字幕表 動画を再生する 英語字幕をプリント So what is human existence? How can you actually sum it up? It turns out it's really pretty simple. We are dead stars, looking back up at the sky. Everything you are, I mean literally the iron in your blood, comes from the instant before a star dies. You cut yourself, and you see that red from that oxygenated hemoglobin. That was the instant of the death of a solar system. The universe began with only the element hydrogen, the very very simplest atom that exists. And the only thing in the universe that can make a bigger atom is a star. The entire periodic table, every element you ever heard of was processed inside the body of a star. That star then unravelled or exploded. And here we are. All a star is, is a dust cloud that is collapsing under the force of gravity. That's it. And when you compress gas together, it actually heats up. There's a time when that's hot enough to set off a nuclear fusion reaction. That actually supports the star. This nuclear explosion inside supports the star against further collapse. But that nuclear fusion reaction is using fuel, it's using hydrogen. And so eventually, that will burn out, and the collapse of gravity will keep going. In the case of a more massive star, the gravity crushes more and more tightly. Things get hotter inside, you create things like carbon, oxygen, nitrogen, until finally, you get to the element iron. It fuses iron together, and instead of energy coming out, energy is actually absorbed. And the core of the star collapses. And that sets off the most violent, brilliant reaction we know of called a supernova reaction. Everything outside the element of iron, everything heavier. All the gold, all the silver, all the lead, all the uranium. That's formed in that supernova explosion. A single star will glow as brightly as entire galaxies, that's hundreds of billions of stars, in that moment of death. And that's what you are. That literally what your body is... Is that instant of death. You know, it's so tempting. Humans have done this before, for literally tens of thousands of years. They think of the stars as eternal. Stars will all burn out someday. There's only a certain amount of stellar fuel, hydrogen. Stars are burning through it. And the stars, as we know them, will all die out in some trillions of years. And the universe will be dark, for the rest of time. Whatever that means. But think about that, we're actually living in Eden right now. We're living in a time when this ten-billion-year-lived thing, the sun, is pouring down free energy, we are using it, we are evolving, we are becoming sentient, we are looking out at the universe. And what an amazing thing to think that that's for a tiny little brief part of the universe's history. And everything else will be dark. It does give you an ownership, about how wonderful this time is. How wonderful your life is right now. Your literal life. But also how wonderful this time of the universe is. Someday I wonder, if people will have myths about the days when stars rained down free sunlight, free energy.