2882: Net Rotations

|< < Prev Comic #2882 (January 17, 2024) Next > >|

Net Rotations

Title text: For decades I've been working off the accumulated rotation from one long afternoon on a merry-go-round when I was eight.

Explanation

This is another one of Randall's Tips, this time a Spacetime health tip.

This comic may refer to a thing that some people with OCD do, which is to spin around to get rid of "net rotations," hence the title of this comic. Cueball (perhaps representing Randall?) takes this one step beyond the typical person with OCD - he calculates the net rotations each day and spins around at the end of the day to cancel this out. In this case, he would be spinning left 17 rotations to return to zero.

The offered reason for the necessity to do this is a physics joke: the reference to spacetime and to one's "worldline" has to do with relativity and the Einstein-Cartan theory, which is an extension of Einstein's general relativity. The theory suggests a coupling between the intrinsic spin of elementary particles (fermions) and the torsion of spacetime, and this comic appears to humorously extrapolate this idea to even supermolecular structures like a human, telling readers to "cancel out your accumulated turns at the end of each day to avoid worldline torsion", where in reality, it is highly unlikely the spin on such a large scale would cause any torsion in anyone's worldline, or their path traced by a particle or observer in spacetime.

A mobile device with position and orientation sensing might be able to keep track of one's net rotations, eliminating the need for calculations. One would need only to do one's spinning while monitoring the device to see when it returned to zero.

The caption suggests that this is healthy and necessary/highly recommended to do this. However, most people don’t, and most people are still OK.^{[citation needed]} In fact, xkcd's own characters are perfectly OK with accumulating net rotations and similar topological excesses.

Possibly a reference to the 1966 novel, The Revolving Boy by Gertrude Friedberg whose protagonist suffered from being out of correct positioning depending on the number of turns he was forced to make in his everyday life.

The relationship between spinning and spacetime was formerly discussed in 162: Angular Momentum.

The title text mentions that Cueball was on a merry-go-round when he was eight and he accumulated so many rotations that he's still trying to counter these rotations to this day.

Transcript

[Cueball is rotating around himself with only one foot on the ground, the other leg raised and bend above the ground and with his arms crossed in front of his chest. There are five circular curves around Cueball from head to legs to indicate this rotary motion. He rotates in front of a whiteboard. On the left of the board there are two vertical helix-like curves going from near the top to the bottom. They are crossing over each other at five points, the first four crossings close to the top, and then one near the bottom. Next to this there are ten rows of illegible scribbles, then a line, then another row of scribbles then a line and at the bottom a row of scribbles which is circled in. There is a large thought bubble above Cueball to indicate that he is thinking to himself while rotating in front of his calculations on the whiteboard.]

Cueball (thinking): ...and three lefts for going down the stairwell at work, two rights from cloverleaf interchanges, minus one for the Earth's rotation...

Cueball (thinking): Okay, that's a net of 17 right.

[Caption below the panel:]

Spacetime health tip: Remember to cancel out your accumulated turns at the end of each day to avoid worldline torsion.

 add a comment! ⋅  add a topic (use sparingly)! ⋅  refresh comments!

Discussion

Wait, so I'm not the only one who thinks about this? 172.71.167.177 23:28, 17 January 2024 (UTC)

No, I also do it, just I do it right after I do the turns so I don't have to remember them all. B for brain (talk) (youtube channel wobsite (supposed to be a blag) 17:24, 19 January 2024 (UTC)

I used to do something similar in the schoolyard. 172.71.131.75 07:23, 25 January 2024 (UTC)

Second! Still, I'm surprised that there are no edits yet. 172.70.210.160 23:58, 17 January 2024 (UTC)

This sounds like the premise of the 1966 sci-fi story The Revolving Boy by Gertrude Friedberg. I recall reading it sometime in the 1960s or ’70s. I wonder whether Randall has read the book too — https://solarbridge.wordpress.com/2011/05/19/the-revolving-boy-gertrude-friedberg/ I'm drawing a blank. 162.158.158.68 01:05, 18 January 2024 (UTC) I had precisely the same thought! But I couldn't remember the title of the book - thanks! (172.70.90.191) Likewise; I read it long ago and would have had to do some net searching to uncover the name. 172.69.189.166 17:48, 20 January 2024 (UTC)

I feel like the "worldline torsion" line needs to be explained moreso than the OCD thing, since "worldline" is a word people might not know and it's the crux of the joke. 162.158.62.50 02:47, 18 January 2024 (UTC)

A worldline is a relativistic concept, the track of a particle (or anything, by extension) through 4D spacetime. Randall is imagining it as a physical object (not a mathematical abstraction) and thus whenever the actual object rotates, its worldline is twisted. Presumably these physical worldlines would build up torsional potential energy as they twisted, and could eventually be damaged if too many twists/year were present.Nitpicking (talk) 02:57, 18 January 2024 (UTC)

Yeah - something like that needs to go in the explanation.172.70.85.47 09:44, 18 January 2024 (UTC)

I would love to know what my net rotations is. Not enough to actually keep track, mind you. 172.70.178.126 02:53, 18 January 2024 (UTC)

I had a season pass to an amusement park a few years ago, and the time I spent on the Scrambler would probably make mine quite difficult to calculate, even if I knew how many times I rode it. 172.69.247.57 04:41, 18 January 2024 (UTC)

Probably depends a lot on whether you suffer from Zoolander's Syndrome. 172.70.91.62 09:48, 18 January 2024 (UTC)

isn't this a refernce to spacetime torsion and the einstien-cartan theory? https://en.wikipedia.org/wiki/Einstein%E2%80%93Cartan_theory

When I used to do plasma donations (they draw blood, centrifuge it, extract the plasma/platelet fraction and return the red and white cells) I would, when telling someone about it, jokingly say that the only side effect was, then I would jump and spin. RIIW - Ponder it (talk) 08:17, 18 January 2024 (UTC)

This comic makes sense in 2D because the space of rotations has fundamental group ℤ, but in 3D wouldn't you have at most ℤ/2ℤ corrections to make, since SU(2) double-covers SO(3)? cf. https://en.wikipedia.org/wiki/Plate_trick Ncf (talk) 09:27, 18 January 2024 (UTC)

Considering the plane in which you are doing your rotation changes during the day due to Earth rotation, I think that it doesn't make sense in 3D at all. But thanks for link. -- Hkmaly (talk) 21:00, 18 January 2024 (UTC)

Is it worth mentioning the real medical conditions of torsion, e. . a torsion fracture (https://en.wikipedia.org/wiki/Torsion_fracture)? Nitpicking (talk) 12:43, 18 January 2024 (UTC)

I immediately thought of medical conditions, too, in my case a torsion of the spine https://www.osmosis.org/answers/sacral-torsion . But the exercises that are supposed to alleviate back pain & torsions caused by one-sided movements (like always twisting/bending left when carrying a load, and twisting/bending right without a load) usually don't involve full rotations. Transgalactic (talk) 00:30, 19 January 2024 (UTC)

Remember that, to do it properly, any turns made in your car also have to be reversed in your car, to account for the rotation of the car's atoms. Go do a full loop through a counterclockwise cloverleaf! (Finding one is left as an exercise to the reader.) 108.162.238.82 13:05, 18 January 2024 (UTC)

Don't think it’s worth adding to the article but thought I would mention it here, anyone who has experience spending a long time in a VR headset will almost certainly have had to do this at some point to untwist the tether. To the point that there are apps you can run that show you how much your rotation has changed from the set 0 orientation. TomW1605 (talk) 13:13, 18 January 2024 (UTC)

Actually I think it's worth mentioning that the line to your virtual world (not quite a worldline, but close enough to make a pun?) will indeed suffer torsions unless you cancel out your net rotations. :-D Transgalactic (talk) 00:30, 19 January 2024 (UTC)

The CPSC recommends merry-go-rounds be limited to 13 ft/sec. https://www.sportsplayinc.com/images/cpsc.pdf For a 10 ft radius, that would be one rotation every 4.8 sec. Over "one long afternoon" (which I'll take as 6 hours) that would amount to 4,469 rotations. If you compensated for this with a mere one rotation per day, the excess rotation would be completely offset in 12 years and 3 months, so "decades" is quite an exageration. User:Loeb

If your merry-go-round had a 20 inch diameter, though (the minimum at which those recommendations apply), at one a day it would take you nearly 147 years.172.69.195.60 09:42, 19 January 2024 (UTC)

It makes me think a lot about 162: Angular Momentum 141.101.98.34 19:45, 18 January 2024 (UTC)

2883 is out, bot's down... someone, i guess^{(talk i guess|le edit list)} 03:05, 20 January 2024 (UTC)

It's always nice to unwind at the end of the day (sorry)172.69.214.5 14:12, 21 January 2024 (UTC)

I might be a little OCD, but not to the degree of this comic. When the internet began and I first started using a browser, I would make sure that I always used the back button to return to the home page because I didn't want to use up computer memory space by accumulating too many links on the "back button" stack. Rtanenbaum (talk) 17:42, 22 January 2024 (UTC)

Who removed the incomplete tag? It's still incomplete, the mouseover text is still unexplained.Danger Kitty (talk)

The answer to that. I must admit, I usually rereview it when our "tidy-uppers" (all honest fellows/fellowesses, I hesitate to add!) think they're right to tidy this aspect up, a number of times the removal of the Incomplete tag has actually gotten me to tweak things (not that it should happen like that), but I seem to have missed this instance, or not spotted any remaining incompleteness if I scanned its post-tag state..

I also think that the importance of the Incomplete tag is now less linked to the actual incomplete state (although obviously it still is, at first), and that it doesn't hurt to leave it up longer, but obviously opinions on that vary. Community opinion may be a bit blurred on this issue. 141.101.99.33 19:26, 2 February 2024 (UTC)

Actually, if you consider rotations along other axes (which you must on any day roll out of bed or get out of it weirdly), then its only coherent to speak of the PARITY of your total torsion, since SO(3) = Z/2Z. Unlike SO(2) which is Z. So good news guys, you only have to turn around at least once! Terdragontra (talk) 01:59, 2 July 2024 (UTC)

Shoot, I don't read close enough, someone already noticed! Terdragontra (talk) 02:01, 2 July 2024 (UTC)