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Making No Sense
 Electrons being fired individually onto a TV screen

The Electron

Nice And Simple... Or Is It?

We are taught at school about the easy to uderstand structure of an atom. The positive charged proton nucleus surrounded by rings of negatively charged electrons.

It's a great model which helps us to understand why chemicals react with other chemicals to form various bonds. For example, if an atom is short of a couple of electrons it will have a +2 charge or if it's got an extra one then it will have a -1 charge. These charges show us how substances can end up reacting with each other to join to form an overall stable compound with no charge. For example 2 Hydrogen atoms each with a -1 charge combine with an Oxygen atom which is +2 to form the very stable substance H2O - ie. water.

Other parts of an atom such as Protons and Neutrons are a bit complex and actually made up of other things such as Quarks, but the Electron appears to be nothing more than that - just an Electron.

So that's the good news, but there are some complications.

You may have heard the experiment involving 2 sources of light passing through 2 slits in a piece of card and the end result is that you get a light - dark - light - dark banding showing up on the wall because light is actually made up of waves and you get light and dark bands because in some places the waves either add together to form a brighter spot or cancel each other out to form a dark spot. Well the Electron can also be classed as a wave because it also demonstrates that property.

Like light however there is also something strange going on...

Use the same two slits and an old tv screen to display the electrons as they arrive but this time use a single source to fire one individual electron at a time. The electron can either pass through one slit or the other but not both. As they are fired one at a time a bit like a gun, you should simply expect to see a thin diffused line on the left side of the screen showing where the electrons had passed through the left slit and a similar line on the right for the other slit...

That is exactly what happens if you block off one of the slits, but...

...leave them both open so that the electron could pass through either and you can see what happens in the diagram opposite as the electrons start arriving on the screen one by one. After a while you start to get the exact same interference band that you got when using two sources!

So a single electron is somehow passing through both slits at the same time and creating the wave interference with itself!

It's one of the major mysteries of quantum physics and shows the dilemna between the normal world we live in and the reality of the quantum world where Newtons laws of physics do not seem to apply.

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