Light travels at about 1 foot per nanosecond.
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
Hold your hand up 12 inches from your face: you’re seeing your hand as it was a nanosecond

ago.
ago.

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

The farther away in space, the more ancient in time.
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 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 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.
You see the Andromeda Galaxy as it was 2.5 million years in the past.

And so on.
And so on.

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

than 13 billion years.
than 13 billion years.

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

to pull matter together into stars and galaxies.
to pull matter together into stars and galaxies.

But we can see something even more distant, and more ancient, than the first 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
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
that are so far away, it has taken the light from that distance very nearly the entire

age of the cosmos to reach us.
age of the cosmos to reach us.

When we look at the most distant parts of the cosmos, in every direction, we see parts
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
of the Universe that are so far in the past, they’re still in the final stages of the

Big Bang.
Big Bang.

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

of creation.
of creation.

We are not the center of the Universe.
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
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.
in nesting-doll layers of cosmic time.

Each concentric sphere is an era.
Each concentric sphere is an era.

We can see the structure of matter changing, like geological strata all around us
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 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 moment the primordial fire began to cool.

The cosmic microwave background surrounds us at every edge of our vision.
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.
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
Thanks to Katie Mack, aka astrokatie, for collaborating with me on this twitter-thread-inspired

video poem.
video poem.

Now, if you’ve ever wondered how we can know things like how far away distant stars
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
and galaxies are, Brilliant.org, this video’s sponsor, has an interactive course on just

that, exploring trigonometric parallax, standard candles, supernova, and more.
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,
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
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!
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%
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
off an annual premium subscription with full access to all of Brilliant’s courses and

puzzles.
puzzles.

Again, that’s brilliant.org/minutephysics.
Again, that’s brilliant.org/minutephysics.