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What Is a Particle? (2020)

quantamagazine.org

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Re: What Is a Particle? (2020)

#151

Post by ziofill »

evanb wrote: post #148
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…

Also a physicist. It's not quite right to call basis vectors particles, even in a free field theory. The particles correspond better to the creation / ladder operators that take you from one Hamiltonian eigenstate to another. In a perturbative interacting case, people still think of particles as these same ladder operators, but they don't connect eigenstates so simply (the interactions generically mix all the states…

Yeah it’s hard to use everyday language to exactly describe these things… And even more difficult to decide where to draw the line where some hand waving is acceptable.

Re: What Is a Particle? (2020)

#152

Post by evanb »

graycat wrote: post #60

Issues: (1) With Itself: Consider Young's double slit experiment: So, have plane with two slits and some distance away a parallel plane with detectors. (A) Several times, shoot a photon at the slit. Observe that the detection locations form parallel lines, i.e., fringes . (B) Cover one slit, repeat, and observe that the detection locations from a smooth hill without fringes. So, from (A) we conclude that the somethin…

You're very close to understanding to quantum eraser experiment / the even more upsetting delayed-choice quantum eraser.

Even though it sounds as though your arguments are gotchas that prove quantum mechanics to be nonsense, it turns out the world really is that way.

https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser

Re: What Is a Particle? (2020)

#153

Post by jerf »

lottin wrote: post #147
jerf wrote: post #144

Earlier quoted context omitted.

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.

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

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.

Re: What Is a Particle? (2020)

#155

Post by graycat »

evanb wrote: post #152
graycat wrote: post #60

Issues: (1) With Itself: Consider Young's double slit experiment: So, have plane with two slits and some distance away a parallel plane with detectors. (A) Several times, shoot a photon at the slit. Observe that the detection locations form parallel lines, i.e., fringes . (B) Cover one slit, repeat, and observe that the detection locations from a smooth hill without fringes. So, from (A) we conclude that the somethin…

You're very close to understanding to quantum eraser experiment / the even more upsetting delayed-choice quantum eraser. Even though it sounds as though your arguments are gotchas that prove quantum mechanics to be nonsense, it turns out the world really is that way. https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser

Gee, I'm not the first to make this mistake about quantum mechanics!

Re: What Is a Particle? (2020)

#156

Post by Koshkin »

spoonfeeder006 wrote: post #154

> “What is a particle?” > > “An irreducible representation of the Poincaré group,” a precocious classmate answered. Me: Looks up Poincare group Also me: Oooookay, that makes absolute perfect zero sense to me

But - again - that is a mathematical construction, which a physical particle is not.

Re: What Is a Particle? (2020)

#157

Post by spoonfeeder006 »

Koshkin wrote: post #156
spoonfeeder006 wrote: post #154

> “What is a particle?” > > “An irreducible representation of the Poincaré group,” a precocious classmate answered. Me: Looks up Poincare group Also me: Oooookay, that makes absolute perfect zero sense to me

But - again - that is a mathematical construction, which a physical particle is not.

I think I'm getting a glimmer of understanding on this now

From what I gather, a set of possible transformations is a group in group theory

Physical space is a type of group, i.e. a Poincare group, and is described by the set of all transformations on objects, or something (i.e. motion or lack thereof)

An irreducible poincare group is a tinest example of physical space, i.e. a 'particle'

So although it has no physical space, yet the irreducible Poincare group is intrinsically (but not practically) capable of those same types of transformations within itself as in the larger Poincare group within itself

E.g. a larger object (many particles) can undergo shears and strains, i.e. internal motion. In theory an infinitesimal particle can, it just doesn't have the space to undergo those

I'm inferring from this that a subset of physical space is also a Poincare group?

Re: What Is a Particle? (2020)

#158

Post by spoonfeeder006 »

Koshkin wrote: post #156
spoonfeeder006 wrote: post #154

> “What is a particle?” > > “An irreducible representation of the Poincaré group,” a precocious classmate answered. Me: Looks up Poincare group Also me: Oooookay, that makes absolute perfect zero sense to me

But - again - that is a mathematical construction, which a physical particle is not.

Yes, mathematical constructions are merely a model of reality

It is interesting to note that (correct me if I'm wrong) perhaps our mathematical constructs are based on a classical intuition and perception of the universe?

And here we are trying to fit that classical intuition into the quantum realm

Perhaps that can be related to why shit gets complicated with particle physics?

Re: What Is a Particle? (2020)

#159

Post by lottin »

jerf wrote: post #153
lottin wrote: post #147

Earlier quoted context omitted.

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

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.

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?

Re: What Is a Particle? (2020)

#160

Post by kstrauser »

mewpmewp2 wrote: post #129
vertnerd wrote: post #123

Earlier quoted context omitted.

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.

Having read some of his lectures, and his autobiography, he was anything but anti-curiosity in him or in others. Watch that through the lens of someone who valued nothing more than asking questions and it might come across differently.
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