Editing 2622: Angular Diameter Turnaround

{{comic
| number    = 2622
| date      = May 20, 2022
| title     = Angular Diameter Turnaround
| image     = angular_diameter_turnaround.png
| titletext = 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.
}}

==Explanation==
This comic references multiple physics and maths concepts, including {{w|Angular diameter}}, {{w|Angular diameter distance}}, {{w|Redshift}}, and {{w|phones|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 {{w|mobile phones}}, such as {{w|iPhone (1st generation)|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 {{w|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.

==Transcript==
:[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 iPhones 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]


{{comic discussion}}
[[Category:Astronomy]]
[[Category:Cosmology]]
[[Category:Math]]
[[Category:Physics]]
[[Category:Smartphones]]
[[Category:Comics with color]]
[[Category:Comics featuring real people]] <!-- title text -->
[[Category:Puns]] <!-- is there a "galaxy" / Samsung Galaxy pun here? -->