# Detecting Virtual Photons & EM Force: A Particle Physics Quandary

• Cluelessluke
In summary, the conversation discusses the concept of virtual photons and their role in the electromagnetic force between charges. It is mentioned that virtual photons are not detected, but are instead mathematical entities used in quantum field theory. The idea of detecting virtual photons and its potential effects on the electromagnetic force is also mentioned, with reference to the Casimir effect and Glauber states. Overall, it is emphasized that understanding of quantum mechanics is necessary to fully comprehend the concept of virtual photons.
Cluelessluke
Hey all, I am an undergraduate taking a particle physics class and we just learned that the EM force was caused by charges "spitting" virtual photons back a forth. In like second grade we learned that the EM force was dependent on the two charges involved (keeping this simple) and the distance between them. Now, if you somehow created a device that could detect, let's say, half of the virtual photons between two given charges, wouldn't the EM force between the two of these charges decrease without changing the charges or the distance between them? (I was told that once you detect a virtual photon, you promote it to a real photon and it no longer plays a role in the EM force between charges.) I think I know just enough about this to be dangerous. Thanks for your time!

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Virtual photons are not detected, they are mathematical concepts/entities when you do perturbative expansion in quantum field theory.

Perhaps best to say that virtual photons are the ones that you don't detect. The distinction is more of a practical one since photons themselves are "mathematical concepts/entities when you do perturbative expansions in quantum field theory". Forgetting this leads to problems like IR divergences and the inability to understand classical light (for which coherent states are necessary -- what is a photon if absorbing it does nothing?)

The idea you are after is related to the Casimir effect, and I invite you to read, say, the wikipedia article on the subject, and ask for clarification if you want. If you're feeling brave you can read up about Glauber states as well. But only if you can quantize the harmonic oscillator in your sleep.

Cheers

So yes, your thinking is dangerous, but as long as you realize that you'll be fine =)

## 1. What are virtual photons and how are they different from regular photons?

Virtual photons are particles that are not directly observable, but rather exist as a mathematical concept in the theory of quantum electrodynamics (QED). They are different from regular photons in that they do not have a physical existence, but rather mediate the electromagnetic force between charged particles.

## 2. How are virtual photons detected?

Virtual photons cannot be directly detected because they do not have a physical existence. However, their effects can be observed through the interactions between charged particles, such as the attraction or repulsion between two charged particles due to the exchange of virtual photons.

## 3. What is the significance of detecting virtual photons?

The detection of virtual photons is significant because it confirms the existence of the electromagnetic force and provides evidence for the validity of the theory of quantum electrodynamics. Additionally, understanding the behavior of virtual photons is crucial for developing a deeper understanding of the fundamental forces of nature.

## 4. Are there any challenges to detecting virtual photons?

Yes, there are several challenges to detecting virtual photons. One major challenge is that they are not directly observable, making it difficult to study their properties. Additionally, the interactions between charged particles can be complex and difficult to measure accurately.

## 5. How does the detection of virtual photons relate to particle physics?

The detection of virtual photons is an important aspect of particle physics because it provides insight into the fundamental forces and particles that make up our universe. Understanding the role of virtual photons in the electromagnetic force is crucial for developing a comprehensive understanding of the subatomic world.

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