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Incomplete analogy that's probably a better starting point: if the tone of a bell is a particle, then the other movements of the bell that don't resonate are vi

by cwillu 4y ago

Incomplete analogy that's probably a better starting point: if the tone of a bell is a particle, then the other movements of the bell that don't resonate are virtual particles. Now, imagine we called the thermal motions of that bell “virtual tones”, and you have an idea why physicists always sigh and emphasize that virtual. particles. are. not. particles.

nine_k 4y ago
If virtual particles "fit the math" the same as real particles, what makes them not real? What do they not fit?
- evanb 4y ago
  What makes particles travel long distances as lumps is that they are on-shell. Virtual particles are not on shell. https://en.wikipedia.org/wiki/On_shell_and_off_shell https://en.wikipedia.org/wiki/On_shell_and_off_shell
- nimish 4y ago
  You don't _need_ them, and IIRC _can't_ (in general) use them if you deal with non-perturbative effects, unless you do stuff like re-summing infinite series of diagrams and that really makes interpreting the ultimately observable effect in terms of virtual particles interacting difficult.
- burnished 4y ago
  An example that comes up in semiconductor is the 'hole' virtual particle. It is the absence of an electron. It is not a real and independent phenomenon. But you can treat it like a particle just fine
  - gizmo686 4y ago
    Electron holes are quasi particles, not virtual particles.
    - burnished 4y ago
      Ah hell, guess I have to start treating the stuff I learned in undergrad into the unreliable narrator category. Thanks for the correction!
  - cwillu 4y ago
    Virtual particles are not particles. Virtual particles are all the disturbances in a field that don't behave like particles do. It's really a terrible name to have entered the lay vocabulary: “virtual memory is something that behaves largely like real memory” is _exactly_ wrong, it's more like “virtual memory is all the circuitry that doesn't perform any memory function, but is still made of silicon”.
- cwillu 4y ago
  The more correct idea is that particles aren't fundamental. There are fields, and a disturbance in one field will cause a disturbance in the fields that the first couples with. Most chains of disturbances die out really fast (“virtual particles”), but some combinations will resonate for a significant amount of time before they die out (“unstable particles”) and others don't die out at all (“stable particles”). And if the lifetime of a disturbance is fairly short compared to the frequency of the disturbance itself, it becomes hard to even make a solid distinction between those types, but again, that's a flaw caused by imposing a categorization scheme (“particles”) based on something that isn't fundamental.

by cwillu 4y ago

nine_k 4y ago

If virtual particles "fit the math" the same as real particles, what makes them not real? What do they not fit?

evanb 4y ago
What makes particles travel long distances as lumps is that they are on-shell. Virtual particles are not on shell. https://en.wikipedia.org/wiki/On_shell_and_off_shell https://en.wikipedia.org/wiki/On_shell_and_off_shell
nimish 4y ago
You don't _need_ them, and IIRC _can't_ (in general) use them if you deal with non-perturbative effects, unless you do stuff like re-summing infinite series of diagrams and that really makes interpreting the ultimately observable effect in terms of virtual particles interacting difficult.
burnished 4y ago
An example that comes up in semiconductor is the 'hole' virtual particle. It is the absence of an electron. It is not a real and independent phenomenon. But you can treat it like a particle just fine
- gizmo686 4y ago
  Electron holes are quasi particles, not virtual particles.
  - burnished 4y ago
    Ah hell, guess I have to start treating the stuff I learned in undergrad into the unreliable narrator category. Thanks for the correction!
- cwillu 4y ago
  Virtual particles are not particles. Virtual particles are all the disturbances in a field that don't behave like particles do. It's really a terrible name to have entered the lay vocabulary: “virtual memory is something that behaves largely like real memory” is _exactly_ wrong, it's more like “virtual memory is all the circuitry that doesn't perform any memory function, but is still made of silicon”.
cwillu 4y ago
The more correct idea is that particles aren't fundamental. There are fields, and a disturbance in one field will cause a disturbance in the fields that the first couples with. Most chains of disturbances die out really fast (“virtual particles”), but some combinations will resonate for a significant amount of time before they die out (“unstable particles”) and others don't die out at all (“stable particles”). And if the lifetime of a disturbance is fairly short compared to the frequency of the disturbance itself, it becomes hard to even make a solid distinction between those types, but again, that's a flaw caused by imposing a categorization scheme (“particles”) based on something that isn't fundamental.