If photons are massless, how can they be redirected? How do they interact with the properties of a mirror for an example?
In: Physics
Photons are massless, but they still interact with the universe.
A mirror, for example, has a thin conducting layer behind the glass (was once silver, but I”m sure it’s something else now). The electrons in the conducting layer kind of absorb some of those photons and then reflect them outward.
Photons are electromagnetic waves. As mirrors are made up of charged particles (i.e. electrons and protons), photons can interact with them.
Whether this interaction results in reflection, absorption or transmission depends on the frequency of the photon and the exact configuration of the material of the medium.
Photons interact with electromagnetic phenomena because they are electromagnetic radiation. However, given that they are massless, you wouldn’t expect them to react to gravity.
But they do. This is because gravity is not best understood as the Newtonian attraction proportional to mass and inversely proportional to distance, but the Einsteinian understanding that energy bends the fabric of reality. Large masses, such as stars, pull space itself towards them, dragging everything which passes through that space as well. Light still travels in a straight line through gravity wells, but the lines themselves aren’t straight because the material they are inscribed upon isn’t. In a very real sense, there is no such thing as a straight line at all.
Human brains aren’t built to imagine this properly. That makes sense, given our origins, but it unfortunately means that we find this objective fact about reality wierd and counterintuitive. The fact is that we’re the weird ones, for not being able to understand something true intuitively.
Light doesn’t have mass, but it is an electromagnetic wave, which means it does interact with anything that has charge, most relevantly including electrons. Basically, when light hits an electron, it gets absorbed and then shot back out in a random direction. Mirrors just have the unique property that when you work out all the interactions it has with light, the only choice light has is to bounce back relative to the direction it came (the self-interaction or reflected light destructively cancels out all light that’s not traveling at an angle equal to the angle of incident).
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