Irregular Webcomic! #341

Okay, there are two types of people who read Irregular Webcomic!:

People who have studied quantum physics. Those people are now rolling on the floor with laughter.
People who have not studied quantum physics. Those people are now scratching their heads and going "WTF?"

So many geekish pedants wrote to tell me that in strip #334 I had made a mistake in specifying a heading of 435, because headings only go up to 360, that I felt I needed to address it and give an explanation. In keeping with the fact that it was only unredeemable geeks who pointed out my "mistake", I offer an explanation that you have to be a serious geek to even understand. Heh heh...

If you don't understand the joke, okay, I'll explain it. Baryons are subatomic particles of a class including protons and neutrons, all of which are fermions and thus have internal symmetry governed by the rotation group SU(2)... er...

Fermions are particles that obey the Pauli Exclusion Principle... er...

The Pauli Exclusion Principle is a law of nature that exludes quantum particles of half-integral spin... er...

Um...

One of the failings of classical physics at the turn of the 19th century was its inability to predict the electromagnetic spectrum of a radiating black body... er...

Classical physics is based on the three laws of motion codified by Isaac Newton in 1686...

Oh, go read about it yourself.

But seriously, I originally used a heading of 435 in strip #334 knowing full well that headings normally only go up to 360. I deliberately chose 435 precisely because I knew it wasn't a standard heading, and just thought it would add some more surrealism. I didn't think anyone would actually call me on it.

2012-11-30 Rerun commentary: Here's where things started getting wacky. In the sense that occasionally my notes about a comic would involve attempting to explain technical or scientific concepts way beyond what one might reasonably expect in a webcomic.

As it turned out, this turned into one of the most popular aspects of Irregular Webcomic! over the years.

Unfortunately this particular one is a bit of a cop-out, devolving into a string of hyperlinks to further information, without actually explaining the concept referred to in the comic.

Okay, so put simply, baryons are subatomic particles, the best known examples of which are protons and neutrons. There are some others, but they don't come up much unless you're a particle physicist. All baryons are fermions, a larger class of particles that also includes electrons (plus another bunch of particles that most non-particle-physicists don't much care about). Fermions are particles that have a quantum mechanical spin value equal to one-half, or three-halves, or five-halves, etc. (Particles with spin values equal to 0, 1, 2, 3, etc. are called bosons.)

Now, fermions have the odd property that when you rotate them by a full 360°, they don't end up in the same quantum mechanical state in which they started. The mathematical function which defines the state of the fermion is negated - it's minus what it started as. You need to rotate it around another 360° to get it back into the state that it started with. In some sense, when you rotate a fermion by 360°, it's "upside down", and you need to rotate it another 360° to bring it right way up again.

In actuality, the quantum mechanical state I've described is squared to produce any of the physical properties that we can measure, so it doesn't really matter at this level if it's positive or negative. So it's not quite as weird as it sounds. From the outside, the particle looks the same, but inside the mathematics describing the quantum mechanical state are flipped.

Anyway, so if the spaceship is made of an odd number of baryons, its total spin if treated as a single quantum particle is...

Oh dang. I think I just found an error in this comic.

EDIT: Wait wait wait... no I didn't. Geez, this stuff is way too complicated to be writing about late at night just to explain a comic I made nearly nine years ago.

Anyway, so if the spaceship is made of an odd number of baryons, its total spin if treated as a single quantum particle is an odd multiple of one-half. So the entire spaceship is (quantum mechanically speaking) one big baryon, meaning it's also a fermion, meaning that if you turn it through 360°, its quantum state gets flipped upside down!

Not that you'd notice this in reality, but then we're outside observers of the comic reality, watching from a privileged position, in which we can see the frames and borders of the comic, the speech bubbles, and, apparently, the internal quantum state of macro-fermions.

You had to ask.