Title text: On the other hand, physicists like to say physics is to math as sex is to masturbation.
Mathematics is the abstract study of topics encompassing quantity, structure, space, change, and others. Physics is a natural science that involves the study of matter-energy and its motion through space and time, along with related concepts such as forces. Physics is described using mathematics. Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure, and properties. As chemical reactions are governed by physical laws (electromagnetism being particularly important), one could say that chemists are studying a subset of physics. Biology is the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. As biological life is the result of a large number of complex chemical reactions, one could say that it is studying a subset of chemistry. Psychology is the study of mental functions and behaviors, why thinking beings do what they do. As thought is (currently) a capability exclusive to living things, one could say that it is a subset of biology. Sociology is the study of society, or the study of groups of people and their interactions. Since a group of people is composed of many individuals, one could say that it is an application of psychology. Of course, one could also say that the fields are all independent, as deriving one from another would require not only good, but perfect understanding of the more fundamental field.
Mathematics has two classifications: pure mathematics (mathematics for its own sake, without any real-world interpretation) and applied mathematics (mathematics intended to solve real-world problems). It is not uncommon for scientists to formulate a problem that can be reduced to a problem already solved by pure mathematicians. Taking this to its logical extreme, the comic arranges the six scientific fields according to the Hierarchy of the sciences, represented by a person on a chart of purity, saying that a field is 'more pure' than the fields depending on it. This is a topic often used in jokes between scientists of various fields as to who is more important. The physicist, Cueball, feels that he is at the top, that all other fields are based upon his... but is ultimately upstaged by the mathematician, Blondie, whose field is so pure that its relationship to more applied fields can be distant or nonexistent. Unlike the others, however, the mathematician notably does not claim that physics is merely applied mathematics, because that claim would be categorically untrue. While physics makes extensive use of applied mathematical methods, physics (and, by extension, all the other sciences) are based on the analysis of experimental data collected about the universe—data which mathematics does not and cannot on its own provide. Later a similar setup was used in 2057: Internal Monologues, although here the different science fields are not ranked against each other, and only the physicist is represented in both comics (although as Cueball in both).
Philosophy is presumably not pictured as it would be so far off to the right end of the image it would require a scroll bar, not that Randall has shied away from large format strips. 
The title text indicates that physicists like to repeat the following quote attributed to Richard Feynman: "Physics is to math what sex is to masturbation.". This ties the title of the comic, "Purity," to tie between various fields, to the topic of sex, as measured by the Purity Test.
- [Six characters are standing on a line with small ticks under each person. Above the two persons most central in the comic is an arrow pointing right. There are labels both above and below the arrow. Beneath each tick is a label. All the labels are listed here in order.]
- Fields arranged by purity
- More pure
- [Above each of the six ticks, there is a person. The last person to the right is the mathematician. She stands at the far right edge of the comic, with much farther distance between her and the second to last person going right. The first four spaces between the first five people are of equal distance. Except for the least pure sociologist, they all say something addressed to the less pure person(s) on their left. The first mute person above the Sociologists tick is Megan. The second person above the Psychologists tick is a bald man with glasses and a goatee beard holding a book under one arm. The third person above the Biologists tick is a Cueball-like guy with a squirming octopus in his hand. The fourth person above the Chemists tick is Ponytail holding up a test tube with bubbles coming out of the top. The fifth person above the Physicists tick is Cueball standing with his hands in his sides. Farthest out, the sixth and final person above the Mathematicians tick is Blondie. She waves to the other five.]
- Psychologist: Sociology is just applied psychology.
- Biologist: Psychology is just applied biology.
- Chemist: Biology is just applied chemistry
- Physicist: Which is just applied physics. It's nice to be on top.
- Mathematician: Oh, hey, I didn't see you guys all the way over there.
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