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Exclusion Principle

Title text: Fermions are weird about each other in a standoffish way. Integer-spin particles are weird about each other in a 'stand uncomfortably close while talking' kind of way.

Explanation

This explanation may be incomplete or incorrect: Created by a SOCIALLY ANXIOUS ELECTRON - Someone who knows more about physics should explain this. Also, the title text needs explanation. Do NOT delete this tag too soon.

This comic is about the four fundamental forces of physics: gravity, electromagnetism, the strong force, and the weak force. In typical xkcd fashion, Randall also adds a joke entry: "Electrons are weird about each other". This is a description of how two or more electrons cannot share the exact same "spot". The name of this property is Pauli Exclusion Principle, and Randall has made xkcd 658 about it. This is not directly a force: electrons on neighbouring spots do not "feel" each others presence and it's not possible to push one electron so hard that it goes into a spot that an electron already has - properties normal forces have. However, the combination of Pauli exclusion with the actual force of electromagnetism makes electrons behave as if there was a force additional to the electromagnetic one, the exchange interaction. This is much harder to understand than simple forces, so Randall jokes that Physicists had given up, resolving to make it a force instead. Randall makes it sounds like Physicists behaved like politicians, changing the laws (of nature) so that they're easier for them. In reality, humanity does not know a way to change the workings of nature, and scientist merely try to figure out and describe how nature works.

The title text expands from electrons to fermions, the class of particles electron belong to, and bosons, the other class of particles. All fermions share the property of electrons of not being able to share the same spot. Bosons on the other hand, can do that - you can put two or really any amount of Bosons into one spot. Randall refers to this as "stand uncomfortably close while talking". This gives rise to quantum effects like superconductivity.

Interactions between electrons are different from how human interactions can depend upon the concept of 'personal space', and they are therefore ‘weird’, which also explains the title text.

Transcript

[Inside the panel, there is an underlined header and a numbered list, with the fifth and last item in red:]

Fundamental Forces

1. Gravity

2. Electromagnetism

3. The Weak Interaction

4. The Strong Interaction

5. Electrons are weird about each other

[Caption below the panel:]

Big news: Physicists have finally given up trying to explain about the "exchange interaction" and agreed to just make the exclusion principle a force.

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