, charm/strange, top/bottom. Combinations of up and down quarks make up protons and neutrons.
• In addition to quarks, there’s another class of particle called the lepton. Leptons can have a charge, like an electron, or they can not have a charge, like a neutrino.

Besides the classification of these tiny particles, the Standard Model also describes how the fundamental forces interact. There are 4; electromagnetism, strong nuclear, and weak nuclear. Gravity is the fourth, but the Standard Model doesn’t like to talk about this black sheep of a force, and intentionally leaves it as a blank space, an exercise for the reader (or some janitor to Good Will Hunting it). Some day either the force of gravity will be incorporated into the Standard Model, or a new model will emerge that explains the universe better than the Standard Model AND incorporates gravity, but until that happens, some hand-waving will occur. Besides, gravity works on such a larger scale than the other three, that its effect over the scale of subatomic particles is considered negligible. *shrug* I’m just repeating what the physicists are saying.

## Keep Up with Bosons and Mesons

The way forces work is with force-carrying particles, a category called bosons. There are a few sub-categories here, because different bosons are responsible for the different forces. Photons and gluons are among them, and the recently discovered Higgs boson, which was theorized a long time ago as being a requirement for the Standard Model to work, so the physicists breathed a collective sigh of relief when it was finally found. There’s also a theorized graviton that would be the force-carrier for gravity, but it hasn’t been discovered… yet (looking at you, Matt Damon).

There’s one more kind of funny-word-on to know about, and that’s the meson. It’s a particle composed of quarks and antiquarks (which makes mesons a subset of hadrons), and which ones and how many lead to a large number of different variants. Mesons are very unstable and last less than a microsecond, decaying into various combinations of other types of particles.

Clear?

## The Experiment

Particles this small are impossible to measure directly, which is why we have the Large Hadron Collider. If one were to try to reverse engineer a cake, one could take pictures of it, do spectral analysis, maybe even taste it. These aren’t options at the subatomic level. Instead, the LHC makes particles move very fast, then bashes them against each other. The bits that result from these collisions have a lot of energy to dissipate, which results in them interacting with electromagnetic fields in tiny but measurable ways. From these collisions, we can work backwards to figure out the secrets of the universe, in much the same way that throwing a grenade at a cake and analyzing the spray pattern might allow you to determine whether the frosting was buttercream or fondant.

In the experiment announced recently (pdf of paper), there was a discrepancy in how a particular variant, the B meson (which isn’t a single variant but a whole class of variants), decayed. The Standard Model says that leptons all behave the same and are identical in every way except for their mass. So when the LHC bashed a whole bunch of particles together (specifically protons vs. protons) and measured the B meson decays, they theorized the subatomic soup that resulted would contain equal parts of electrons and muons. Instead they found 15% fewer muons than they expected.

They couldn’t exactly look at the nutrition label, so they’re left wondering if what they found was a fluke, or if the recipe was wrong. If it’s the former, then it will have beaten the odds by 3 sigma (which corresponds to a 1 in 740 chance of a fluke). In particle physics, this is merely eyebrow-raisingly interesting, as it’s not a large enough exponent to satisfy them. If it’s the latter, it means big things for the Standard Model. That could mean either revisions to the Standard Model, or possibly understanding if there’s a difference between the leptons (other than their mass alone), ending what was formerly called lepton universality.

Unfortunately the testing machine, much like a McDonald’s ice cream machine, is down for servicing, so we’ll have to wait until 2022 before the upgraded LHC can deliver some frosty mesons and give us an answer about the Standard Model.

## Fool Me Once, Well, Keep Fooling Me

Calling this eyebrow-raisingly interesting as opposed to earth-shatteringly amazing is an appropriate response, as we’re no strangers to the teasings of the physicists. There have been a number of anomalies over the last decade in particle physics that have all been overturned eventually as more data came in. There’s a vast difference between a 3 sigma anomaly and a 5 sigma (1:3.5 million) discovery, and we’ve been seduced by this before. Maybe you remember in 2011 the superluminal neutrinos that turned out to be an improperly attached fiber optic cable. In 2015 there was the 750 GeV bump with a significance of 3.9 that ended up being a statistical fluctuation the next year when data was collected again. In 2016 there was an anomaly with the B meson that seems to have faded, too.

Each of these anomalies leads to hundreds of papers and theorizations and new types of physics until the next set of data sends them into the shredders to make pulp for the next round of papers, and the machine grinds on, with journalists siphoning headlines from these papers and drawing wild conclusions about warp speed and time travel and new particles like the leadingmeon.

And yet, forward progress keeps happening, slowly and scientific methodically, as we move towards understanding the workings of the universe. Maybe in the decades to come they’ll laugh at our quaint Standard Model like we look at the four elements of Earth, Water, Air, and Fire, but we will have gotten to that point by moving through where we are today, so I’ll continue to read about it and nod like I pretend to understand what they’re talking about, and respect the complexities of the process of measuring things so small. After all, my day job as an electrical engineer relies on making electrons move in ways that were inconceivable a century ago; maybe the discovery of lepton non-universality will eventually lead to the downfall of Amazon and Uber.

## 50 thoughts on “Something’s Up In Switzerland: Explaining The B Meson News From The Large Hadron Collider”

1. William Wesley says:

unfortunately the publishing is the point, not the understanding, as in boxing or chess a final resolution is not actually desired, all the money is made through conflict in print.

1. Alex Rossie says:

Aptly the McDonalds ice cream machine if down for servicing because the money is made by selling the machine to the franchise and then repairing it constantly.

The money isn’t actually in delivering ice cream to customers…

2. Jimmy Wiggy says:

🤣 best physics review I have read in a long time. Hilarious!

1. Goody Rather says:

Agreed. Quite a few chuckles in here. Keep it comin’!

3. Gravis says:

I’m just glad to know that people are still probing the depths of reality. I am curious about the feasibility of a spaceborne collider, especially now that the lift capacity per launch has been drastically increased and the launch cost decreased. It’s not a very accessible for us earthbound humans but space seems like an ideal location for many of these experiments.

1. Chewy says:

What do you imagine would be advantageous about having a “spaceborne collider”? Perhaps I am missing something but I don’t see any new questions being answered. The collider instrumentation by design is meant to contain within fields so if I understand correctly the physical location should be moot, also assuming location did have some type of effect upon the experimental process wouldn’t that be a bad thing?

2. Eric Weatherby says:

If we can be reasonably certain that the colliders aren’t going to be causing any huge explosions or releasing dangerous amounts of radiation or so on, then the logistics advantages of building them on earth make that the logical choice.

I’d be interested in hearing your ideas on why spaces would be good. I do have to admit that building an equatorial collider around the moon would certainly be *cool*.

Hi there, accelerator physicist and operations specialist here. This idea was floated years ago because you don’t have to worry about radiation affecting surrounding areas, and you have no space constraints so your magnetic fields don’t have to be as high (i.e. larger circumference permitted). However, from an operational perspective, I can say that we’re constantly performing maintenance and responding to failures on our accelerators; putting our machines up in space makes accessing them even harder! Since colliders/accelerators are often pushing the boundaries of what the equipment can do (power supplies, computation, magnetic and RF fields), uptime is not 100%, so human intervention is a fact of life for us.

1. Anonymous says:

“accelerator physicist and operations specialist”

+1 That sounds impressive.

Nah just lots of syllables. I rely on real engineers and technicians to do the actual work, trust me.

Hi Adam. Could you please send me an email ? I would like to interview you. I have some documentation I am hoping to have validated as well. Thank you much.
Florida

2. No Nonsense..... says:

Greetings from a long time “electricity hacker”…. I’ve been able to figure out most of this “mess”, did get an intro to much of it decades ago. Had to do a lot of recalling! My forte’ is in electrical areas, but a lot of changes have happened over quite some time. Our lives have been influenced by the semiconductor industry, with transistors, tunnel diodes, light emitting diodes, The standard idea of sine-wave theory has been replaced with digital bits, thus revolutionizing everything. I’ve kept up with it enough to realize that “all that is needed” are a few Albert Einsteins again! Simply stated, today’s “ordinary” household computers are the result of the need for a human/machine interface to allow for interaction. Now, the idea of a research collider on the moon is within grasp, with problems of gravity, sun particles, et all, to be solved. Thanks to everyone for the insightful inputs! About math – I recall a very astute computer programmer who could dream up lots of ideas to accomplish quite vexing problems, yet she had no idea of multiplication tables and following algebra formulas! Everyone has some good ideas for solving problems!!

1. Jay Carlisle says:

Do consider that the language of precision is not a subject intended for the general public to hold any save a not nil understanding of suitable for a functional labor force while winnowing out natural talents for potential future development should circumstance warrant by those who oversee the social indoctrination programs tagged as education at the secondary level as if a passive act offering teaching could be mandated and upon leading the Houyhnhnms to water it follows that They can be made to think If the public were intended to hold fluency in communication of specifics it wouldn’t be taught as a stand alone abstract subject that dictates one route method as the single correct means of solving a given set of problems like anointing the cut/paste function as properly done only with the pulldown menu method with none of that fast and loose business which will result in the loss of a letter grade for each instance appearing in a students capture log
Were the intent ment to maximize lil Johnny’s knowledge meeting his full aptitude the mathematics would be incorporated into the subject mater as it is required in function and all valid approaches would be available with the specifics a subjective and contextual determination in details but shaking out in large part early on with the key differ being who’s allowed into the Lyceum and who’s in the number not By the time limit process might be conceptually abhorrent enough to spark preference for infinitesimal analysis its only gonna surprise at a mile off depending on observation point over/under
The focus is more on stand in line, raise Your hand, sign Your name in the upper right hand corner while quite a few so called subjects are not as purported When economics fails to make any practical predictions boom or bust and also fails in popularizing its findings such that its uncommonly rare to find a layman that can give a simple definition of dollar suggesting the subject instead is more accomplished in fostering disinformation in the public facilitating fractional reserve fiat dollars in a unsustainable grey goo perpetual growth model system taking on the properties of a sigel in public perception it makes some amount of practical sense how such disingenuous manipulation might be considered advantageous enough to implement
It was pretty chilling when the common core kid said “We’re both right” and I found order of operation was being argumentative trying to be right just to win
God help Us all should that kid end up designing a bridge some dark day
Anyway I told Y’all that to ask this
Aren’t the returns seriously diminished at really large circumferences?
And anyway the equatorial collider would suffer from no Corvallis effect. That’s how You find an equatorial point by finding where water just sloughs through a draining container without rotation
Catastrophic effect on spin
Please try and be more careful in the future

1. Jace says:
4. Dan says:

I believe Starlink is rapidly moving towards deploying a spaceborne collider.

1. Onetruegod says:

Yeah. I think its called Skynet…

2. Viz says:

It’s already done penning trap in space was already done and FTL micro quantum communications satellites deployed using the tech that hawkings developed back when his theoretical ideas went into practice. Primordial black hole drive engines were born and penning trap gwave drives just went online lhc is and engine. Non college grad thoughts from the autistic spectrum don’t really give two Fs

5. abjq says:

Don’t we get a better vacuum in LHC than we get in space (near earth)?

1. Pat says:

Depends on what you mean by “near earth.” Low earth orbit? Yeah, definitely. Geo? Nope. Surface of the moon? Pretty close.

Pressure at LHC is about 0.1 nanoTorr, or a few million “things” every cubic centimeter. Obviously space is thinner than that (standard rule of thumb is the ISM is an atom/cubic centimeter), but it takes a while to drop ~12 orders of magnitude in pressure.

Moon is about 50 times better vacuum than LHC (at night). An accelerator literally orbiting in space is a little silly – surface of the moon would be more reasonable. However as Adam pointed out above, I always find the people who think we can just happily build an unattended top-end scientific experiment *hilarious*.

1. RetepV says:

Only reason to have one in space, I think, would be to be in a place where gravity of the Earth interferes less with the experiments. I’m by far not into this stuff. But it occurs to me that we might have problems fitting gravity into the model because we are in a gravity well. It can’t be just a coïncidence that exactly *gravity* is what we are having trouble with. It’s all around us, we experience it all the time… But maybe *that* is actually the problem.

1. Pat says:

Meh, there are reasons like “you can’t practically build an accelerator that large on Earth because… because… politics, I guess?”

Going into space doesn’t actually “get rid” of gravity. You don’t experience it because you’re constantly in free fall (the equivalence principle). But even that’s an approximation for a macroscopic object.

“It can’t be just a coïncidence that exactly *gravity* is what we are having trouble with.”

It’s really not surprising that it’s difficult to fit gravity into any particle physics theory: gravity is like, 30+ orders of magnitude weaker than all the other forces.

6. Viz says:

It’s already a reality and in use for G wave penning trap engines to propel use to deep space utilizing quantum navigation quantum communications waypoints FTL

4. Mark Hambleton says:

Nice work. Thanks. Really good piece for the ‘totally out of their depth, but perversely interested nonetheless’.

5. Biomed says:

At this time it still sounds like a replay of Laurel and Hardy’s “Who’s on first?”.

It will continue to become more clear over a few more decades as we simply refuse to accept not knowing.

1. Piecutter says:

Perhaps you mean Abbott and Costello’s “Who’s on First?”?

1. Piecutter says:

And if you need it made clear, Lou would have been a great theoretical physicist. His mathematical skills could prove the impossible using multiple equations to come to the same answer:

1. Mike says:

Isn’t that the basis of the new math that they are teaching now?

6. David Misel says:

It’s good to mix humor with serious science stuff.
Makes me feel as if I understand what’s happening in the big world of tiny particles.

7. Anonymous says:

Earth, wind, air, and fire, huh?

Ha! Whoops. Fixed. Thanks for pointing it out.

2. J.J. A. says:

Hey I wonder what would happen if you mix them all together.

8. dukwon says:

“In 2016 there was an anomaly with the B meson that seems to have faded, too.”

Which one do you mean? The P5′, R(K*), R(ϕ), R(D) and R(D*) anomalies are alive and well.

By the way, the LHCb experiment is wholly located in France, not Switzerland, albeit right up against the border.

1. singlemale says:

are you sure. Some farmer may have moved the border like they did in Belgium

1. Patrick says:

That’s true. But the accelerator is across France and Switzerland.

9. Patrick says:

“maybe the discovery of lepton non-universality will eventually lead to the downfall of Amazon and Uber.” That’s a surprising angle 🤣. Someone who actually worked on these measurements.

10. Alice Lalita Heald says:

A video would worth 1000^2 words here.

11. Dan says:

I must admit, every time I read the word “meson”, I hear it in jar-jar binks’ voice.

12. J Titus says:

I suspect as physicists tools offer more resolution they will find smaller and smaller particles with shorter and shorter lives. It could go on forever…

1. Pat says:

Particle physicists call pretty much everything “a particle” but they’re really just bound states of quarks in new and different configurations. There’s no real thought or evidence that the fundamental particles (leptons, quarks) have *any* substructure whatsoever.

In other words, these particles aren’t getting “smaller”. They’re just new configurations of quarks. It’s basically like investigating the spectroscopy of atoms: the difference is that since the structure of the theory is *much* more complicated, the number and structure of bound states configurations is *much* more rich.

For instance, the delta-+ particle is really just an excited proton, much like if you excite hydrogen by heating it up and it flows at specific frequencies. But because it’s particle physics, it gets called a new particle instead of “excited proton.”

13. Mikey says:

Rather than the “stamp collecting” (taxonomic) approach to physics, wouldn’t it be nice to write a GPU shader in pycuda or numpy to plot SU(3)xSU(2)xSU(1) ?

The idea being, a Dirac Spinor (electron) is plotted as a soliton, a standing (Compton) wave. A nucleus would be illustrated as a shell of such tetragonal soliton lattice, exchanging boson-waves. It would be neat to see a dumbell shaped lattice fission as a moderated neutron-soliton, propagating at the appropriate velocity causes the shell-droplet to pop.

Need some clever ways to render bi-quaternions, that is an 8 dimensional wave function in three dimensions.

Something like the plots at https://github.com/portsmouth/fibre

I have trouble even getting my Vive sensors to work in Linux with Khronos drivers. I’ve used numpy to plot matrices, but the math is over my head, and I probably won’t ever find the time – https://www-fourier.ujf-grenoble.fr/~panchish/ETE%20LAMA%202018-AP/lecturesZETAS2018/Special%20unitary%20group%20-%20Wikipedia.pdf

1. Pat says:

Physics is *way more* than the gauge groups: pretty much all of the interesting stuff comes in how the symmetries are *broken*. The gauge structure tells you why, for instance the particles in the Eightfold Way all have *similar* energies and decays but the actual *physics* is in how it *differs* from exact.

The gauge groups also don’t tell you about the mass structure, which sectors the groups act on, and the alignment of the eigenstates between groups, or what currents the interactions couple to, for instance.

1. Pat says:

That should say *group* structure, not *gauge* for the Eightfold Way. And yes, that SU(3) (of up/down/strange) isn’t the QCD SU(3) (of color) but that’s partly the point: the mass structure and number of quarks add a *huge* amount to the richness of the theory and they’re not in the gauge group structure at all.

1. Mikey says:

After watching some youtube videos from Siggraph2019, Game2020 and Cohl Furey, I gathered that the 3-2-1 group structure signified a sort of recursive triple Maxwell equation, with divinely arbitrary coupling constants empirically derived. I’ve actually coded Maxwell equations and DSP.

Since some here are familiar with the electronics concepts, those might elucidate the physics for those unfamiliar with the parallel universe of physics conventions and nomenclature, since different professions like to use different terms for similar things. To me (now), the quantum vacuum is an 8-fold zero-bandgap semiconductor for soliton modes. Which is probably as far as I can go without years of math. I thought plots of configurations of the fields and momentum/spin of different particles would be more insightful than a table.

1. Pat says:

Yeah, science communication is really poor on this stuff. All of the descriptions I’ve seen are pretty universally bad. You’ve either got math-heavy theorists who are obsessed with naming math terms (… weird) or experimentalists who similarly ignore the underlying symmetry.

The reason for the table is actually the *broken* symmetry. Look at the table – the “SU(3)” part is a tiny label in the corner of the quarks, saying “oh yeah, there are really 3 of these guys but they all act identically”.

And the fact that there are 3 generations is some (presumably) broken higher symmetry, as is the fact that “up/down” and “electron/neutrino” are different particles. If the symmetries were unbroken, you’d just have a single “quark” with a little “x3 color/x3 generation/x2 weak isospin/arbitrary phase” label, and a single “lepton” with “x3 generation/x2 weak isospin/arbitrary phase”.

I’ve never really understood the point of calling things out as the full symmetry product space, because the only one that really matters for “taxonomy” are the *broken* symmetries. The unbroken symmetries just result in weird structure constants.

14. Well, the new theory is actually an old theory: the Aether Theory. Ooohhh. Tesla used this theory to come up with all of his inventions and it was the reigning theory of the late 1800’s, based on Newtonian physics.

It’s a very simple theory: the entire universe is filled with an electromagnetic fluid.

This theory explains gravity and dark matter (heavy bodies spinning fast enough to attract other bodies, outer edges of galaxies spinning as fast as the center) and anything electromagnetic (EM).

The theory also has this side hustle, where faster than gamma oscillations have vibrations so fast that particles form, based similarly to cymatics, where harmonics creates form at various overtones; these structures creating or absorbing radiation (a pressure modality in this Aether).

It’s where the word Aether or Ether comes from.

But in the late 1800, two scientists tried to prove this theory, the Michelson/Morley experiment (MMX).

They thought that if the Earth is traveling through this Aether, they should be able to measure this “Aether wind” as a pressure hitting the Earth.
So, they used an interferometer (laser split into two beams and reconverged at the same point), which could detect this Aether pressure.

What happend was they got a null signal, nothing!
It ruined science. No one knew what to think, Aether theorists were appalled and the scientific community scrambled to figure something out.

Einstein, who was also an Aether theorist, used math to break it down. He knew the Aether math was still valid and useful (aside weird anomalies like Mercury’s orbit weirdly out of sync with the common barycenter of the solar system and others), so he split the Aether theory into two: gravatational waves and E=MC2 (speed of light (C) = speed of Aether).

Thus the current foundation for our scientific models: standard model, quantum mechanics, string theory, etc.

There are a few problems with this though.
We use interferometers in space LIGO/LISA, etc, and those get signal from gravitational waves, also Aether theorists primarily believed in a God or intelligent design. Michelson was a huge proponent for the church; his invalidation of the Aether theory was primarily the basis for the scientific community to push atheism.

One of the reasons God was such an easy explanation: most believed in a God, but also, you can’t get something (like the big bang) from nothing. Enter Hawking, he saved the day! He came up with the idea of 4th dimensional universe bubbles, rubbing against each other, creating energy that would make particles.

This convinced the scientific community there was a possibility of this big bang from universe bubbles, but recent equations fall short, due to false vacuum decay, as well as the fact we would see more indication of pull or force from an outside universe; which there is none so far; so this is still being studied, but it’s rather impossible to study forces outside our universe.

But! Here’s the fun part!

The MMX is horribly invalid.
See, we have this fun protective EM field, which keeps us alive from the sun’s harmful rays. We see this in the Aurora borealis, we’ve since studied this field and know very well it’s there.

It also blocks all of any Aether wind. In fact, if you turn a spinning interferometer on its side, you actually get a signal (measuring the pressure of this EM field), as seen here: https://youtu.be/7T0d7o8X2-E

There are other obvious issues with the standard model, including the measurement of the Higgs boson, which puzzled scientists, which then came up with the standard model 2. Other theories like Higgs field and QM have stated that all these subparticles each have their own field, but it’s widely known that everything is made up from fields, due to when freezing particles, you get more of a wave function.

So, science is super close; everything is a field, but why not just one field, like the Aether theory?

Well, it makes a lot of sense.

See, after Tesla’s (and the German Nazi scientists, who were all Aether theorists) work was taken underground; all this Aether work vanished.

Aether not only explains light as an EM pressure in this medium, but it explains: flying saucers (instant quadrillionaire, if you mine the asteroid belt, hello Elon), Tesla’s death ray (a similar microwave device used by the military to disperse crowds), endless energy, mind control (TMS based devices), etc.

It’s basically has access the most destructive science ever. It also proves how the military could already be flying our own saucers (reverse EM pressure against “gravitational waves” (i.e. fluidic Aether).

Another weird thing is that it makes sense why “science” would continue to study this; these EM forces are being detected with EM sensors, which means all sorts of things will look correct… not to mention, those who “fund” “science” control the main narrative.

Problem is, the jig is up! The scientific community is finding too many errors, without “one medium to rule them all”, so yeah, B measons and all the other inconsistencies of the standard model.

I’m not suggesting that we ditch scientific research; it’s all quite useful, but math doesn’t tell you what to research, it only can validate studies on that research. We need to at least look through the eye of Aether again, to re-study each experiment done with gravatational waves, EM forces and particles.

Think of this, Aether has really never been disproven, but standard model has been constantly disproven and is disassociated from gravatational waves.

Also, maybe weird anomalies, like Mercury’s orbit will make more sense, when we study new data from the Parker Solar Probe (et al new solar satellites) and see that the sun doesn’t have a perfectly centered axis, which would account for the odd barycenter and why you “sometimes” have to use Einstein over Newton… maybe you don’t and Newton is just fine for everything.

It’s all how we think stuff works, Aether proves matrix theory or intelligent design; why not bring back spirituality, now that we know the pitfalls of religion?

1. Loren Heyns says:

You lost me with the last sentence. What about Aether proves intelligent design? We would we need to be spiritual in trying to prove matrix theory? Are you saying matrix theory is unprovable?

15. RubyPanther says:

My understanding is that gravity is left blank because it isn’t really believed to be a fundamental force. However, because we can’t sense or measure the shape of space-time directly, we have to use a fake force to describe the effects of the topology of space-time. Basically, mass changes the shape of space-time; or you could equivalently say that deformations in space-time create mass. And the direct path that this mass travels goes over these deformations. But we can’t see or intuit the deformations directly; we expect a “straight line” to be where space-time would be if it wasn’t deformed. So pretending that gravity is a force allows us to maintain this useful geometric concept of a straight line even when we’re talking about motion in the real world.

So it is not actually waiting to be solved at all. There are simply no gravitons to discover.

1. Pat says:

“My understanding is that gravity is left blank because it isn’t really believed to be a fundamental force.”

So to be clear, gravity gets left out because it doesn’t appear to be a *gauge* force like the others – not one we know how to deal with. Some gravity theorists are *really* obsessed with the whole idea of “there’s no native background spacetime, it’s matter matter matter” but that’s a philosophical point more than anything else.

“But we can’t see or intuit the deformations directly”

This is the odd thing about that idea – yes, we can. The Universe, for some reason, got *driven* to “flat background geometry” to *very* high precision. So the idea that “there’s no a priori background metric” is… well… silly. Maybe *fundamentally* there isn’t one, but *something* (canonically, inflation) shoved everything out in such a way as to *impose* a fundamental flat metric on the Universe.

So nominally you could say “well, yes, but we can *imagine* Weird Universe where inflation didn’t happen, and curvature can just be anything!” and – yeah, I mean, you *could*. So what? Still live in this universe, which means we can “group” inflation + gravity together, call the two of them “gravity” and hey look, now we’ve got a background metric.

“So it is not actually waiting to be solved at all. There are simply no gravitons to discover.”

Gravitons might end up being something weirdly emergent in the Universe, but there *will* be something we can call a graviton. It’s just a natural consequence of quantum mechanics. You get up to the Planck scale, and gravity is so strong that it’s just impossible to have certain configurations quantum mechanically, because the energy states don’t work.

The “solution” to “quantum mechanics + GR” can’t be “there’s no actual problem.” Get up to the Planck scale, and *neither* of the theories will work. And whatever the final solution is, there’s going to be *something* like a graviton.

That being said it’s important to understand that when we say “oh, there’s a particle,” it’s really just a way of naming things. An up quark is just an excitation of the “up” portion of the quark field (…it’s more complicated than that, even, but let’s just go with that), exactly like a fundamental mode of a drum. Just like you can’t create a standing wave on a drum other than in certain patterns, you can only create quarks in certain field configurations too. So a “graviton” in some sense ends up being the same way – it’ll just be the fundamental excitation of spacetime itself, which we *know* has to be limited in how it can be excited.

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