Virtual Particles: Explained in Layman's Terms

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http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html

I am new to physics and have been struggling with the idea that forces are just "action at a distance" and that fields are invisible/incorporeal (can only be detected by the influence they exert) and permeate throughout all of space. The article above describes forces as being mediated by virtual particles, which made me feel more confident that fields were actually some form of matter/energy interaction. The virtual photons are apparently transferring momentum between charged bodies, but I got lost in the physics jargon as to how this ends up working. What are the similarities/differences between photons and virtual photons wrt the em field? I think one deal with a static field and one with a fluctuating field, but I'm not completely sure. Are all forces mediated by virtual particles? What experiments have verified that virtual particles exist? Further down in the article it states that the propagation of the virtual photons is ftl. Does this have anything to do with quantum entanglement? I've also heard of the virtual particles in reference to electron-positron pairs, Dirac sea, and zero point/ vacuum energy. Does this have anything to do with the above description or something completely different? I would greatly appreciate it if anyone could explain this virtual particle subject to me in layman's terms. Thank you.

 

[Fredrik]

The virtual photons are apparently transferring momentum between charged bodies, but I got lost in the physics jargon as to how this ends up working.

I don't think it's possible to explain how this "ends up working" without getting really deep into the mathematical stuff.

What are the similarities/differences between photons and virtual photons wrt the em field? I think one deal with a static field and one with a fluctuating field, but I'm not completely sure.

The biggest difference is that a real photon can make a detector click, but a real one can't. The only difference I can think of in addition to that is that virtual photons don't have to satisfy $E^2=p^2c^2+m^2c^4$. (This implies that their speeds don't have to be c).

Are all forces mediated by virtual particles?

All forces in all quantum field theories. There is a QFT of gravity (hence "graviton") but it isn't very useful since it lacks a nice mathematical property called renormalizability.

What experiments have verified that virtual particles exist?

I could answer this with "none of them" as well as "all of them". Virtual particles show up in the mathematics when you expand a certain function in a series and consider each term separately. To say that virtual particles "exist" is equivalent to saying that the individual terms of that series describe what's "really happening", while the sum doesn't. I don't think there's any justification for that. Hence "none of them" is a reasonable answer to your question. However, they are a part of a method to calculate the probabilities of each possible result of any experiment, and these methods work extremely well. Every experiment that involves quantum mechanics in any way is evidence of that. Even the existence of stable atoms is evidence of that. Hence "all of them" is also a reasonable answer to your question.

Personally, I don't think of virtual particles as a description of what's really happening. I think of them as a part of the easiest way to do calculations.

Further down in the article it states that the propagation of the virtual photons is ftl.

When you do the calculations I talked about you're supposed to integrate over the momentum, so all speeds up to infinity are included.

Does this have anything to do with quantum entanglement?

No.

I've also heard of the virtual particles in reference to electron-positron pairs, Dirac sea, and zero point/ vacuum energy. Does this have anything to do with the above description or something completely different?

Forget about the Dirac sea. It's an old model that's been replaced by quantum field theories.

The calculation method I mentioned also includes virtual particles popping in and out of existence in the vacuum. This is sometimes mentioned as an explanation for a non-zero density of vacuum. I'm not sure I like that explanation though. The result of the calculation is that the density of vacuum is infinite. If we try to guess a cutoff energy and only include smaller energies than the cutoff in the integrals, the result is still many orders of magnitude too high. If we take the cutoff to be the Planck scale, the result is a ridiculous 120 orders of magnitude too large.

 

[denian]

First of all, don't worry if you're feeling overwhelmed by all the physics jargon - it can be a lot to take in! But let's break down the concept of virtual particles in simpler terms.

In short, virtual particles are particles that pop in and out of existence in the quantum world. They are not physical particles like the ones we are familiar with, but rather they are fluctuations in the fields that permeate throughout space. These fields are essentially invisible forces that interact with particles and give them their properties, such as mass and charge.

One way to think about it is like a sea of particles constantly fluctuating and creating temporary "ripples" in the fields. These ripples can interact with other particles, transferring energy and momentum between them. This is how forces are mediated - the virtual particles act as messengers between particles, carrying the force from one to the other.

Now, you mentioned the similarities and differences between photons and virtual photons. Photons are the physical particles that make up light and electromagnetic radiation. Virtual photons, on the other hand, are the fluctuations in the electromagnetic field that mediate the electromagnetic force between charged particles. So while they both involve the same type of field, they are different in that photons are physical particles while virtual photons are not.

Not all forces are mediated by virtual particles, but the electromagnetic and strong nuclear forces are. The weak nuclear force is mediated by a different type of virtual particle called the W and Z bosons.

As for experiments that have verified the existence of virtual particles, there have been various experiments in quantum electrodynamics (QED) that have shown the effects of virtual particles. For example, the Lamb shift and the Casimir effect are both phenomena that can be explained by the presence of virtual particles.

The statement about virtual photons propagating faster than light is referring to their "off-shell" nature, meaning they do not follow the usual rules of particles traveling at the speed of light. This does not have anything to do with quantum entanglement.

Finally, the mention of virtual particles in relation to electron-positron pairs, Dirac sea, and zero-point energy is all connected. These are different ways of conceptualizing the presence of virtual particles in the quantum world. The idea of a Dirac sea, for example, suggests that the vacuum of space is filled with virtual particles constantly popping in and out of existence.

I hope this helps to clarify the concept of virtual particles for you. It is a complex