[divs1210]

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.

[binary132]

I get it but I still think these sorts of concepts are also just another level of mathematical abstraction that isn’t necessarily “really what it is” any more than a rotating ball or a math equation or any of the other ideas are “really what it is”

[lottin]

It's very frustrating. The idea that the universe is made of fields is nonsensical. I don't understand why so many physicists keep saying that.

[antonvs]

If you don’t invest the statement “the universe is made of fields” with more meaning than necessary, then it makes more sense.

A quantum field is just a mathematical construct that models an aspect of what can happen at every point in spacetime. The fields follow rules for how they interact, and fluctuations in the fields and interactions between them, according to their respective rules, provide a good model for the universe we observe.

If you consider this purely mathematically, it’s hard to argue with. The models in question make very accurate predictions, can correctly model the vast majority of observations we know how to make, and don’t predict many things that we don’t observe. In other words, all the evidence is that it’s a very good model - a very good fit for the universe we observe.

From this perspective, one way to interpret the statement that “the universe is made of fields” is simply that the universe conforms to the quantum field model. Again, this claim is hard to argue with - it seems to me like a true statement, and there’s a lot of evidence for it.

Hawking & Mlodinow explored this in their description of what they called “model-dependent realism” - see: https://en.wikipedia.org/wiki/Model-dependent_realism

If perspectives like these don’t satisfy you, and you want to try to develop an understanding beyond mathematical models, then you have a tough problem to solve: how to go beyond the models that we know how to construct, to something that somehow gives you some sort of more fundamental insight. But what would that even look like? How would you test it? What would make this approach more true than existing theories?

In short, an answer that satisfies the criteria that you want it to satisfy may simply not be possible.

[jerf]

The Universe May Do As It Damned Well Pleases.

Maybe it is "made of fields", maybe it isn't, but "I think that's nonsense", which is just a gussied up way of saying "my intuition rejects that", is not a valid judgment method. The universe does not check with our intuition before doing what it Damned Well Pleases.

[lottin]

So you think the universe might be made of, say, subordinate clauses?

[jerf]

Whether or is or it isn't, it does it without consulting you or me or our intuitions.

I assume you meant that as an obvious absurdity, but if you were going for that you probably should have avoided the concept of "language", which can be Turing Complete. Still, the main point is, whatever it is, it is, and it isn't asking us for permission to be what it is.

[lottin]

My point is that physical reality cannot be made of something that doesn't exist physically, such as mathematical objects, abstract concepts or more generally ideas of any kind. Do you not agree that this must be true?

[binary132]

One of the ultimately epistemological puzzles to me is the question of what math really is. Like, obviously, it is fundamentally descriptive. “Two and two makes four” is pretty straightforwardly talking about something “out there”. And when we’re talking about fields, we are clearly also describing something that is really happening, that is really “out there”; it’s not the math itself that is the real thing, but rather it is a language for accurately describing and analyzing real things. But at some level, the real things it’s describing become so abstract and immaterial that they might as well be magic, or spirit. And it seems to me like our minds also contain and experience such things, too. Very advanced math and physics necessarily start to border on philosophy or theology.

[travisjungroth]

One way of viewing it is that math is games. Not in the winner sense, but in the activities with rules sense. Addition is a game.

Some games make you better at other activities. Like, playing chess could make you better at logistics because you’re practicing planning and managing losses.

Some games match some real world situations so tightly that we can go through them step by step and solve the real world situation in the game. You can play addition to figure out two apples and two more makes four apples.

Whether the game is “real” or not is immaterial. It just needs to be internally consistent and matched to the right thing.

There’s also the idea that math is another world that we can visit, similar to the dream world. But that’s a whole other thing.

[fasa99]

The idea that it's an abstraction is 100% accurate. That physics is a discrete set of fields with field rules and interaction rules, and what we observe is a scaffold on top of that. It's like okay, let's say the math is right and we have a set of fields, what are they and where are they from, how do we manipulate them. Then the physicists, often driven by ego, is want for an explanation and points to vibrating strings and such, and finally they knock on the door of the empiric physicist and say "can you do an experiment to show that I'm right" "sure, build a machine the size of the universe and I could test that" and that's the state of physics the last gorillion years

https://www.youtube.com/watch?v=FYJ1dbyDcrI

[travisjungroth]

So in the viewpoint I’m describing you can definitely call it an abstraction. And abstraction has a vibe of intentionality to it, at least for me. That brings up something I didn’t mention, which is you can make a math game on purpose, to match with something in the real world. You can also make them up for fun (people don’t usually call it “for fun”, but that’s actually a fair label for theoretical mathematics IMO) and then discover the application later.

This is neat! I think it happens less in the physical world, just making up a tool and then finding its application later. It does happen in chemistry.

[itishappy]

The magnetic field is one which you've probably had a chance to experience for yourself. Wave a magnet around a magnetic field and you can feel it has a different effect at different points in space. Fields are just time and space varying values for physical properties. Is the universe being composed of magnetism and a few related fields really so nonsensical?

[binary132]

Not really, until you go “well, what’s magnetism made of?” and the answer is “a field!” That’s pretty nonsensical.

[itishappy]

I disagree! I think fields are very intuitive and it's everything else that's nonsensical!

Magnetism isn't made of anything. It is a field, and it's one your can interact with directly.

Compare that with, say, table salt. "What's table salt made of?" Uh. It's made of atoms entirely unrelated to salt, like sodium and chlorine. "What are atoms made of?" Uh. They're made of tiny electric particles zipping around at relativistic speeds but bound together by forces like magnetism.

Richard Feynman does a better job than me of describing this exact problem in one of my favorite physics videos of all time:

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

[binary132]

“Magnetism isn’t made of anything” is a nonsensical statement, of course it is made of something, we just don’t know what. That’s why “it’s made of fields” is nonsensical, it’s no different than saying “it’s made of atoms” and then refusing to think about what an atom is. “Atoms aren’t made of anything, it IS an atom”.

[blahblahblah10]

A great lesson one learns as a physicist is that one must develop a new intuition mainly through years of practice. So when you say "It's very frustrating", I interpret it as "this doesn't seem reasonable to me". But it doesn't have to be reasonable - none of us have any intuition for what happens at scales far different from our everyday lives.

The real question you raise is a very good one - how seriously should physicists take mathematical theories. If we were building a statistical model of, say, house prices and construct a reasonable linear regression model, we certainly don't believe that the market plugs the parameters of a house into the model to decide the price. The model is an approximation of the real dynamics of the market and this approximation might not hold in the future.

On the physics front, I would argue no one would consider a quadratic in speed air resistance term in Newton's second law, a fundamental feature of the universe. One can build a reasonable model that results in that term and it might even be a good approximation for some fluids in some speed/density range.

But, when it comes to more fundamental (as of today) theories like quantum electrodynamics, electroweak theory, quantum chromodynamics (all quantum field theories), or even general relativity (modulo discussions of quantum gravity) - both the predictive power and accuracy of these theories is so stunning (matching all the data generated at colliders like the LHC), that one starts wondering if we are no longer dealing with models but a true description of nature. The mathematical descriptions are also so constrained unlike the house price example above, that one can't just make modifications to the theories without violating core principles (and experimental data) like unitarity, causality, locality, Lorentz invariance etc. This only reinforces this view that perhaps this is close to a true description of what we see.

Now it is entirely possible (but IMO not probable) that this whole view will be upended and replaced by a very different physical picture. In a sense, string theory (which is now discredited heavily in the public's eye but that's a story for another day) was an attempt at a different physical picture that resulted in very rich structures that had nothing to do with physical reality.

So, physicists say that because the more time you spent understanding and studying quantum field theory and as more experiments are done (all the collisions at the LHC verify the standard model's predictions including the Higgs once its mass was known), it only reinforces that there's something deep about the current theories even though we have several unsolved problems (dark matter, dark energy, quantum gravity, fine-tuning problems).

Addendum 1: I'll add a book that is not accessible to non-physicists but gives a glimpse into the actual struggle of research and building intuition for something very abstract:

https://www.amazon.com/Feynman-Lectures-Gravitation-Richard-...

Feynman, like many others, spent considerable time applying all his powers to understand general relativity from a QFT perspective but eventually it didn't pan out (for anyone).

[Koshkin]

"It's very frustrating. The idea that Earth revolves around the Sun is nonsensical. I don't understand why so many astronomers keep saying that."

[binary132]

“It just is how it is, no we don’t know why, just accept it”

[jiggawatts]

Spin is easy as long as you avoid trying to draw a direct analogy with ordinary rotation.

It’s just the statement that the object spinning is attached to its surroundings in a smooth and continuous fashion. Less rigid object, more a patch of space-time fabric spinning.

There’s a video here: https://youtu.be/LLw3BaliDUQ?feature=shared

[im3w1l]

It's worth keeping in mind that we don't yet have the sought-after Theory of Everything. We have a bunch of theories that mostly work in their domain of validity. These field theories are supposedly very accurate we don't actually know if they are the final word.