5 ms·

But what is a "real" particle anyway?

by acjohnson55 11y ago

Conjoiner 11y ago
The difference between a bullet made of real particles and one made of math is that the real one can kill you.
- randallsquared 11y ago
  That's true for values of "you" reading this in 2015, at least. :)
- dvdkhlng 11y ago
  Quasi-particles are not just math. They have measurable properties that are like properties of real particles (just like "holes" in P-type semiconductors can be measured to behave like quasi-positrons). Or, replying to your proposition: "With the holodeck safeties off, even holographic bullets can kill." - Picard, First Contact. :)
  - losername 11y ago
    > just like "holes" in P-type semiconductors can be measured to behave like quasi-positrons I'm sorry to ask because I should actually know this, isn't the remaining positive charge accounted to the protons in the core? A moving "hole" is just a figure of speech.
- fsloth 11y ago
  Hmm, I think you got it in reverse. We are talking about of properties of real physical things all the time here. We just can't expect to instantiate any random piece of math in the real world - like take a specific vector subspace and try to use it as a katana, that would be silly. We take a physical system and apply some mathematical properties to it. In the case of bullet I think what is interesting is to model it's energy, E = 1/2 mv*v. Now, if we take the kinetic energy of a bullet, and apply it to any other object, and then instantiate this object in the real world the lethality of the object depends on the nature of the object. A ball of hay of a diameter of 1 m in 1 atm 10 meters away with the kinetic energy of a bullet does not sound lethal. An object more like a bullet, like an iron nail, probably can be. Gummy bear? Who knows. The point is, the maths here are about physical things, although it can take a lot of experimental work to manufacture a specific physical system that exhibits behaviour which is modeled with specific piece of math.
dvdkhlng 11y ago
"real" particles are those that can leave the holodeck ([1]) "quasi-particles" vanish at the doorstep :) [1] https://en.wikipedia.org/wiki/Holodeck https://en.wikipedia.org/wiki/Holodeck PS: replace "holodeck" with "tantalum arsenide crystal" to yield a less off-topic comment.
- empath75 11y ago
  That's a really good explanation.
- tobias2014 11y ago
  What about strongly interacting theories? Are quarks and gluons quasi-particles then too? They can't leave the holodeck aka. Hadron. I think this could break your classification :)
- daveloyall 11y ago
  Thank you for this explanation. But hey, speaking of TNG... Can't you just stick on of those fancy crystals in your computer? Wait, computers made out of crystals? Did that just happen? :)
  - fnordfnordfnord 11y ago
    Computers are already made out of fancy crystals. But these new crystals would be even fancier than the old ones.
deleted 11y ago
[deleted]
- phreeza 11y ago
  I am afraid there is no nice way to say this, almost all of what you wrote there is completely wrong.
  - selimthegrim 11y ago
    Agreed. Quasiparticle does not mean it's evanescent or has imaginary energy! Back to scattering class....
  - knieveltech 11y ago
    Don't be lazy. If you see errors please provide correction so the rest of us can benefit!
    - deleted 11y ago
      [deleted]
raverbashing 11y ago
One example happens in semiconductors You have n-type material, where the charge carriers are electrons. So far so good (a real particle) In p-type material, the charge carriers are the absence of an electron (called a hole). It is of course, not a real particle, but it carries charge as well as a real particle.
- jpmattia 11y ago
  > You have n-type material, where the charge carriers are electrons. So far so good (a real particle) Even that: It's a quasi particle. It's an electron with an effective mass, which differs from the mass of an electron in free space. The effective mass arises because of the collective electron interaction with the crystal atoms. At a range of high energies, the electron even exhibits the same behavior you'd expect from a relativistic particle (with something different than c for the ultimate velocity.)
- losername 11y ago
  That's just a figure of speech. The charge of an ion stems from the ratio of electrons to protons. To every "hole" there is a proton, which is a particle. I am repeating myself.
  - johntb86 11y ago
    It's not just a figure of speech, it's a useful abstraction. The protons don't move, but the holes seem to do that. Not only that, if you pretend the holes have a certain amount of mass you can predict how they move, and they move similarly to how a positibly-charged particle would move in the same circumstances.
yk 11y ago
In this context, the particles that appear in the Standard Model. So a quasiparticle can be understood in terms of the underlying structure of matter ( a crystal in this case), a 'real' particle can not be understood in terms of some underlying mechanism. Granted, "can not be understood in those terms yet" is preliminary and a not really satisfying definition.

But what is a "real" particle anyway?

Conjoiner 11y ago

The difference between a bullet made of real particles and one made of math is that the real one can kill you.

randallsquared 11y ago
That's true for values of "you" reading this in 2015, at least. :)
dvdkhlng 11y ago
Quasi-particles are not just math. They have measurable properties that are like properties of real particles (just like "holes" in P-type semiconductors can be measured to behave like quasi-positrons). Or, replying to your proposition: "With the holodeck safeties off, even holographic bullets can kill." - Picard, First Contact. :)
- losername 11y ago
  > just like "holes" in P-type semiconductors can be measured to behave like quasi-positrons I'm sorry to ask because I should actually know this, isn't the remaining positive charge accounted to the protons in the core? A moving "hole" is just a figure of speech.
fsloth 11y ago
Hmm, I think you got it in reverse. We are talking about of properties of real physical things all the time here. We just can't expect to instantiate any random piece of math in the real world - like take a specific vector subspace and try to use it as a katana, that would be silly. We take a physical system and apply some mathematical properties to it. In the case of bullet I think what is interesting is to model it's energy, E = 1/2 mv*v. Now, if we take the kinetic energy of a bullet, and apply it to any other object, and then instantiate this object in the real world the lethality of the object depends on the nature of the object. A ball of hay of a diameter of 1 m in 1 atm 10 meters away with the kinetic energy of a bullet does not sound lethal. An object more like a bullet, like an iron nail, probably can be. Gummy bear? Who knows. The point is, the maths here are about physical things, although it can take a lot of experimental work to manufacture a specific physical system that exhibits behaviour which is modeled with specific piece of math.

dvdkhlng 11y ago

"real" particles are those that can leave the holodeck ([1]) "quasi-particles" vanish at the doorstep :) [1] https://en.wikipedia.org/wiki/Holodeck https://en.wikipedia.org/wiki/Holodeck PS: replace "holodeck" with "tantalum arsenide crystal" to yield a less off-topic comment.

empath75 11y ago
That's a really good explanation.
tobias2014 11y ago
What about strongly interacting theories? Are quarks and gluons quasi-particles then too? They can't leave the holodeck aka. Hadron. I think this could break your classification :)
daveloyall 11y ago
Thank you for this explanation. But hey, speaking of TNG... Can't you just stick on of those fancy crystals in your computer? Wait, computers made out of crystals? Did that just happen? :)
- fnordfnordfnord 11y ago
  Computers are already made out of fancy crystals. But these new crystals would be even fancier than the old ones.

deleted 11y ago

[deleted]

phreeza 11y ago
I am afraid there is no nice way to say this, almost all of what you wrote there is completely wrong.
- selimthegrim 11y ago
  Agreed. Quasiparticle does not mean it's evanescent or has imaginary energy! Back to scattering class....
- knieveltech 11y ago
  Don't be lazy. If you see errors please provide correction so the rest of us can benefit!
  - deleted 11y ago
    [deleted]

raverbashing 11y ago

One example happens in semiconductors You have n-type material, where the charge carriers are electrons. So far so good (a real particle) In p-type material, the charge carriers are the absence of an electron (called a hole). It is of course, not a real particle, but it carries charge as well as a real particle.

jpmattia 11y ago
> You have n-type material, where the charge carriers are electrons. So far so good (a real particle) Even that: It's a quasi particle. It's an electron with an effective mass, which differs from the mass of an electron in free space. The effective mass arises because of the collective electron interaction with the crystal atoms. At a range of high energies, the electron even exhibits the same behavior you'd expect from a relativistic particle (with something different than c for the ultimate velocity.)
losername 11y ago
That's just a figure of speech. The charge of an ion stems from the ratio of electrons to protons. To every "hole" there is a proton, which is a particle. I am repeating myself.
- johntb86 11y ago
  It's not just a figure of speech, it's a useful abstraction. The protons don't move, but the holes seem to do that. Not only that, if you pretend the holes have a certain amount of mass you can predict how they move, and they move similarly to how a positibly-charged particle would move in the same circumstances.

yk 11y ago

In this context, the particles that appear in the Standard Model. So a quasiparticle can be understood in terms of the underlying structure of matter ( a crystal in this case), a 'real' particle can not be understood in terms of some underlying mechanism. Granted, "can not be understood in those terms yet" is preliminary and a not really satisfying definition.