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What Is a Particle? (2020)

quantamagazine.org

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Re: What Is a Particle? (2020)

#121

Post by Traubenfuchs »

elashri wrote: post #9
AlbertCory wrote: post #2

I'm reading "The Big Picture" (Sean Carroll) right now. I'd love to have a real physicist explain this, but: When we think of what a particle IS, we often think as though it were dirt, or a billiard ball, or something. As though there were some other substance of which it's made. At least I do. But the definition is as low as you can go. It's hard to wrap your head around that. Unless you're trained to do so, I guess…

> 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 t…

So we have the three spatial dimensions, + time as 4. dimensions and at any of those 4-part coordinates there are additional properties like mass/spin/etc., some of much always come together or at least strongely correlate, and those values not being zero means there is a particle there and every value corresponds to a certain „field“ and it not being zero means the field is excited?

Re: What Is a Particle? (2020)

#122

Post by kayo_20211030 »

prng2021 wrote: post #47
kayo_20211030 wrote: post #27

Earlier quoted context omitted.

Did you take the time to read the original piece? Even the smart people can't agree. What gives you the faith that a "particle" is not a human construct? What on earth does "fundamental" even mean except being the bottom turtle we can see on the particular mountain of turtles at which we're looking. "Countless"(?) people around the world are not researching particles. They're doing particle physics as they understand…

When you say particles are whatever we say they are, I assume you believe particles are subjective. I'm saying particles are objective, like a "wavelength" as opposed to subjective, like "morals". If you are saying even objective things are whatever we say they are, then this is a useless discussion. Obviously every word is defined with other words and all words are human creations. So yea in that sense, literally ev…

I was saying that I don't know what a particle is, and neither does anyone else, but subjective isn't quite the correct word.

What I am sayings is that there are many useful interpretations of what a particle "is" that allows science to progress. The theoreticians and the experimentalists use, sometimes even form, those interpretations to help them along in their work. I'm saying that they yet remain interpretations, even analogies; and it really doesn't matter whether those folks believe in an objective reality or not, good work still gets done. Maybe it's subjective in that sense, but a particle is whatever they say it is; and nothing more can be said with certainty unless you dive into philosophy.

You can measure a perturbation in a field, or a track in a bubble chamber, and call it a particle. Then you can work backwards to an "objective" representation, and a particle still becomes whatever you say it is. It's still scientific, consistent, mathematically rigorous, and in line with theory and observation, but it remains a human construct. You can't escape that. Ultimately, one is free to believe that there is some fundamental thing; and, maybe there is and maybe there isn't.

> literally everything we know of is whatever we say it is

Of course "literally everything we know of is whatever we say it is". That, precisely, is my point. It most certainly does not mean that we can just state anything as true unless it is sensible, consistent, observable and verifiable; and expect not to be challenged.

Re: What Is a Particle? (2020)

#123

Post by vertnerd »

aaa_aaa wrote: post #50
lisper wrote: post #45

Earlier quoted context omitted.

Richard Feynman gave what I consider to be the best possible answer to questions like this: https://www.youtube.com/watch?v=Q1lL-hXO27Q

At first I was impressed with that video. Then I felt he does not have an answer and unnecessarily gets edgy with it, because question is valid.

Feynman grapples with the question the same way we would grapple with a question from a child: "why is the sky blue?" If you drill down into the explanation, you ultimately reach a statement that everyone just accepts as true, or you simply end with, "no one knows".

Re: What Is a Particle? (2020)

#124

Post by tel »

ziofill wrote: post #87
AlbertCory wrote: post #2

I'm reading "The Big Picture" (Sean Carroll) right now. I'd love to have a real physicist explain this, but: When we think of what a particle IS, we often think as though it were dirt, or a billiard ball, or something. As though there were some other substance of which it's made. At least I do. But the definition is as low as you can go. It's hard to wrap your head around that. Unless you're trained to do so, I guess…

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 might try on a sentence like "this classical particle is generated by the interaction between... other... particles" but I'm clearly at a loss there.

On basis of that, I'd be more likely to say "QM needs to describe everything as a wave, and sometimes certain kinds of localized 'wave-packets' move around coherently, and that's what we'd call 'particles'". That also seems to gel with less coherent states where it feels like there's not really a particle to be found.

So, I'm curious why you'd prefer to relate the eigenstates themselves as particles. Again in the oscillator case, the eigenstates themselves seem less coherent and seem to behave less classically than I'd hope.

My best guess is that the property those states have that is not as well replicated by the "particle as a coherent wave packet phenomenon" is that they have well-defined energy quanta. But that's just a bit of a stab in the dark here. It perhaps makes more sense from the perspective of "particles are the things that we're able to measure in detectors" POV, though.

Re: What Is a Particle? (2020)

#125

Post by lottin »

binary132 wrote: post #61
divs1210 wrote: post #53

Earlier quoted context omitted.

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 cha…

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”

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.

Re: What Is a Particle? (2020)

#126

Post by im3w1l »

divs1210 wrote: post #53
AlbertCory wrote: post #2

I'm reading "The Big Picture" (Sean Carroll) right now. I'd love to have a real physicist explain this, but: When we think of what a particle IS, we often think as though it were dirt, or a billiard ball, or something. As though there were some other substance of which it's made. At least I do. But the definition is as low as you can go. It's hard to wrap your head around that. Unless you're trained to do so, I guess…

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 cha…

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.

Re: What Is a Particle? (2020)

#127

Post by lottin »

bbor wrote: post #114
griffzhowl wrote: post #92

Earlier quoted context omitted.

So what is a field?

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.

Re: What Is a Particle? (2020)

#128

Post by im3w1l »

griffzhowl wrote: post #92
bbor wrote: post #44

Earlier quoted context omitted.

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.

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.

Re: What Is a Particle? (2020)

#129

Post by mewpmewp2 »

vertnerd wrote: post #123
aaa_aaa wrote: post #50

Earlier quoted context omitted.

At first I was impressed with that video. Then I felt he does not have an answer and unnecessarily gets edgy with it, because question is valid.

Feynman grapples with the question the same way we would grapple with a question from a child: "why is the sky blue?" If you drill down into the explanation, you ultimately reach a statement that everyone just accepts as true, or you simply end with, "no one knows".

The way Feynman answered it looked extremely condescending and anti curiousity. Being pedantic for no reason. When answering you should try to guesstimate what the asker who is not an expert in your field is looking for and then start explanation relative from there.

At certain point, yes, you do have to say that either you don't know or humans haven't figured it out yet.

Re: What Is a Particle? (2020)

#130

Post by binary132 »

lottin wrote: post #125
binary132 wrote: post #61

Earlier quoted context omitted.

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”

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 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.
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