Can humans survive interstellar travel?

Imagine a future one hundred maybe two hundred 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

I'm Daniel. I'm a particle physicist and the longest flight I've ever taken was fourteen hours.

Hi. I'm Kelly Wiiner Smith. I studied parasites in space, and I think the longest flight I've taken was twelve 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?

Don't That's what makes it a Yeah, I gotta 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 US. 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. Broadoslava was beautiful.

Well what's your experience like on these long flights, because I always feel like, oh, fourteen 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 gonna 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 restoids. 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 gonna do.

You're not gonna spend ten thousand dollars for that flight, that's right. Yeah, no, 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

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, and 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?

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, et cetera, 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 sought in suspended animation yet. But if you're talking about generations of humans, if as human we've sorted all the problems of sustaining reproduction and nutrition and health, I wonder whether the risks of the dangers posed by cosmic rays will actually be less in deep space. We do 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 tradeoff and you're lose in both situations.

It depends on how far away the other stars. If the star we're trying to get to is there one that we're going to share our 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 two mens who leave Earth going to interstellar space will not be alive because it takes approximately twenty two to twenty five thousand years to exit our solar system. And that opens up the question about children in space to continue to journey, because the adults who begin the journey will not live to exit our solar system.

So no, if we allow for human reproduction all root, which is a big if, humans would encounter significant survival challenges, not the least which is that our physiology is ill equipped to handle zero gravity and excessive radiation exposure in the vein of we do not know what we do not know. There are likely other factors that terrustrial living either provides for us or protects us from that we would faithfully 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, generationships. 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 Danielankelly dot org 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 timeframe 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 eighty thousand 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 one hundred years Marvel will make enough movies to get you to Alpha Centauri.

I think there might be enough fast and furious movies to make sure.

I would not make it to Alpha Centauri fast and furious movies. I would rather push myself out the airlock.

But our he 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 Furius that makes me go, whoa that

Okay, all right, I'll take another look at the Fast and 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 kind of 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 forty years if you can travel at ten percent the speed of light. Yeah, 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

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 also need to somehow find that fuel.

Yeah.

Right, basically you have to use Jupiter as your rocket. Yeh.

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 one hundred and fifty billion dollars 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. Yea, yeah, hey, 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 scalactic cosmic radiation and

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

I am always so impressed by how eloquent you are when I put 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 Christofferetti 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 US side, ammonia is used to cool the space station is also toxic. So the protocol for what you do when there's an ammonia leak as you run over to the Russian side, you close

Off your clothes. Why do you have to take off your clothes as 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 want to bring it over to the Russian side. So you got to 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

Yeah, this is actually really fascinating from an engineering point of view. You know, what's happening is that these particles

Wow.

So, yeah, electronics are very sensitive to high levels of radiation. And if you are relying on your electronics to keep you alive and an eighty thousand 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 galctic 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 padding your interstellarship 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, 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 regulis from the surface of the Moon, but also you could go to the asteroids and extract water from the asteroids. In 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 free fall and feeling the equivalent of no gravity, that their bones start breaking down, their muscles start breaking down.

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 four hundred and thirty seven days. That was Valeri Polyi call. 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 one percent of the density of their hip bone per month, and we don't know if

On, wait, I'm gonna imagine it. Hold on. Hmmm, yeah that seems gooey.

Yeah, yeah, that is such a dive response. The gooeyness is not a problem.

Man, But now you're in space, you have like weird balls of goo.

It's oh, imagine trying to do a C section in space with like the blood floating around your head anyway unpleasants.

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 had a blowout on my lap and we couldn't get up for thirty minutes, and oh man, nobody liked me. And it brought a change of clothes for her, but not for me, but she sat on my lap anyway. All Right, these problems can 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.

My gooey imagination is filling in the details for me.

Yes, oh oh yeah, you're really into Guey 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 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,

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 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

I'm not trying to be negative today.

The facts that we're going to get into though, all right, So we're 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.

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 you know, 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 ask a question, you 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 twenty to twenty two 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've probably figured.

It out, hope, so, or you're all dead.

Yeah, And I mean that also means at some point you're gonna stop benefiting from any new knowledge that is created on Earth because it's gonna 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 gonna

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 that 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?

Ooh question?

I don't know.

We better though, yeah, including the Scottish one. That the Scottish one turns out to be totally made up.

There's no Scottish wikip 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 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 my goodness, the best intentions. Anyway, you should 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 gonna be cut off from the mothership or we're not going to get the latest advancements in quantum computing

You can bring a ton of knowledge with you, but you know, if you set me down next to a bunch of textbooks on quantum computing, I could do nothing with that information. Like 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 whatich 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.

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 interstellar trip, but you should bring a couple cleanly physicists probably, Yeah.

I think the real problem here is that you need a breadth of notice, 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 ten people. And I'm guessing that's where you're going to go next, is like how big a community you need not just have the knowledge, but also to like have healthy babies.

Yeah, so I'm going to be focusing on the healthy babi's part, but this occupation's part is really important, and it's very hard to have a concrete answer for it because it depends on what you're willing to live without. I heard once that there's something like one hundred thousand medical specialties, and that number seems unreasonably large. But let's

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 need a lot of pencils on an eighty thousand 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

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 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?

Yeah, exactly. It feels like you're cutting that very tip off a very complex pyramid of manufacturing and civilization, and it's going to rumble 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, Like, just to make a pencil requires an enormous manufacturing capacity and lots of different specialties.

Our global supply chains are amazing. We rely on them for so many things. That pencil takes a million people. Thing came from somewhere in one of these days. I want to figure out, was it a Milton Friedman essay?

I do no holpu with't Malcolm Gladwell, because you can't trust anything in these.

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 to allisantaries?

Unfortunately, No, I couldn't figure out a way to really shoehorn parasites and more than once.

I'm ready for it though, when you ring it 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 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

I wonder, from an evolution air 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 spacefaring, hearty human that can like I don't know, extrude pencils from

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

Well, dig into that for a moment for us, Like what is it 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

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 ninety eight people.

If ninety eight thousand or ninety eight people.

Ninety eight individuals. What if every generation they mate it with whoever a computer program told them to mate with based on their genetic makeup. 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.

And 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 ten thousand individuals on the planet, and here we are, you know, eight billion people later doing pretty well. So it's not implausible to me that you could 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 one hundred to five hundred. 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.

Keeping in mind our constraints. Even if money isn't an optical, 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 that was really interested in your comment about how you could keep it down to around one hundred if

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

I think it's funding the mental image of that of freeze dried sperm. Why wouldn't you have them, you know, like delicate test tubes, you know, imagining like you know, liquid nitrogen flowing over them and something. Instead your words give me a mental image of like a barrel of the stuff.

You started this guy theme, and I was just kind of running with it. But you're right, they'll probably be in viles in a tube of liquid nitrogen or something like that. Yeah, 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

Yeah, exactly. I think that's super fascinating and it touches on another whole area of questions of like how 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 being the right person. It's crazy, But you know, on ships, the captains in charge and for a reason. And so anyway, that's whole other issue we could dig into another time of laws

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 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 eighty thousand 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 nonstarter. The next step up from that would be hibernation. And so hibernation you have a reduced 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 bear, squirrels, marmots,

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

Probably all right, So we can't just knock people out with nik will. 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 humansicles? 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.

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 will 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.

Right, they freeze them after they die. Don't you need to freeze them before they die, otherwise you're just thawing a core.

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. 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 plant. 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 dot gov.

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 onlike 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 anti freezing their blood. So the way anti freezing 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 burst 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 substances and a freeze 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,

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 Tartar grades, to try to figure out a way where we could cryogenically preserve life people thaw them out and

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 there's like, oh, here's a date palm whose parent grew like thousands of years ago and it just sat there it 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 eighty thousand 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. Just one of you was frozen for two years.

That is amazing. Reproductive technology is incredible, the things that we're able to do.

Yeah, 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 frames necessary to get to Alpha Center. 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

You're out in the 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 do not want to say no, it's impossible, but it seems like, yeah, pretty implausible.

I would say within my lifetime, not gonna happen, right, But science often has breakthroughs that surprise me, and in a couple of 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 like 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 to 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

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 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 all 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 Centauri, 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 seven hundred and forty two on your trip.

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