Editing 1489: Fundamental Forces

{{comic
| number    = 1489
| date      = February 20, 2015
| title     = Fundamental Forces
| image     = fundamental_forces.png
| titletext = "Of these four forces, there's one we don't really understand." "Is it the weak force or the strong--" "It's gravity."
}}

==Explanation==
[[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 {{w|Fundamental interaction#Overview of the fundamental interaction|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. {{w|Gravitation|Gravity}} was first mathematically characterized in 1686 as {{w|Newton's law of universal gravitation}}, which was considered an essentially complete account until the introduction of {{w|general relativity}} in 1915. The {{w|Electromagnetism|electromagnetic force}} does indeed give rise to {{w|Coulomb's law}} of {{w|electrostatics|electrostatic}} interaction (another {{w|inverse-square law}}, proposed in 1785), but a much more comprehensive description, covering full {{w|Classical electromagnetism|classical electrodynamics}}, was only given in {{w|Maxwell's equations}} around 1861. The {{w|strong interaction|strong}} and {{w|weak interaction|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 {{w|proton}}s and {{w|neutron}}s but between the {{w|quark}}s that form them. Unlike gravity and electromagnetism, the strong force {{w|Asymptotic freedom|get stronger with increasing distance}}: It is ''loosely'' similar to the {{w|Hooke's law|restoring force of an extended spring}}. However, all stable heavy particles are neutral to the strong force, due to being made up of three "{{w|quantum chromodynamics|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 {{w|van der Waals force}} between molecules. This residual strong force is carried by {{w|pion}}s 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 {{w|beta decay}}, a form of radioactivity. Over even shorter distances, {{w|electroweak theory|and much higher temperatures}}, the weak interaction and electromagnetism are essentially the same, thus being merged to form the {{w|electroweak force}}. The electroweak force was also mentioned in a later comic, [[1956: Unification]].

The title text touches upon a strange paradox regarding gravity: in isolation it is the simplest and easiest to understand of the four forces, with well-understood equations that can be taught to the layman with clear-cut examples (as it is the one force everyone experiences on a regular basis). However when taking other forces into account gravity turns out to be the {{w|Quantum_gravity|hardest to reconcile}} with a coherent (quantum) understanding of {{w|Theory of everything|all four forces together}}.

==Transcript==
:[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 this inverse square law:
::: F<sub>gravity</sub> = G m<sub>1</sub>m<sub>2</sub>/d<sup>2</sup>
<!-- When math arrives, use the following:
::: <math>F_{gravity}=G\frac{m_1m_2}{d^2}</math> -->
: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<sub>static</sub> = K<sub>e</sub> q<sub>1</sub>q<sub>2</sub>/d<sup>2</sup>
<!-- When math arrives, use the following:
::: <math>F_{static}=K_e\frac{q_1q_2}{d^2}</math> -->
::...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!'''''

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Physics]]