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Katie Mack Explains The Big Bang To John Green

2024-04-27 · collab / interview · John, Katie Mack · 4:10 · watch on YouTube

Topic: Science & nature · mode: Explainer · tags: self promotion, guest or collab

In a clip from the podcast Crash Course Pods: The Universe, astrophysicist Katie Mack explains to John that the Big Bang theory means only that the universe was hot and dense 13.8 billion years ago and has been expanding and cooling since, known from receding galaxies and from the light of the early hot, dense soup.

What is said

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

00:00:00 — John asks Katie Mack how we know what happened in the first minute of the universe

00:00:20 — Katie Mack explains the Big Bang theory: hot dense beginning, expansion and redshift, extrapolation back, confirmation in the 1960s

  • ★★★ Katie Mack: Katie says the popular idea of the Big Bang, a singularity, a tiny infinitesimal point that exploded in all directions, is not really what astronomers mean by the Big Bang theory. — 00:00:28
  • ★★ Katie Mack: Katie says what astronomers mean is much closer to the theme song of the TV show The Big Bang Theory, which she uses as an example because it is actually pretty good. — 00:00:43

  • ★★★ Katie Mack: Katie says the Big Bang theory is just the idea that the universe was hot and dense in the beginning, 13.8 billion years ago, and has been expanding and cooling since. — 00:01:06

    “the Big Bang Theory is just the idea that the universe was hot and dense in the beginning”

  • ★★★ Katie Mack: Katie says the theory originates in the observation that the universe is expanding now: all the distant galaxies are seen moving away from us. — 00:01:17

  • ★★ Katie Mack: Katie explains that the expansion stretches the light of distant galaxies from visible to infrared, an effect like a passing siren dropping to a lower pitch. — 00:01:27
  • ★★ Katie Mack: Katie says things moving away get redder (longer wavelengths) and things moving toward us bluer (shorter), at all wavelengths of light from radio to gamma rays. — 00:01:49
  • ★★ Katie Mack: Katie says expansion does not mean objects are expanding: galaxies move apart because the empty space between objects is expanding. — 00:02:10
  • ★★ Katie Mack: Katie says the expansion of the universe has been known for a long time, since about the 1920s. (hedged) — 00:02:17
  • ★ John remarks that the 1920s is not that long ago. — 00:02:24
  • ★★ Katie Mack: Katie replies that the expansion was seen as soon as we could know there are other galaxies: those far enough away are moving away from us. — 00:02:25
  • ★★★ Katie Mack: Katie concludes that if the universe is expanding now it must have been smaller in the past, with the galaxies closer together. — 00:02:34
  • ★★★ Katie Mack: Katie says squeezing things makes them hot and dense, so extrapolating back gives a universe that began as a hot, dense soup of energy. — 00:02:44
  • ★★★ Katie Mack: Katie says the idea had been floated for a long time, and confirmation came in the 1960s when astronomers began to see the light of that hot, dense soup. — 00:03:11
  • ★★ John sums up: receding galaxies and glimpses of the early hot, dense soup are two independent ways of knowing the universe used to be hot and dense. — 00:03:25

00:03:44 — John plugs The Universe, the new Crash Course podcast with Dr. Katie Mack

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Mentioned

Central: Big Bang · expansion of the universe · Katie Mack

Also: Projects: Crash Course

Works: Crash Course Pods: The Universe · The Big Bang Theory

Concepts: cosmic microwave background · Doppler effect · electromagnetic spectrum · gamma ray · gravitational singularity · Infrared · redshift

Also centred on Big Bang: Mindblowers with Hank and John

Also centred on expansion of the universe: How Big is the Universe?

Also centred on Katie Mack: We’re Here Because... Something Broke · The Weird Timescales of the Universe

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