This might sound tautological but a particle is, well, a thing that behaves like a particle.

Those behaviors are something like:

- it has momentum - it's state is uniquely defined by a position in space and a velocity

What's not a particle? A wave (well, until 1900 or so ...).

Sort of like asking "what is a number?"

A number is a thing that obeys certain rules. (You can add them; there's an `identity `, for every number there's a number which if you add together gives zero, etc).

That allows things like `(3 + 5i)` to be a number, for example.

Particle spin explained:

Imagine a ball that’s rotating,

Except it’s not a ball, and

It’s not rotating.

(popular particle physics meme)

From what I understand of QFT, the Universe is made of fields of different types, and a “fundamental particle” is just an excitation (wave) in the corresponding field.

For example, a photon is a wave in the universal electromagnetic field, A charm quark is a wave in the universal charm quark field, etc.

I’m not a trained physicist, so I might be wildly wrong.

> we often think as though it were dirt, or a billiard ball, or something

The problem lies that it is hard to imagine something that does have zero dimensions. You can get the example of ant walking into 2D and it is unaware of third dimension to explain we are have something similar for space-time 4D (although not the same picture exactly as time is different from spatial dimensions). But we don't have an idea how to approximate a mental picture of what a zero dimension could be. So you have something that does not occupy a volume in space (Talking strictly about elementary particles here) in the classical sense.

This does not mean they are abstract concept. According to QFT -Quantum field theory- you would think (by training) of particles are excitations or quanta of their respective fields. Fields are there always (vacuum is just filled with fields) and particle appears when they are excited (more complex processes occurs). So you would think of each particle as a manifestation of a quantum field that permeates the universe. What is interesting (and probably confusing to most people) is that these fields are not zero-dimensional, instead, they exist everywhere in space and time. But the quanta (particles themselves) are considered point-like with no spatial extension.

In practice physicists will think about particles properties (i.e charge, mass, interactions, spin) ..etc instead of what this particle actually is from that point of view. This is often for practical reasons. You are a working physicist and you learned from your training that you shut up and calculate (or implement if you are doing experimental particle physics as you spend most of your time coding) by this stage.

Richard Feynman gave what I consider to be the best possible answer to questions like this:

https://www.youtube.com/watch?v=Q1lL-hXO27Q

I've only got a physics minor, so hardly an expert, but I felt like quantum mechanics got a lot easier once I started thinking of a particle as merely a situation which has some probability of causing a state change in a detector of some kind.

https://youtu.be/j2oSyAfPzWg?si=bwM2NAsORzkqLQLk

Fun fields discussion on what particles are…

I mean I can not speak for you, but I do not think that the problem necessarily is that people think of them as made from some stuff, I think what causes the most trouble is the desire to visualize particles.

The trouble is that an electron is an electron and it is nothing like anything you have ever seen in your macroscopic classical world. It shares some aspects with billiard balls and some with water waves but it is not like either. And it does not switch between being a billiard ball and a water wave, it always is the same thing, it always is an electron.

It just happens that in certain situations the billiard ball properties are more apparent and in others the water wave properties and in yet other situations neither of the two analogies will help. I think that is what trips people really up, they want to visualize their electron as one thing they know, as something they have an intuition for, but no such thing exists.

And electrons being electrons also means that they are not excitations in quantum fields. Those fields are mathematical models that describe the behaviour of electrons, they are not the electrons. Certainly not in the very direct sense of nature is just mathematics because I can differentiate, integrate, and square fields at will but I can not do this to electrons. And even the less direct interpretation, there are real entities in the universe that behave exactly like our mathematical fields, does not seem likely, what would the gauge symmetries mean?

It's a useful fiction, but the map is not the territory. This sounds blithe but ... it is as close as you will get to the truth.

I only got the bachelors' version of physics, though I did take some grad classes, so here is what I will tell you:

The human mind learns from experience and it thinks of things in terms of the past experiences it has had. We are big assemblages which exist in a narrow range of temperatures (think in terms of Kelvin). Our experience is classical, in the Newtonian sense: we move at not a particularly notable fraction of c, we are too warm to note the strangenesses which happen below, say, twenty or four or a thousandth of a Kelvin (superfluids and BECs are out), we are too cold to have a great internal experience of plasma, leaving us to be creatures of solid and liquid, with a sort of inferred understanding of gas. We are too large to feel the quantum realm, in the sense that the uncertainty principle is not obvious to us from what we have felt.

So, we must make do with abstractions, with fictions, with approximations. Conscious that we are the epitome of the six blind men trying to understand the elephant through touch alone, we try to break our understanding, to search for flaws in our inferences. Yet this does not grant us true experience when we run across, say, the electron. We try to think of it like a billiard ball, but we can say that a billiard ball is this wide, yet we are fairly sure at this time that the electron has no radius, no diameter, that it might as well be a geometric point. Every time we try to measure, we can only establish a smaller and smaller upper bound for the confounded thing's radius. That's not like our lives at all!

The reality of this electron is that if we get it going fast enough, it stops getting much faster no matter how hard we smack it. That's not like our reality. If we try to pin down where it is, the more we do it, the harder it is to figure out how fast and in what direction it moves. And as we work to ascertain the velocity (and therefore momentum), we lose sense of this bit of weirdness' position.

You eventually have to develop an understanding based not on experience at all.

Perhaps this was unique to me, but the first time I understood integration in calculus, I had a brief moment of dizziness as I apprehended this new thing. You know how you are working a math problem and you have a good idea of what the answer is already, a sense of what the magnitude and direction might be? I had ground my way through vector and tensor calculus, and had been working a problem in gravitation and relativity class when I sensed what the resulting tensor would look like, the shape of it, in the sense that I would know if my figures were way off. I nearly fell off the chair, my head spun so.

If you care to, you can do this for a particle.

Particle is a cloudy, fuzzy thing that can fly and wobble through space. It can be more sharp or more fuzzy and when it overlaps with another fuzzy particle object they might exchange a neat portion of momentum, angular momentum and energy and violently reshape becoming sharper or fuzzier (that's the wave function collapse and expansion) then they go again on their separate merry ways.

Sometimes when particles meet or even spontaneously they can split or merge altering other parts of their nature (unrelated momentum, energy and angular momentum). This happens for example when neutron decays into proton and electron.

Sometimes they get stuck together because of electromagnetic force and they resonate in interesting harmonies and travel together. That's atoms. Interestingly when they are resonating in those harmonies they become quite fussy about amounts of energy they prefer to exchange and they do it only in a very specific quanta.

And there's a class of particles called quarks that travel together all the time as they are always tightly bound with each other and can never get free despite possessing incredible amounts of energy they continuously exchange. That's nucelus.

We really don't like this image because fuzziness is actually two dimensional in every point of our already 4 dimensional space-time and described by complex numbers so we prefer to focus on those brief moments when particles interact since if we have a lot of particles that are bound together to form measurement apparatus they are so sharp that the interaction they participate in squash other particles nearly to a point and we can declare that the measure particle collapsed to have some momentum, or location, or spin described by a single vector instead of a cloud. It neatly turns out that the square of complex number fuzziness describes the probability that a fuzzy particle will interact with a sharp one (one of those bound together in measurement apparatus) with a specific outcome.

I’m not a physicist, but as an arrogant philosopher of science: isn’t it just field excitation? Like, every particle looks like a circle bouncing around a 2D piece of paper, but if you look reeaaaaally closely it’s just a localized 3D spike of energy in a usually 2D field of energy? So it’s made of the field/paper itself.

I must be under-thinking this, but that’s what’s worked pretty convincingly for me.

The same is true about the terms "waves" and "fields" when it comes to quantum mechanics.

They're analogies. The concepts need names, but I think they do more harm than good because people then start with a mental model of a membrane or a surface - something they have experience seeing waves in. And then after 1 or 2 steps where the analogy helps, it breaks down, and people start being confused.

Of course the alternative isn't any better. If they had named it a "Wazoo function" and a "Quantum Flarg" everyone would've just kept asking "OK but what IS a Wazoo? What IS a Flarg" and not been satisfied with a "Yeah, it's a fundamental own thing".

Feynman, of course, has a pretty definitive response on the difficulty of this problem: https://www.youtube.com/watch?v=Dp4dpeJVDxs

it was in fact called the "Goddamn Particle" originally, referring to how difficult it was to detect it. The name was changed later to "God Particle" for publishing reasons.

https://en.m.wiktionary.org/wiki/God_particle

So, its all gravity, if you turn the sock inside out? Just taking different colors and shapes?

Actually it doesn't seem to be that simple. Higgs Boson seems to contribute mainly to masses of leptons (mostly electrons) and bosons W and Z. And that influence goes to zero at high energies of the measures system making W and Z weightless and merging electrostatic and weak interactions into a singular electroweak interaction.

Quarks get most of their mass from QCD with very minor contribution from Higgs Boson. And nobody has any idea where the mass of neutrinos comes from.

It also has no influence on photons and gluons.

Higgs seems to be very peculiar and not very universal mechanism. I wonder if one of the potential future approaches won't do away with Highs Boson (together with virtual particles) as artifacts of specific math approach and interpretation without any physical manifestation.

Higgs was detected, sure, but it was detected through an interpretation of the data through the best available mathematical model which some postulate might contain some purely mathematical constructions along the way to the ultimate real world result.

We understand matter perfectly well. Look at the size and scope of the engineering marvels that have been constructed on the surface of this planet and in our low orbit. It's astonishing.

What we don't understand is the fundamental structure of that matter or of our Universe. I personally feel that the people ostensibly "in charge" of this effort are a little chagrined at their decades of inability to produce not only a cohesive result but even a reasonable intermediate explanation that they intentionally couch these problems in the most arcane and impenetrable language available to them.

In any case, you shouldn't feel discontent for humanity, as we've simply discovered all the easy problems, cleverly worked out all the average problems, and now all we're left with is the intractably hard ones. It's very likely that a different type of effort we haven't engaged in yet will be necessary to make progress.

There are about 16 particles in the standard model. We've only mastered the electron, proton, photon, and have dabbled in using neutrons and neutrinos. Imagine the possibilities if we some day are able to use all the remaining particles?

Constantly trying to resolve an incomplete abstraction. They are trying to reverse engineer the Universe. I can usually read half way through these articles before I'm completely lost in the abstractions.

Starting with the axiom that what I am experiencing is actually representative of reality to begin with.

It's just a puzzle and should be taken as such.

The impression this article and many other things like it leaves me with is that we are struggling to get language and an abstractions out of our way.

We have to use them to talk about things and work with them, but they all “leak.”

   When I consider your heavens,
   the work of your fingers,
   the moon and the stars,
   which you have set in place,
   what is mankind that you are mindful of them,
   human beings that you care for them?
   You have made them a little lower than the angels
   and crowned them with glory and honor.
   You made them rulers over the works of your hands;
   you put everything under their feet:
   all flocks and herds,
   and the animals of the wild,
   the birds in the sky,
   and the fish in the sea,
   all that swim the paths of the seas.

Aren't you describing quantum field theory (QFT)?

Anyway, what exactly is a field besides a mathematical object? What is it made of?

Checkout energywavetheory.com. It's essential the Aether, but really makes you think.

No it would be very hard to actually have a consensus on proton decay. If it decays then according to the measurements (or the limits on the lack of the measurement) lifetime of such decay will be more than the universe age (Even without all the puzzle about Hubble constant tension and age of universe measurement disagreements). It was predicted first time by SU(5) theory and many other theories since then but the experiments rules out some of them (including original SU(5)) [1]

I would be personally interested in proton decay as it could be indirect indication for magnetic monopoles [2].

[1] https://en.wikipedia.org/wiki/Proton_decay?useskin=vector#Pr...

[2] https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.52...

You can't detect without affecting.

My idea for resolving this is that electron is never a point-like particle. It's always a cloud, just larger or smaller. When it's detected it gets reshaped to be narrower. Mass, energy, momentum and such are a quantities ascribed to the whole cloud and exchanged only on the moment of interaction.

Think about diffraction. Photon or electron that passes through a small hole had it's moment messed up proportionally. It becomes large again.

Interesting question is where's the gravity in all of this. There are various ideas how to match quantum uncertainty to shape of space-time.

"Things are named before they are understood." -- Matt Strassler

We're not asking questions about human constructs like what is moral or what is the ideal form of government. We're trying to understand what the most fundamental building block of reality is, which is something objective. Something independent of whether of not people ever existed.

So no, countless people around the world aren't wasting their lives researching particles when the answer is simply, it's whatever we say it is.

discovery vs invention is a question in mathematics as well. trying to say they're invented isn't clever, it's just a trick of language, like how gravity is merely a theory. particles are theorized to exist via theoretical physics and math, and then tested for experimentally. or as the saying goes, all models are wrong, some are useful.