0:00 For the first 380,000 years of its existence, the entire universe was a thick, glowing fog that you couldn't see through.0:09 That's right.0:10 An opaque, super-hot soup of particles and energy.0:13 And then, in a single moment, it all became transparent.0:18 Wait, so the whole universe just… switched on?0:21 That feels like it connects back to what we were talking about in Episode 16, with the weird rules of quantum physics running things at the very beginning.0:33 It absolutely does!0:34 Before that moment, the universe was so small and so dense, it was basically a realm of pure quantum mechanics.0:42 But to get there, we have to start at the beginning.0:46 Or, you know, as close to the beginning as we can get.0:50 Okay, take us there.0:52 Everyone says "The Big Bang." But what does that actually mean?0:57 Was it a big… bang?0:58 That's the number one question!1:00 And the name is a little misleading.1:03 It wasn't an explosion happening in space, like a firework.1:07 It was the beginning of space and time itself.1:11 Imagine the entire universe—everything we see, every star, every galaxy—squeezed into a point smaller than a single atom.1:20 I...1:20 honestly can't imagine that.1:22 That breaks my brain a little.1:25 It breaks everyone's brain!1:27 But start there.1:28 An incredibly hot, incredibly dense point.1:31 And then, it started expanding.1:33 Not into anything, mind you.1:35 Spacetime itself started stretching.1:38 Oh, okay.1:39 So it's not like it's filling up an empty room.1:42 The room itself is getting bigger.1:45 EXACTLY.1:46 A perfect analogy is baking raisin bread.1:49 As the dough rises and expands, the raisins move away from each other.1:54 But they aren't, like, crawling through the dough.1:58 The dough itself is carrying them apart.2:01 Every galaxy is a raisin in the expanding dough of the universe.2:05 Wow.2:06 Okay.2:06 I'm a raisin.2:07 I can work with that.2:09 So the universe is expanding and...2:11 cooling down?2:12 Yep.2:13 Just like how steam cools and condenses into water, the universe cooled as it expanded.2:19 At first, it was just a soup of pure energy.2:22 Then, as it cooled a bit, fundamental particles like protons and electrons started to form.2:29 But it was still a chaotic, hot mess.2:32 A cosmic fog.2:33 Right, the glowing fog you mentioned at the start.2:37 So light couldn't travel?2:39 Not freely, no.2:40 It was like light trying to get through a really dense cloud.2:44 A photon would get zapped out and immediately bump into an electron and get absorbed.2:51 It couldn't go anywhere.2:53 For hundreds of thousands of years, the universe was dark, even though it was glowing.2:59 That seems like a contradiction.3:01 How can it be glowing but dark?3:04 Because the light was trapped!3:06 But then, after about 380,000 years, the universe cooled to about the temperature of the surface of the sun.3:14 And at that point, something amazing happened.3:18 It was finally cool enough for the protons and electrons to pair up and form the first real atoms—mostly hydrogen and helium.3:27 And what did that change?3:29 Everything!3:30 Suddenly, all those loose electrons were locked into atoms.3:34 The fog cleared.3:35 For the very first time in history, light could travel across the cosmos in a straight, uninterrupted line.3:43 Oh, wow.3:44 So that's the first sunrise.3:46 The REAL first sunrise.3:48 It is!3:48 And here's the part that gives me goosebumps.3:52 We can still see the light from that moment.3:55 It's stretched out and cooled over billions of years, so it's not visible light anymore.4:02 It's microwaves.4:03 We call it the Cosmic Microwave Background.4:06 Wait, so the static on old TVs… is that really part of it?4:10 A tiny, tiny percentage of it, yes!4:13 It's the oldest picture of the universe that exists.4:17 It’s a baby picture of the cosmos, just 380,000 years old.4:21 So from that point, with this clear space and these simple atoms of hydrogen and helium… gravity just started doing its thing?4:31 Gravity took over.4:32 It started pulling those atoms into massive clouds, which collapsed under their own weight, getting hotter and hotter until—BAM—the first stars ignited.4:43 Those stars then cooked up heavier elements and exploded, seeding the universe with the material to form planets, and eventually, us.4:53 So every single thing we are, and everything we see, started in that tiny, hot dot.5:00 Every atom in your body was forged in a star that was born from the echoes of that initial expansion.5:07 It's the ultimate origin story.5:10 We are, quite literally, made of stardust.5:13 I think that's a much better name for it than the Big Bang.5:17 The Great Unfolding, maybe.5:19 I like that.5:20 Let's go with that.
