explain xkcd - User contributions [en]

3264: 720 Ollie

2026-06-29T23:02:56Z

130.76.187.55: /* Transcript */ physics

{{comic
| number = 3264
| date = June 26, 2026
| title = 720 Ollie
| image = 720_ollie_2x.png
| imagesize = 257x325px
| noexpand = true
| titletext = This discovery was key to his demonstration of regular/goofy symmetry violation, which won him gold in the theory portion of the X Games.
}}

==Explanation==
{{incomplete|This page was created by a spin-½ boson. Don't remove this notice too soon.}}

{{w|Tony Hawk}} is an American skateboarder credited with inventing the {{w|Aerial_(skateboarding)#Common_aerial_tricks|720}}, a trick (under normal circumstances) involving two full mid-air rotations. 'Ollie' in the comic's name refers to a basic skateboarding move that pops the skateboard up off the ground. Hawk tells [[Cueball]] that doing a single 360° spin causes him to land backward rather than forward. This is unexpected, since a 360° turn in the X-Y plane is a full revolution, meaning that it should normally return him to his original position, rather than performing a half-rotation, which is normally the result of a 180° (or 540°, etc.) spin. As repeating this would reverse his reverse, doubling this to a 720° spin is what finally allows him to land forward. Normally, revolving 360*''n'' degrees, for any whole number ''n'' (0, ±1, ±2, etc.), would leave him pointing the same direction as he started, but here he lands with the opposite orientation if ''n'' is odd, and returns to the same orientation only if ''n'' is even.

The caption reveals that this is because Tony Hawk is a {{w|spin 1/2|spin-½}} {{w|fermion}}. Spin-½ fermions have the unusual property that they must be rotated through two full turns before returning to their original configuration. This explains Tony Hawk's paradox, but is unusual because spin-½ particles are normally very small, only occurring in quantum physics, rather than the Newtonian physics that is used for most larger objects. Since Tony Hawk is not a subatomic particle,{{Citation needed}} it is unclear how his skateboard tricks could be described only by quantum physics.

'''Fermions''', which include the protons, neutrons, and electrons that make up atoms, are a classification of particles or groups of particles whose intrinsic angular momentum (aka "spin") is a half-integer multiple of the {{w|Planck_constant#Reduced_Planck_constant|reduced Planck constant}}; the behavior of these objects' spin is described via {{w|spinor}}s — a type of complex vector. This is in contrast to '''bosons''', whose spin is an integer multiple of the reduced Planck constant and is described by the normal Euclidean vectors you know and love.

Since Hawk invented the 720 in 1985, larger {{w|Aerial (skateboarding)|mid-air rotations}} have been invented (up to {{w|Aerial_(skateboarding)#Common_aerial_tricks|1260}} — three and a half rotations), and according to the comic they can have even stranger quantum properties.

The title text is a riff on the {{w|Nobel Prize}}-winning discovery of {{w|CP violation}} (something that may have been on [[Randall]]'s mind recently due to the [[3263: Baryon Asymmetry|prior comic]]'s subject matter). The {{w|Footedness#Goofy stance vs. regular stance|regular and goofy stances}} of riding a skateboard, which respectively refer to having the left or right foot forward, could be considered a physical quality of the "skateboarder particle", as values of charge and parity are of subatomic ones. The {{w|X Games}} are a prestigious 'street sport' event that includes competitions in skateboarding as well as other related board and bike disciplines, though not a 'theory' event. The parallel is made between winning a gold medal for impressive skateboarding skills (and demonstrating new tricks in the process, as Tony Hawk has been known to do) and earning the Nobel Prize medal for scientific achievement in physics or one of the other established prize categories. So far, nobody has done both of these, but if this comic were true, perhaps Tony Hawk could be the first to do so.

"Goofy matter", and Tony Hawk's involvement in physics, is also the subject of [[2967: Matter]]. Skateboarding is also the subject of [[296: Tony Hawk]].

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}
:[Tony Hawk and Cueball are talking. Tony Hawk is holding his skateboard. An image, above the heads of Tony Hawk and Cueball, depicts Tony Hawk doing two 360-degree turns on a skateboard]

:Tony Hawk: Something weird I've noticed is that if I do a 360 ollie, I land backward. I have to do a 720 to land going forward.

:Caption: Tony Hawk discovers that he's a spin-½ fermion.

{{comic discussion}}<noinclude>
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring real people]] 
[[Category:Sport]]
[[Category:Skateboard]]
[[Category:Physics]]

3265: Asteroid Threat

2026-06-29T23:01:52Z

130.76.187.55: /* Transcript */ space?

{{comic
| number = 3265
| date = June 29, 2026
| title = Asteroid Threat
| image = asteroid_threat_2x.png
| imagesize = 345x424px
| noexpand = true
| titletext = Paleontologists have long worried that the dinosaurs blasted into space 66 million years ago will one day complete their orbits and fall back down.
}}

==Explanation==
{{incomplete|This page was created by a reentering dinosaur. Don't remove this notice too soon.}}

It's generally agreed by scientists that most {{w|dinosaurs}} went extinct as a result of the {{w|Chicxulub asteroid}} impacting the Earth near the Yucatán Peninsula 66 million years ago, either directly or indirectly. This comic posits that another asteroid is soon going to hit the Earth again. Because the impact location will be on the exact opposite side of the planet (the antipode), the comic takes the absurd notion that because it will act the 'opposite' way, it reverses all the original effects and bringing dinosaurs back from extinction, which is absurd.{{Citation needed}}

The general consensus is that the dinosaurs went extinct as a result of the environmental effects of the impact, those that weren't in the immediate vicinity of the impact itself, but the title text (in a possibly separate treatment) suggests that it actually launched the dinosaurs alive into space, thus circling the Sun in a long orbit that will some day intersect with the Earth again and, absurdly, they will land still alive. Which is ridiculous, as not only would they have to somehow survive the initial impact (apparently strong enough to have knocked them into space), then survive the airless vacuum of space, survived all the way to the present day and then their presumably meteoric return to the Earth's surface - a thoroughly impossible feat. But the comic acts as if they are going to be able to land back on the Earth and take control again.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}

:[Two images of Earth are shown. At the top left is a small one, centered on southern {{w|West Africa}}, showing the Atlantic Ocean and the east coast of South America, with a dotted line through the Earth entering at the Yucatán Peninsula and exiting at the east-central Indian Ocean. Taking up most of the rest of the panel is a large Earth image centered on the Indian Ocean and containing a target symbol, comprising a circle and four spokes, aimed at a location in the east-central Indian Ocean.]

:[Caption below image:]
:Dire news: An asteroid is on course to hit the earth exactly ''opposite'' the Yucatán Peninsula, bringing ''back'' the dinosaurs.

{{comic discussion}}<noinclude>
[[Category:Dinosaurs]]
[[Category:Space]]

3265: Asteroid Threat

2026-06-29T23:01:26Z

130.76.187.55: /* Transcript */ cat