Skip to content

The Weird Timescales of the Universe

2024-05-23 · collab / interview · John, Katie Mack · 3:39 · 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, Katie Mack explains to John that recombination begins the cosmic dark ages, millions of years of cooling gas, and that cosmic timescales get weird because epochs are counted by how much happens; early density variations from quantum fluctuations seeded stars and galaxies.

What is said

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

00:00:00 — Katie Mack on recombination, the first neutral atoms and the start of the cosmic dark ages: cooling hydrogen gas and condensing clouds

  • ★★★ Katie Mack: Katie says recombination is the moment the first neutral atoms are able to form, and that era begins what is called the dark ages of the cosmos. — 00:00:00
  • ★★ Katie Mack: Katie says the era is called the Dark Ages because the primordial plasma has cooled but there are no stars yet; the universe is mostly hydrogen gas with a little helium. — 00:00:27
  • ★★ Katie Mack: Katie says that while the gas cools and the universe expands, gravity keeps pulling together clouds of cold gas, which start to condense. — 00:00:27

00:01:00 — The weird timescales of the universe: the dark ages last millions of years because little happens in them

  • ★★★ Katie Mack: Asked by John whether 'a while' means two seconds or ten years, Katie says the Dark Ages last millions and millions of years. — 00:01:00
  • ★★ John protests that they cannot count 10 to the negative 35 seconds and 10 to the negative 15 seconds as 'a while' and then also call several million years 'a while'. (playful) — 00:01:00
  • ★★★ Katie Mack: Katie says cosmic timescales get weird because eras are counted by how much is happening: there can be millions of years of cold hydrogen gas in which not much happens. — 00:01:00
  • ★ John jokes that this is great for them, since they now look able to get through the season, and he is starting to believe in them. (playful) — 00:01:30

00:01:54 — Early density variations make some gas clouds denser; quantum fluctuations from inflation explain the structure of the universe

  • ★★ Katie Mack: Katie says the physics of the cosmic dark ages is very simple: you can write down equations for gas cooling, and the gas just does that. — 00:01:54
  • ★★★ Katie Mack: Katie says that because there were little variations in density, some clouds of gas start to become denser than others over time. — 00:01:54
  • ★★ Katie Mack: When John suggests that a perfectly uniform observable universe would never have had stars and galaxies, Katie says random particle motion would still give fluctuations, so something would eventually happen, but differently and much later. — 00:02:23
  • ★★ John sums up that we are only here in this current state because of the early quantum fluctuations that came with inflation, and Katie agrees. — 00:02:48
  • ★★★ Katie Mack: Katie says those early fluctuations are why there is structure in the universe as we know it. — 00:02:48
  • ★ Reeling from the idea, John says he is going to not panic and just listen. (playful) — 00:02:48

00:03:12 — John plugs The Universe, the new Crash Course podcast with Dr. Katie Mack

In the description and comments

  • ★★ The description says John and Katie Mack will walk through the history of the universe over the next 11 episodes, and the first three episodes are out now. — video description
  • ★ The description asks viewers to subscribe to the podcast at complexly.io/theuniverse. — video description

Threads in this video

Mentioned

Central: cosmic dark ages · Katie Mack · quantum fluctuation · recombination (cosmology)

Also: Projects: Crash Course

Works: Crash Course Pods: The Universe

Concepts: atom · cosmic inflation · expansion of the universe · galaxy · Gravity (concept) · helium · hydrogen · observable universe · plasma · star

Also centred on Katie Mack: Katie Mack Explains The Big Bang To John Green · We’re Here Because... Something Broke

← Previous: Getting Personal about Getting Personal · Next → An Ancient Apocalypse