Daniel and Kelly’s Extraordinary Universe - Can humans survive interstellar travel?
Episode Date: June 12, 2025Daniel and Kelly talk about how to keep humans healthy and happy during interstellar voyages. See omnystudio.com/listener for privacy information....
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Imagine a future 100, maybe 200 years from now.
In-space manufacturing has come a long way, and we can now build colossal structures
using resources collected from the moon and the asteroids.
First interstellar ship has been built and is getting loaded up with supplies for a long trip to Alpha Centauri.
It's now time to pick the crew who will be the ambassadors for humanity should we meet intelligent life in the neighboring solar system.
How many people will we send?
How should we pick them?
What dangers will they face en route and what will their lives be like during this journey?
In our last episode, we talked about the rockets that could carry us to distant stars.
Today, we're going to talk about the squishier side of things,
focusing on some of the human stuff you'd have to deal with on an interstellar journey.
Welcome to Daniel and Kelly's Extraordinary Universe.
Hi, I'm Daniel. I'm a particle physicist,
and the longest flight I've ever taken,
was 14 hours.
Hi, I'm Kelly Weiner-Smith.
I study parasites in space, and I
think the longest flight I've taken was 12.
I've been down to Brazil. I haven't
really kept track of how long my flights were.
Where were you going? I went to an absolutely
ridiculous slash amazing boondoggle
conference in Fiji
on the island of Morea, where
the University of California has a research
station, and we were there to talk about dark
matter, of course.
So I brought my daughter, and we did a lot of
snorkeling and hiking, and we
rode horseback of the mountains and tried to keep the horses from eating pineapple plants and
it was an amazing time. But wow, the flight was long. What made it a boondoggle? Why do you need
to go to a tropical island to talk about dark matter? You don't. That's what makes it a boondoggle.
Yeah. I got to be honest, ecology has a lot of that too. It's like, why do you need to go to the
glorious rainforest to answer questions about frogs when you've got frogs in the U.S.? But I get it.
We like go into beautiful places. Yeah, it's one of the perks of being a scientist.
is getting to travel to weird, random places to meet with your colleagues.
That's true. That's true. I love getting to see new places. I often get invited to places that I never
actually really wanted to go to. But once I get invited, I'm like, yeah, I want to go to Slovakia.
And I love Slovakia. Pratislava was beautiful.
Well, what's your experience like on these long flights? Because I always feel like, oh, 14 hours,
no big deal. I'll just watch a few movies. And then like two movies in, I'm like, wow, get me off this plane.
and then like four movies in
I'm going to kill myself
and then by the time I land I'm like
hmm that wasn't so bad
I hate it
I have a very similar experience
I can't sleep I try to sleep I can't sleep
I'm not comfortable
every once in a while I'll get lucky
and there'll be no one else in the row
and I can just like lay down
and at least then I feel kind of rest-ish
or restoid
I know I hate it too
and then I always feel kind of angry
at the people in first class
because they've got like a much nicer setup.
But, you know, what are you going to do?
You're not going to spend $10,000 for that flight.
That's right.
That doesn't seem worth it.
Nope.
But if I was an astronaut and I was going to the moon or to Mars or to Alpha Centauri,
I might want the engineers to build in a seat that can fully recline.
What do you think?
Heck, yes.
You do have to have a completely different mindset to really enjoy super long trips.
Like Jim Lovell and Frank Borman were on a Gemini trip around the Earth.
And I think they were up there for something like two weeks.
And it was a really tiny space.
And at least on airplanes, like, yeah, the bathroom is small.
It's super inconvenient.
I hate it.
But it's got a door.
And the Gem and I didn't.
And so Frank Borman tried to go all 12 days without having a bowel movement.
And I think he made it like eight days or something.
And then he was like, Jim, I can't wait anymore.
I'm about to make a delivery.
Oh, gosh.
Yeah.
So anyway, it could be worse.
So you're saying that the cutting edge super distant travel
is less convenient and less comfortable
than like economy flights across the country
that doesn't make any sense to me.
Well, you know, you've got to pay
for all of the space that you send up there
and it's super expensive.
And I mean, let's be honest,
anybody who's told you get to go to space
is going to put up with whatever you give them.
And so they're definitely going to go.
But there was a recent SpaceX trip
where there were complaints about the bathroom also.
I think it was the dragon capsule.
Restrooms in space are just hard to pull off well.
I think this is another case of like
my over-optimistic rose-colored glasses
when it comes to space travel, imagining that the problems we have with, like,
airplane flights are not going to be even worse on space trips.
They're somehow all going to be comfortable and get along, and the food is going to be
amazing like it is on Star Trek, right?
That's why I was excited that today we're going to dig into, like, the reality of a potential
interstellar trip.
What's it going to be like?
Will there be doors on the bathrooms?
How far back will the seats recline?
And will they have anything besides peanuts and pretzels?
Well, let's dig in and find out.
So this is part two of our interstellar travel series.
We talked about the kinds of rockets that get you to space in the last episode.
And today we're talking about the squishy human side of things.
And so we asked our listeners, can humans survive interstellar travel?
Why or why not?
Here's what they had to say.
Humans could survive interstellar travel with terraform spaceships.
And over multiple generations, they could get somewhere interesting.
There are so many unknown issues with closed ecosystems in order to produce the food that we need in the form of plants, etc.,
that I'm too sure that we've solved all the problems necessary in order to have a long-duration interstellar travel.
With our current technology, I don't think it's possible, but maybe with advances in propulsion and radiation shielding and artificial gravity from propulsion,
that might be possible.
One human couldn't survive
because we haven't sorted suspended animation yet.
But if you're talking about generations of humans,
as human we've sorted all the problems
of sustaining reproduction in nutrition and health,
I wonder whether the risks of the dangers posed by cosmic rays
will actually be less in deep space.
We'd only then have to worry about the problem of re-entry
into the new stellar system.
I think generally it's possible,
but you have the problem that when you go fast,
you have cosmic rays that are really high energy,
and if you go slow, it takes forever.
So it's a trade-off and you lose in both situations.
It depends on how far away the other star is.
If the star we're trying to get to
is the one that we're going to share UR clouds with
in about a million years or so,
then that's much more achievable than a star on the other side of our galaxy.
I say no, because the first humans who leave Earth going to interstellar space will not be alive
because it takes approximately 22 to 25,000 years to exit our solar system.
And that opens up the question about children in space to continue the journey
because the adults will begin the journey will not live to exit our solar system.
So no.
If we allow for human reproduction on route, which is a big if,
humans would encounter significant survival challenges,
not the least of which is that our physiology is ill-equipped to handle zero gravity
and excessive radiation exposure.
And in the vein of we do not know what we do not know, there are liking other factors that
terrestrial living either provides for us or protects us from that we would fatefully and tragically
encounter on the interstellar voyage.
We can imagine traveling to other solar systems, but can we deal with all the questions,
radiation, food, power sources, generation ships?
We just don't know enough at this point.
Those are super fun answers, and if you find yourself speaking back to the podcast with
your own answers, then send us those answers and we'll put them on the pod so that everyone
else can hear what you have to say. Just write to us to questions at danielandkelly.com. And we
will share your insights with the world. Looking forward to hearing from you. And we've been
very excited to have more women sharing their responses lately. So let's keep that up. Go women.
Well, do you think our listeners also have rose colored glasses and they're underestimating the
difficulty of traveling to space or do you think they have a realistic sense? We have a really nice
range of people who are super optimistic, and I would maybe say not quite reasonably so. And then
people who are maybe a bit more down on the enterprise than is necessary. We've got a lot of
variability. I think it depends a lot on the time frame that you're willing to consider for this
question. All right. Well, let's dig into the problem why space travel is so much harder than
airplane trips, or if it's just airplane trips times a thousand. Tell us what basically are the
obstacles here to traveling in safety and comfort to another solar system.
Well, as you pointed out in the last episode, space is vast.
And so if we're going to Alpha Centauri, that is four light years away.
So with current technologies, we're talking about 80,000 years.
That's a lot of human generations.
That's a lot of movies to watch.
Wow.
Oh, my gosh.
Yeah.
Maybe in the next 100 years, Marvel will make enough movies to get you to Alpha Centauri.
I think there might be enough Fast and Furious movies to make it.
I'm not sure.
Oh, my God.
I would not make it to Alpha Centauri on Fast and Furious movies.
I would rather push myself out the airlock.
But all right.
No, you're missing out.
You're missing out.
Fast and Furious is fantastic because they don't take themselves seriously.
Like every movie, they have an even more ridiculous stunt.
They're like, oh, yeah, how about a space shuttle?
Okay.
How about a submarine on the ice with a torpedo?
It's ridiculous and fantastic and really creative.
I watch a lot of terrible movies.
And there's always something new in the Fast and Furious that makes me go, whoa, that was cool.
So, yeah, don't overlook them.
Okay, all right.
I'll take another look at the Fast and Furious.
Furious series. I didn't imagine I would say that phrase today, but there you go.
But I don't think we want to travel the stars fast and furious. I think it's going to be more like
slow and calm is the way to go. That's what I would like. And with no explosions or anything like
that. So you said that we could get to Alpha Centauri in 40 years if you can travel at 10% the speed
of light. So we're going to talk about a range of different options. What if you could get there
fast if the technology works out? And what if you need to get there over the course of multiple
generations. So you need to have a generational ship sometimes called an arc, and this field has a good
sense of humor. So sometimes they call the study archaeology.
Awesome.
Which I love. That is very cool.
All right. So one human thing we're going to need to overcome is this whole money situation, because
the cost of a project like this is probably going to be massively prohibitive. So you talked about
how much mass would be needed to hold the propellant, and that for chemical rockets,
the tank would have to be as big as Jupiter.
Yeah, and then you'd also need to somehow find that fuel.
Yeah, right.
Basically, you have to use Jupiter as your rocket.
Yeah, many layers of problems here.
But, you know, if you're talking about bringing humans that are awake,
you're also going to need space for recreation areas,
space for schooling, space for medical facilities, places to grow food.
The International Space Station is the most expensive human-made object ever,
and it's clocking in at about $150 billion.
And it usually holds seven people uncomfortably.
So this is going to cost a lot of money, but we're basically just going to ignore the financial side of the question?
We are. Yes. Right. So let's assume that money is no longer an object. Yay. That's right.
Humanity has decided we absolutely must do this. Okay.
What kind of problems are the humans going to encounter? As you might remember from our conversations on Mars and the moon, space has a lot of radiation that is bad for humans. It has two kinds of radiation that are not very common here on Earth, and that's galactic cosmic radiation and solar particles.
events. And these are bad for equipment and for people. And I'm kicking over to Daniel. Tell us about
galactic cosmic radiation and solar particle events. Yeah. So the sun puts out a lot of light, but it also
shoots out a lot of other stuff. You know, they're protons, they're electrons. Basically, it's just
spewing plasma. We call this the solar wind. And it's moving at high speed. So these particles are dangerous
because any one of them hits your body tears through it like a little tiny bullet. You can rip apart
DNA, you can destroy cells, it's not good. One random one, you're probably fine, but you take
enough of these, you're getting cancer. And down here on the surface of the Earth, we don't worry
about this because while the solar wind is hitting the Earth, the atmosphere protects us. It's
an enormous, very thick, very massive blanket. And the whole idea is that when you go out into space,
you no longer have that atmosphere. So you have to replicate that with shielding. Galactic cosmic rays
are a whole other question. They're basically radiation from other stuff in the galaxy, like
the combined radiation from other stars and from black holes and from other weird stuff we've
never even figured out. Like there are particles that are so high energy. There's nothing in the
universe we know of that can make particles go that fast and yet we see them. So there's like really
fascinating physics mysteries there. But from a human survival point of view, you don't want these
super duper high energy particles hitting you. Basically, space is filled with tiny bullets and you got
to go up there with a bulletproof vest. I am always so impressed by how eloquent you are when
it puts you on the spot. Bravo. So we're going to need to shield against this kind of stuff.
And it's not just a problem for human bodies. It's also a problem for our machines. Did I tell
the story on the show before about Terry Vertz and Samantha Christophoretti when the ISS had a
false alarm? Oh, tell us. All right. So you've got Terry and Samantha in space on the International
Space Station and an alarm starts going off. And Terry's not immediately sure what this alarm means,
but Samantha has memorized all the alarms. And it's an ammonia leak. And on the U.S. side, ammonia
is used to cool the space station,
but ammonia is also toxic.
So the protocol for what you do when there's an ammonia leak
is you run over to the Russian side,
you close the first hatch, you take off your clothes,
you close the second hatch with you on the other side.
You take off your clothes?
Why do you have to take off your clothes?
Just make it more fun and dramatic.
Well, yeah, I mean, one, sure,
but also that ammonia could cling to your clothes
and you don't wanna bring it over to the Russian side.
So you gotta hope the Russians have some undies
they'll be willing to loan you.
And so they ran over.
They closed the first hatch, but they didn't smell the ammonia.
And this is an important sort of lesson about how humans respond.
Like, it sort of doesn't matter what protocols you put in a place when one human is looking at another human and they're both like, am I going to really see you naked right now?
They decided to just skip that step.
And they went in with all of their clothes over to the Russian module.
Interesting.
It did turn out it was a false alarm.
And the reason you go to the Russian module is because they use glycol to cool their side, which is not as toxic.
And so if the leak was coming from anywhere, it was the U.S. side.
Anyway, it was later determined that the most likely reason that this alarm got switched on
was because the computer had been hit with galactic cosmic radiation, which messed with the equipment
and started setting off alarms.
You could have cancer, cognitive declines, your machines could start breaking down.
So this is a problem we need to take seriously.
Yeah, this is actually really fascinating from an engineering point of view.
You know, what's happening is that these particles are passing through your equipment.
sensitive bits of it are mostly made out of silicon
and when a high energy particle passes through
it leaves a trail of ions
you know it like kicks electrons and leaves holes
and this is how these things work also right
they like separate the holes and the electrons
and so all of this equipment can get like a false bit
like you can have a zero in your memory
and then it can turn it to a one or something
and so these kind of cosmic ray bit flips
are a real concern and like massive data centers
worry about this also but they have a lot of error correction
and so they have like duplication
and cross-checking to basically remove this.
So you can either have a lot of duplication
or you can try to make it radiation hard by shielding it.
Even folks who are using diamonds instead of silicon
because diamond has a lot of the same electrical properties,
but it's radiation hard.
You can grow diamond.
It's much more expensive and there's not a huge industry for this.
But like at the Large Hadron Collider,
there's very intense radiation near all of our sensitive detectors.
So every couple of years, we've got to pull it out
and swap in a new one because it's basically ruined.
Wow.
So yeah, electronics are very sensitive.
sensitive to high levels of radiation. And if you are relying on your electronics to keep you
alive and an 80,000 year journey in all of your grandkids and great grandkids, then yeah, you
want those things to work. Yeah. And so the shielding could come in the form of things like
water. Like you could store your water supply on the outside. Would that help with galactic cosmic
radiation too, Daniel? Yeah, with various kinds of it. Yeah. Okay. But mostly. You basically just
need high Z mass. Like you need atoms with a lot of protons and neutrons between you and the radiation.
Got it. I've also seen proposals for scraping the regolith off the moon and patting your interstellar ship with it. That would be complicated, but it's a solution.
That would be pretty cool because then your ship looks like a rock, you know? Yeah.
You're like floating through space, like masquerading as an asteroid or something.
Well, another complicated problem we're going to need to solve is what do you do about no gravity?
Right, but the takeaway from the shielding is an important one, right? It makes our ship big and massive and heavy and that makes it expensive, right?
But fortunately, money is no hurdle for us, so cool.
That's right.
In-space manufacturing might help with this a lot.
So, you know, you could, like I mentioned, go get the regolith from the surface of the moon,
but also you could go to the asteroids and extract water from the asteroids,
and that way you don't have to pay to boost it from Earth.
But one way or another, it's going to be an expensive, massive project.
Yeah.
All right.
So problem number one is radiation.
Yes.
And problem number two is going to make the design of our vehicle even more complicated.
And problem number two is that there's no gravity in deep space.
So we know from astronauts on the International Space Station and the space stations that came before
that when they are essentially in freefall and feeling the equivalent of no gravity, that their bones start
breaking down, their muscles start breaking down, and the gravity on Earth and the fact that we're
constantly moving around and submitting our bones and muscles to gravity and then the pressure
of our bodies as we run around, that makes our bones and muscles strong. That's like a cue our
bodies need to keep these things toned. Without those cues, they just start to decay because you're not
using them. So bodies start falling apart. Additionally, we see declines in vision, and we think that's
because the fluids in our bodies without gravity to pull them down, sort of accumulate near our heads
and change the shape of our eyes. There's also some evidence that there could be some cognitive
declines. Basically, we're going to want some gravity when we're living out our lives on a ship.
And folks out there might be thinking, well, you know, we're adapted to life on Earth, but if we
spend it long enough in space, maybe our bodies are just going to adapt. Maybe we don't need those bones
and those muscles because, hey, we're all floating around to the blue Danube anyway, right?
Why do we care about degradation of our bones and our muscles if we're just floating in space?
Yeah, so that's a great question.
We don't actually know that we could survive long term.
So the longest anyone has ever been in space, I think, is 437 days.
That was Valeri Polikov.
So we don't even have, like, more than a year and a half of consecutive time in space.
We know that astronauts lose something like 1% of the density of their hip bone per month.
And we don't know if that tapers off eventually, but if you imagine trying to have babies in space.
Hold on. Wait, I'm going to imagine it. Hold on. Oh, yeah. That is such a guy response. The gooiness is not a problem, man.
But now you're in space. You have, like, weird balls of goo. It's like this.
Oh, imagine trying to do a C-section in space with like the blood floating around your head. Anyway, unpleasant.
Or imagine like a diaper explosion, you know, like loss of containment in space. I don't know about that.
Loss of containment.
You've had that experience.
You know what I'm talking about.
We've all had the like transatlantic flight with loss of containment of the diaper.
Like, ooh.
No, I did.
Right when a plane was taking off, my daughter had a blowout on my lap.
And we couldn't get up for 30 minutes.
And oh, man, nobody liked me.
And I brought a change of clothes for her, but not for me.
But she sat on my lap.
Anyway, all right, these problems only get more difficult in space.
So we don't know, for example, that women's hips will be able to survive childbirth.
And we just generally don't know if you can survive a lifetime.
But maybe you can.
So let's say that you can.
Let's say that not only can you survive, but you can also go through reproduction in zero gravity,
which, again, I think is highly unlikely, but we don't have a lot of good science for that.
There's a lot of reasons why you'd want at least a little bit of gravity.
And, you know, a lot of them have to do with things like using the restroom.
So we talked a little bit about how that's unpleasant at the start of the show.
My gooey imagination is filling in the details for me.
Yes, thank you.
Oh, yeah.
You're really into gooey today.
It's only going to go downhill from here.
When I was researching a city on Mars, every space vehicle that I read about had a story about
escapees where the escapees were like bits of feces that kind of floated out.
It's just hard to keep things clean.
Everything is more of a pain in the rear end.
If you have just a little bit of gravity, surgery gets easier, restrooms get easier, farming gets
easier.
We're almost certainly going to need at least a little bit of gravity just to like hold our
stuff down and make our lives easy.
And if you hope that your descendants or whoever is arriving in the distant solar system is going to be able to get off the ship and walk around on this new alien planet, they're going to have to have some bones and muscles, right?
So it makes sense to maintain that capacity on the trip.
Absolutely.
So not only are we going to have this massive object, but this massive object needs to have at least some areas that are spinning to create artificial gravity so that you've got some of that force keeping your body strong or helping, you know, the brown trout swim down the river in the right direction.
All right. So we've talked about radiation. And that might be a solvable problem with enough shielding. And we talked about gravity might be a solvable problem if we have acceleration or something spinning or something like that. So so far I'm feeling kind of optimistic about how our kids, kids, kids, kids, kids might be able to walk off the ship and stand on a planet around Alpha Centauri. So let's take a break. And when we come back, Kelly's going to tell us about how that's all an impossible dream.
I'm not trying to be negative today.
The facts that we're going against you, though.
Get fired up, y'all.
Season two of Good Game with Sarah Spain is underway.
We just welcomed one of my favorite people and an incomparable soccer icon,
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The guest list is absolutely stacked.
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I feel like the overall consensus was like, people were just obsessed with this,
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I don't know what you think is for her.
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Well, I don't even know if they're staying together, Sarah.
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All right.
back and we're talking about whether we could survive an interstellar trip, whether it's a good
idea to build an arc where people can have their babies and their babies, babies, babies can one
day visit an alien solar system or whether these problems are insurmountable. We've talked about
radiation, we've talked about money, we've talked about gravity. Now, Kelly, tell us about
knowledge. Why do we need to make sure knowledge doesn't decay along the way? Well, we've already
talked about how difficult it is to store knowledge in computers, or at least how careful you need
to be to protect it from radiation.
But another problem you're going to have
is that the farther you get from Earth,
the longer the communication delay.
So if people are living on Mars, for example,
there's a minimum three minute communication delay
just because it takes a long time for the message to go
from Mars to Earth and then from Earth to Mars
when you're ready to respond.
I think that's really fascinating because the Earth is not small,
but it's small compared to the speed of light.
So you can have what feels like an instantaneous phone call
with somebody in Tokyo, right?
And the lag is imperceptible.
But then once you go to the moon or to Mars, like now it really ruins what it feels like to have a conversation, right?
You can like ask the question.
You've got to wait like six minutes to hear the answer.
That's like not a conversation.
It's more like writing letters back and forth.
It is.
Yeah.
I mean, I think even on the moon, you can have a close to real time conversation, maybe a little bit of an awkward delay.
But when you get to Mars, it's a minimum of three minutes, a maximum of something like 20 to 22 minutes.
But when you're starting to get to Alpha Centauri, it's just going to keep extending, extending,
extending until at some point you're not communicating anymore. So for example, if you like need
IT support, you're like, hey, my MacBook is crashing. You don't want to wait four years for the answer
to be like, turn it on and off again. That's right. It's not helpful anymore at that point. You
probably figured it out. Hope so. Or you're all dead. Yeah. And I mean, that also means at some point
you're going to stop benefiting from any new knowledge that is created on Earth because it's going
to be hard to get it to you and probably at some point impossible to get it to you. But it also means
if somebody has an illness that you don't have anyone on the ship who's an expert in that
you're on your own, the surgical procedure that you're doing. You better hope you downloaded a good
YouTube video for it because nobody's going to walk you through it in real time. You really are
on your own. Yeah, you can't look things up unless you bring like all of human knowledge with you
somehow, download Wikipedia onto your ship's computers. I mean, that seems like it could be a good
idea anyway, doesn't it? No, absolutely. Yes. For both entertainment purposes and, you know, knowledge
purposes, you should bring as much information with you as you can. That would absolutely be worth
the storage space, in my opinion. What do you think takes more storage space like Wikipedia or
all the Fast and Furious movies? Are you taking Wikipedia in every language? Oh, good question.
I don't know. We better, though. Including the Scottish one, though the Scottish one turns out to be
totally made up. There's no Scottish, wait, what? There is a Scottish Wikipedia, but it's mostly
written by a guy who just invented what he thought Scottish should sound like. Oh my God. Yeah, it's bad.
I am regularly amazed by the amount of time that humans are willing to put into messing with
each other. That must have taken a long time.
Oh, yeah. He thought he was doing something good. No, he was like, hey, nobody else has done this.
And I know how to do it, right? So the best intentions. Anyway, you should go read that story. It's hilarious.
Okay. But anyway, what is the impediment though to just bringing all of human knowledge with us and saying,
like, all right, we're going to be cut off from the mothership or we're not going to get the latest
advancements in quantum computing at the same moment? Maybe they can beam them
to us as they come in, so we're a little behind. But why can't we just bring it all with us?
You can't bring a ton of knowledge with you. But, you know, if you sat me down next to a bunch
of textbooks on quantum computing, I could do nothing with that information. I mean, maybe after
a couple generations I could. But this ties into the next problem that we're going to deal with,
which is you have to pick which humans you send with you and what kind of knowledge they have
and how many of them you get. But I'm guessing you had another limitation in mind. Was it how
many hard drives you'd have to bring? Or should I stop trying to guess what you're thinking?
No, I think that your point is valid that you can bring a bunch of knowledge, but just having that
knowledge isn't enough. You need people who can digest it and people who can put it to work. So you're
essentially saying, make sure you bring enough physicists on board. You know, you guys are good
for a lot of stuff. I don't know how many practical problems. Also, you have to worry about,
like, hygiene.
On an interstellar trip, but you should bring a couple cleanly physicists,
I think the real problem here is that you need a breadth of knowledge, right?
And so there's a question of like, what is the minimum size of a community that has enough technical knowledge and expertise to basically run independently of Earth?
Because it's not like two people.
It's not 10 people.
And I'm guessing that's where you're going to go next is like how big a community do you need, not just to have the knowledge, but also to like have healthy babies.
Yeah.
So I'm going to be focusing on the healthy babies part.
but this occupation's part is really important and is very hard to have a concrete answer for
because it depends on what you're willing to live without.
I heard once that there's something like 100,000 medical specialties, and that number
seems unreasonably large, but let's even say there's like a thousand medical specialties.
Okay.
You'd probably want one person from each of those specialties or like duplicates of all of those
people, but you also need janitors and plumbers and engineers and farmers and there's just
so many different kinds of people you would like to have there, but you might not be able to
have everyone you want there. Like, you know, you probably couldn't have three of every medical
specialist if there are 100,000 kinds. So you're going to have to sort of pick and choose and
decide what you're willing to do without. I think there's also an interesting interplay there
between are you just trying to survive the trip or are you trying to bring the seeds of a future
civilization with you? Because think about just like pencils. Okay, you're going to need a lot of
pencils on an 80,000 year journey, maybe you could just stock a bunch of pencils, right?
Bring a bunch of pencils or like light bulbs or whatever.
And you might be able to survive the journey and not use of all the light bulbs and pencils.
But once you get there, you might still want light bulbs and pencils in a thousand years.
And so what you need to do is bring like the manufacturing capacity to produce all of the goodies
that we expect for a certain quality of life or to severely restrict the goodies that you're
expecting these people to live without. So you really need to bring your entire manufacturing
supply chain and pipeline with you if you're going to cede a civilization on the other end of this,
not just like visit Alpha Centauri and turn around and come back. Yeah. So let's jump for a second
to a conversation about what you bring with you. So yeah, you would want to maybe bring all the
manufacturing stuff to make pencils. Additionally, we should have invited Katrina on the show briefly
because you're going to want to make sure, for example, you have a diversity of microbes. But how do you
know which ones to bring? You just bring all the poop on.
earth. That's the easy solution. That's what she would say. Okay, but a lot of that poop on earth has
parasites. And while I don't want to live in a world without interesting parasites to study,
I think most people would, although I prefer parasites that aren't infecting people. But anyway,
so yeah, you've got to figure out what kind of microbes. And that requires knowledge that we don't
necessarily even have yet. What kind of microbes do you want to bring with you? But you'll also
need to bring medicine. But medicine expires and 80,000 years is a long time. So you're probably
going to want to bring the equipment that you need to make more medicine. And there are some
designs for 3D printers that will print medicine on demand, but you need to make sure you've got
the raw materials for that. Yeah, exactly. It feels like you're cutting the very tip off a very
complex pyramid of manufacturing and civilization, and it's going to crumble eventually. It feels
very difficult to maintain the same level of civilization if you're not bringing the whole
pyramid with you. And it turns out the pyramid is huge, right? Just to make a pencil requires
an enormous manufacturing capacity, lots of different specialties.
global supply chains are amazing. We rely on them for so many things. That pencil takes a million
people thing came from somewhere. And one of these days I want to figure out, was it a Milton Friedman
essay? I don't know. I hope it wasn't Malcolm Gladwell because you can't trust anything in those
books. We're on the record now. All right, let's go ahead and just accept that there's a lot of
stuff that you're going to need to bring if you want to keep your standard of living reasonably high.
And also a lot of stuff that you're going to need to bring or be able to build so that you can
replace parts of your ship as they break down over time in the very harsh environment of
space. So now let's jump to biology. The good part. Let's get to the good part.
All right. Are we talking about parasites? Minimum number of parasites to bring the
entire. Unfortunately, no. I couldn't figure out a way to really shoehorn parasites in more than
once. I'm ready for it, though. When you're ringing up, I'm ready for it. Okay, good.
But how big a group do we need, like biologically, to keep our community healthy and to make
sure we don't like all suffer from some genetic defect that like one guy has on board how big a
population do we need yeah this is a really difficult question so we don't necessarily know what
kind of diversity we need so it would be great to have people for example that are resistant to
radiation in case we can't shield all of it but we don't really know what genes are important for
that at this point so the more diversity you can have the better you also want people who are not
closely related to each other because we all have some genes that are carrying the code for
negative traits. So, you know, it could be sickle cell anemia or something like that, where
if you get two versions of the gene that caused the disease, you're in a lot more trouble
than if you just have one. I wonder from an evolutionary point of view, if this is a scenario where
you actually want to be susceptible to radiation because it induces a higher mutation rate in
your babies, and that might mean that you lose a bunch because, like, they have bad mutations,
but you also might like invent some new weird like space-faring hearty human that can like,
I don't know, extrude pencils from some new orifice or something useful. I don't know.
Like is there a possibility there that more mutation might actually be beneficial?
So mutation is a mechanism through which you get more genetic diversity and some of that could be
good. I think our expectation would be statistically you'd probably get a lot more things
breaking than a lot more things resulting in pencils coming out of your nose at appropriate times
or something. And I think a lot of those mutations are going to be, you know, like causing cancer
as you're older and not necessarily resulting in like really well adapted babies. But who knows?
Who knows? All right. So I've seen a bunch of estimates for how many people you need.
And you do need to be careful about who these people are. So like, yes, we talked about you want
doctors and stuff like that. But when you're thinking about the number of people you need,
the number of people over 60, it's great to have their knowledge, great to have their help, but they're not going to be contributing to having children. So you need to think about the number of reproductively aged individuals. And you need to think a little bit about the mix of people. So if you bring, you know, 10,000 men, you better also have artificial wounds or something at that point. So you need to think about the makeup. Well, dig into that for a moment for us. Like, what is the best gender ratio? I mean, because like a woman can't be pregnant from two men simultaneously, but a man can have multiple partners.
It depends on what your goal is, and frankly, it depends on what your culture is willing to accept.
Because I think you don't want to send people into interstellar space under conditions that they would, you know, find a porrent.
Yes.
If your goal is to just have as many babies as possible and you've set up the interstellar ship to be able to scale to feed and provide oxygen for a rapidly expanding population, then you could send exclusively women who got pregnant using embryos that you sent with you.
There are ways to maximize the speed at which the population increases, but I don't necessarily know that the goal and root is going to be to increase numbers as fast as possible.
Because if you just wanted to have a lot of people, you could have just started with a lot more people.
So I think you want to find a make up where you can sustain your population numbers, and I don't necessarily know if the best way to go is 50-50.
Well, I think your point is a good one, though.
If you want your people to be happy, then you're going to have to create an environment they're going to like to live in.
And currently most people enjoy monogamous relationships or, you know, one-to-one ratios, which means you're going to need roughly a gender balance.
So I found an estimate where someone did a computer simulation and they found that you could possibly get away with 98 people if...
98,000 or 98 people?
98 individuals.
What?
If every generation they mated with whoever a computer program told them to mate with based on their genetic makeup.
Yep. So this is an interesting thought experiment for a lower bound. But if you're thinking about what humans are willing to accept, that's probably not going to work out.
For this study, how do they define success? You have like a population downstream that's healthy and doesn't have a lot of recessive traits that are hurting people?
I forget the exact details, but it was something like after five generations, would you expect the population to still persist or would they have had inbreeding problems or something like that?
Well, it's really fascinating because I've heard some of these studies that speculate the humanity might have had bottlenecks early on, you know, down to like as many as 10,000 individuals on the planet.
And here we are, you know, 8 billion people later doing pretty well.
So it's not implausible to me that you can get down to a few thousand.
Ninety-eight seems kind of crazy.
And there are plenty of people who will also point out that there are indigenous peoples living in populations of something like 100 to 500.
But what those numbers often miss is that those.
indigenous populations are often interacting with others and intermarrying. And so actually the
population that is interbreeding is much larger than the individual communities themselves.
But yeah, I've seen estimates that seem pretty reasonable that range from about 5,000 to 40,000
people of reproductive age. The 40,000 numbers seemed a little bit more realistic to me.
So it was taking into account the ability to survive five generations, even if a black plague-like
catastrophe comes along. And so this is incorporated.
Like, what if some bacteria in our gut mutate and kills 25% of us?
Like, you might have to assume that every once in why you're going to lose people.
So estimates range from 98 to about 40,000 and really depend on the assumptions you're making.
Well, keeping in mind our constraints, even if money isn't an obstacle.
Of course, in reality, it is.
And we know that size is an issue and fuel and all that stuff.
And so if what we want to do is keep the ship small, then we want to keep these numbers low.
And I was really interested in your comment about how you.
you could keep it down to around 100 if people accepted, you know, computer-assigned dating.
And I'm wondering how far we could push that?
Like, could we make it even lower if we assume some sort of advanced technology to, like,
modify your genetics or correct issues or something?
Couldn't the interaction between biology and technology really change how small we could go?
I hear a lot of engineers propose stuff like this, and it totally makes sense.
It's true it could work.
But when ideas like this come, like, head-to-head with human behavior, they tend to fall apart.
I mean, you could have five women who start the trip with a vat of freeze-dried sperm from lots of different people, and you could maybe make it.
But now you've got problems with, well, do you have enough doctors and enough engineers and enough people to work the farm?
So there's a lot of reasons why going big has a lot of benefits.
I think it's funny in the mental image of that of freeze-dried sperm.
Why wouldn't you have them in like delicate test tubes, you know, imagining like, you know, liquid nitrogen flowing over them or something.
And instead, your words give me a mental image of like a barrel of this stuff.
You started this gooey theme and I was just kind of running with it.
But you're right, they'll probably be in vials in a tube of liquid nitrogen or something like that.
Yeah, we'll treat them better.
Delicately clinking glasses and stuff like that.
That's right.
Having technology to help with reproduction and bringing along extra genetic diversity in the form of embryos,
stuff like this can really help with diversity problems.
But again, each generation you're going to have to deal with the wants and desires of the humans
who are there who are going to want to find partners that make them feel complete and who may
or may not be comfortable with being told, hey, your partner isn't as genetically diverse as you might
want. Sorry, this is what five generations and an interstellar ship does. So you are going to have
the embryo for which we provide 50% of the genetic information. And not everybody is likely to
love that. And then what do you do when people get pregnant unintentionally? Yeah, exactly. I think that's
super fascinating. And it touches on another whole area of questions of like,
You manage the people on board and what laws do you have and what punishments can you do?
Like you're shooting people out the airlock.
If they're not dating the right person, it's crazy.
But, you know, on ships, the captain's in charge and for a reason.
And so anyway, that's a whole other issue we could dig into another time of laws on board interstellar chips.
For now, let's take a break.
And when we come back, let's hear about a strategy that might make that all moot.
What if everybody just sleeps their way to Alpha Centauri?
Get fired up, y'all.
Season two of Good Game with Sarah Spain is underway.
We just welcomed one of my favorite people and an incomparable soccer icon,
Megan Rapino, to the show, and we had a blast.
We talked about her recent 40th birthday celebrations, co-hosting a podcast with her fiancée Sue Bird,
watching former teammates retire and more.
Never a dull moment with Pino.
Take a listen.
What do you miss the most about being a pro athlete?
The final.
The final.
and the locker room.
I really, really, like, you just,
you can't replicate, you can't get back.
Showing up to the locker room every morning
just to shit talk.
We've got more incredible guests
like the legendary Candace Parker
and college superstar AZ Fudd.
I mean, seriously, y'all.
The guest list is absolutely stacked for season two.
And, you know, we're always going to keep you up to speed
on all the news and happenings
around the women's sports world as well.
So make sure you listen to Good Game with Sarah Spain
on the IHeart Radio app,
Apple Podcasts or wherever you get your podcasts.
Presented by Capital One, founding partner of IHeart Women's Sports.
I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast.
Here's a clip from an upcoming conversation about exploring human potential.
I was going to schools to try to teach kids these skills and I get eye rolling from teachers
or I get students who would be like, it's easier to punch someone in the face.
When you think about emotion regulation, like you're not going to choose an adaptive strategy.
which is more effortful to use unless you think there's a good outcome as a result of it,
if it's going to be beneficial to you.
Because it's easy to say, like, go you, go blank yourself, right?
It's easy.
It's easy to just drink the extra beer.
It's easy to ignore, to suppress, seeing a colleague who's bothering you and just, like, walk the other way.
Avoidance is easier.
Ignoring is easier.
Denial is easier.
Drinking is easier.
Yelling, screaming is easy.
Complex problem solving, meditating.
You know, takes effort.
Listen to the psychology podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.
When your car is making a strange noise, no matter what it is, you can't just pretend it's not happening.
That's an interesting sound.
It's like your mental health.
If you're struggling and feeling overwhelmed, it's important to do something about it.
It can be as simple as talking to someone, or just taking a deep, calming breath to ground yourself.
Because once you start to address the problem,
You can go so much further.
The Huntsman Mental Health Institute and the Ad Council
have resources available for you at loveyourmind today.org.
We're siblings.
Like, you fight, you disagree.
It's really hard to be in a partnership.
You judge. Yeah, you judge each other.
You lead differently, and we've gotten to that edge.
Hey, I'm Simone Boyce, host to the Bright Side,
and this week I'm joined by Hollywood Power Sisters, Aaron and Sarah Foster.
They open up about navigating the judginess of Hollywood,
dealing with rejection and the pressure of running a bit.
business with your sibling. And yeah, they're spilling the tea on season two of their hit Netflix
series. Nobody wants this. I feel like the overall consensus was like, people were just obsessed
with this will, they, won't they? Like, that's the thing, right? It's just intoxicating. You want to be
able to sustain that for as many seasons, but you also have to like marry them off eventually. I don't
know what you get in season four. You'll marry them off, Aaron? Well, I don't even know if they're
staying together, Sarah. Y'all, this conversation is honest, hilarious, and everything you didn't know you needed
this week. Listen to the bright side on the iHeartRadio app, Apple Podcasts, or wherever you get your
podcasts.
All right, we're back, and we are facing all the questions for taking humans to another solar
system, radiation and gravity and breeding and knowledge, and all these things require
keeping people awake, having a functioning society on board, people sitting there munching on
their snacks and watching fast and furious. What if, Kelly, we decide not to? What if we just put
everybody out for the journey? What if we can like freeze them or hibernate them? You see this a lot
in science fiction. Is that realistic? Where is the technology now? It's not realistic with current
technology, but I wouldn't say it's absolutely impossible. You can't just put everybody to sleep as
sleep is technically defined because while you're sleeping, you still have metabolic processes
happening. You're still aging. So if you were asleep, you'd still need to have like fluids put in
through an IV. You'd need to be fed. Machines would have to roll you over. Sleeping wouldn't really
cut it. It'd be like a coma and nobody wants to be in a coma for 80,000 years. And you can't live
that long even in a coma, right? It doesn't extend your life to sleep. Right. Exactly. That's a
total non-starter. The next step up from that would be hibernation. And so hibernation, you have a
reduce temperature. You still have some metabolic stuff happening, but the metabolic activity is way
down. So like your caloric needs go way down. You need less. You're using the restroom less, stuff like
that. And there's lots of animals that hibernate. You know, you've got bears, squirrels, marmits,
prairie dogs, groundhogs. Hybernation happens a lot. But it's worth noting that, one,
hibernation doesn't keep these animals alive forever. And sometimes animals die while hibernating.
So it's not like you're 100% safe when you go into a hibernation state.
And can every animal hibernate?
I mean, bears and squirrels, they do these things themselves.
But like, I've never hibernated.
Do humans hibernate?
I would like to hibernate sometimes when it's too cold out.
But no, humans do not hibernate.
It's not clear how we would put humans into a hibernation like state.
It's tantalizing that other mammals can do it, but it doesn't necessarily mean that if we learned the right tricks,
humans could do it too.
Humans do sometimes survive being very cold, so like in a very hypothermic state.
And every once in a while, if people have particular problems, so I've read about somebody
who had rabies and they were trying to slow down the movement of rabies and give the body some
time to respond and the vaccine some time to work.
And so they essentially put the person in a very cold state to slow things down.
And people can survive, but it's not like it's great for the body and it's not like it's extending
their lifetime. So you would still end up with people dying in a hibernation state, probably.
All right. So we can't just knock people out with NyQuil. We can't just turn down the
temperature a little bit so people get cold and hibernate. What if we go even colder? What if we
like dip everyone in liquid helium and turn them into human circles? Will that help? Is that possible?
I mean, you hear about this all the time on science fiction and on The Simpsons, for example,
or Futurama. I forget which one it is.
But is this just fictional nonsense or is the science moving us in that direction?
Scientists are trying to move us in that direction. Some of them are. So there have been people who very soon after they passed away had their body cryogenically frozen in the hopes that at some point we'll figure out the cure for their disease or figure out some way to sort of wake them back up again or figure out some way to upload their brain to a computer once we really understand brains so that their consciousness or something can be brought back to life.
They freeze them after they die?
Don't you need to freeze them before they die?
Otherwise, you're just thawing a corpse, right?
I was under the impression that for ethical purposes, you do it, like, as soon as they're dead
and then hope you can find some way to get everything moving again.
To undead them.
To undead.
I mean, you know, people's, like, heart stops.
You could say they're dead, but you can get them kicking again as long as you do it quickly.
Interesting.
I think that's the plan.
But, you know, if anybody has, like, frozen people and want to tell us about it, we'd love more
information, but it's...
Call us at fbi.g.O.V.
That's right. That's right. Yes.
I'm hoping that you had permission and signed waivers and stuff first.
All right, but before we try this on humans, I imagine we're going to test this on like frogs or kittens or something.
How is that progressing?
Well, so there are some animals that freeze naturally.
So, for example, there are some frogs in cold climates that have something like antifreeze in their blood.
So the way anti-freeze in your car works is it lets things get a little bit colder without actually freezing.
I think that there's some combination of that.
happening and the cells also using some additional mechanisms to make them robust to avoid
bursting as water expands?
Yeah, I think that is what's happening.
I think for frogs, what's happening also is that, like, they're producing some substance
this antifreeze, you say, which maybe prevents ice crystals from forming.
And so, like, basically, if you dope water with this stuff, then its chemical properties change.
And I think it's so incredible that water has this bizarre behavior that when it freezes,
it gets larger.
It's very unusual, right?
Most things, when you freeze them, they get smaller.
But the fact that ice is less dense than water means fish, for example, can survive in the lake, right?
Because the ice is on the top rather than on the bottom, but it also means that if you freeze, you explode.
So it's this funny double-edged sword of chemistry.
Well, I believe there are some fish in Antarctica who can survive freezing also if they end up in that, like, frozen layer of ice.
So the point is there's a variety of animals that can survive freezing.
And while humans at this point cannot survive freezing, maybe there's some lessons that we can learn from these animals
or from tardigrades to try to figure out a way
where we could cryogenically preserve life people,
thaw them out, and bring them back to life.
But it's worth noting that as far as I know,
there's never been a frog, for example,
that was frozen for 10,000 years
and then brought back to life, you know?
Like, we talked about some tardigrades
that managed to be frozen for a very long time.
But I think, you know, when you get to vertebrate level,
it's even harder to survive freezing for a very long time.
So it's not clear that cryogenics will be compatible with the human body or that it will be compatible with the human body on the timescales needed to get to Alpha Centauri.
It's too bad we don't have the biological technology of plants.
You know, seeds are incredible.
I read stories where they like dug up ancient seeds and like planted them and gave them water.
And they sprouted.
And it's like, oh, here's a date palm whose parent grew like thousands of years ago.
And it just sat there.
It's totally shelf stable for thousands of years.
It's incredible biological technology.
It's too bad we don't have seeds.
You know, trees make no sense to me.
My husband has been gardening lately, and he'll say things to me about like, oh, well, you can just cut that branch off and put it in the soil and you'll get a new tree.
And I'm like, that's not how life works.
You can't do that to me.
But it works with trees.
I know.
I remember saying to him, like, why can't I just stick my arm in the ground and grow a new person?
That's right.
Yeah, trees are wild.
And so some of the most sci-fi-ish plans I've come across involve things.
like having an artificial womb with freeze-dried embryos that you send with you.
Because embryos, we can freeze and revive, right? That's amazing.
It is amazing. Yeah. And so I don't know that you can freeze them for 80,000 years for the
trip to Alpha Centauri. But, you know, if you get there faster, and you can probably move
much faster if you don't have squishy humans on board to worry about.
Some of my best friends have two kids, and both of them came from frozen embryos. One kid is
two years older, but they're actually the same age. It's just that one of them has been unfrozen for
two more years. And I think about that every time I see these brothers, I'm like, you guys are
actually the same age. It's just one of you was frozen for two years. That is amazing.
Reproductive technology is incredible, the things that we're able to do. So you're going to put this
in the maybe category that we potentially could develop cryogenic technology that could freeze
humans and unfreeze them after thousands of years. It's not clear how we would do it now, but you're
not going to say it's impossible. I'm going to put the cryogenic humans on the fairly unlikely.
Oh, no.
For the time frame is necessary to get to Alpha Centaur.
If you could get one of those propulsion techniques to get you there in like five years
and you just had to freeze people so they didn't get bored during the trip, then maybe
you could get away with that.
But when you think about what else humans would need when you wake them up, it starts
getting complicated.
So, you know, if those humans ever want to have a fresh egg, you also need to figure out a way
to get the chickens going.
You know, you also need to store the food for them.
Like, it gets incredibly complicated.
But, you know, maybe you could just bring a bunch of genetic material with you and have a lot of robots that start planting the farm, you know, a couple months before the humans are going to be gestated in the artificial womb.
But now who's going to raise them?
Like, as a parent, it is amazing to me how much work it takes to get children to, like, just shower or brush their teeth.
Like, there's so much nagging that needs to happen.
You're out in a crowd and you look at all those people and you're like, wow, all these people were raised.
some parents like taught these humans how to survive and exist in a crowd and like be functional like
that's so much work wow it is yeah culture is incredible the fact that we've managed to get ourselves
here by like policing each other's behaviors is fantastic all right well i see you struggling to not be
the negative nelly and to not want to say no it's impossible but it seems like yeah pretty implausible
i would say within my lifetime not going to happen right but science often has breakthroughs
that surprised me. And in a couple lifetimes, maybe it would happen. But the embryos and parental
robots thing, that's a cultural issue, right? We think that technologically, that might actually
be possible. I mean, you might get weird humans that might kill all each other or they might
launch nukes back at us or something. But in terms of like getting people to the other planet
and growing them there, that could work, right? It's possible that it could work. I mean, I think
there's a lot of things we don't understand very well. So, for example, when babies are born through a
mother's body. They get slathered in bacteria that are important for the way their bodies work.
They get food for the bacteria in their guts from breast milk. I think we don't really understand
what would happen to humans if they were raised by robots and only encountered other babies
of a similar age or other people of a similar age. But somebody should write a sci-fi novel about
that. Or we should just do it and see what happens. Yeah. That sounds totally ethical. Totally.
All right. So it sounds like there's a lot of challenges to getting humans from
here to Alpha Centauri. Even if you've solved all the physics problems we raised in the last
episode, there are a lot of biological problems, a lot of cultural problems, a lot of technological
problems to solve, getting the humans there safely. Yes, and we didn't touch on a lot of the
society, the cultural, the ethical problems. There's a lot more stuff we could talk about. And also,
I recommend Ed Regis's book Starbound, which is all about interstellar travel and some of the
challenges that you encounter along the way. That was an interesting read. So if somebody wants to sell
you a ticket to Alpha Centari, we're going to officially recommend, maybe.
Maybe. Yeah, I would not buy that ticket, but I'm sure other people would, and I'm sure it would be an amazing experience.
Yeah, and I hope you enjoy Fast and Furious number 742 on your trip.
Enjoy.
Daniel and Kelly's Extraordinary Universe is produced by IHeart Radio.
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