2622: Angular Diameter Turnaround

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Angular Diameter Turnaround
Thank you to Katie Mack for teaching me about this effect, and to Janelle Shane for describing redshifts as 'like galaxies sinking into a pool of dilute blood,' which is how I'll see them from now on.
Title text: Thank you to Katie Mack for teaching me about this effect, and to Janelle Shane for describing redshifts as 'like galaxies sinking into a pool of dilute blood,' which is how I'll see them from now on.


This comic references multiple physics and maths concepts, including Angular diameter, Angular diameter distance, Redshift, and mobile phones, although mobile phones are not a core science at this time.[citation needed]

The comic shows the galaxies of the universe as Samsung Galaxy mobile phones, pairing the age we see them at from earth, the degree they are redshifted, and how much of the sky they take up, known as their angular diameter. The mobile phones that are closer and older have depleted batteries, whereas the batteries are full for those phones from which the light is still only beginning to reach us. This is how galaxies appear in the sky if they were phones that had batteries lasting billions of years, the light reaching us from deeper into the past as it comes from objects that are farther away. Phones at a low battery may be a reference to 1373: Screenshot, where Randall commented that it is hard to pay attention to any phone with a low battery as the need to charge it is so urgent.

An important takeaway from this comic is that the events that occurred at the very start of our universe are etched in our sky as if they are still happening now, in a detailed faint timeline, that we are still learning more and more from. Using the mobile phone metaphor helps as, when the technology space was young and smaller there were mobile phones, such as the original iPhone, which one might still remember despite there being many more recent and better ones in a more crowded market space.

Randall's intent appears to be to highlight how just a few very distant galaxies occupy incredibly large proportions of the sky and are seen as they were at a very young age. Mobile phones have this similarity, of massive presence, relatively early stages of new technology, and bringing information from far away.

The large galaxies can be seen in dark red in the background as if the unimaginably ancient child galactic bodies are looming forebodingly behind everything else. The title text refers to galaxies falling into a pool of dilute blood. This isn't what redshift actually is [citation needed] (rather, it's an effect on the wavelength of light), but is an evocative comparison.

This physical concept has a lot of juxtaposition of things that usually contradict, and Randall has put energy into attempting to highlight that.

Katie Mack tweet: https://twitter.com/AstroKatie/status/1516548836709343238

A spacetime diagram possibly has reasonable visualizations of the kinds of relations bodies have when they are moving this far apart, including angular diameter distance. Simultaneity no longer exists at such distances. Distance is debated too, although that would be a different article.


[Cueball and a row of 7 spiral galaxies, the first 5 growing sequentially smaller and the last 2 growing larger]
Angular Diameter Turnaround
[A spiral galaxy emitting light and Cueball in a small circle with closely spaced grid lines, captioned "T=1b yr."]
[A stretched truncated circle with widely spaced gridlines, with the galaxy at one side and Cueball on the other, and light following a curved path through the stretched space to Cueball, captioned "Now (T=13.8b yr.)". Cueball is thinking "Big!"]
Illustrated using phones instead of galaxies
(Brightness and redshift adjusted to keep phones visible)
Things that are far away look smaller, but things that are really far away look bigger, because when their light was emitted, the universe was small and they were close to us.
[numerous mobile phones scattered in space, with numbers visible on their lockscreen. The closest is brightly lit and says "13 billion years after the Big Bang" on the screen. Subsequent phones behind this one are smaller, fainter and more red, until they reach "3" (the rest of the text is too small to read). From this point, the phones grow larger, although they continue to get fainter and redder. Subsequent phones show "2", "1", "500 million", "200 million", "50 million", "20 million" (which is larger than the original "13 billion years after the Big Bang" phone) and a very large, faint phone so big that only the word "thousand" is visible, with the rest of the screen obscured behind other phones or so large it extends off the panel]

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Slightly creepy, NGL172.69.34.10

Warning, horrible content: The universe was created by the severed bloody hands of google employees convincing phone manufacturers to ditch the previous phone backends and explode the google play store throughout reality in a mess of intergalactic gore. Our planet developed from an angrybirds download, nourished by the decaying corpse of the owner who played it all their life. 20:37, 20 May 2022 (UTC)

So apparently this is a real thing, which I never knew wikipedia:Angular_diameter_distance#Turnover_Point 20:46, 20 May 2022 (UTC)

Could be related to comic 1422, what with both containing expanding phones analogous to some cosmic structure. 21:46, 20 May 2022 (UTC)

1422 has been crapped. 21:50, 20 May 2022 (UTC)

So confusing…I thought that 13 billion years ago they had flip phones. JohnHawkinson (talk) 22:32, 20 May 2022 (UTC)

Before this explanation is marked “complete” it had better mention that “sinking into dilute blood” is a terrible (one could even say ignorant or stupid) description of red shift, completely missing the fundamental cause and completely distorting the effect. 23:23, 20 May 2022 (UTC)

Pretty sure that was just a description of its appearance? -- 10:18, 21 May 2022 (UTC)
Randall implies this was an analogy among people who knew the physical underpinnings well. But I agree that it, and the concept of mobile phones, are neither pleasant nor appropriate at all for the outer reaches of our universe. 15:28, 21 May 2022 (UTC)
I’m wondering if Randall read this and the next one, Goofs, is a subtle jab at commenters here who don’t understand similes. He doesn’t say it works like that. He says it LOOKS like that. There’s nothing unpleasant about blood. I find my own to be dear to me. And to claim it’s “inappropriate”, well, let’s just say I’m not gonna gatekeep but if you think a simile someone else shared with Randall, possibly and likely someone with the credentials to back it up, is “inappropriate” because you think blood is icky, perhaps you would consider showing yourself out?
It's also delicious in a black pudding. 09:03, 24 May 2022 (UTC)
Either way, whoever is on about “ as if the void beyond were hell” should remove that. Randall doesn’t imply anything about a void beyond (there isn’t one), nor hell (my body is full of blood but i lack any hell inside me). 20:41, 23 May 2022 (UTC)

Congratulations, you won a brand new galaxy!

Your new galaxy will be delivered in only 3 billion years, to a drop-off point only 1 million light years from your home planet. With this cutting-edge protogalaxy, which will be mature upon delivery, you will find incredible features such as:

  • supermassive black hole
  • exotic space-faring lifeforms
  • intriguing dense matter that does not emit radiation; you'll never have enough
  • unique and enthralling galactic formations, each with ancient magical myths told in history by the space-faring lifeforms
  • and the ability to grow brand new stars of your very own! 00:07, 21 May 2022 (UTC)

I assumed the reference was that very old cell phones (1990s etc.) were enormous - think carphones; technology allowed them to shrink (giving, say, the Nokia 8850 I owned in 1999 and the original smallish iPhone), and then recent phones have (on average) grown again as the benefits of a larger screen area have been seen to outweigh the convenience of a smaller device. Also older phones tended to have batteries that lasted longer, mostly because neither the screen nor the processor were pulling much power. It's not just that the original iPhone was smaller than current ones (nor, for some of us, does the original iPhone count as an "early cellphone"). Am I alone in this interpretation? The description (at time of writing) didn't seem to cover that. 10:15, 21 May 2022 (UTC)

Yes, early cell phones were huge, like the size of a suitcase (hence they were usually kept in a car and called a "carphone.") At first much of this was having a larger battery before they had the modern sort of rechargeable electronics, and then it took time to gradually be able to shrink the other required electronics, but then they kept making them smaller, to the point where people would joke about how small they would be in the future (like in the movie Zoolander he had a phone that was like an inch in size). However once smartphones came along that had a large screen and were used for a lot of things other than actual phone calls (and text messaging), people wanted larger screens, so they started increasing in size again, just to be able to make the screen larger, and also the increased functionality increased the battery drain and they thus needed more space for a bigger battery. However, all the phones pictured in the comic are modern design smartphones with the whole phone surface being a touchscreen, so it's questionable to apply that idea to the comic.--
On second thought, the prevous comic before this one mentioned Zoolander, so that was likely on Randall's mind....-- 23:57, 24 May 2022 (UTC) 23:55, 24 May 2022 (UTC)

The phone model shown doesn't look that much like a Samsung Galaxy. More like an iPhone. Oh, well. Nutster (talk) 15:50, 21 May 2022 (UTC)

I hope we'll be able to procure a charger for our galaxy before it runs out. 15:52, 21 May 2022 (UTC)

If it is sinking into a hellscape, it'll presumably require one of those cursed connecters. 09:05, 24 May 2022 (UTC)

Isn't it just wonderful when your favorite comic strip teaches you something fundamental, important, and which you had no idea of prior to reading it. This is definitely one of XKCD's crowning glories (although, admittedly, not all that funny!). SteveBaker (talk) 15:18, 22 May 2022 (UTC)


Something good is happening!!!!!! 21:22, 20 May 2022 (UTC)

No. It just means you can't get a date tonight. Again. (I presume you're the "crap"per, right? Eager to fill your own worthless life by making everybody else actually feel useful... How ironic.) 00:08, 21 May 2022 (UTC)
I thought it was just a visitor I worried I had badly depressed with my story of severed google hands, wanting to add positivity. 00:21, 21 May 2022 (UTC)
the "crap"er is a bot called "Explain xkcd server admin". -> https://www.explainxkcd.com/wiki/index.php/User:Explain_xkcd_server_admin/common.js Firestar233 (talk) 00:11, 21 May 2022 (UTC)
Yes, same (style) as the umpteen previous times. No imagination and rather boring.
Now I'm limited in what I can do (still, been reverting pages left right and centre, to hold my bit up) but the "Hooray!" commenter (as, I suspect, the one who 'wished the crap would happen again' the other day, or words to that effect) seems to be very much like someone's idea of taunting us, thus proving that he (if you'll excuse that assumption) can't get laid and for some reason they haven't discovered the more solo method of getting their rocks off, so he's rubbing up against us and trying to generate the satisfying feeling of friction in his groin.
(You know when your dog has a favourite stuffed toy? Like that.)
Pretty boring, really, for us. But small things amuse small minds. And maybe that's the reason why. Also having small... 'feet'. Too shy to show his 'feet' to girls. Can't earn enough to get 'feet' enlargement surgery. No personality either. Pity. 02:43, 21 May 2022 (UTC)

WH3R3 C4N 1 G37 7H15 M4NY F0N3Z? (jk, 1 41r34dy h4v3 4b0u7 31gh7 0f 7h3m) 02:59, 21 May 2022 (UTC)

The crap is spreading...

The Esolang wiki is being crapped. We aren't the only ones... 18:11, 21 May 2022 (UTC)

I imagine there'll be a esolong called "crap" becore too long (if there isn't already) with which a decrappifier can be written. Knowing the people who used to be in that field, anyway. Sort of whitespace/brainf*ck-inspired thing, probably.
(Too late now, but I hope it's not because we kept archive copies of our scripts around for others to pick up, independently of the original idiot.)
But this goes both ways. If they come up with a better answer to the problem, maybe we can get it working here too. I leave it to those in the know to perhaps keep half an eye on that, though. 10:13, 22 May 2022 (UTC)
Their solution seems to be "have an admin always monitoring the wiki." I got blocked pretty quickly. 15:45, 22 May 2022 (UTC)
Arab Soyjak and other site vandalism is repeatedly changing the comic title to "Arab Soyjak" and the image to a picture of Osama bin Laden, and being awfully rude in the edit summaries; also has a history of vandalism along with various associated IP addresses - however also having made actual contributions to the wiki, etc etc, I haven't checked other IP addresses that are associated; 416: Zealous Autoconfig is one of the pages that are currently vandalised </ramble> bubblegum-talk|contribs 02:56, 22 May 2022 (UTC)

I have blocked the IP address. --Kynde (talk) 14:30, 23 May 2022 (UTC)
Please don't block IP addresses here. Unlike most wikis, the reverse proxy on this one basically randomizes them, so the blocks don't necessarily stop the vandal and often do affect non-vandals. 17:04, 23 May 2022 (UTC)

Red shifted objects...

...would not necessarily look red to the human eye. A light source that peaks in the ultraviolet or x-rays would turn blue when that objects light gets lowered into the visible spectrum. The real meaning of "red shift" is what happens to spectral lines. Algr (talk) 15:44, 23 May 2022 (UTC)

I'm very confused as to why one would use the iPhone 1 as an example of a very old, but very memorable phone, rather than the Nokia 1100 15:54, 23 May 2022 (UTC) Tomas

Date of comic

The day before this comic was released, NASA released a huge new report that astronomers are calling Hubble’s magnum opus. Analyzing 30 years of data from the famous space telescope, the new study makes the most precise measurement yet of how fast the universe is expanding. WhiteDragon (talk) 18:42, 23 May 2022 (UTC)