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What Is a Particle? (2020)

quantamagazine.org

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Re: What Is a Particle? (2020)

#61

Post by binary132 »

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…

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”

Re: What Is a Particle? (2020)

#62

Post by pgotibojgg »

danbruc wrote: post #55
criddell wrote: post #26

Earlier quoted context omitted.

> And electrons being electrons also means that they are not excitations in quantum fields You’re going against the dominant interpretation of QFT here, aren’t you?

I have no idea whether or not most physicist think that there are actually quantum fields in the universe. The Navier–Stokes equations provide a good description of milk mixing into my coffee, but should I therefore conclude that my coffee mug is filled with density and velocity fields and that what coffee really is, is a region in spacetime with a nonzero value of the coffee density field? Quantum fields have gauge…

Do you think photons are real?

Because according to QFT they only exist because of the gauge symmetries. Photons are the solution to the redundant symmetries. Remove those redundant symmetries and you also need to remove the photons.

Universe "fixing a gauge" means no photons and no electromagnetic field, because the electromagnetic field IS the gauge symmetry.

Re: What Is a Particle? (2020)

#63

Post by binary132 »

auntienomen wrote: post #46
criddell wrote: post #26

Earlier quoted context omitted.

> And electrons being electrons also means that they are not excitations in quantum fields You’re going against the dominant interpretation of QFT here, aren’t you?

Yep. Also, ignoring all the ways in which an electron isn't an electron. Electrons can be created and destroyed, and they are both indistinguishable and exchangeable. We can't assign identity to them, thanks to their Fermi statistics. They're just methods of explaining clicks in a detector. I worked in particle physics for years and never once saw an electron. :-)

Joke: “birds aren’t real”

Woke: “electrons aren’t real”

Re: What Is a Particle? (2020)

#64

Post by binary132 »

danbruc wrote: post #55
criddell wrote: post #26

Earlier quoted context omitted.

> And electrons being electrons also means that they are not excitations in quantum fields You’re going against the dominant interpretation of QFT here, aren’t you?

I have no idea whether or not most physicist think that there are actually quantum fields in the universe. The Navier–Stokes equations provide a good description of milk mixing into my coffee, but should I therefore conclude that my coffee mug is filled with density and velocity fields and that what coffee really is, is a region in spacetime with a nonzero value of the coffee density field? Quantum fields have gauge…

I think this is why “shut up and calculate” is popular

Re: What Is a Particle? (2020)

#65

Post by AlbertCory »

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.

I just watched it. I don't think he's edgy.

You can't explain it in terms of anything else, which was sorta my original point. Maybe he could have been more touchy-feely in his answer, but that wasn't his nature.

Re: What Is a Particle? (2020)

#66

Post by User23 »

binary132 wrote: post #64
danbruc wrote: post #55

Earlier quoted context omitted.

I have no idea whether or not most physicist think that there are actually quantum fields in the universe. The Navier–Stokes equations provide a good description of milk mixing into my coffee, but should I therefore conclude that my coffee mug is filled with density and velocity fields and that what coffee really is, is a region in spacetime with a nonzero value of the coffee density field? Quantum fields have gauge…

I think this is why “shut up and calculate” is popular

Or as Newton more eloquently put it hypothesis non fingo.

Re: What Is a Particle? (2020)

#67

Post by ww520 »

ItCouldBeWorse wrote: post #25
ww520 wrote: post #24

That's why calling Higgs Boson the God particle is not quite right. It's the Higgs field that gives mass to the other particles, not the Boson. A Higgs Boson is just an excitation of the Higgs field; it doesn't give mass to other particles. In fact it's the Higgs field modifying the other fields causing their excitations (particles) to slow down when passing each other, thus gaining masses.

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

It’s more like Higgs field gives mass to other particles whose masses warp spacetime that gives gravity.

Re: What Is a Particle? (2020)

#68

Post by khazhoux »

michaelsbradley wrote: post #36
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.

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 answer of "the universe was created by a creator" is no more satisfying. It claims to answer everything, by answering nothing (since "a creator always existed" is axiomatic).

Re: What Is a Particle? (2020)

#69

Post by scotty79 »

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 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.

Re: What Is a Particle? (2020)

#70

Post by scotty79 »

This article contains a very neat description of what is energy, momentum and spin and why they there. Energy is just a quantity that's preserved when shifting through time, momentum is a quantity preserved by shifting through space. And spin is a quantity preserved by rotation in space-time.

General relativity treats energy and momentum jointly so I guess basically energy-momentum is a quantity preserved in space-time translations and spin is a quantity preserved in space-time rotations. (in flat space-time, I think?)

I guess that's why those Poincare symmetries are rarely mentioned when talking about particles. They seem to come more from sheer geometry of space-time than anything else. Particle physicists are mainly interested in all other symmetries (because they were harder to figure out). It also must be bad feeling that while you are trying pull gravity into your framework, more than half of the symmetries that the objects you spent your career observing obey, come from general relativity not from your framework.

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