Ask Ethan: How do photons mediate both attraction and repulsion?
In our Universe, photons are one of the essential ingredients to matter — and life — as we know it. Light of all types (visible, infrared, ultraviolet, etc.) is made up of photons, and photons can be absorbed or emitted by charged particles, including within atoms, allowing for all sorts of vital processes and phenomena like photosynthesis, radiation, and even what we perceive as “color.” But photons serve another function that’s more fundamental: they themselves are the particles that mediate the electromagnetic force. When charged particles attract, repel, or are bent in a magnetic field, it’s the photon that does the heavy lifting, as it’s the underlying cause behind all of these interactions.
So how is it, then, that this one species of particle, which happens to be both massless and electrically neutral, is responsible for all of these phenomena? How can “exchanged photons” do it all: cause attraction, repulsion, or a perpendicular bending force? That’s what Jon Joseph wants to know, writing in to ask:
“The electromagnetic force is mediated by photons. And unlike all other forces, the electromagnetic force can be either attractive or repulsive depending on the sign of the charges involved. What is the difference between those virtual photons that mediate the attractive electromagnetic forces versus the repulsive electromagnetic force? Don’t photons come in essentially one flavor?”
