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Do virtual particles travel at the speed of light, or do they have 'virtual rest mass'?
Since they are a mathematical fiction, I'm not sure it matters.Do virtual particles travel at the speed of light, or do they have 'virtual rest mass'?
What about the photon propagator?They do not exist in the first place:
Misconceptions about Virtual Particles
As discussed in detail in the companion article, virtual particles are defined as (intuitive imagery for) internal lines in a Feynman diagram.www.physicsforums.comThe Physics of Virtual Particles
There is considerable confusion about various notions around the concept of particles of subatomic size, and about the notion of a virtual particle.www.physicsforums.com
I mean, well, they exist, but it's just a name for propagators appearing in perturbation series used in QFT. And when I look at my notes, I don't see any propagators flying around at the speed of light
Well, as you can see: ##\frac{-\eta_{\mu\nu}}{k^2+i\varepsilon}## - it's standing still - in the rest frame of this page of courseWhat about the photon propagator?
How do you define the velocity of a straight line segment?So let's recap: we've been told that virtual particles:
1) don't exist - or perhaps they do
2) don't move - or perhaps they've stationary
Virtual particles have endpoints in configuration space, so of course they can have defined velocities.
BTW, I read those links when you posted them on another thread, and wasn't convinced. Full of circular reasoning, and never gave an operational meaning of "exist".They do not exist in the first place:
Misconceptions about Virtual Particles
As discussed in detail in the companion article, virtual particles are defined as (intuitive imagery for) internal lines in a Feynman diagram.www.physicsforums.comThe Physics of Virtual Particles
There is considerable confusion about various notions around the concept of particles of subatomic size, and about the notion of a virtual particle.www.physicsforums.com
I defined exist = having a state, which is necessary to talk about probabilities of observation.BTW, I read those links when you posted them on another thread, and wasn't convinced. Full of circular reasoning, and never gave an operational meaning of "exist".
Having a measurable effect. Virtual particles mediate forces (which we can measure) and other stuff (which we can also measure).I defined exist = having a state, which is necessary to talk about probabilities of observation.
What is your operational meaning of the word?
When I said that they don't exist I meant that they don't exist the way real particles do - everything is explained in the insight articles.don't exist - or perhaps they do
Wasn't convinced of what? "Virtual particle" is a name for a certain line you draw on a paper when you want to do some calculation. That's what all textbooks on QFT I have seen say. The only books that give them any realness are pop-science books. Have you ever done any calculation using Feynman diagrams? Have you drawn any Feynman diagram? If you did, at what velocity did the internal line you draw on your paper move?BTW, I read those links when you posted them on another thread, and wasn't convinced.
you integrate all that out.Virtual particles have endpoints in configuration space
Yes, you can integrate them out, but you don't have to.When I said that they don't exist I meant that they don't exist the way real particles do - everything is explained in the insight articles.
Wasn't convinced of what? "Virtual particle" is a name for a certain line you draw on a paper when you want to do some calculation. That's what all textbooks on QFT I have seen say. The only books that give them any realness are pop-science books. Have you ever done any calculation using Feynman diagrams? Have you drawn any Feynman diagram? If you did, at what velocity did the internal line you draw on your paper move?
Besides
you integrate all that out.
Virtual particles appear only in perturbative methods and it's only a name physicists gave to certain part of the mathematical expressions. You seem to be stuck on a pop-science view of them. And as I said in other thread, you can derive Casimir effect without virtual particles.Virtual particles mediate forces (which we can measure) and other stuff (which we can also measure).
Um, what? There is no ad hominem. You simply don't accept the very definition of a virtual particle that physicists use.PS ad hominems ignored.
Lots of effects in physics have multiple explanations or valid models. One valid model does not invalidate another.Virtual particles appear only in perturbative methods and it's only a name physicists gave to certain part of the mathematical expressions. You seem to be stuck on a pop-science view of them. And as I said in other thread, you can derive Casimir effect without virtual particles.
Unless virtual particles contradict the Casimir effect - which would be an amazing claim - then this is irrelevant, incorrect or confused.That does not mean that every single part of the model correspond to reality. Expecially when it contradicts the definition of that part. And the definition of virtual particles is as straightforward as it could be.
Your view of them contradicts their definition. And also it contradicts the consensus among physicists (probably that's why your last thread was closed), and contradicts what most textbooks on quantum field theory say. Student Friendly Quantum Field Theory by Klauber has even one whole chapter (chapter 10) discussing related issues.Unless virtual particles contradict
From the truncation I gather that you accept that virtual particles do not contradict the Casimir effect. If so, then we are only disputing what "exist" means. Which is not subject to operational resolution.Your view of them contradicts their definition. And also it contradicts the consensus among physicists (probably that's why your last thread was closed), and contradicts what most textbooks on quantum field theory say. Student Friendly Quantum Field Theory by Klauber has even one whole chapter (chapter 10) discussing related issues.
But only on paper. In this sense, the exponential function also exists since it is ubiqitous in the derivation of measurable effects.Having a measurable effect. Virtual particles mediate forces (which we can measure) and other stuff (which we can also measure).
can be justified under a suitably abstract definition of velocity... but it’s pedagogical malpractice to toss them into this discussion.Virtual particles have endpoints in configuration space, so of course they can have defined velocities