How Long Can Humans Outrun Extinction?
Modern humans evolved a couple hundred thousandyears ago. And between ice ages, volcanoes, climate change,earthquakes, droughts, floods,and Reddit being down sometimes, we’ve seen some stuff. But on cosmic timescales, two or three hundredthousand years is just a drop in the bucket. The longer we’re around, the more likelywe are to witness something truly Earth-shattering,whether metaphorically or literally. And someday, if we’re still here,we’ll have to face things like Earth melting as it’s engulfed by the Sun. Or the Sun going out. Or galaxies colliding. One way or the other, we’re going to haveto leave home if we want to survive. And even if we had fancy starships,how long could we actually outrun extinction before the universe became uninhabitable to us?It’s such a big question that we’ve madea special, extra-long episode about it. Because the answer is a surprisingly longtime. Now, to be clear, we probably won’t haveto leave home any time soon. So there’s plenty of time to get our spaceshipsready. Like, we might hear a lot about climate changethese days,but no matter how destructive and disruptiveit is,researchers don’t think that it will threaten our entire species. There are plenty of variables to consider, but overall,the odds are pretty good that we’ll get through it one way or another. The same goes for one of the Internet’sfavorite doomsday scenarios: a supervolcano. Even though that would be rough, it probablycouldn’t take us all out;there are just too many people spread throughout the world. But we will have to leave Earth someday. Because even if we dodge a huge asteroid impactor the takeover of artificial intelligence,our planet will eventually stop being habitable,thanks to the Sun. The Sun brightens as it ages. And generally, that will make Earth warmerover the next few hundred million years,which will cause all kinds of problems. For example, rocks tend to erode more easilyat higher temperatures, so in the future,more new, rocky surfaces will be exposed tothe atmosphere than today. Exposed rock can react with carbon dioxide,so the more exposed rock there is,the less CO2 will be left in the atmosphere. That might seem like a good thing, given howworried we are today about climate change. But remember that plants need CO2 like weneed oxygen. And according to some estimates, in about800 million years,there actually won’t be enough of the gas left in the atmosphere for photosynthesis. If those estimates are right, that would bethe end of all life on Earth bigger than a bacterium,and they’d go extinct about abillion increasingly warm years later. Future people might prevent this by buildingsomething to block the extra sunlight,or they could use repeated asteroid flybys togravitationally inch Earth’s orbit away from the Sun. But they might also decide that Earth justisn’t worth it anymore, and could leave. The most obvious option would be to go toMars, since it’s closest. We’d still have to give the planet an atmosphereand a liveable temperature,but with a dash of terraforming, we’d be fine, althoughMars still won’t be a permanent solution. Five or six billion years from now, the Sunwill finally start running out of hydrogen fuel in its core. After that, it will fuse helium, and it willstart growing. First, it will engulf Mercury, and then Venus. And 7. 6 billion years from now, its outerlayers will probably pass through Earth’s orbit, too,likely destroying almost everythingwe’ve ever built. The people on Mars wouldn’t be much betteroff, either. Mars will never fall into the Sun, but itwill become too hot to be comfortable for life. And with the Sun so much closer,solar radiation will rip apart any Martian atmosphere our descendants try to create. But we wouldn’t be out of options yet. Because while the Sun balloons, the outersolar system may have it pretty good. Jupiter’s moon Europa and Saturn’s moonEnceladus are both ice-covered today,but they’ll heat up as the Sun expands and willeventually become water worlds. And, briefly, we could live there. But again, that wouldn’t last forever. In fact, we might be on the move after aslittle as a hundred thousand years, once more,because of the Sun. Around that time, the Sun will have expanded so much that its outer layers will finally escape into space,leaving behind a tiny whitedwarf star surrounded by a big, cloudy nebula. Comparatively speaking, white dwarfs don’temanate much energy,so the newly-minted one at the center of the solar system will leave the remaining planets and moonsas cold as interstellar space. And without a good heat source, there’sno usable energy. So any civilization that’s still aroundwill have to move on. By this point, though, we’ll probably justfold our Dyson spheres into overhead compartmentsand head off to colonize some other planetarysystem. Because, hey, if we haven’t figured outinterstellar travel in seven billion years,well, we’ll have a problem. But let’s assume we figure it out, and don’tspend the next forever binging Netflix. Today, the closest star is Proxima Centauri,which is about four light-years away. It’s a red dwarf star, which means it willlikely outlive the Sun,and it already has a potentially-habitable planet. But since red dwarfs also emit some seriouslydangerous flares every now and then,it might not be our best choice. Besides, current estimates suggest that there are billions of planets out there that could support water,so we have plenty of otheroptions. Which is good, because, today,there’s really no way of knowing where Proxima Centauri will be that far in the future. Stellar orbits in the Milky Way naturallyget rearranged over billions of years,so Proxima Centauri might not be our closestneighbor anymore. Also, and maybe more importantly, the MilkyWay won’t exactly be a thing in seven billion years. It will probably collide with the AndromedaGalaxyeven before the Sun expands into the inner solar system. Or, at the very least, they’ll pass closeenough to each other to cause some chaos. Thankfully, there’s almost no chance ofstars actually smashing into each other,since stars are just too spread out. But the collision will make long-term wayfindingtricky. Stars will be thrown all over the place whilethe new galaxy, known as Milkomeda,takes shape over billions of years. Yes, that is the real proposed nickname, andno, I don’t support it. So maybe the next star we’ll go to hasn’tbeen discovered yet, or born. And, even if we do have the technology toleave the solar system,we’ll have to watch out for the dangers of interstellar space. For example, we’ll have to keep an eye outfor supernovas,since colliding gas clouds will produce lots of enormous, short-lived stars that explode at the end of their lives. And radiation from those explosions couldeasily wipe us out mid-journey. But if we do learn to safely travel to newstars,that would allow humans to keep thriving for a long time. We’re talking trillions of years. Because even when our new home star goes out,we could hop over to another system. As a bonus, the formation of Milkomeda will also make a good number of smaller, longer-lived stars like our Sun,so we’ll have a lotof options. But even though trillions of years is an unimaginablylong time, it’s not forever. Eventually, all the Sun-like stars in theuniverse will wink out, one after another,and there won’t be enough big clouds ofhydrogen-rich gas left to replace them. But even then, that won’t be the end ofhumanity. Our corner of space will get darker and cooler,since it will be lit mainly by tiny, long-lasting red dwarfs. But we could still survive around them, likeour ancestors huddled around their flickering campfires. We would have to find a way to live with theviolent solar flares, though. Or if nothing else, we would have to finda way to harness the red dwarf’s energywithout being in range of those flares. But assuming we figure that out, we’ll beable to stay alive long into the future. Eventually, though, even those stars willdie, along with any remnants like white dwarfs. And finally, the universe will be black. At this point, our only decent source of energywill be black holes,since there will still be plenty of those floating around, with gas falling into them all the time. If our descendants are surviving on homemade,nuclear fusion power, which seems likely,considering all the stars will be gone, they’llneed that gas to keep making energy. Of course, with black holes gobbling up that gasand the expansion of the universe spreading it out more and more diffusely,it will behard for them to find enough fuel. There will always be the odd proton or deadplanet gliding through the vastness of empty spacethat we could somehow harness resourcesor energy from. But just about everything else is eventuallygoing into a black hole. Fortunately, it will take a while for blackholes to vacuum the universe,and that’s putting it lightly. For you fans of metric prefixes, astronomersestimate that it will be about a billion yottayearsbefore there’s pretty much nothing out therebut black holes. That’s a billion trillion trillion years,or a one with 33 zeros after it. And I think we can agree: That’s a longtime. Many physicists who are trying to combine everything we know about the universe into a single elegant ideathink that, coincidentally,protons will decay after about this much time, too. And that would definitely be the end of alllife. But if they’re wrong, physicists and mathematicianshave found thateven in that dark, black hole-filled universe completely devoid of raw materials,life could still persist. They’ve discovered that if you dive close to a spinning black hole and drop something in it just the right way,you can steal energyfrom the black hole itself. The exact mechanism for how it works is prettycomplicated, and at the end of the day,no one is totally sure if you could power a civilizationthis way. But for now, we think it’s still an option. And we have time to figure out the details. Then again, black holes aren’t forever,either. In 1974, Stephen Hawking published his discoverythat black holes very, very slowly radiate energyin a process now known as Hawking radiation. Hawking radiation is incredibly weak for anyreasonably large black hole,so it’s not like we could use it to heat our space colonies. But the important part is that it causes blackholes to slowly shrink. And after almost a googol years, that’sa 1 with one hundred zeros after it,even the biggest black holes in the universe willevaporate due to Hawking radiation. After that, it’s hard to imagine any kindof life flourishing. There won’t be many atoms left,and any energy will be so uniform that we won’t really be able to do anything with it. This is known as the heat death of the universe,and it’s how today’s best cosmological models predict the universe will finally end. Even here, though, there may be the tiniestglimmer of hope. In 1979, the physicist Freeman Dyson, thesame guy who made Dyson spheres famous,imagined an organism that worked kind of like a computer:When it’s on, it uses energy to think ordo something,and when it’s sleeping it does essentially nothing. Dyson was able to show that by sleeping forlonger and longer between each pair of thoughts,the organism could live an infinite amountof time, but only ever use a tiny bit of energy. So with a big enough battery, this thing couldlast forever. And that brings us to our final thought:By this point in time, humans might not technically be humans anymore, thanks to evolution. In fact, we might have changed so much thatnobody will remember that time we had ten fingers and breakable bones and disease. Realistically, that day could come much soonerthan trillions of years from now. So maybe we could become, or even choose tobecome,this weird species that waits a quadrillion years between thoughts. Maybe we’ll decide that’s worth immortality. Or, maybe we’ll just decide we’ve livedlong enough. But, hey, we have a long time to sort outthose decisions. In the meantime, the best thing we can dois keep taking care of the planet we have,so we can make the most of the next 800 millionyears. Because, ultimately, scientists can tell us a lot about what the universe will be like in the far-off future. But as for what humans will do until then…well, that’s up to us. Thanks for watching this special episode ofSciShow Space!If you’d like to see us do longer episodeson other topics, let us know in the comments!And as always, if you want to keep up withour latest episodes,you can go to youtube. com/scishowspace and subscribe.