(Intro)

(0:00) The universe is big, really big, bigger than that. No, you’re not thinking big enough. It’s so massive that it makes my brain hurt. It’s so ginormous, we teeny tiny humans can barely, just barely get our brains to comprehend it. But, just because we can’t really fully understand how big the universe is, doesn’t mean it’s not important. The universe is our home. We should at least poke around. So, how big is the universe?

(0:45) Let’s start off with our cosmic address. That’s where we live in the universe. You could say my current cosmic address is the Crash Course Kids Studio, Toronto, Canada, North America, Earth, the solar system, the Milky Way Galaxy, the observable universe, the universe. Knowing our cosmic address helps us understand where the things in the sky are. Things like stars, asteroids, planets, even other galaxies. Every time we go up and out, a level in our cosmic address, the actual space we’re talking about gets more spacious. Distances in space are so large that scientist had to come up with a whole new way of measuring them. You can’t talk about space using miles or kilometers. The numbers get so big that they just sound like nonsense. That’s where a light-year comes in. It sounds like a measure of time, because it has the word year in it, but it’s really a measure of distance. Light is the fastest thing we know in the whole universe, clocking in at a whopping 300,000 kilometers a second. In one second light can travel around the Earth, the whole Earth, seven times! It’s moving so fast our brains can’t detect that it’s moving at all.

(1:52) So, a light year is the distance that light can travel in one year. Does your head hurt yet? Well, buckle up because we’re just getting started. Back to our big question. How big is this universe of ours? Nobody knows! Really! That’s pretty weird, right? Well, that’s partly because the only part of the universe we know about is what we call our observable universe, the parts that we can actually see or observe in any direction. Some things are so far away that light from those objects haven’t even reached us yet. That is the limit of our observable universe. Beyond that, we don’t know what’s out there. But even sticking to the observable universe, we’re going to need to scale things way down to understand any of it.

(2:37) Let’s try to visualize our cosmic address on a scale that we can handle. Let’s use this room as our scale. It’s about ten meters, by ten meters, the size of an average classroom. If the sun were the size of this room, the earth would be about this big. Ok, not too crazy. Now, imagine our whole solar system were the size of this room, this would be the sun. Don’t see anything? That’s because it’s just a grain of salt. A grain of salt! Yeah! That’s our sun. And the Earth’s orbit around the sun would be about the size of this disk. At this scale, the earth is just a microscopic bacterium. We can’t even see it. At this size, our whole big huge solar system is just a grain of salt.

(3:20) Now, what if the entire Milky Way galaxy were the size of this room? Our solar neighborhood would be this big. Ho-Boy! Now, for the finale, the biggest thing we know, the observable universe. Imagine the observable universe is this room. Can you spot the Milky Way? Nope! It’s just way too small. It’s not that it’s just un-seeable, it’s smaller than microscopic, the whole Milky Way. Are you dizzy? I’m dizzy.

(3:45) So, that gives you an idea of the size of the things in the universe, but what about the size of the space? You know that the sun is the closet star to the Earth. But what is the second closest? That would be Proxima Centauri, it’s 4.24 light-years away. That means that it takes light from that star four years to reach us. By comparison, it takes the sun’s light 8 minutes to get to Earth. If you want to visit the suns closet star friend traveling in the fastest object humans have ever built, it would still take 19,000 years to get there! And that’s only 4.24 light-years away. The observable universe is, are you ready for this? 93 Billion light-years across. Even using light years, it’s so big, it still sounds kind of like nonsense, huh?

(4:35) So, space. It’s big. Really big. Mind bogglingly big, but it’s also our home. Even if we’re just unbelievably small little things floating on a speck of dust in a teeny tiny galaxy, we’re still here. And we know where we are in the universe and that’s pretty awesome. But, I think I need to go lie down now.