Light’s energy comes in packets, quanta, each with an energy proportional to the light’s frequency, so bluer light has more energetic quanta. Each quantum is taken up whole, by one electron.

Light is a quantum field. Its energy comes in quanta, photons, each taken up whole at one place. But the chance of finding a photon here or there spreads and interferes like a wave: each photon interferes only with itself. So light makes interference stripes and knocks out electrons alike.

Light is a quantum field. Its energy comes in quanta, photons, each taken up whole at one place. But the chance of finding a photon here or there spreads and interferes like a wave: each photon interferes only with itself. So light makes interference stripes and knocks out electrons alike.

Quantum theory applies to everything, observers included, and nothing ever collapses. An observer measuring something branches: each branch sees one definite outcome, and every outcome the equations allow is seen in some branch. All the branches are actual, none more real than the rest.

Quantum theory applies to everything, observers included, and nothing ever collapses. An observer measuring something branches: each branch sees one definite outcome, and every outcome the equations allow is seen in some branch. All the branches are actual, none more real than the rest.

Reality is a multiverse, as Everett’s theory says, and single-particle interference shows it. Photons sent through slits one at a time stop reaching some places when more slits are open, so something coming through the other slits interferes with them: shadow photons, which are the photons of other universes. Every kind of particle has such counterparts, and they make up a huge number of universes like ours.