字幕表 動画を再生する 英語字幕をプリント Hey, who turned out the stars? Hello? Seriously, where did they go? Is this the end of the Universe? Are we about to get all wiped out? This is WHAT IF, and here's what would happen if all the stars in the Universe exploded at the same time. For every galaxy that's visible from Earth, there are nine smaller ones that we can't see, even with all the technology we've developed. That's 90% of all space stuff in the observable universe that we're missing out on. We can't even see all the stars in the Milky Way. Our home galaxy is just too cluttered with gas, dust, smaller stars and one supermassive black hole. All that makes it impossible to tell how many stars there really are out there. But whatever that number is, it sure has a lot of zeros in it. Watching them explode all at once might mean that the Earth is about to become nothing more than dust in space. But there's also a scenario in which we could make it out alive. All stars eventually exhaust their nuclear fuel and die. Some of them depart modestly, first swelling to the stage of a red giant and then slowly cooling down over billions of years. More massive stars explode into a blinding burst of light, known as a supernova. As stars go supernova, they spit out a superheated shockwave in all directions, along with a lot of radiation. Supernovas exploding 30 light-years away from Earth, could send us so much radiation that it would start ripping apart our ozone layer. Once the ozone layer was damaged enough to allow just 10% more UV rays to hit the planet's surface, nearly all marine life would be wiped out. With two-thirds of the ozone layer gone, people living in mid-latitude cities - from London to Melbourne - would start getting severe sunburns. Not even SPF 1000 would save your skin from that much radiation. Some stars would take it a step further. They'd collapse to form black holes. From Earth, this would appear as a lot of bright flashes in the sky. Because of the huge distances involved, the explosions would happen in slow motion. You could see one star exploding for over ten years as the light from it continued to travel towards Earth. You wouldn't hear any explosions. Sound waves need molecules to travel through. Since space is a vacuum, there'd be no volume, only a really cool light show. Technically, it's possible. Our planet's surface would be wiped out and all the oceans would boil away. Any survivors would be forced underground, watching out for further damage from exploding stars. But at least life on Earth could have a chance. Am I forgetting something? Right, we'd be sharing our neighborhood with one exploding star. If the Sun were to go supernova, all life on Earth would definitely come to an end. The surface of our planet would become 15 times hotter than the surface of the Sun right now. That alone would vaporize Earth within a few days. Lucky for us, the Sun isn't massive enough to go supernova. But if it exploded, it would send matter in all directions; raining down on Earth 22 hours after the explosion. I'm not going to lie to you. It would be all bad in the end. But then, exploding stars might form new stars and new planets orbiting them. It would be the beginning of a new Universe, possibly with new habitable worlds and new life forms. But that's a story for another WHAT IF.