Eli5: what is superposition of particles and how is it possible?
In: Physics
Essentially there is some uncertainty associated with a particles momentum and position. You can either know its position and very little about its momentum or know its momentum and very little about where it is. In this way its a balancing act of determining a rough area of where a particle is likely to be and a rough estimate of where its likely to go.
This is part of the basis for superposition in that you cant make accurate predictions about both properties so at any one time it could be anywhere (within reason) and going any direction (also within reason).
Edit: More background. By doing so much as looking at, measuring, or otherwise interacting with a particle, you force its “wave function” to “collapse”, which is just fancy talk for forcing the particle to make a decision about where it is. Any disturbance, however brief, causes superposition to be violated and results in “the most likely” outcome. (Don’t think too much about that).
A popular thought expirement for this is schrodingers cat:
Imagine a cat in a soundproof box with a poison vial inside attached to a radiation monitor. The vial breaks (silently) if a single atom inside the box decays.
Because of the uncertainty associated with subatomic particles (mainly position), it may spontaneously be disturbed at just the right moment that the area its “likely” to be in extends beyond the wall of the atom and can possibly “jump” out, causing atomic decay. Because there’s no telling when that will happen, in between the time you close the box and open it to see if the cat is alive, the life of the cat is in superposition.
“Superposition” is a word that means that the math that describes a particle adds together nicely. When I say “add” I mean literally the operation of addition, like 2+2=4.
So what does that really mean, physically? Well, particles are, at least in some sense, waves. We describe them as functions [just like this](http://www.science4all.org/wp-content/uploads/2013/01/Wave-Function1.png). Okay, not exactly like that, there’s also imaginary numbers involved, but don’t stress on that as this is ELI5.
In a sense, the wave function sort-of-kind-of is the particle, or at least the square of the wave function (called the probability density function) sort-of-kind-of is the particle.
And this is where we get to superposition. When people talk about particle superposition, they mean that when 2 particles are occupying the same region of space, the wave functions add together, [just like this](https://s3-us-west-2.amazonaws.com/courses-images/wp-content/uploads/sites/1989/2017/06/13225738/figure-17-10-04a.jpeg). That’s all there is to it. If the height of the waves at a specific point are 2 and 5, they add up to 7 at that spot.
How is it possible? It’s a general property of basically everything unless there’s a specific phenomena that physically causes the particles to separate. It’s just like how if two ocean waves collide they can add together to make a bigger wave, or how noise cancelling headphones add the negative version of a sound wave to the ambient noise in a room so the total sound wave adds up to 0.
To do this in an eli5 manner, consider a swing with no friction so it swings really well without naturally slowing down all the time. If you push it softly at random intervals, some of your pushes make it go faster and some pushes make it go slower (if you push it forward when it is swinging back toward you). Superposition is where you push that swing at the perfect time right at the top of the arc so that each push makes it go faster and faster exponentially. Superposition is where particles act as waves, which is a bit like a swing being pushed, and the waves line up perfectly so that the overall force of the wave is stronger. E.g. in the superposition of light, this means the light looks a lot brighter.
Latest Answers