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Doomsday scenarios are a lot of fun in science fiction,
not so much in reality, which is tough
because global catastrophes happen.
We don't know what or when the next will be.
So how do we survive the next end of the world?
Most of life on Earth is wiped out on a pretty regular basis.
You probably already know about the Cretaceous-Paleogene event,
sometimes also called the Cretaceous-Tertiary, or K-T,
event.
It killed the dinosaurs.
In that case, we're pretty sure that a giant asteroid or comet
was the culprit, slamming into the Chicxulub peninsula
in modern Mexico.
The resulting global firestorms, followed by severe climate
change, wiped out up to 3/4 of all animal and plant species
and signaled the end of the 80-million-year-long Cretaceous
period.
We already talked a bit about the inevitability
of giant impacts in the future and what we
might do to protect ourselves.
But impactors are not the only existential threat
to life on Earth.
There have been at least five mass extinctions
over the past 500 million years.
We see them written plain as day in the fossil record,
especially in the sudden drops in diversity
of fossil sea life in deep cores drilled from the ocean floor.
Some of these events were probably
caused by giant space rocks.
But others may have been due to massive bursts of volcanism,
leaps in evolution overturning the biosphere's equilibrium,
or even nearby exploding stars.
The regularity of these events, every 100 million years or so,
tells us that more will come.
Some may not be so easy to deal with as an asteroid impact.
It's time to us what we need to do in order to survive
the next end of the world.
You know, what?
Finding the answer is a big responsibility,
possibly even too big for spacetime alone to handle.
What we really need is a world-renowned imaginer
of possible futures, someone with a physics degree
and recent expertise in rescuing humanity
from doomsday scenarios.
We need Neal Stephenson.
Oh, hey Neal.
Thanks for miraculously appearing.
Good to be here.
OK, Neal.
We're trying to save humanity here.
By happy coincidence, your recent-- and frankly,
quite riveting-- book "Seveneves"
explores our prospects in the event
of horrendous global catastrophe.
You know what?
You say it in the first line of the book, so it's no spoiler.
The moon explodes.
The resulting inconveniences have humanity
scrambling for survival.
Now you're on record as saying that this particular event
isn't necessarily plausible.
But would you say there are other threats that we
should be concerned about?
That is absolutely the case.
So the most obvious example would be just a big asteroid
coming in and striking the Earth on short notice, which
would be-- could be as destructive, or even more
destructive, than what's in my book.
In "Seveneves," the nature of the disaster
is such that the human race gets a couple of years
during which to prepare for what is going to come.
But in the case of a big asteroid impact
or a nearby supernova, it could come with so little warning
that we might not have time to do much about it.
OK.
So lead time is important.
And one of the coolest concepts in "Seveneves"
is that of the space ark, a vessel designed
to support potentially many generations of people
off-planet, insurance against extinction.
This sounds hard.
How much lead time would we really need
to build this thing, assuming we started right now?
Well, I think if everyone in the world
got involved behind it that we can
do a heck of a lot in a couple of years.
In the book that I wrote, in "Seveneves,"
two years is the span of time that people
have in which to do something.
And it's not quite enough to really do a terrific job of it,
but it's enough to put a survivable ark into space.
Nice to know we could actually do something that quickly.
But as you say, we might not even have that much warning.
On the other hand, given that we know
that some of these catastrophes will happen eventually,
in a way we've already been given the lead time.
We just don't know what the catastrophe will be
or how long we have.
So what should we do?
In the ideal situation where we could really
plan these things out and come up
with a totally engineered scheme for insuring our survival,
we'd have to have eggs in a lot of different baskets.
We'd have to have some places that were deeply
shielded from radiation in case it was, say, a gamma ray burst.
We'd have to have facilities that
were off-planet in the case of something that
struck the Earth.
And so on and so forth.
OK, Neal, the book is great.
And on top of today's tips on extinction survival, in general
you're getting us thinking about this extremely important stuff.
I think you've secured your place on the ark--
Oh, thank you.
MATT O'DOWD: If it comes to that.
Well, let's hope it doesn't.
Thanks for having me on.
Bon voyage, Neal.
So there we have it.
There are diverse threats.
Space is trying to kill us, the Earth is trying to kill us,
and at the moment we are trying to kill us.
Each threat requires a different approach to survival.
Ultimately, our prospects depend on how much warning we have.
Let's look at the possible scenarios.
Big space rock.
This is the biggest threat from space itself.
Any asteroid or comet bigger than a few kilometers
diameter has the potential to cause extreme climate change
and mass extinction.
However, we're also in the best shape here.
In collaboration with international search programs,
NASA's Near-Earth Object Program has located 90% of objects
larger than one kilometer in diameter that
crossed Earth's orbit.
None are going to hit us any time soon.
That said, smaller rocks can still
have a devastating, albeit not-species-threatening,
effect.
And we need to expand our detection programs
to find all of these and to be really
100% sure about the big ones.
Most of the other cataclysms that
may have caused previous mass extinctions
will probably give us at least some warning
and are somewhat easier to see coming than an asteroid.
For example, massive volcanism doesn't just happen.
The biggest threat right now is the Yellowstone supervolcano,
whose eruption would cause devastation
across the United States.
But we're monitoring its activity
and we know that it's not a current threat.
Nor would it be an extinction-level threat anyway.
Anything bigger would be even more monitorable.
But then you've got to ask, what about future generations?
Do we trust them to keep a constant watch on the heavens,
on global volcanic activity, and on potential threats
from the biosphere?
It may be a bit optimistic to assume
that out technological progress and vigilance will never
be interrupted for the rest of ever.
It only takes a couple of lazy generations
to miss that big asteroid.
And then kapow.
That's why people like Neal Stephenson and Elon Musk
speak against having all our eggs in one basket.
If we want to last millions of years,
we may need to become interplanetary.
Colonies on Mars, Venus, the moon,
and in artificial habitations-- space arks--
are excellent insurance against global annihilation.
Multiple independent bases for humanity
are also powerful safeguards against our own inclination
to destroy our own world.
But there is one threat that no settlement
on any planetary surface or space hotel in the solar system
can protect us from-- that's an exploding star.
A supernova explosion within 30 light years
would destroy the ozone layer, leading
to a horrible hard ultraviolet bath and the worst sunburn
ever.
It would ionize the upper atmosphere,
resulting in some unfortunate chemistry.
For example, a huge amount of smoggy nitrogen oxide
would blanket the planet, causing a supernova winter.
Fortunately, we know for sure that there
are no stars ready to go supernova
within any dangerous distance.
But what about gamma ray bursts?
When a very massive star goes supernova,
the resulting collapse of the core
into a neutron star, or black hole,
can produce these insanely powerful jets
of high-energy radiation, powerful enough
to do the same damage as a nearby supernova,
but from 6,500 light years away.
Now we'd have to be unlucky enough to be
in the path of the jet.
But it's estimated that this happens
once every billion years or so.
This is one hypothesis for the mess extinction event
that ended the Ordovician period 450 million years ago.
There's currently at least one star
within the danger zone that could produce a gamma ray
burst.
And we wouldn't know it was coming until it hit us.
No planetary surface or space ark in the solar system
would be safe from a supernova or a gamma ray burst.
Against these, it seems we have two options.
If we want really long-term survival for humanity-- one,
build deep underground arks, or better, underground cities,
and actually keep them occupied permanently,
because we may not know when the next gamma ray burst is coming.
Or two, get the hell out of the solar system
and start colonizing the galaxy beyond the 30-light-year range
of a supernova and beyond the width of a typical gamma ray
burst death beam.
But interstellar travel is hard.
Look, we talk about it here.
Is it too hard to be worth it for the sake of some
not-even-quite-human-anymore descendants millions of years
from now?
Let me know what you think in the comments.
And also, be sure to let me know if you
have any bright ideas for extinction-proofing humanity.
Best answers get a spot on the ark.
See you next time on "Space Time."
Last week we talked about the spectacular weirdness
of the single particle double-slit experiments.
Let's get to your questions.
AFastudiousCuber asks, how can something
be "fundamentally" random?
Well, Einstein would say they can't-- God, dice, nature,
et cetera.
But this is the interpretation of Bohr
and is fundamental to the Copenhagen Interpretation.
That suggests that the wave function
is nothing more than a distribution of probabilities,
and that when the wave function collapses,
the properties of the resulting particle
are picked randomly from that probability distribution.
It's a non-deterministic interpretation.
Any deterministic interpretation requires that the wave function
conceal what we call hidden variables, that
may change over time and space according to the wave function,
but that at any one instant are real.
The issue with these hidden variable ideas
is that they require instantaneous communication
across the wave function, or between entangled particle
pairs, in order to satisfy experimental results.
However, that so-called non-locality
may be preferable to the frankly slightly unhinged metaphysics
of the Copenhagen and other non-physical interpretations.
vhsjpdfg inquires after the wave functions and interference
patterns for massive objects.
Well, wave functions for macroscopic objects
are incredibly complicated because they're comprised
of countless quantum particles.
You can define a theoretical wavelength
of a macroscopic object's wave function--
it's the de Broglie wavelength, and it's very, very small.
You could theoretically cause double-slit interference
with a macroscopic object, but to do
so you'd need slits whose separation is
similar to their de Broglie wavelength.
And given that this is 100 times smaller
than the Planck length for anything within a human's mass,
getting double-slit interference for something truly macroscopic
is probably genuinely impossible.
Some of you wondered why we didn't
talk about what happens when you try
to measure which slit the particle went through
or talk about quantum eraser.
Uh, yeah, we did, next week.
Oh, sorry, causality.
Yeah, we'll get to it next week.
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