Saturday, June 25, 2011

The Double Slit Paradox

So the double slit paradox experiment is good introduction to the weirdness of quantum physics.

So lets start this explanation off with things we can all understand. Imagine there is a guy with a machine gun and was shooting a wall in front of him. The gunner is not aiming at all so when he shoots a spray the spread of all the bullets would hit the entire wall so each point on the wall has the same chance of being hit by a bullet.

Now we put a metal wall in front of the wall with one vertical slit allowing the bullets to travel through. Now when he shoots his gun bullets would concentrate right behind the slit and barely hit any where else. If we were to put two side by side slits, like anyone would expect, there would be only two similar sized areas as the slits on the wall. Since the bullets don't interact with each other nothing spectacular happens.

Actually made these first three images believe it or not

The white levels on the back wall shows the intensity of the wave
So now we can more away from solid objects and move to waves. The most common and visible type of wave is water waves like in the ocean or like ripples. For this example we'll have a ripple tank, which is just a tank with water in it and has a wall that comes out of the surface and has slits in it to let the water waves through. So when we have one slot the maximum height of the waves is right behind the slot and spreads out away.

Notice the interference pattern in the back. 
When we add two slots something more interesting happens. The wave splits into two waves and these two waves interact with each other in a pattern known as the interference pattern. When two crests meet together they add up and get twice as high as the normal wave but when a crest and a trough meet they cancel each other out and the intensity of the waves at that point becomes nearly zero.

Nice top down .gif of how the interference works

So now we under stand how particles and waves react when going through one and two slits. When particles are shot through two slits we see two similar slits in the back, and when waves are shot through two slits we see an interference pattern. So now we go to the quantum level!

So lets imagine we have us an electron gun that shoots electrons out towards a surface that can detect electron collisions. So when there is nothing in the way every spot in the wall has an equal chance of being hit by the electron. When we have a barrier with one slit we see the similar vertical slit that happens in both both particles and waves. So that doesn't help us to see if electrons are true particles or behave like waves. So let us put two slits in this barrier. When scientists first did this they were surprised to see an interference pattern like with waves. They figured that the electrons near each other when they're are shot interfere with each other so they decided to configure the electron gun to shoot another electron when the last one hit the back so only one electron would be in the air at a time. When they did this the same interference pattern came up. 

Scientists figured that the electron has a 50% chance of going through slot one and a 50% chance of going through slot to so if it has the possibility of doing something something on the quantum level will do it, meaning that the electron goes through both and none of the slots at the same time!

To see what was really going on down there scientists set up detector to see exactly which slot an electron goes through or what it could possibly mean to go through two slots at once. However once they set up the detector the electrons acted like particles and two vertical slits appeared in the back. 

This means that particles on the sub atomic level objects act like particles and waves. When particles are not observed they exist in every possible position and take every possible path they could given by the Heisenberg Uncertainly Principle and the Planck constant forming a wave function. But when a particle becomes observed (whatever that really means) the wave function that holds all the possible positions and states "collapses" into one of it's possible state and that is when we say "There it is" but once we stop looking at it it expands into all of its possibilities again!

So that's it for now. Eventually I will post about the other introductory quantum paradox "Schrodinger's Cat", go into more depth about Heisenberg's Uncertainty Principle and other quantum funkiness.  

Here is a cat until the mean time

1 comment:

  1. I haven't slept in at least 40 hours. This just hurt my brain so bad x) Still pretty interesting.