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What Is a Particle? (2020)

quantamagazine.org

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Re: What Is a Particle? (2020)

#131

Post by dgoodell »

lottin wrote: post #127
bbor wrote: post #114

Earlier quoted context omitted.

It’s everything! Idk, I don’t think the universe owes us an answer there. What is a human? Well, it’s a human. You can think of all sorts of mental tools for understanding humans (eg “species”), but ultimately they just are .

No... a field is mathematical representation. The universe is most definitely NOT made of fields.

Are you saying that the universe cannot be represented by mathematics?

I imagine you could use that argument to shoot down pretty much any explanation.

Re: What Is a Particle? (2020)

#132

Post by contravariant »

im3w1l wrote: post #128
griffzhowl wrote: post #92

Earlier quoted context omitted.

So what is a field?

A function that takes a point in space as input. The output can be various things, e.g. a scalar field gives a (possibly complex) number as output.

That's a bit too simple, not all functions work well as fields (differentiability is quite desirable) and you have no way to interact with the fields that way.

I think principal bundles come closest to what physicists call fields. Though I'm holding open the option that really the things in most equations are more like elements of the corresponding Lie-algebra.

Re: What Is a Particle? (2020)

#133

Post by travisjungroth »

binary132 wrote: post #130
lottin wrote: post #125

Earlier quoted context omitted.

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.

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 rat…

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.

Re: What Is a Particle? (2020)

#134

Post by ziofill »

tel wrote: post #124
ziofill wrote: post #87

Earlier quoted context omitted.

Physicist here. You are right that the mental picture we get when we use the term “particle” is a little ball or something like that. It is unfortunately a confusing name… You need to begin with a field, like the electromagnetic field for instance. When you look at its properties like energy, polarization and so on, in order to write down a state of the field you need to specify all of them in a way or another. In qu…

As an amateur, I think I follow most of this, at least at some level, but I don't follow why you'd unify the basis elements and particles. Thinking of a quantum harmonic oscillator, the eigenstates have some kind of localization that feels particle-like, but the oscillating pattern of a coherent solution seems "more particle-like" and arises out of the interference between those eigenstates. In particle-speak, I migh…

You are exactly right at the end when you say that particles are what makes a detector go click. Let me try to clarify further. The "particleness" is not about localization, but about energy quantization. In fact, a single photon can be very non-localized, because spatial position is a different Hilbert space and it can be entirely independent of the energy. So the packets you are referring to are particles only if in their energy Hilbert space they correspond to a well-defined photon numbers, and that's why the analogy with classical particles only goes so far. To add to the confusion, one can speak of packets localized in phase space (e.g. coherent states, like the light produced by a laser) and packets localized in physical space like a short pulse, and these refer to different Hilbert spaces.

Re: What Is a Particle? (2020)

#135

Post by disambiguation »

khazhoux wrote: post #4

I'm honestly surprised that more people don't go mad in certain fields. If I ponder for 10 minutes the inexplicability of the universe's existence, or the vastness of space, my mind starts to breaks down.

    1.1 INTRODUCTION: THERMODYNAMICS AND STATISTICAL MECHANICS OF THE PERFECT GAS

    Ludwig Boltzmann, who spent much of his life studying statistical mechanics, died in 1906, by his own hand. Paul Ehrenfest, carrying on the work, died similarly in 1933. Now it is our turn to study statistical mechanics.

Re: What Is a Particle? (2020)

#138

Post by bbor »

lottin wrote: post #127
bbor wrote: post #114

Earlier quoted context omitted.

It’s everything! Idk, I don’t think the universe owes us an answer there. What is a human? Well, it’s a human. You can think of all sorts of mental tools for understanding humans (eg “species”), but ultimately they just are .

No... a field is mathematical representation. The universe is most definitely NOT made of fields.

Ok fair: they're things that right now are best understood using the term Field. I don't understand what kind of answer you're hoping for that would be better than this -- what kind of answer to "what is a particle" wouldn't be describable by mathematics?

By saying "the universe is fields", I'm saying "it's distributions of energy across spacetime". That's seemingly a consensus. Why demand that that energy must also form into strings or even tinier spheres or spheres in an alternate dimension or something? We have described fields in detail, I say Mission Accomplished

Re: What Is a Particle? (2020)

#139

Post by amai »

gweinberg wrote: post #137

For some reason this page makes my monitor flicker. Anyone else have this problem? Anyone know why it happens?

Do you have an external monitor connected to your Mac Pro Laptop?

If so, disable True Tone and disable auto brightness on all screens. That might help.

Re: What Is a Particle? (2020)

#140

Post by dandragona »

gpsx wrote: post #74
skzv wrote: post #16

Earlier quoted context omitted.

Aren't you describing quantum field theory (QFT)? Anyway, what exactly is a field besides a mathematical object? What is it made of?

I did study quantum field theory and I have a hard time viewing a fermion as a continuous field, whereas a gauge field I do view as a continuous field. I view a fermion as a true point particle, kind of like it is in a lattice. The fermion still has a wave function of course. It is very different from the wave function of a gauge field. The wave function of an electric field is a wave function over field configuratio…

I'm still new to learning about these things, but is the viewpoint that a particle is a field excitation sort of the thing about starting with a lattice in the ground state with a field defined on the points of the lattice, then some excitations happen which cause the field to enter a particular "mode". This mode is the particle?
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