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  • Light travels at about 1 foot per nanosecond.

  • Hold your hand up 12 inches from your face: you're seeing your hand as it was a nanosecond

  • ago.

  • Everything you look at is, to one degree or another, in the past.

  • The farther away in space, the more ancient in time.

  • You can't see the Sun as it is now, but you can see it as it was about 8 minutes ago.

  • You can't see Alpha Centauri now, but you can see it 4.4 years ago.

  • You see the Andromeda Galaxy as it was 2.5 million years in the past.

  • And so on.

  • With powerful telescopes, we can see galaxies whose light has been traveling to us for more

  • than 13 billion years.

  • We see them shining in a universe that's still young, where gravity has barely begun

  • to pull matter together into stars and galaxies.

  • But we can see something even more distant, and more ancient, than the first galaxies.

  • If we peer out far enough, in between the galaxies, we can see parts of the Universe

  • that are so far away, it has taken the light from that distance very nearly the entire

  • age of the cosmos to reach us.

  • When we look at the most distant parts of the cosmos, in every direction, we see parts

  • of the Universe that are so far in the past, they're still in the final stages of the

  • Big Bang.

  • So far away, so far back, the space is completely filled with a dense, roiling plasma, the fire

  • of creation.

  • We are not the center of the Universe.

  • But we are the center of our own perception as light reaches us from afar; we lie embedded

  • in nesting-doll layers of cosmic time.

  • Each concentric sphere is an era.

  • We can see the structure of matter changing, like geological strata all around us

  • The most distant layer of time that we can see is the light that has been traveling since

  • the moment the primordial fire began to cool.

  • The cosmic microwave background surrounds us at every edge of our vision.

  • We are embedded in shells of cosmic time, and the final one is fire.

  • Thanks to Katie Mack, aka astrokatie, for collaborating with me on this twitter-thread-inspired

  • video poem.

  • Now, if you've ever wondered how we can know things like how far away distant stars

  • and galaxies are, Brilliant.org, this video's sponsor, has an interactive course on just

  • that, exploring trigonometric parallax, standard candles, supernova, and more.

  • Or if you want a small daily dose of science, Brilliant has a short problem of the day,

  • every day, that gives you just enough background information to figure out a math or science

  • puzzle; in fact, here's one about measuring the distance to the stars!

  • You can sign up for free at brilliant.org/minutephysics, and the first 200 people will also get 20%

  • off an annual premium subscription with full access to all of Brilliant's courses and

  • puzzles.

  • Again, that's brilliant.org/minutephysics.

Light travels at about 1 foot per nanosecond.

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B2 cosmic brilliant distant brilliant org universe org

Shells of Cosmic Time (ft. @AstroKatie)

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    Summer posted on 2021/03/21
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