Physics 101 – The Double Slit Experiment Explained



As enlightened individuals and readers of The Good Human, we ask many questions about our planet….and I feel that there is value in learning how our Universe works at an atomic level, in the quantum world.

Physics is baffling, but it can help us to recognise the bigger picture. Or at least to recognise that there is a tonne of stuff that we just don’t know! There has been huge interest in the article that was published last week about the big bang and quantum gravity, so I wondered if there would be space for some further discussion around physics. Particularly as there is huge synergy between many areas of spirituality and physics.

We choose to examine a phenomenon which has in it the heart of quantum mechanics. In reality, it contains the only mystery. ~R. Feynman

So in order to unravel ‘the only mystery’ I wanted to start with Richard Feynman’s infamous 1965 experiment – The Double Slit! It is absolutely mind-blowing and a perfect illustration of the apparent illogical way that our world works when you get down to the quantum level. You can read all three volumes of his lectures here.

I implore you to watch this video before we go any further… can explain this phenomenon far better than I can.

So the first crazy fact here is that electrons can act as a particle or a wave. They can even act as a wave when they are fired individually – i.e. when there is nothing to interfere with it’s path.

When anaylsed in the world of mathematics it is considered that each individual electron goes through both slits, and neither, and only the left one as well as only the right one. Confusing? Yes. Amazing? Definitely!

The pattern below is what we see when particles are fired at a double-slit:

New Journal of Physics
New Journal of Physics

The pattern below is what we expect to see when waves are fired at a double slit (interference pattern):

New Journal of Physics
New Journal of Physics

Incredibly, this is the pattern that develops after a series of individual electrons are fired at a  double slit:



  1. Please check the Afshar experiment. Also the wave function is a statistical formula. Particles go through 1 slit or the other. The wave patern is only visible after a cumulative build up of individual impacts. I have yet to see any experiment that shows an individual particle make multiple strikes on the detectors or screens or exist in 2 places at once. You could say “Well the wave collapsed” but that is a poor explanation that relies on some unknown function to convert some photon/electron from ephereal wave to singular point. We can accurately collide particles together, we have videos of electrons in flight, and we can balance particles on the head of a pin. The wave/particle duality explanation needs to be discarded for a factual explanation; theyre small and hard to track individually because theyre influenced by virtually everything, so until or unless we specifically want to view an individual, the best and easiest way to make predictions about them is to make a statistical estimation based on their properties. The statistical model was developed recognizing that to directly view an individual is to ultimately alter its behaviour and properties.

    Conciousness does not bring reality into existance. The stars in the universe that we havent observed yet wont pop into existence when we finally poke a telescope their way. The is nothing in this universe that isnt essentially being observed at all times in all places.

    1. You make a great point! There are many people that argue both sides of this – especially regarding the wave/particle duality. I love your comment about stars popping into existence! I will have a look at the Afshar experiment, thanks for directing me to that. Thank you for commenting.

  2. The double slit experiment has an assumption: A stream of single particles must be used. Only then the interference pattern will confirm that the particles are waves.

    But do we have the technology to generate a stream of single particles, i.e. one after another? I do not think so. The narrowest beam that we can generate will shoot millions of particles simultaneously at every time instant, thus invalidating the conclusion of the DSE.

    Moreover, can you isolate an electron? All objects in the universe are continuously and simultaneously interactive with each other for all time. If you try to isolate earth from its solar system, the earth will die. Its environment will vanish, all humans will be dead, etc. The same thing will happen to an isolated electron, it will not remain an electron.

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