How Long Can Humans Outrun Extinction?

Modern humans evolved a couple hundred thousand
years 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 hundred
thousand years is just a drop in the bucket. The longer we’re around, the more likely
we 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 have
to 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 made
a special, extra-long episode about it. Because the answer is a surprisingly long
time. Now, to be clear, we probably won’t have
to leave home any time soon. So there’s plenty of time to get our spaceships
ready. Like, we might hear a lot about climate change
these days,but no matter how destructive and disruptive
it 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’s
favorite doomsday scenarios: a supervolcano. Even though that would be rough, it probably
couldn’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 impact
or 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 warmer
over the next few hundred million years,which will cause all kinds of problems. For example, rocks tend to erode more easily
at higher temperatures, so in the future,more new, rocky surfaces will be exposed to
the 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 how
worried we are today about climate change. But remember that plants need CO2 like we
need oxygen. And according to some estimates, in about
800 million years,there actually won’t be enough of the gas left in the atmosphere for photosynthesis. If those estimates are right, that would be
the end of all life on Earth bigger than a bacterium,and they’d go extinct about a
billion increasingly warm years later. Future people might prevent this by building
something to block the extra sunlight,or they could use repeated asteroid flybys to
gravitationally inch Earth’s orbit away from the Sun. But they might also decide that Earth just
isn’t worth it anymore, and could leave. The most obvious option would be to go to
Mars, since it’s closest. We’d still have to give the planet an atmosphere
and a liveable temperature,but with a dash of terraforming, we’d be fine, although
Mars still won’t be a permanent solution. Five or six billion years from now, the Sun
will finally start running out of hydrogen fuel in its core. After that, it will fuse helium, and it will
start growing. First, it will engulf Mercury, and then Venus. And 7. 6 billion years from now, its outer
layers will probably pass through Earth’s orbit, too,likely destroying almost everything
we’ve ever built. The people on Mars wouldn’t be much better
off, either. Mars will never fall into the Sun, but it
will 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 outer
solar system may have it pretty good. Jupiter’s moon Europa and Saturn’s moon
Enceladus are both ice-covered today,but they’ll heat up as the Sun expands and will
eventually 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 as
little 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 white
dwarf star surrounded by a big, cloudy nebula. Comparatively speaking, white dwarfs don’t
emanate 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’s
no usable energy. So any civilization that’s still around
will have to move on. By this point, though, we’ll probably just
fold our Dyson spheres into overhead compartmentsand head off to colonize some other planetary
system. Because, hey, if we haven’t figured out
interstellar travel in seven billion years,well, we’ll have a problem. But let’s assume we figure it out, and don’t
spend 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 will
likely outlive the Sun,and it already has a potentially-habitable planet. But since red dwarfs also emit some seriously
dangerous 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 other
options. 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 naturally
get rearranged over billions of years,so Proxima Centauri might not be our closest
neighbor anymore. Also, and maybe more importantly, the Milky
Way won’t exactly be a thing in seven billion years. It will probably collide with the Andromeda
Galaxyeven before the Sun expands into the inner solar system. Or, at the very least, they’ll pass close
enough to each other to cause some chaos. Thankfully, there’s almost no chance of
stars actually smashing into each other,since stars are just too spread out. But the collision will make long-term wayfinding
tricky. Stars will be thrown all over the place while
the new galaxy, known as Milkomeda,takes shape over billions of years. Yes, that is the real proposed nickname, and
no, I don’t support it. So maybe the next star we’ll go to hasn’t
been discovered yet, or born. And, even if we do have the technology to
leave the solar system,we’ll have to watch out for the dangers of interstellar space. For example, we’ll have to keep an eye out
for 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 could
easily wipe us out mid-journey. But if we do learn to safely travel to new
stars,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 lot
of options. But even though trillions of years is an unimaginably
long time, it’s not forever. Eventually, all the Sun-like stars in the
universe will wink out, one after another,and there won’t be enough big clouds of
hydrogen-rich gas left to replace them. But even then, that won’t be the end of
humanity. 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, like
our ancestors huddled around their flickering campfires. We would have to find a way to live with the
violent solar flares, though. Or if nothing else, we would have to find
a way to harness the red dwarf’s energywithout being in range of those flares. But assuming we figure that out, we’ll be
able to stay alive long into the future. Eventually, though, even those stars will
die, along with any remnants like white dwarfs. And finally, the universe will be black. At this point, our only decent source of energy
will 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’ll
need 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 be
hard for them to find enough fuel. There will always be the odd proton or dead
planet gliding through the vastness of empty spacethat we could somehow harness resources
or energy from. But just about everything else is eventually
going into a black hole. Fortunately, it will take a while for black
holes to vacuum the universe,and that’s putting it lightly. For you fans of metric prefixes, astronomers
estimate that it will be about a billion yottayearsbefore there’s pretty much nothing out there
but 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 long
time. 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 all
life. But if they’re wrong, physicists and mathematicians
have 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 energy
from the black hole itself. The exact mechanism for how it works is pretty
complicated, and at the end of the day,no one is totally sure if you could power a civilization
this 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 discovery
that black holes very, very slowly radiate energyin a process now known as Hawking radiation. Hawking radiation is incredibly weak for any
reasonably 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 black
holes to slowly shrink. And after almost a googol years, that’s
a 1 with one hundred zeros after it,even the biggest black holes in the universe will
evaporate due to Hawking radiation. After that, it’s hard to imagine any kind
of 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 tiniest
glimmer of hope. In 1979, the physicist Freeman Dyson, the
same 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 or
do something,and when it’s sleeping it does essentially nothing. Dyson was able to show that by sleeping for
longer and longer between each pair of thoughts,the organism could live an infinite amount
of time, but only ever use a tiny bit of energy. So with a big enough battery, this thing could
last 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 sooner
than trillions of years from now. So maybe we could become, or even choose to
become,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 lived
long enough. But, hey, we have a long time to sort out
those decisions. In the meantime, the best thing we can do
is keep taking care of the planet we have,so we can make the most of the next 800 million
years. 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 of
SciShow Space!If you’d like to see us do longer episodes
on other topics, let us know in the comments!And as always, if you want to keep up with
our latest episodes,you can go to youtube. com/scishowspace
and subscribe.

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