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ALL of Wikipedia in One QR Code?

2015-08-28 · explainer · Hank · 3:54 · watch on YouTube

Topic: Science & nature · mode: Curiosity & trivia

Hank works out that the text of English Wikipedia (about 24 TB) would fit on a QR code 27 km on a side, readable only from lunar orbit with a James Webb-sized aperture and a far better sensor: possible, but not with current technology.

What is said

The parts of the video and what is said in each (★ — how much it matters to the video).

00:00:00 — What a QR code is: visual data, each 2-by-4 block one byte

  • ★★ Hank says a QR code visually represents data, like barcodes, snapcodes, facial expressions or writing, and each block of 2 by 4 squares codes one byte, one character. — 00:00:02

00:00:26 — The question (all of Wikipedia on one QR code?) and the sizing maths: 24 TB, 2 mm blocks, 27 km a side

  • ★★★ Hank asks whether all of Wikipedia could be printed on one QR code and scanned by a camera, calling it a dumb question of the kind he enjoys answering. (hypothetical) — 00:00:26 · Wikipedia
  • ★★★ Hank says just the text of just the English Wikipedia is about 24 terabytes, 24 trillion bytes. — 00:00:42 · Wikipedia
    • a number in question (doubtful): "about 24 terabytes" — check against the recording (size of english wikipedia)
    • a number in question (doubtful): "24 trillion" — check against the recording (size of english wikipedia)
  • ★★★ Multiplying by 8 squares per byte, taking the square root and assuming 2 mm blocks, Hank gets a QR code 27 km on a side holding all of Wikipedia. (hypothetical) — 00:00:49 · Wikipedia

00:01:18 — Reading it: 90-degree camera at 13.5 km, move it to the Moon, the diffraction limit, gamma rays vs a huge aperture (James Webb), a new sensor

  • ★★ A camera with a 90-degree field of view would have to be 13.5 km away to capture the whole code. (hypothetical) — 00:01:28
  • ★★ At that distance the atmosphere would distort the image too much, so Hank proposes putting the QR code on the Moon's surface with the camera orbiting about 13.5 km up. (hypothetical) — 00:01:35
  • ★★★ Hank explains the diffraction limit: when light passes through a camera's aperture, the ratio of aperture size to wavelength blurs anything below a certain size; the fix is a bigger aperture or shorter wavelength. — 00:01:49
  • ★★ Gamma rays have a very small wavelength but very high energy, so a phone camera would need to detect them and the code would need special gamma-absorbing ink, since they fly through normal ink. — 00:02:22
  • ★★ Hank prefers a huge aperture, such as the James Webb Space Telescope, already in development, modified for a wider angle; its aperture could conceivably resolve 2 mm pixels from 13.5 km. (hedged) — 00:02:40
  • ★★ James Webb lacks a sensor to capture it all at once, so a new sensor with like 10,000 times the resolution of today's best military spy cameras would be needed; Hank is confident it can be built in time. (playful, hedged) — 00:03:06

00:03:30 — Answer: yes, possible, though not with current technology

  • ★★★ Hank's answer: yes, Wikipedia can be printed as a scannable QR code, not really with current technology, but it is possible. (hypothetical) — 00:03:30 · Wikipedia

00:03:39 — Sign-off; may have got something wrong; thanks to Henry from MinutePhysics

  • ★★ Hank says he's not entirely sure and could have got something wrong, and thanks Henry from MinutePhysics for helping with the maths. (unsure) — 00:03:41

In the description and comments

  • ★★ In the description Hank invites viewers to check his maths and tell him if he got anything wrong, and links MinutePhysics' 'How Far Can Legolas See' and a video decoding a QR code by hand. — video description
  • ★★ Hank notes that he did not correct for the distortion at the edge of the wide-angle shot, but he and Henry went through the calculation and found it did not affect the overall result. — video description

Threads in this video

Mentioned

Central: diffraction limit · QR code · Wikipedia

Also: barcode · gamma ray · James Webb Space Telescope · Moon · Snapcode

Only in the description or credits: Henry Reich · How Far Can Legolas See?

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