Tony does his best to make you smarter, despite the comments section.
Travel back in time to the late 1800’s. The Physics world is getting pretty cocky. The general consensus is that everything that can be discovered has been discovered. Sure, there are a couple small questions, but these were just minor issues.
One of these questions was the nature of light. Some people thought light was a particle called a photon, while others thought it was a wave. The debate raged on for years, but then some guy named Albert Einstein came along and gave a new answer.
This was a crazy answer. How could a particle be a wave? But he proved it with the Photoelectric Effect, part of his amazing year. What does it mean? How is it possible?
The answer is that the “wave” describes a probability that the particle is at a certain location. This probability wave travels through space until it’s forced to decide. What makes it really weird is that this wave acts 100% like a wave, and not at all like a particle, while the particle acts 100% like a particle and not at all like a wave.
Waves can interact with each other to add together or subtract from each other. That looks something like this.
Obviously particles can’t add and subtract from itself like this. It would just move in a straight line. But what a particle will do is be discrete. Like a football. You can have 1 football, you can have 3 footballs, but you can’t have 2.34 footballs. That’s not the case with a wave, you can have any value you want. 2? Sure thing. 3.82? No problem.
When light hits and object (or is omitted), it has to do so one photon (a particle of light) at a time. That’s what the “quantum” in “quantum mechanics” means.
This wave/particle duality manifests itself in many ways. For example, think about an atom. It looks something like this, right?
Except no, that picture is a lie. Like photons, electrons are also both a particle and a wave, and when they orbit around the nucleus they act like a wave. They form what’s known as the electron cloud around the nucleus, which looks something like this.
The most famous example of this duality is the double slit experiment. If you send light through two slits the waves interfere with each other, so the light leaves a bar pattern.
Amazingly this occurs even if you send the light through one photon at a time. And of course, when the light actually hits the screen it does so as a complete photon, since it’s also a particle as well.