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:

New Journal of Physics
New Journal of Physics

Now to add further weirdness to the mix, it has been found that matter can act as both a wave and a particle depending on whether or not it is being observed. So is is true that the electrons knew that they were being watched?

Some scientists think that they can!

Bach et al published a study in 2013, which aimed to demonstrate Feynman’s hypothesis on a practical level. This extract is from his research.

Double-slit diffraction is a corner stone of quantum mechanics. It illustrates key features of quantum mechanics: interference and the particle-wave duality of matter. In 1965, Richard Feynman presented a thought experiment to show these features. Here we demonstrate the full realization of his famous thought experiment. By placing a movable mask in front of a double-slit to control the transmission through the individual slits, probability distributions for single- and double-slit arrangements were observed. Also, by recording single electron detection events diffracting through a double-slit, a diffraction pattern was built up from individual events.

The team took measurements of the position of electrons fired individually, with a mask in a series of positions. First blocking both slits, then one slit, then none and then the opposite slit. The double-slit pattern was seen when the electrons had access to both slits, but not seen when one slit was blocked. You can watch the pattern of electron build up on the video below.

Their experiments do correlate with Feyman’s way of thinking. It opens the door to far more questions!

If tiny electrons behave as waves……

…….and if tiny electrons are affected by being observed…..

….can the tiny electrons that make bigger things (such as human beings) also behave like waves and change depending on whether we are being observed?

What do you think? “Everything that can happen does happen“? Or is that quite enough physics for you thank you very much? We would love your feedback!

8 thoughts on “Physics 101 – The Double Slit Experiment Explained”

  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.

    • 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.

      • You cant argue the facts. You could but would be the same as arguing that your a dog and not a human, pointless and theres plenty of proof, you being a human and the double slit. Whoever wrote this article or paper left out many pieces. The writer even has the name and date of the creator completely wrong. This test was first done in 1801 by Thomas Younge with 1 slit and added the 2nd in 1807, not 1965. 164 years off, look into this expriement just for 30 mins and you’ll see..

  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.

    • You should do some studing or just go watch anyother video about this expriement. Of course they did this expriement by firing one particle at a time. They still do this expriement, one of the reason places like fermi labs was created, where they collide 2 particles into each other, at the speed of light.

  3. Im just so lost as to why you say its R. Feynmans double expriement from 1965? This is 164 years off.. Even if your talking about when a certain version of the double slit was added, you never said that or gave credit to the real person who created this expriement.
    This expriement was first done in 1801 by Thomas Young.. Only 1 slit was tested in 1801, with the 2nd slit added in 1807.
    Young was ridiculed, since he proved Issac Newton wrong. Some skeptics would say they dont have to believe him, and some were offened to even disagree with Newton.


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