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Virtual Particle Confusion 
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#1
Mar2612, 10:45 AM

P: 5

Layman here. Two questions on Virtual Particles.
I am not trying to make some claim to spontaneous generation, just curious about how to expand the holes in my knowledge... which is about the level of a post grad engineer who likes to buy the popular physics books in stores to read. 1) Where is all the spontaneously created matter? So, I understand that according to one physics interpretation that there are virtual particles (pairs of particles that are spontaneously created and destroyed alomst instaneously). The most often written example is a matter and antimatter pair. So, I know that Charge Parity violation exists. So if there is not perfect parity in a matter anti matter collision, how come the universe has been crushed into a singularity yet, due to the spontaneously created matter that is left over from virtual particle annihilations? 2) Has there been any work on understanding the impact of the Big Rip (expansion of space ever accelerates) on virtual particles? The idea is this. The fastest they can go is light speed, or slower if they have mass, will call it speed c. Plankc Time has a constraint on being the smallest unit of time, t. This implies that the farthest apart a virtual particle interaction can occur c*t (simplified probably). My question is, if the Big Rip (Dark Energy) ever nets large enough acceleration, then space will have expanded before the virtual particles had a chance to annihilate. Is that about right? 


#3
Mar2612, 12:21 PM

P: 5

Well. Thanks. I guess.
So does that mean virtual particles dont work the way I assumed? Or are virtual particles something of an old theory that has been disproven some time ago? 


#4
Mar2612, 01:48 PM

Sci Advisor
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P: 4,160

Virtual Particle Confusion
shifty123, Virtual particles are fine. But unfortunately the account of them you hear from popsci sources is rather far off.
Here's an analogy: take a system with spin and prepare it in the spin up state, S_{z} = +½. Now ask what is the spin along the xaxis, S_{x}. Answer: it's a quantum superposition, 50 percent S_{x} = +½, 50 percent S_{x} = ½. But one should not say the system is constantly jumping back and forth between the two! 


#5
Mar2612, 03:49 PM

P: 5

Thanks Bill_K. That helps a bit.
Its almost as if you knew about the violent storm, quantum foam etc, that I read about! Those exact words even. If the vacuum state is time independent then that definitely takes care of the issue I was wondering about. Ok. Is this the correct interpretation? So I guess the answer is if there is a CP violation that occurs for fermion virtual particles, then regardless of the number of superposition states that they could possibly live in, there is should be a positive bias towards matter virtual particles surviving. However since the VPs are time independent there is no "time" for this imbalance to "manifest"? 


#6
Mar2612, 06:39 PM

P: 1,417

Also, I don't think virtual particles are bound by the speed of light(?)



#7
Mar2712, 10:38 AM

Sci Advisor
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#8
Mar2712, 11:34 AM

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P: 4,160

Congratulations, Demystifier, I figured somebody would walk into that. Did I say "number operator"?
The number operator for a Dirac field is N = N^{+}  N^{}, the number of electrons minus the number of positrons, also proportional to the total charge. Yes, N commutes with the Hamiltonian and any stationary state such as the vacuum state is an eigenvalue of N. But consider for example a photon selfenergy diagram in which a photon temporarily becomes a positronelectron pair. I count two particles in the intermediate state, don't you? "Two" is obtained from N^{+} + N^{}. 


#9
Mar2712, 06:00 PM

P: 4,663

* Serber also in same issue of Phys Rev 


#10
Mar2712, 10:49 PM

P: 166

Virtual Particles: What are they? by Matt Strassler.



#11
Mar2812, 03:34 AM

Sci Advisor
P: 4,612

Saying that virtual particles are real is like saying that when you have one apple, you actually have 2 apples and 1 apple because you can write 1 apple = 2 apples + (1 apple) 


#12
Apr112, 02:24 PM

P: 1,417

But Demystifier, don't certain versions of de Broglie Bohm interpret virtual particles to be as real as any normal particle? (same ontological status) Yet that seems kind of incompatible with your 1 = 2 + (1) argument.



#13
Apr112, 05:08 PM

P: 4,663

I think that Uehling's model for the disturbance of virtual electron positron pairs in strong Coulomb fields is a real effect
Phys. Rev. 48, 55–63 (1935) "Polarization Effects in the Positron Theory" and has been rigorously tested in recent years (muonic and pionic atoms) and found to be still correct. So are we just arguing semantics? See http://philoscience.unibe.ch/documen.../uehling35.pdf 


#15
Apr1612, 07:51 AM

P: 1

virtual particles just participate in the interactions,the momentum can be indefinitely large!!



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