Fundamental Forces
Fundamental Forces
[Cueball is holding his hands up while giving a lecture to an off panel audience.] Cueball: There are four fundamental forces between particles: (1) Gravity , which obeys the inverse square law: F gravity = G m 1 m 2 /d 2 Off panel audience: OK...

[Cueball is still holding his hands up while continues the lecture to the off panel audience.] Cueball: (2) Electromagnetism , which obeys this inverse-square law: F static = K e q 1 q 2 /d 2 ...and also Maxwell's equations Off panel audience: Also what?

[Zoom in on Cueball as he continues the lecture to the off panel audience.] Cueball: (3) The strong nuclear force , which obeys, uh ... ...well, umm... ...it holds protons and neutrons together. Off panel audience: I see. Cueball: It's strong.

[Cueball finishes the lecture to the off panel audience and spreads out his arm for the final remark.] Cueball: And (4) the weak force . It [mumble mumble] radioactive decay [mumble mumble] Off panel audience: That's not a sentence. You just said “Radio- Cueball: – And those are the four fundamental forces!

Cueball is acting here as someone teaching physics at a basic level, perhaps a high school science teacher. He seems to understand the general idea of the four fundamental forces , but his understanding gets progressively more sketchy about the details. The off-panel audience, probably a student or class, is interested, but quickly begins to realize Cueball's lack of understanding. Instead of acknowledging the problem directly, Cueball simply blusters onwards.
The comic also outlines how progressively difficult it gets to describe the forces. Gravity was first mathematically characterized in 1686 as Newton's law of universal gravitation , which was considered an essentially complete account until the introduction of general relativity in 1915. The electromagnetic force does indeed give rise to Coulomb's law of electrostatic interaction (another inverse-square law , proposed in 1785), but a much more comprehensive description, covering full classical electrodynamics , was only given in Maxwell's equations around 1861. The strong and weak forces cannot easily be summarized as comparably simple mathematical equations. It's possible that Cueball does understand the strong and weak interactions, but is completely at a loss when he tries to summarize them.
The strong force doesn't act directly between protons and neutrons but between the quarks that form them. Unlike gravity and electromagnetism, the strong force gets stronger with increasing distance : It is loosely similar to the restoring force of an extended spring . However, all stable heavy particles are neutral to the strong force, due to being made up of three " colors " (or a color and the appropriate "anticolor") of quarks. Between protons and neutrons there is a residual strong force, analogous in some ways to the van der Waals force between molecules. This residual strong force is carried by pions and does decrease rapidly and exponentially with distance due to the pions having mass.
The weak force is much weaker than electromagnetism at typical distances within an atomic nucleus (but is still stronger than gravity), and has a short range, so has very little effect as a force . What it has instead is the property of changing one particle into another. It can cause a down quark to become an up quark, and in the process release a high-energy electron and electron anti-neutrino. This is known as beta decay , a form of radioactivity. Over even shorter distances, and much higher temperatures , the weak interaction and electromagnetism are essentially the same, thus being merged to form the electroweak force . The electroweak force was also mentioned in a later comic, 1956: Unification .
The title text refers to the fact that it is gravity that appears to be the simplest and easiest to understand of the four forces, but turns out to be the hardest to reconcile with a coherent (quantum) understanding of all four forces together .
[Cueball is holding his hands up while giving a lecture to an off panel audience.] Cueball: There are four fundamental forces between particles: (1) Gravity , which obeys the inverse square law: F gravity = G m 1 m 2 /d 2 Off panel audience: OK...

[Cueball is still holding his hands up while continues the lecture to the off panel audience.] Cueball: (2) Electromagnetism , which obeys this inverse-square law: F static = K e q 1 q 2 /d 2 ...and also Maxwell's equations Off panel audience: Also what?

[Zoom in on Cueball as he continues the lecture to the off panel audience.] Cueball: (3) The strong nuclear force , which obeys, uh ... ...well, umm... ...it holds protons and neutrons together. Off panel audience: I see. Cueball: It's strong.

[Cueball finishes the lecture to the off panel audience and spreads out his arm for the final remark.] Cueball: And (4) the weak force . It [mumble mumble] radioactive decay [mumble mumble] Off panel audience: That's not a sentence. You just said “Radio- Cueball: – And those are the four fundamental forces!
