Regarding Particles in the Double Slit Experiment

Posted by Youssef Moawad on: 13/05/2017, in Physics

Why am I posting this?

I have recieved some brilliant constructive feedback about my previous article, Observers affecting reality? The Double Slit Experiment, and since it has been pointed out that I have misinterpreted some of the results from performing variations of the modern double slit experiment, I thought I would publish a short correction post after doing some further research into the topic. I will be updating the previous article by providing a link to this post and by striking through some of the misconveyed information.

This article will be fairly short and will be structured such that it directly corrects some of the points I made previously.

Explanation: use of a "camera" to detect electrons

I tried to simplify the use of a detector to see which slit electrons pass through by using the common "camera" analogy. I also implied that "unplugging" this camera or not looking at the data changes what we see at the screen.

I should explain that firstly this "camera" is really a device which will interfere with the passing electrons in order to detect them. A simple camera cannot "see" the electrons as they do not simply reflect light.

In the Copenhagen interpretation, when this device makes a measurement to see which slit an electron passes through, the device collapses the wavefunction of the electron, making it behave as a particle and as such two bands are seen on the screen just as we expected to see with particles or marbles. If this device is turned off, and so does not make a measurement, it does not interfere with the passing electron, so its wavefunction is not collapsed and we see the familiar interference pattern that occurs with waves.

Another example of a detector can be some sort of filter through which electrons can pass which would be placed on one of the slits and records data of when an electron passes through it. Details about such an experiment are explained in the article mentioned in the source for this.

[Source: Which-way detector unlocks some mystery of the double-slit experiment]

Correction: Consciousness affecting electron behaviour

This, I think, was the main flaw point in the article. I think this is because plenty of other sources that try to explain such phenomena tend to use oversimplified terms to convey some point to the reader. And we like such explanations because they tend to feature us, as human beings, as key players in the quantum world; saying things like "look, we're important in the outcome of this and that!" whereas we really aren't. Indeed, there's a plethora of key quantum phenomena happening in all such situations that provide explanations to such interpretations. These phenomena are well studied and understood.

This results in these misinterpretations spreading very quickly as pop-science. I regret taking part in spreading this particular explanation and will make more effort in the future to more deeply research the topics about which I choose to write.

Indeed, what I tried to imply about consciousness in the previous article is briefly explained in the previous section of this article.

Clarification: The quantum eraser experiment

Towards the end of the article, I wrote about a quote from The Big Bang Theory about how if we try to detect which slit a photon goes through after it actually goes through one, then the photon will act as if it were always a particle rather than a wave. However, this does not imply that the photons travel back in time to change their decision or that casuality is violated. Plenty of research has been made regarding this and explains this phenomenon in detail. You can find more here in this Wikipedia entry.


I hope I managed to correct and clarify some of the topics I talked about previously. This goes to show the importance of your feedback about these articles, so please keep it coming. If you would like to discuss this further, please do contact me or leave a comment in the comments section.

What's next?

Just to give a quick update about what I plan to write about next. I believe my next article will be the third part of the Particle Physics series and I will be discussing particle interactions and Feynman Diagrams. Furthermore, after I wrote about symmetry in Symmetries: The Beauty in Physics, I wanted to see if there was a way to visualise the symmetries and conservation laws in particle interactions in a way similar to how we visualise symmetries in geometrical shapes like squares. So I started working on something about which I will be writing soon.

Thanks for reading!


You may also be interested in:

Observers affecting reality? The Double Slit Experiment

Particle Physics, Part 1: Why is the Standard Model so cool?

Symmetries: The Beauty in Physics