What Are Virtual Particles and How Do They Work?

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Discussion Overview

The discussion centers around the concept of virtual particles, particularly virtual photons, exploring their nature, implications in quantum mechanics, and their role in quantum field theory. Participants express varying levels of understanding and seek clarification on whether these particles can be considered "real" and how they interact with observable particles.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether virtual particles are merely mathematical constructs or if they have any real existence, suggesting a lack of clarity in their understanding.
  • Another participant argues that the reality of virtual particles is a complex issue, stating that in quantum mechanics, something is not considered real unless it can be observed or measured, referencing the uncertainty principle.
  • It is proposed that virtual particles interact with observable particles, affecting their properties, such as the mass and motion of electrons, and that they are responsible for carrying forces in quantum field theory.
  • A participant mentions the anomalous magnetic moment of the electron as a successful prediction of quantum field theory, which relies on the concept of virtual particles.
  • Some participants discuss the concept of virtual photons borrowing energy, raising questions about the nature of energy conservation in this context and whether repayment of borrowed energy can occur before borrowing again.
  • One participant introduces the idea that virtual particles may have probable properties rather than a definite physical identity, involving complex quantities that lead to probabilistic outcomes when measured.

Areas of Agreement / Disagreement

Participants express differing views on the reality of virtual particles, with some suggesting they are not real while others argue for their significance in quantum field theory. The discussion remains unresolved regarding the nature of energy conservation in relation to virtual particles.

Contextual Notes

Some claims about virtual particles depend on interpretations of quantum mechanics and quantum field theory, which may involve assumptions about measurement and observation. The discussion includes references to complex concepts that may not be fully defined or agreed upon by all participants.

EL
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Hi everyone! Time has come for my first thread in this nice forum:

I wonder if someone could explain the concept of virtual photons (and virtual particles in general)? Have I understood it right that they are just a mathematical construction and are not in any way "real"?
I have a lack of knowledge in particle theory, but am familiar with basic quantum mechanics, so hopefully I will be able to understand an explanation at a rather high level...
 
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Whether virtual particles are real or not is a moot question.

Here's the idea. In quantum mechanics nothing is really real unless you can observe it or measure it. In order to be observable, a particle has to have some minimum amount of energy for some minimum amount of time; this comes out of the uncertainty principle that says the product of those two things has to be bigger than a certain number.

So it's possible to conceive of a particle whose energy is not big enough or whose lifetime is not long enough to permit a true quantum measurement, but still both of them could be greater than zero. The world could be full of such particles, and the measurements would never show it.

Well, quantum field theory takes those particles seriously. It says they interact with observable particles, for example they make the electron which emits and absorbs them a bit heavier, and a bit more sluggish in motion, than it would be if they didn't exist.

Furthermore, QFT says that the virtual particles are the ones that carry the forces. For example with photons, the "real" photons make light, and other forms of electromagnetic radiation, but the virtual photons carry the electric force; a charged particle is charged because it emits virtual photons. And the other bosons, that carry the weak and strong forces, behave the same way. Real particles interact with each other by exchanging virtual bosons.

This is the story quantum field theory tells, and the justification, the reason you should at least consider beliving in it, is that it makes fantiastically correct predictions. That bit above where I said that interacting with virtual particles made the electron sluggish? It's called the anomalous moment of the electron, and the prediction, based on virtual particles, matches experiment to six decimal places.

For several decades the theorists and experimenters were in a kind of race. The experimenters would rack their brains and come up with a new way to measure down to another decimal place. And the theorists would grind through the next level of calculations (in the same theory mind you, this is not about epicycles) and come up with another decimal place of their own. And the two would match!
 
Thanks a lot! Everything is now clear (except for the word "moot" =))...
Does anyone know any good litterature or links about this subject?
 
Originally posted by EL
Thanks a lot! Everything is now clear (except for the word "moot" =))...
Does anyone know any good litterature or links about this subject?

"Moot" has unfortunately two completely opposite meanings (like "fast"). The first, which I did not intend, is of a completely settled question. The second is of a much discussed question. That is the one I meant.

The different meanings come from the practice in law schools of using moot (settled) court cases for study and discussion.
 
Ok, I just never had heard the word "moot", because english is not my main language...
 
virtual photons do not conserve energy, they borrow energy and repay.
 
Originally posted by garytse86
virtual photons do not conserve energy, they borrow energy and repay.

If virtual photons borrow energy?..can they also borrow after a repayment has been made? Do they always follow convensional lending practise's?..ie..is repayment possible pior to borrowing?
 
Originally posted by garytse86
virtual photons do not conserve energy, they borrow energy and repay.
In hep physics lingo, they are off-shell
 
Originally posted by EL
Thanks a lot! Everything is now clear (except for the word "moot" =))...
Does anyone know any good litterature or links about this subject?

It's a shame English is not your first language, because you made a great joke by accident!

Njorl
 
  • #10
Hehe. It was, hmmm, on purpuse...=)

Just to make something clear...I didn´t ask for litterature about the word "moot"...so, again, anyone who has some texts to recommend about virtual particles?
 
  • #11
Originally posted by EL
so, again, anyone who has some texts to recommend about virtual particles?

start here
 
  • #12
One might think of virtual particles being primarily of probable properties rather than with a definite physical identity. The action (energy-time or momentum-displacement) of a virtual particle is less than Planck's constant, h, and involves complex quantities that interfere toward a resultant probability - say, that an electron has a .5 chance of being within an Angstrom of a particular atom. When measured, the particle is said to be real, and takes on the definite properties bestowed from one possibility of many.

Forgive my rambling; I gave blood today.
 

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