← negishoyu.dev

WORLDLINES

Episode 2

Sources, data and method

“Slice the Universe in Half: How Many Stars Would You Hit?”

Episode
"Slice the Universe in Half: How Many Stars Would You Hit?"
Video
https://youtu.be/GY68oHRqsnQ
This page
https://negishoyu.dev/worldlines/ep02/sources/
Version
for the final render (10:06.8), with its English original audio and seven other audio tracks, as uploaded on 2026-10-20. Timestamps (m:ss.s) come from the timing table of the final Japanese voices (freeze v13el3, fingerprint 711f53b51e93); the picture and the voices in every language follow this table.
Script
Japanese master script r4 (plan/lines-v13.tsv, file hash 76b1bccbbace). English lines are quoted from the English dub, which is the video's original audio track (plan/l10n/en/script.tsv, file hash 8b9588ef27cc, 2026-10-19). The quotes match the final English mix (each recorded line was checked against the script with speech-to-text).
Last updated
2026-10-21

Worldlines is an animated series in which two characters test a question against real data. This page lists, for every factual claim and every number shown or spoken in Episode 2, where it comes from, what we computed ourselves, and what it does not show.

Corrections

This table lists mistakes found after publication: the date, the time in the video, what was wrong and what is correct. To report a mistake, in the facts or in any of the translations, please leave a comment under the video.

DateTime in videoLineWhat was wrongWhat is correct
———No corrections yet.—

How to read this page

Each claim lists:

The question in this episode is a thought experiment: a flat plane of zero thickness, passing through Earth, frozen at one moment, sliced through the universe as it is today. "Hit" means the plane passes through a star. Nothing is physically cut.

Numbers at a glance

Every number shown on screen or spoken in the episode, and the claim that gives its source. Some numbers are shown on a card but not spoken in every language.

NumberWhere (time · line, or the card on screen)Claim
46 cm2:39.2 · 3.02; card "46 cm"C03
7½ times around the Earth in one second3:01.6 · 3.09C04
8 minutes, 4 hours2:56.4 · 3.08, 3:01.6 · 3.09; cards "8 min", "4 h"C05
4.2 light-years; 1 light-year; 4 years3:13.6 · 3.11, 3:21.0 · 3.12; card "4.2 light-years"C06
100,000 light-years; 100,000 years3:30.2 · 3.14, 3:35.7 · 3.15; card "100,000 light-years"C07
2.5 million light-years; 25 Milky Ways3:43.5 · 3.17, 3:48.1 · 3.18; card "2,500,000 light-years"C08
100 million light-years; 1,000 Milky Ways4:05.0 · 3.22; card "100,000,000 light-years"C09
13.8 billion years4:31.1 · 3.28, 4:42.6 · 3.30; card "13,800,000,000 years"C11
×3,700,000,000,000,000,000,000,000,000card at 4:48.9 · 4.01C13
more than 100 billion stars0:30.2 · 1.12, 6:25.2 · 7.15, 7:01.8 · 8.12C01
1 in 10,000; 10 million; tens of millions0:22.6–0:42.2 · 1.10–1.14, 5:50.8 · 6.03; card "10,000,000"Ideas (not claims)
1, 2, 3, 4 (tags on the stars hit) and "4"6:10.0–6:23.2 · 7.02–7.14; card "GUESS 10,000,000 · ACTUAL 4"C16
1 mm, 29 km6:37.2 · 8.04, 6:50.2 · 8.08; cards "1 mm", "29 km"C17
110,000 galaxies; card 114,2357:12.2 · 9.04, 7:16.6 · 9.05C19
440,0007:17.6–7:30.5 · 9.06–9.07; card "440,000"Ideas (not claims)
counter 4 → 5 → 10 → 100 → 1,000 → 10,332; band "5,000–20,000"; card "GUESS 440,000 · ACTUAL ≈10,000"7:46.2–8:05.0 · 10.02–10.07; 9:13.5–9:22.0 · 12.02–12.04C20, C26
40 times, 44 times8:05.0 · 10.08, 8:11.4 · 10.10C21
11 galaxies (2 untouched, 6 grazed, 3 cut near the middle); 1 star8:33.4–8:50.1 · 11.06–11.10C23, C24
one star per ten galaxies8:50.1 · 11.11C24

Claims

0:00Slice the universe: how many stars?

C01The Milky Way has more than 100 billion stars

  • Time: 0:30.2 · 1.12. Recalled at 6:25.2 · 7.15 and 7:01.8 · 8.12.
  • What we say / show: "Milky Way? Over a hundred billion stars." (Comet, inside the guess below) / "Wait, wait, wait. A hundred billion stars, sliced end to end, and four?!" / "So out of a hundred billion, only four get hit." No number on screen.
  • Class: MODELED (the number; no board).
  • Source: our computation from the stellar mass of the Milky Way, (6.08 ± 1.14) × 10¹⁰ solar masses — Licquia & Newman 2015, ApJ 806:96, arXiv:1407.1078 — abstract only [F15], and 2.46 living stars per solar mass of stars (Method M3) [F06].
  • Our computation: 6.08 × 10¹⁰ × 2.46 ≈ 1.5 × 10¹¹ stars, between 100 and 200 billion [F16].
  • License: citation only.
  • Known limits: the count rests on how many small, faint stars there are. "More than 100 billion" holds across our range; we do not mix in counts made by other methods [F16].

Ideas the characters test (not claims) · 0:22.6–0:49.2

  • 1.10–1.14 (0:22.6–0:44.1): Comet's hypothesis: "I think a horizontal slice would hit tens of millions of stars!" Asked why: "Milky Way? Over a hundred billion stars. One in ten thousand hit? Ten million. Whole universe? Tens of millions!" Asked where "one in ten thousand" comes from, Comet answers: "From me, just now!" This is a character's guess, not a claim.
  • 1.15 (0:44.4): Sescha turns it into something to test: "Good reasoning, I think. So let's check your hypothesis." The episode tests it on the Milky Way (C15–C16) and on the observable universe (C19–C20).

1:07What do we slice with?

C02Cats sit on warm things

  • Time: 2:04.4 · 2.22
  • What we say / show: "Of course. Cats sit on warm things." On screen: the Chief has climbed onto the warmed-up test slicer and fallen asleep on the letter.
  • Class: no class (room scene).
  • Source: everyday knowledge.
  • Known limits: a common habit, not true of every cat at every moment.

2:37How far does the observable universe go?

C03The Chief is 46 centimeters long

  • Time: 2:39.2 · 3.02 (and 2:42.3 · 3.03 / 2:43.7 · 3.04)
  • What we say / show: "Life-size. 46 centimeters." / "You measured?" / "I keep records." On screen: a translucent, sand-colored plane in the outline of the Chief asleep (the "loaf"), with a dimension line and the card "46 cm".
  • Class: SCENARIO (the size of the plane).
  • Source: a typical domestic cat is about 46 cm from head to rump, not counting the tail (about 30 cm): Wikipedia "Cat" (Size section) and Animal Diversity Web "Felis catus" — secondary [F31]. The outline of the sleeping pose is 45.1 cm long in the proportions of the character art, rounded to 46 cm [F88].
  • Our computation: none here; the enlargement is in Method M1.
  • License: —
  • Known limits: cats vary in size; 46 cm is the Chief's length in this episode, not a rule for cats.

C04Light goes around the Earth 7½ times in one second

  • Time: 2:45.0 · 3.05 (picture) / 2:49.5 · 3.06 / 3:01.6 · 3.09
  • What we say / show: the plane grows until the sleeping outline lies over the top of the globe. "The Chief's on top of the Earth!" Later, from the Solar System: "At seven and a half Earth laps a second, four hours! But the Chief misses the Sun." (Comet)
  • Class: MEASURED.
  • Source: equatorial radius 6,378.137 km — NASA Earth Fact Sheet, https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html — official page (values checked through a search summary, 2026-10-11) [F47]. Speed of light 299,792.458 km/s (SI definition).
  • Our computation: 2π × 6,378.137 km = 40,075 km around the equator; 299,792.458 ÷ 40,075.017 = 7.48 times per second.
  • License: Earth imagery, Data D2.
  • Known limits: measured along the equator; around the poles the Earth is slightly smaller.

C05Sunlight takes 8 minutes to reach Earth, and 4 hours to reach Neptune's orbit

  • Time: 2:56.4 · 3.08 / 3:01.6 · 3.09; cards "8 min", "4 h".
  • What we say / show: "The Sun, eight minutes by light. Neptune's orbit, four hours." / "At seven and a half Earth laps a second, four hours! But the Chief misses the Sun." On screen: the plane covers the Solar System; a front of light runs out from the Sun to the Earth's orbit ("8 min") and on to Neptune's orbit ("4 h"); the Sun shines a little above the plane.
  • Class: MEASURED.
  • Source: the astronomical unit, 149,597,870.7 km (IAU 2012 definition); Neptune's semi-major axis, 4,514.953 × 10⁶ km — NASA Neptune Fact Sheet, https://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact.html — official page (via a search summary) [F48].
  • Our computation: 149,597,870.7 ÷ 299,792.458 = 499 s (8 min 19 s); 4,514.953 × 10⁶ ÷ 299,792.458 = 15,060 s (4.18 h).
  • License: —
  • Known limits: "eight minutes" is rounded down from 8 min 19 s. Neptune's orbit is not the edge of the Solar System; the Oort cloud is thought to reach more than a light-year out [F56]. Whether the plane misses the Sun depends on the time of day: the plane is level at the observatory in the afternoon, so the Sun lies above it.

C06The nearest star, Proxima Centauri, is 4.2 light-years away

  • Time: 3:13.6 · 3.11 / 3:21.0 · 3.12; card "4.2 light-years".
  • What we say / show: "Next star, Proxima Centauri. 4.2 light-years. Each takes light a year." / "Now four years..." On screen: the edge of the plane runs out past the Solar System; one bright star close by, a dotted ring at one light-year; the plane passes the star without touching it.
  • Class: MEASURED.
  • Source: the parallax of Proxima Centauri, 768.0665 ± 0.0499 mas (a Gaia EDR3 value, as listed in Reylé et al. 2021, A&A 650:A201, Table 1, arXiv:2104.14972 — full text) [F24]. We quote the number only; no Gaia images or tables appear in the video.
  • Our computation: 1 ÷ 0.7680665″ = 1.302 pc = 4.2465 light-years, rounded to 4.2; light takes about 4¼ years.
  • License: citation only.
  • Known limits: "nearest star" means nearest to the Sun.

C07The Milky Way is about 100,000 light-years across, and we live away from its center

  • Time: 3:24.2 · 3.13 (picture) / 3:30.2 · 3.14 / 3:35.7 · 3.15; card "100,000 light-years".
  • What we say / show: stars multiply into a river, then a spiral; the plane cuts into the disc at a slant, and its center, "here", sits in an outer arm, not at the center; a dimension line across the disc carries the card. "Our Milky Way. 100,000 light-years across." / "Now 100,000 years..."
  • Class: the size MEASURED (a round figure); the 3D Milky Way is an ILLUSTRATION built on a NASA/JPL-Caltech illustration (Data D1).
  • Source: Bland-Hawthorn & Gerhard 2016, ARA&A 54:529, arXiv:1602.07702 — full text: thin-disc scale height 300 ± 50 pc, scale length 2.6 ± 0.5 kpc, the Sun 8.2 ± 0.1 kpc from the center, and no clear evidence of a sharp edge [F35, F49]. "About 100,000 light-years" is the diameter usually quoted — secondary [F35].
  • Our computation: 8.2 kpc = 26,745 light-years, about 27,000, from the center to "here" [F80].
  • License: illustration, Data D1.
  • Known limits: the disc has no sharp edge; disc stars have been found more than 26 kpc from the center (López-Corredoira et al. 2018, A&A 612:L8 — abstract only) [F35]. The figure is a round number, not a measured edge.

C08Andromeda, the nearest big galaxy, is 2.5 million light-years away: 25 Milky Ways

  • Time: 3:39.0 · 3.16 (picture) / 3:43.5 · 3.17 / 3:48.1 · 3.18; card "2,500,000 light-years".
  • What we say / show: Andromeda, a smaller spiral marked with a ring, passes under the head of the plane; a dimension line from "here" to it carries the card. "The next big galaxy over, Andromeda." / "Twenty-five Milky Ways away..."
  • Class: MEASURED; the 3D spiral is an ILLUSTRATION (the same model as the Milky Way).
  • Source: NASA, "The Galaxy Next Door", and NASA Science, "Andromeda Galaxy" — official page (via a search summary): the Milky Way's nearest major galactic neighbor, about 2.5 million light-years away; a NASA Hubble article puts it at about 25 times the width of the Milky Way [F57, F58].
  • Our computation: 2,500,000 ÷ 100,000 = 25.
  • License: —
  • Known limits: smaller galaxies, such as the Large Magellanic Cloud, are closer; "the nearest big galaxy" is not "the nearest galaxy" [F57]. Andromeda's size differs between sources, so the episode does not state it. Where Andromeda sits relative to the plane depends on the date and time of the slice.

C09Galaxies are arranged like a web, and one "bubble" is about 100 million light-years across

  • Time: 3:50.6 · 3.19 (picture) / 3:55.6 · 3.20 / 3:58.4 · 3.21 / 4:05.0 · 3.22; card "100,000,000 light-years".
  • What we say / show: galaxies multiply and gather into threads, walls and a web, dark inside its cells. "What's this? Like a web." / "Galaxies form a web. Threads and walls. In between, nearly empty bubbles." / "One bubble is a thousand Milky Ways in a row."
  • Class: the typical size MEASURED (from reviews); the web on screen MODELED (Data D3).
  • Source: cosmic voids are typically 10–100 Mpc across (about 30–300 million light-years): Wikipedia, "Void (astronomy)", and van de Weygaert & Platen 2009, "Cosmic Voids", arXiv:0912.2997 — secondary (read through a search summary) [F50].
  • Our computation: a void of about 30 Mpc ≈ 100 million light-years; 100,000,000 ÷ 100,000 = 1,000.
  • License: —
  • Known limits: voids come in a wide range of sizes; 100 million light-years is a typical size, not a rule. Voids are not completely empty; a few faint galaxies are drawn inside them (3.23). The web on screen is computed, not a map of real galaxies (Data D3).

C10Farther galaxies look redder, because space is expanding

  • Time: 4:09.3 · 3.23 (picture) / 4:12.8 · 3.24 / 4:15.7 · 3.25 (picture) / 4:19.7 · 3.26
  • What we say / show: the galaxies deeper in the picture are redder; the color depends only on distance. "Aren't the faraway galaxies red?" Light from one red galaxy travels toward us as a wavy line; under it, the grid widens, the waves stretch, and white turns orange, then red. "Space is expanding. Light got stretched on its way here, and turned red."
  • Class: the relation MEASURED (cosmological redshift); the colors on screen ILLUSTRATION.
  • Source: cosmological redshift and the Hubble–Lemaître law — everyday knowledge in astronomy (textbook); not checked against a primary source for this episode [F46].
  • Our computation: the color of each galaxy on screen comes from its distance from Earth only (Method M8) [F82].
  • License: —
  • Known limits: the shift is drawn in visible colors; for the most distant galaxies, the light shifts past red into the infrared [F46]. Real galaxies also have their own colors, which the picture ignores.

C11Light from the edge of the observable universe took 13.8 billion years to reach Earth

  • Time: 4:25.1 · 3.27 (picture) / 4:31.1 · 3.28 / 4:42.6 · 3.30; card "13,800,000,000 years".
  • What we say / show: the plane grows again until the round of its belly reaches the edge of the observable universe; the deepest part glows a deep red. "Observable universe's edge. Light took 13.8 billion years to reach Earth." / "That's one old postmark..."
  • Class: MEASURED (a value of the standard cosmological model).
  • Source: Planck Collaboration 2020, A&A 641:A6 (Planck 2018 results VI), arXiv:1807.06209 — age of the universe 13.787–13.805 billion years, depending on the data combination; abstract only, Table 2 through a search summary [F51, F81].
  • Our computation: with H0 = 67.4 km/s/Mpc and Ωm = 0.315 (radiation at the standard value), our integration gives 13.79 billion years [F51].
  • License: citation only.
  • Known limits: the edge is not 13.8 billion light-years away. While the light traveled, space expanded; the edge is now about 46 billion light-years away (C13, Method M1) [F03, F52]. The observable universe is not the whole universe.

C12The background glow is the oldest light

  • Time: 4:38.1 · 3.29
  • What we say / show: "The universe's background light. The oldest light." On screen: a dim, deep-red glow behind the edge.
  • Class: the statement MEASURED; the glow on screen ILLUSTRATION.
  • Source: the cosmic microwave background, released when the universe was about 370,000–380,000 years old (redshift about 1,090), the radiation mapped by the Planck satellite — Planck Collaboration 2020, arXiv:1807.06209 — abstract only [F87].
  • Our computation: none.
  • License: —
  • Known limits: the background light reaches us as microwaves, invisible to the eye; the red glow is a picture of where it comes from, not what it looks like. It is not light from the very beginning: it was released about 370,000–380,000 years later [F87].

4:48Does the universe fit in the Chief's belly?

C13The observable universe fits inside the round of the Chief's belly; the head, ears and tail tip stick out

  • Time: 4:48.9 · 4.01 (picture; card "×3,700,000,000,000,000,000,000,000,000") / 4:53.4 · 4.02 / 4:58.7 · 4.03
  • What we say / show: the camera pulls back; the observable universe becomes a dimly glowing ball, crossed through its middle by the Chief-shaped plane. The ball fits inside the round of the belly; the head and ears stick out into the black, and so does the black tip of the tail. No galaxies are drawn outside the ball. "Ma'am... the observable universe fits in the Chief's belly." / "The head, ears, and tail tip stick out."
  • Class: SCENARIO (the size of the plane); the size of the observable universe MODELED.
  • Source: radius of the observable universe today, 46.1 billion light-years (14.14 Gpc), from our integration with the Planck 2018 values H0 = 67.4 ± 0.5 km/s/Mpc and Ωm = 0.315 ± 0.007 (arXiv:1807.06209 — abstract only) [F03, F52].
  • Our computation: Method M1. The largest circle inside the belly of the sleeping outline has a radius of 11.934 cm. To fit 46.13 billion light-years inside it takes ×3.657 × 10²⁷, rounded up to two figures: ×3.7 × 10²⁷. The circle then has a radius of 46.67 billion light-years (1.2% to spare), and 47% of the plane lies outside it [F88].
  • License: —
  • Known limits: the outline follows the character art of the Chief asleep. Nothing is drawn outside the ball, because nothing beyond the observable universe can be mapped (C14).

C14Light from the parts that stick out will never reach Earth

  • Time: 5:02.0 · 4.04 / 5:03.7 · 4.05 / 5:09.7 · 4.06 / 5:13.2 · 4.07
  • What we say / show: "Sticking out where?" / "Out of sight. Space keeps expanding, so light from there never reaches Earth." / "So the stars at the Chief's ear tips..." / "Nobody's seen them." On screen: the camera drifts toward the black between the edge of the ball and the far ear tip, where no galaxies are drawn.
  • Class: MODELED.
  • Source: our integration with the Planck 2018 values (C13) [F60, F83]: the edge of the observable universe (the particle horizon) is now 46.13 billion light-years away; light leaving us today can reach places no farther than 16.68 billion light-years (the event horizon). So light from anywhere farther than about 62.8 billion light-years, sent at any time, can never reach Earth.
  • Our computation: with the plane at ×3.7 × 10²⁷, the near ear tip is about 64 billion light-years from Earth, the far ear tip about 106 billion, and the farthest point of the outline (near the front paws) about 109 billion [F83].
  • License: —
  • Known limits: "never" holds for the head and the far ear (about 103–109 billion light-years). For the band just outside the edge (46–63 billion light-years), light that left long ago will reach Earth in the far future. The near ear tip lies close to that boundary. "Nobody's seen them" holds for everything outside the edge. We make no claim about what lies beyond the observable universe.

5:16Slice the Milky Way: how many stars?

C15Space has no up or down; along the Milky Way's disk is the angle that hits the most stars

  • Time: 5:19.9 · 5.02 / 5:30.2 · 5.05 / 5:32.4 · 5.06 / 5:35.7 · 5.07 (picture) / 5:40.0 · 5.09 / 5:44.7 · 5.11
  • What we say / show: "First, we check the Milky Way. Then the whole observable universe." / "Where's horizontal?" / "No up, no down. So we choose." The plane shrinks until the Milky Way fits in its belly, tilts, and lies flat along the disk. "Along the Milky Way. This angle hits the most." / "This way, we can check it fairly!"
  • Class: MODELED.
  • Source: our computation (Method M2) [F17, F74]: the average number of stars hit by a plane through the Milky Way's center, by its tilt from the disk — 0°: 3.78; 5°: 2.07; 10°: 1.48; 30°: 0.81; 45°: 0.68; 90°: 0.57.
  • Our computation: as above; "no up or down" is everyday knowledge (space has no preferred horizontal).
  • License: —
  • Known limits: laying the plane along the Milky Way favors the Milky Way. One plane cannot be laid along every galaxy (C23); Comet's "fairly" is answered at 8:26.8 · 11.05.

Ideas the characters test (not claims) · 5:47.6–6:07.2

  • 6.03 (5:50.8): Comet's guess for the Milky Way, from the hypothesis at 0:22.6: "My hypothesis? Ten million in the Milky Way!" Comet writes "10,000,000" on a card.
  • 6.06–6.07 (5:54.8–6:07.2): "Locals, make your guess too! If we slice the Milky Way at the angle that hits the most, how many stars get hit?" Five seconds to guess, with Comet's card, a blank answer card ("A:") and an hourglass; the music stops.

C16Sliced along its disk, the Milky Way's hundred billion stars give about four hits

  • Time: 6:08.7 · 7.01 / 6:10.0–6:23.2 · 7.02–7.14 (tags 1–4; card "GUESS 10,000,000 · ACTUAL 4") / 6:25.2 · 7.15
  • What we say / show: "Then let's slice it." A ring of light spreads over the plane from "here"; each star it touches lights up and stays, with a number tag. "One!" "Two!" "Three!" "Four!" The ring crosses the far edge, and nothing more lights up. "Four." The card now shows the guess and the result side by side: "GUESS 10,000,000 · ACTUAL 4". "Wait, wait, wait. A hundred billion stars, sliced end to end, and four?!"
  • Class: MODELED.
  • Source: our computation from published values (Method M2) [F17, F71, F85].
  • Our computation: on average 3.78 stars hit (range 2.3–5.5). The plane passes through "here", about 20 pc above the Milky Way's mid-plane, which gives 3.54 on average. The video shows one slice with four hits; at this average, four is among the most likely outcomes (about one slice in five gives exactly four).
  • License: —
  • Known limits: the result rests on a model of the Milky Way (disc thickness, number of stars, average star size); it is an estimate, not a count of real stars. The four stars on screen are not particular real stars. The spreading ring shows the slice step by step; it is not a physical wave.

6:32Why so few?

C17If the Sun were a 1 mm grain of sand, the nearest star would be 29 km away

  • Time: 6:34.4 · 8.02 / 6:35.7 · 8.03 (picture) / 6:37.2 · 8.04 / 6:40.7 · 8.05 / 6:46.4 · 8.07 / 6:50.2 · 8.08 / 6:51.4 · 8.09 / 6:55.1 · 8.10 (picture); cards "1 mm", "29 km".
  • What we say / show: "Think of it this way." Sescha holds out a grain of sand in her palm. "This grain's the Sun. One millimeter." / "How far do you think the next star is?" After three seconds to think: "Um... the next room over?" / "Twenty-nine." / "Twenty-nine kilometers?! A day's walk!" A dimension line and the card "29 km" between two grains; no map.
  • Class: MODELED (a measured distance, rescaled).
  • Source: the distance of Proxima Centauri (C06) [F24]; the Sun's nominal radius, 6.957 × 10⁸ m (IAU 2015 Resolution B3, arXiv:1510.07674 — full text) [F12].
  • Our computation: 4.2465 light-years ÷ the Sun's diameter (1,391,400 km) × 1 mm = 28.87 km, rounded to 29 km. Walking 29 km at 4–5 km/h takes 6–7 hours (everyday knowledge).
  • License: —
  • Known limits: rounded; "a grain of sand" here means a grain 1 mm across.

C18Stars are so far apart that a plane hits only the few lying right on it

  • Time: 6:56.6 · 8.11 / 7:01.8 · 8.12
  • What we say / show: "Twenty-nine kilometers apart, they're hard to hit with a slicing plane..." / "So out of a hundred billion, only four get hit." Behind them, the four stars that lit up.
  • Class: MODELED.
  • Source: our computation (Method M2) [F17].
  • Our computation: on the 1 mm scale an average star is about 0.4 mm across (average radius 0.40 times the Sun's) [F11], with its neighbors kilometers away. A plane hits a star only if the star's center lies within one star radius of the plane.
  • License: —
  • Known limits: 29 km is the gap to the Sun's nearest neighbor; toward the Milky Way's center, stars are closer together, and the model includes this [F17].

7:05And the whole observable universe?

C19Near the plane lie about 110,000 galaxies the size of the Milky Way

  • Time: 7:08.7 · 9.03 (picture) / 7:12.2 · 9.04 / 7:16.6 · 9.05 (card "114,235")
  • What we say / show: the camera pulls back from the Milky Way, and the plane grows again until it crosses the observable universe; only the galaxies near the plane glow faintly. "Near this plane, 110,000 Milky Ways." Card "114,235".
  • Class: MODELED.
  • Source: our computation (Method M4) [F18, F71].
  • Our computation: all the stars in the observable universe expressed as Milky Way–sized galaxies (7.2 × 10¹⁰), of which those with centers within 15 kpc of the plane: 114,235 (64,000–145,000 across the ranges of the stellar-mass density and of the Milky Way's stellar mass).
  • License: —
  • Known limits: real galaxies come in all sizes; counting small galaxies one by one gives more (180,000–480,000, depending on how small we go) [F18]. "Milky Way–sized" is a unit of counting, not a census. The card shows the model's value; the line rounds it.

Ideas the characters test (not claims) · 7:17.6–7:43.4

  • 9.06–9.08 (7:17.6–7:32.0): "Four each. Times 110,000... 440,000!" / "I take back the tens of millions! That's my new hypothesis!" A red line crosses out the first guess; the new card reads "440,000". Comet's hypothesis, tested in C20 and explained in C25.
  • 9.09–9.10 (7:32.0–7:43.4): "Locals, make your guess too! If we slice the observable universe, how many stars get hit?" The second guessing time (five seconds), again with a blank answer card and an hourglass.

C20Sliced through the whole observable universe, about 10,000 stars get hit (5,000–20,000)

  • Time: 7:44.9 · 10.01 / 7:46.2–7:54.7 · 10.02–10.03 (counter from 4 to 10,332) / 7:54.7 · 10.04 / 7:55.7 · 10.05 (band "5,000–20,000") / 7:56.7 · 10.06 / 8:03.0 · 10.07 (card "GUESS 440,000 · ACTUAL ≈10,000")
  • What we say / show: "Then let's slice it." The ring spreads from the Milky Way across the observable universe, crossing galaxy after galaxy; only now and then does a star light up. The counter runs 5, 10, 100, 1,000 and stops at 10,332 at the edge. "Ten thousand?!" / "A range. Five to twenty thousand. Star counts and sizes aren't all known yet." Then the guess and the result side by side: "GUESS 440,000 · ACTUAL ≈10,000", with the band "5,000–20,000".
  • Class: MODELED.
  • Source: our computation (Method M3) [F13, F71], from the stellar-mass density of today's universe (Madau & Dickinson 2014, ARA&A 52:415, §5.4 and Table 2, arXiv:1403.0007 — full text) [F04], the initial mass function (Kroupa 2001, MNRAS 322:231, eq. 2, arXiv:astro-ph/0009005 — full text) [F05], the census of stars within 10 parsecs (Reylé et al. 2021, Table 3 — full text) [F08, F09], star radii by type (E. Mamajek's table of dwarf stars, version 2022.04.16, after Pecaut & Mamajek 2013 — full text, the table itself) [F10], and the size of the observable universe (C13).
  • Our computation: about 1 × 10²² stars in the observable universe (0.72–1.11 × 10²²) [F07]. A plane through Earth hits 10,332 of them (computed range 5,871–11,150). Allowing for how stars are counted, how big they are, and how galaxies cluster gives 5,000–20,000 [F13].
  • License: citation only.
  • Known limits: an estimate with a wide range, but under these inputs never zero and always more than a thousand [F13]. The counter's steps show the ring's progress (Method M9), not separate measurements; how often a star lights up is in C24.

C21Comet's 440,000 was off by about 40 times

  • Time: 8:05.0 · 10.08 / 8:11.4 · 10.10 / 8:12.6 · 10.11
  • What we say / show: "440,000 and 10,000... Off by a factor of forty..." / "Forty-four." / "Nitpicky!"
  • Class: MODELED.
  • Source: our computation [F73, F78, F84].
  • Our computation: from the spoken numbers, 440,000 ÷ 10,000 = 44. From the model's values, 4 × 114,235 ÷ 10,332 = 44.2; from the model's averages, 41.5 (37–49) [F73].
  • License: —
  • Known limits: the ratio hardly depends on how many stars there are or how big they are, since both enter the guess and the result in the same way [F73].

8:14How do other galaxies get sliced?

C22A galaxy is a thin disc

  • Time: 8:20.6 · 11.02 (picture) / 8:23.6 · 11.03
  • What we say / show: a 3D Milky Way close up; the camera circles round to show it edge-on, thin. "Thin disks."
  • Class: the shape MEASURED; the 3D picture ILLUSTRATION (Data D1).
  • Source: Bland-Hawthorn & Gerhard 2016 (C07): the star-rich layer is 1,000–2,000 light-years thick, against about 100,000 across — 1/50 to 1/100 of the diameter [F35].
  • Our computation: none.
  • License: illustration, Data D1.
  • Known limits: the Milky Way stands in for galaxies in general; not every galaxy is a thin disc (elliptical galaxies are not). The count in C20 does not depend on galaxy shapes; the "one in ten" in C24 does.

C23One plane cannot match every galaxy's angle, and most cuts miss the middle

  • Time: 8:25.2 · 11.04 (picture) / 8:26.8 · 11.05 / 8:33.4 · 11.06 (picture) / 8:37.4 · 11.07 / 8:40.8 · 11.08 (picture) / 8:42.8 · 11.09
  • What we say / show: the plane lies along the Milky Way's disc again, with its four lit stars. "The Milky Way got the angle that hits the most. One plane can't do that for the rest." The camera pulls back: a pale band above and below the plane, as thick as the Milky Way's radius, and 11 galaxies at random angles; the ring reaches them one by one, and each cut glows. "Slanted or edge-on, cuts are just thin lines." Of the 11, two are not touched, six are grazed at the edge, three are cut at a slant nearer the middle. "And usually, it misses the middle. It grazes an edge, or passes above or below."
  • Class: MODELED; the 11 galaxies on screen are an ILLUSTRATION of the model's proportions.
  • Source: our computation (Method M5) [F43, F74, F86].
  • Our computation: for galaxies whose centers lie within 15 kpc of the plane, at random angles and positions (thin-disc model, 6,000 trials): 19% are not touched, 53% are grazed at the edge, 27% are cut nearer the middle, and 80% of the hits come from that last group. The random angle alone cuts the average 5.5 times (0.69 stars per galaxy, with the plane still through the center); where the plane passes cuts it a further 7.7 times [F74].
  • License: —
  • Known limits: the 11 on screen show the proportions (2 / 6 / 3, close to 19 / 53 / 27%); they are not real galaxies.

C24About one star for every ten galaxies sliced

  • Time: 8:48.6 · 11.10 (picture) / 8:50.1 · 11.11
  • What we say / show: of the 11, one star lights up, in a galaxy cut at a slant near its middle. "Ten galaxies sliced for just one star..."
  • Class: MODELED.
  • Source: our computation [F43].
  • Our computation: at random angles and positions, 0.090 stars per galaxy on average (92% of galaxies give none): about one star per 11 galaxies. The observable-universe count gives the same ratio: 114,235 ÷ 10,332 = 11.06.
  • License: —
  • Known limits: "ten" is Comet's round figure for about eleven.

C25Comet's 440,000 assumed every galaxy was sliced like the Milky Way

  • Time: 8:54.1 · 11.12 / 8:59.4 · 11.13
  • What we say / show: "Your 440,000? All sliced like the Milky Way." / "...I guess I multiplied based on a wrong assumption."
  • Class: MODELED.
  • Source: our computation [F41, F73].
  • Our computation: 4 stars per galaxy (the Milky Way, sliced along its disk) × 110,000 = 440,000. With random angles and positions, the average is 0.09 per galaxy (C24): 0.09 × 114,235 ≈ 10,300, the count in C20.
  • License: —
  • Known limits: —

9:10The answer to the letter

C26The answer to the letter: about 10,000 stars, between 5,000 and 20,000

  • Time: 9:13.5 · 12.02 / 9:19.3 · 12.03 / 9:20.6 · 12.04
  • What we say / show: back in the room, the Chief sleeps on the letter on the slicer. "Answer: slicing the observable universe hits about 10,000 stars!" / "Five to twenty thousand." / "Five to twenty thousand!"
  • Class: MODELED.
  • Source: as C20 [F13].
  • Our computation: as C20.
  • License: —
  • Known limits: as C20. The letter asked about "the universe"; the answer is for the observable universe (C13, C14).

The rest of this chapter (the ending, and the request to subscribe) makes no factual claims.

What this video does not claim

  • That anything is physically cut, or that a plane could be laid across space. The slice is a thought experiment: a plane of zero thickness, frozen at one moment.
  • That the counts are exact. Four and about 10,000 are estimates, with the ranges given (C16, C20).
  • That the stars and galaxies on screen are particular real ones. The Milky Way and the other galaxies close up are drawn on an illustration, and the web of galaxies is computed (Data D1, D3).
  • That the observable universe is the whole universe, or anything about what lies beyond it (C14).
  • That all cats are 46 cm long, or anything about cats beyond the habit in C02.

Data

D1Milky Way illustration: NASA/JPL-Caltech, PIA10748

  • What: "Our Milky Way Gets a Makeover (Artist Concept)", PIA10748 (3 June 2008), an artist's concept of the Milky Way seen face-on, based on Spitzer observations. We use it as the surface of a 3D model of the Milky Way whose shape comes from the published disc scales (C07).
  • Where: https://photojournal.jpl.nasa.gov/catalog/PIA10748 (the page now moves to NASA Science). File PIA10748.jpg, JPEG 5,600 × 5,600, 2,049,707 bytes, SHA-256 aa6e5e2e96f0f7f3ab6499389a35cbf0899190f6cfc0196fe85acf4e5f9077d8, downloaded 2026-10-12.
  • Credit: NASA/JPL-Caltech (the illustration is widely credited to R. Hurt, SSC/Caltech).
  • License and conditions: JPL images may be used for any purpose with the credit "Courtesy NASA/JPL-Caltech", in a way that does not suggest NASA endorsement (JPL Image Use Policy, as recorded in our ledger). This video is not endorsed by NASA. We show no NASA logo or insignia.
  • Class: ILLUSTRATION.
  • Used in: C07, C16, C22, and every Milky Way scene. The other galaxies seen close up (Andromeda in C08 and the 11 galaxies in C23–C24) are drawn with the same model.

D2Earth imagery: NASA/GSFC SVS and NASA Earth Observatory

  • What: day side — NASA/Goddard Space Flight Center Scientific Visualization Studio, Blue Marble Next Generation data courtesy of Reto Stöckli (NASA/GSFC) and NASA Earth Observatory (SVS ID 3615); night side — NASA Earth Observatory / NASA/GSFC, Earth at Night (Black Marble 2016). Credit line: "Earth imagery: NASA/GSFC SVS; NASA Earth Observatory".
  • License and conditions: as for D1: no suggestion of NASA endorsement, no NASA logo (NASA, "Guidelines for using NASA Images and Media", https://www.nasa.gov/nasa-brand-center/images-and-media/ — checked 2026-10-04 for Episode 1).
  • How used: the globe at the Earth stop (2:45.0 · 3.05). The globe is turned so that Japan is at the top, under the center of the plane, with the north pole toward the celestial north pole; this is a choice for the picture.
  • Class: the images MEASURED (satellite imagery); the orientation ILLUSTRATION.
  • Used in: C04.

D3Cosmology, and the computed web of galaxies

  • Parameters: Planck 2018 (results VI, TT,TE,EE+lowE+lensing): H0 = 67.4 km/s/Mpc, Ωm = 0.315, Ωb = 0.0493, ns = 0.965, σ8 = 0.811, T_CMB = 2.7255 K — Planck Collaboration 2020, A&A 641:A6, arXiv:1807.06209 (H0 and Ωm checked in the abstract; σ8 and ns as used by our team, not re-checked for this episode) [F03, F45].
  • The web on screen: computed from density fluctuations with these parameters, moved forward with the Zel'dovich approximation (Zel'dovich 1970, A&A 5:84 — not re-checked) [F45]. The way galaxies cluster follows the real universe; the position of each galaxy is not real. The arrangement of the Local Group and the shapes and colors of the galaxies are ILLUSTRATION. Data file build/web/data/cosmos/cosmos.json (seed 20261010).
  • Class: MODELED (the web); ILLUSTRATION (placement, shapes, colors).
  • Used in: C09–C13, C19, C20, C23.

D4Sources at a glance

SourceIdentifierWhat we readUsed in
Planck Collaboration 2020 (Planck 2018 results VI), A&A 641:A6arXiv:1807.06209abstract only (Table 2 through a search summary)C11–C14, C20, D3
Madau & Dickinson 2014, ARA&A 52:415arXiv:1403.0007full text (§5.4, Table 2)C20, M3
Kroupa 2001, MNRAS 322:231arXiv:astro-ph/0009005full text (eq. 2)C01, C20, M3
Licquia & Newman 2015, ApJ 806:96arXiv:1407.1078abstract onlyC01, C19, M2, M4
Bland-Hawthorn & Gerhard 2016, ARA&A 54:529arXiv:1602.07702full textC07, C16, C22, M2
López-Corredoira et al. 2018, A&A 612:L8—abstract onlyC07
Reylé et al. 2021, A&A 650:A201arXiv:2104.14972full text (Tables 1 and 3)C06, C17, C20, M3, M6
E. Mamajek, table of dwarf-star properties, version 2022.04.16 (Pecaut & Mamajek 2013)https://www.pas.rochester.edu/~emamajek/EEM_dwarf_UBVIJHK_colors_Teff.txtfull text (the table)C18, C20, M3
IAU 2015 Resolution B3 (nominal solar radius)arXiv:1510.07674full textC17, M6
IAU 2012 definition of the astronomical unit—everyday knowledgeC05
NASA Earth Fact Sheet; NASA Neptune Fact Sheetnssdc.gsfc.nasa.gov/planetary/factsheet/official page (through a search summary)C04, C05
NASA, "The Galaxy Next Door"; NASA Science, "Andromeda Galaxy"—official page (through a search summary)C08
van de Weygaert & Platen 2009, "Cosmic Voids"; Wikipedia, "Void (astronomy)"arXiv:0912.2997secondary (through a search summary)C09
Wikipedia, "Cat"; Animal Diversity Web, "Felis catus"—secondaryC03
Zel'dovich 1970, A&A 5:84—not re-checked (the method of D3)D3

Further reading

A similar question was asked on Physics Stack Exchange in 2018: "If I sliced the universe in half, would the slice go through a star?" (question 388802, 26 February 2018), https://physics.stackexchange.com/questions/388802.

Method

M1The Chief-shaped plane, and how far we enlarge it (SCENARIO)

  1. The plane is the outline of the Chief asleep (the "loaf" pose), taken from the character art: 45.1 cm long in the art's proportions, called 46 cm on screen (C03). It has zero thickness, and its center is always "here", at the observatory on Earth.
  2. The largest circle that fits inside the belly of the outline has a radius of 11.934 cm.
  3. Radius of the observable universe today (the particle horizon), from our integration with H0 = 67.4 km/s/Mpc, Ωm = 0.315 and radiation at the standard value: 14,145 Mpc = 46.13 billion light-years [F03, F52, F60].
  4. Magnification for the observable universe to fit inside the circle: 46.13 billion light-years ÷ 11.934 cm = 3.657 × 10²⁷; on the card, rounded up to two figures: ×3,700,000,000,000,000,000,000,000,000. At that size the circle has a radius of 46.67 billion light-years (1.2% to spare), the plane is 176 billion light-years long, and 47% of its area lies outside the circle [F88].
  5. For the Milky Way slice (from 5:35.7 · 5.07) the plane shrinks until the Milky Way fits in its belly, about ×6 × 10²¹ (no card on screen) [F88]; from 7:08.7 · 9.03 it grows back to the size in step 4.
  6. The event horizon (the farthest place that light leaving here today can ever reach): 5,114 Mpc = 16.68 billion light-years; with step 3, nothing farther than about 62.8 billion light-years can ever be seen from here (C14) [F60, F83].
  • Notes: plan/v12/notes-numbers.md §4 (the same method as plan/v10-calc/t2_cards.py, applied to the sleeping outline).

M2Slicing the Milky Way (MODELED)

  1. Model of the Milky Way: a thin disc (scale height 300 ± 50 pc), a thick disc (900 ± 180 pc) and a bulge, with a disc scale length of 2.6 kpc, weighted 4.5 : 0.7 : 0.88, counted out to 15 kpc from the center [F35]. Stellar mass 6.08 × 10¹⁰ solar masses, 2.46 stars per solar mass: 1.5 × 10¹¹ stars [F15, F16]. Average star radius 0.40 times the Sun's, from the census of stars within 10 parsecs [F11].
  2. A plane along the disc through the center hits, on average, the sum over the three parts of (stars in the part ÷ its thickness) × the average star diameter: 3.78 stars. Moving the stellar mass by ±1σ, the thin-disc thickness by ±50 pc and the average radius between 0.34 and 0.42 together gives 2.3–5.5 [F17, F71].
  3. Through "here", about 20 pc above the mid-plane, with an exponential profile: 3.54 on average [F85].
  4. Tilted from the disc, through the center: 0° 3.78, 5° 2.07, 10° 1.48, 30° 0.81, 45° 0.68, 90° 0.57. At a random angle through the center: 0.69. At a random angle and a random position: 0.090, with no hit 92% of the time [F43, F74].
  5. On screen, one slice is shown, with four hits at 18,000, 26,200, 32,400 and 44,700 light-years from "here" (the second in the bulge; the center is 26,745 light-years away). The ring stops at 77,000 light-years, past the far edge of the disc (76,745 light-years) (scene notes, plan/v12/notes-numbers.md §5).
  • Code: scratch/calc/v503_check.py (a copy of docs/ep1-relaunch-angles/raw/concepts/V5-03-calc/v503_check.py) and scratch/calc/ep02_extra.py, both kept outside version control; notes plan/calc-v1.md §4.2.

M3Slicing the observable universe (MODELED)

  1. Stars: today's stellar-mass density, 5.8 × 10⁸ solar masses per cubic megaparsec (the model integral of Madau & Dickinson 2014, with a Salpeter initial mass function; observations give 6.0 ± 1.0 × 10⁸ and 10^8.59), × 0.66 to convert to a Kroupa initial mass function [F04, F05].
  2. Living stars per solar mass of stars: 2.46, from the initial mass function, lifetimes of 10 billion years × m^−2.5, a giant phase lasting 10% of the lifetime at 10 solar radii, and the masses of remnants [F06].
  3. Volume of the observable universe: 1.185 × 10¹³ cubic megaparsecs (M1, step 3). Stars in it: 1.08 × 10²² (0.72–1.11 × 10²²) [F07].
  4. A flat plane through the middle of a ball of randomly placed stars hits, on average, (stars per volume) × (average star diameter) × (area of the plane inside the ball). With an average radius of 0.40 solar radii: 10,332, computed range 5,871–11,150 [F13, F71].
  5. Allowing for how stars are counted, how big they are, and how galaxies cluster: 5,000–20,000 [F13].
  • Code: scratch/calc/v503_check.py; notes plan/calc-v1.md §3 and §4.3.

M4Counting the galaxies near the plane (MODELED)

  1. Total stellar mass of the observable universe ÷ the Milky Way's stellar mass = 7.2 × 10¹⁰ Milky Way–sized galaxies [F18].
  2. Those whose centers lie within 15 kpc of the plane: 114,235 (64,000–145,000 across the ranges of the stellar-mass density and the Milky Way's stellar mass) [F18, F71].
  3. Counting real galaxies one by one instead (from the galaxy stellar-mass function of Baldry et al. 2012, MNRAS 421:621, arXiv:1111.5707 — abstract only) gives 180,000–480,000; this count is not used in the video [F18].
  • Notes: plan/calc-v1.md §4.4.

M5Galaxies sliced at random (MODELED)

  1. Galaxies whose centers lie within 15 kpc of the plane, each at a random angle and a random position, with the thin-disc model of the Milky Way, 6,000 trials: 19% not touched, 53% grazed at the edge, 27% cut nearer the middle; 80% of the hits come from the last group [F86].
  2. Average stars hit per galaxy: 0.090 (no hit for 92% of galaxies): about one star per 11 galaxies [F43].
  3. The 11 galaxies on screen (from 8:33.4 · 11.06) are a sample drawn with these proportions: 2 not touched, 6 grazed, 3 cut nearer the middle, and one hit.
  • Code: scratch/factcheck/mw_split.py [F43]; notes plan/v12/notes-numbers.md §6.

M6The grain of sand (MODELED)

4.2465 light-years × 9.4607 × 10¹² km = 4.0175 × 10¹³ km; ÷ 1,391,400 km (the Sun's diameter) × 1 mm = 28.87 km [F24]. Notes: plan/calc-v1.md §3.

M7Light-travel times at the stops (MEASURED, with our arithmetic)

Speed of light 299,792.458 km/s. Earth's equatorial circumference 40,075.017 km → 7.48 times around per second; 1 au → 499.0 s; Neptune's semi-major axis → 15,060 s (4.18 h); Proxima Centauri, 4.2465 light-years → about 4¼ years; the Milky Way, 100,000 light-years → 100,000 years; the edge of the observable universe → 13.79 billion years [F47–F52, F58]. Code: scratch/v6script/calc_v6.py and scratch/proto-voice/v7/work/calc_v7.py (outside version control).

M8Colors by distance (ILLUSTRATION)

Each galaxy is colored by its present distance from Earth only, from white near us through orange to red at the edge (table redshift_color in plan/v12/stations-v12.json) [F82]. The close-up galaxy at 4:15.7 · 3.25 is about halfway to the edge. The colors show the relation in C10; they are not measured colors.

M9Cards by scene

Scenes by chapter: S01 = 0:00 · S02 = 1:07 · S03 = 2:37 · S04 = 4:48 · S05–S07 = 5:16 · S08 = 6:32 · S09–S10 = 7:05 · S11 = 8:14 · S12 = 9:10. Numbers on the cards are written with every digit, and their units and labels are in English only.

CardSceneClassClaim
"46 cm"S03SCENARIOC03
"8 min", "4 h"S03MEASUREDC05
"4.2 light-years"S03MEASUREDC06
"100,000 light-years"S03MEASUREDC07
"2,500,000 light-years"S03MEASUREDC08
"100,000,000 light-years"S03MEASURED (a typical size)C09
"13,800,000,000 years"S03MEASUREDC11
"×3,700,000,000,000,000,000,000,000,000"S04SCENARIOC13
"10,000,000" and the blank answer card "A:"S06no class (Comet's guess and the viewer's card)ideas
tags 1–4; "GUESS 10,000,000 · ACTUAL 4"S07MODELEDC16
"1 mm", "29 km"S08MODELEDC17
"114,235"S09MODELEDC19
"440,000" and the blank answer card "A:"S09no class (Comet's guess and the viewer's card)ideas
counter 4 → 10,332; band "5,000–20,000"; "GUESS 440,000 · ACTUAL ≈10,000"S10MODELEDC20
  • The counter in S10 follows the ring's radius: 10 at 1.11 billion light-years, 100 at 4.45 billion, 1,000 at 14.33 billion, 5,000 at 32.08 billion, 10,332 at the edge (46.13 billion). The galaxies the ring has crossed by then: 66, 1,062, 11,016, 55,259 and 114,235 (scene notes, plan/v12/notes-numbers.md §5).

M10 · Code and versions

Paths are relative to project/worldlines/episodes/ep02-chief-slice/ in our working repository. File hashes are SHA-1 (first 12 characters) of the files as used for the v10 render (2026-10-18); files under scratch/ are kept outside version control. The files used for the upload are in commit c7d8e7bf6 (2026-10-20). The code and the derived tables are not published; this page describes the method and lists the files and versions we used.

FileRoleFile hash
scratch/calc/v503_check.pystar counts; the observable-universe slice; random Milky Way slices (a copy of docs/ep1-relaunch-angles/raw/concepts/V5-03-calc/v503_check.py)8f2a1827f201
scratch/calc/ep02_extra.pythe Milky Way along its disc; ranges; galaxies near the planed22520c7528c
scratch/factcheck/mw_split.pygalaxies sliced at random (M5)99869fb229e2
plan/v10-calc/t2_cards.pythe circle inside the outline, and the magnification (method of M1)b42997a2d7a1
plan/v12/stations-v12.jsoncards, the counter's progress, colors by distance7f41377b1aa8
build/tools/cosmos-data.mjsthe computed web (D3)21d3df2a10a6
build/web/data/cosmos/cosmos.jsonthe computed web, seed 20261010 (D3)8db083daa1f3
build/web/src/lib/cosmos-v5-milky.jsthe 3D Milky Way and the other galaxies on the illustration (D1)d05247768350
build/web/src/v10/parts/v13-p1-uni.jsthe trip from 46 cm to the edge, with the Earth stop (D2)bbdec1729e33
plan/lines-v13.tsvJapanese master script r476b1bccbbace
plan/l10n/en/script.tsvEnglish lines (the English audio track and subtitles)8b9588ef27cc

Production notes

"The channel's creator" is one person. "AI agents" are Claude agents working in Claude Code. Tool names are given only where our records name them.

RoleDone byWhat happenedTools named in our records
Question, direction, approvalThe channel's creator (one person)Chose the topic, a cat-shaped slice through the universe (2026-10-09); watched the full cuts and gave notes; asked for the guesses and the actual numbers to be shown side by side, and for the slices to be shown in 3D (2026-10-16); chose the ending (2026-10-16) and the music level; proofread the script line by line and reworded the line at 5:03.7 (2026-10-18). On 2026-10-18: approved the full cut v9 and its music, asking that the universe in the Chief's belly stay still while the Chief breathes in its sleep; chose the new poses and the Japanese and English titles; listened to the Japanese voice track, asked for a calmer Sescha and chose her settings, marked ten lines whose delivery or reading was off, chose among the retakes and approved the Japanese voices; asked for the seven other languages to use the same voice settings. watched the final English master with subtitles and checked the pronunciation; flagged one long silence after a line, which was fixed in six languages; approved all eight language tracks for upload (2026-10-19)—
Research and fact ledgerAI agentsFound and read the sources and recorded in the fact ledger how much of each was read (full text, abstract, secondary). Computed the estimates in Method M1–M8.Claude (Claude Code)
Script (Japanese master)AI agents, with the creator's notesWritten and revised by AI agents over many drafts, tested with LLM readers given no context, then revised again. The creator's notes on the script were applied by one AI author agent, keeping their intent.Claude
Fact checksAI agentsFact-check passes compared the script and the cards on screen with the fact ledger. This page was compared with the script, the fact ledger and frames of the v10 render.Claude
Translations (English, French, Italian, German, Spanish, Chinese in simplified and traditional characters, Korean)AI agentsEach language was translated scene by scene from the Japanese master by an AI agent, following a written style guide, notes on how each character speaks, a glossary of 147 terms, and the context and time limit of every line. In the first review round, two more AI agents checked each translation: one read it straight through as a native speaker would, without seeing the Japanese; the other compared it with the Japanese line by line. A second round checked the revised lines. When the Japanese voices were final, the lines whose wording or tone had changed were re-checked in all seven languages, and the revised lines were read again by a separate AI agent without context (2026-10-18). The translations have not been checked by human native speakers. If you speak one of these languages and a line sounds wrong or unnatural, please tell us in the comments under the video.Claude (Claude Code)
Character artAI image generation, edited by script; selected by the creatorAs in Episode 1: poses were generated as sheets, cut out, and fixed with deterministic pixel-editing scripts. The jumping and back-view poses added for this episode were made the same way and chosen by the creator (2026-10-18).Astra (gpt-6-astra), run through codex exec
Boards, room, animation, the 3D universeCode written by AI agentsThe paper-style boards, the room and all motion are drawn by code (JavaScript, Canvas 2D, three.js), recorded in headless Chrome and encoded with ffmpeg. No image generation was used for the boards, the room or the universe; the Milky Way and the other galaxies close up are drawn on a NASA/JPL-Caltech illustration, and the Earth uses NASA imagery (Data D1, D2).Claude; headless Chrome; ffmpeg
Data processingCode written by AI agentsMethod M1–M8; the computed web of galaxies (Data D3).Python (standard library); Node.js
MusicScore by an AI agent; sample libraries; rendered and mixed by scriptThe score was written by an AI agent and rendered without a graphical interface by our command-line music pipeline (final render 2026-10-18), using sampled instruments from the GarageBand and Logic sound libraries (strings, flute, clarinet, piano, French horn, bassoon, harp, and a hall reverb), Sonatina Symphonic Orchestra v4.0 (vibraphone, second violins, marimba; CC Sampling Plus 1.0; credited in the description) and VSCO 2 Community Edition (violin ensemble, timpani, percussion; CC0). The Apple sound libraries may be used in our own music and video, but the sounds may not be redistributed on their own. The music sits under the voices at one constant level, with no ducking, and stops for the two guessing times and one pause to think.Claude; bgmctl 1.1.0
Voices, Japanese trackSyntheticThe same two character voices as in Episode 1, designed from text prompts with ElevenLabs voice design. The lines were generated with Eleven v4, two takes per line, and every take was checked for misread words with ElevenLabs speech-to-text. After listening, the creator asked for a calmer Sescha: her lines were generated again with steadier settings and a calm delivery direction. The creator then marked ten lines whose delivery or reading was off; for those, we generated alternatives with other delivery directions and punctuation, and the creator chose among them by listening (2026-10-18).ElevenLabs
Voices, English and the six other dubbed tracksSyntheticEnglish is the video's original audio track; French, Italian, German, Spanish, Chinese and Korean, like the Japanese track, are extra audio tracks on the same video. Each of these languages uses its own versions of the two character voices, made from the Japanese-track voices with ElevenLabs Voice Remix (changing only the language and accent), as in Episode 1. The lines were generated with Eleven v4, with the same settings and delivery directions as the Japanese track (the creator's choice, 2026-10-18). For French, Italian, German, Spanish, Chinese and Korean, one take was generated per line, and a line was generated again only where ElevenLabs speech-to-text showed a misread word, a doubled reading or a direction read aloud. For English, Sescha's lines and seven of Comet's were generated this way; Comet's other English lines come from an earlier recording of two takes per line, chosen with speech-to-text. Code placed each language's lines into the Japanese timing slots: a line may run into the following picture-only pause, or be time-stretched by at most 5% without changing pitch. Lines that still did not fit, or left a much longer silence than the Japanese, were shortened or completed in translation and recorded again. Every track uses the same music and sound effects as the Japanese track, at the same levels.ElevenLabs
SubtitlesCodeNine subtitle tracks (Japanese, English, French, Italian, German, Spanish, Chinese simplified, Chinese traditional, Korean), generated by code from each language's spoken lines. The Japanese subtitles follow the Japanese voices, with their punctuation matched to the takes the creator chose. Subtitles are separate tracks and are not burned into the picture. The eight translated tracks are timed to each language's placed voices.—
Text on screenCodeThe few words and numbers on screen are drawn by code in typefaces that come with macOS: Avenir Next (the distance labels, the counters, the cards and their words GUESS and ACTUAL) and Futura (the series name on the title card, the guessing cards, and the labels "1 mm" and "29 km"). The macOS license (macOS Tahoe 26, section 2E) lets users use the included fonts to display and print content while running macOS; the text is drawn into the video frames on our Mac, and no font files are embedded or shared (license text checked 2026-10-08 for Episode 1).—
Sound effectsStock sound library; synthesizedPaper, pin, clock, brass and stamp sounds from 効果音ラボ (soundeffect-lab.info) and 効果音辞典 (sounddictionary.info), from the set used in Episode 1: commercial YouTube use allowed, credit optional, no redistribution (terms checked 2026-10-03); trimmed and mixed by script. The dome's opening and closing sounds were assembled by script from the same set. The slicer's hum and the Chief's sleeping breath are synthesized.—