Quantum Physics and the Double Slit Experiment

If we randomly shoot a small object say a marble at the screen

we see a pattern on the back wall where they went through the slit and hit

Now if we add a second slit

we would expect to see a second band duplicated to the right

Now let's look at waves

The waves hit the slit and radiate out striking the back wall

with the most intensity directly in line with the slit

The line of brightness on the back screen shows that intensity

This is similar to the line the marbles make But

when we add the second slit

something different happens If the top of one wave meets the bottom of another wave

they cancel each other out

So now there is an interference pattern on the back wall

Places where the two tops meet are the highest intensity

the bright lines and where they cancel there is nothing So when we throw things

that is matter through two slits we get this

Two bands of hits

And with waves we get an interference pattern of many bands

Good so far Now

let's go quantum

An electron is a tiny

tiny bit of matter

like a tiny marble

Let's fire a stream through one slit

It behaves just like the marble a single band

So if we shoot these tiny bits through two slits we should get like the

marbles two bands

What An interference pattern

We fired electrons

tiny bits of matter through We get a pattern like waves

not like little marbles How

How could pieces of

matter create an interference pattern like a wave

It doesn't make sense

But physicists are clever

They thought maybe those little balls are bouncing off each other and creating that

pattern So they decide to shoot electrons through one at a time

There is no way they could interfere with each other But after an hour of this

the same interference pattern is seen to emerge The conclusion is inescapable

The single electron leaves as a particle

becomes a wave of potentials goes through both slits and interferes with

itself to hit the wall like

a particle But mathematically it's even stranger It goes through both

slits and it goes through neither

And it goes through just one and it goes through just the other

All of these possibilities are in superposition with each other But

physicists were completely baffled by this So they decided to

peek and see which slit it actually goes through

They put a measuring

device by one slit to see which one it went through and let it fly

But the quantum

world is far more mysterious than they could have imagined

When they observed the electron went back to behaving like a little marble

It produced a pattern of two bands

not an interference pattern of many

The very act of measuring

or observing which slit it went through meant it only went through

one not both

The electron decided to act differently

As though it was aware it was being watched