Natural Order and Science

[Alex K]

What's the conceptual difference between particles in a detector (which is made from particles) and "two other particles"?

The difference is not in the concept in terms of what "is" a particle, but that are involved differently. The particles that can be observed are those registering on your eyes ( or any detectors you wish to use). So you can say they interact with you (or an observer/detector). The virtual particles are those involved in the interaction between other particles. Therefore, they are not interact with you (or any other observer/detector). The word "virtual" is to distinguish these two cases, but a photon is a photon whether it interacts with you, hence its a "REAL" particle, or it interacts between two electrons, hence "VIRTUAL".

You again make an arbitrary distinction between "other particles" and "you or observers".
Why do you say that virtual particles don't interact with you or other observers? That's just not true. The electrons in your eye are affected by virtual particle effects just as any other electrons. The electrons in your eye for example have an anomalous magnetic moment , ergo they interact with virtual particles.