>> Kevin Coots: Thank you for coming. My name is Kevin Coots, and I'm happy to welcome
Charles Adler to the Microsoft Research Visiting Speaker Series. Charles is a professor of physics at St. Mary's College of Maryland, and he is here to just discuss his book Wizards,
Aliens, and Starships: Physics and Math in Fantasy and Science Fiction. As we all know, science fiction and fantasy writers have come up with some brilliant and innovative ideas, but which concepts might actually happen and which wouldn't work at all? Charles will discuss these ideas and show the physics and math behind them. Please join me in giving him a very warm welcome.
>> Charles Adler: Thank you all for having me here, and thank you for plucking me out of the
East Coast ahead of the big storm. It's a great pleasure to be here where the weather is much nicer than it is out there. I'm going to talk to you today about the ideas of science in science fiction. And the issue is, the connection between science and science fiction is sometimes close and sometimes fairly distant. Now if you think about science fiction, it's fiction. It's not science.
If it were science it would be PBS special rather than a movie or something like that, but I think though that a lot of writers and especially movie directors have this idea that science fiction basically means, because we are thinking about all these fantastic things, alien life, space travel, other things like that happening in there, that a lot of people who write these books have this tendency to think, and maybe a lot of viewers as well, that essentially science fiction means anything goes. And I would like to challenge that idea right now.
I'll start off right now with a nice example from a recent film. This is from the film Star Trek:
Into Darkness. We see here a scene where Sherlock, sorry, I mean John Harrison, a.k.a. Khan, is viewing a scene of massive destruction here which he’s just caused on earth and then just immediately after the scene, we are not quite sure what's going on, all of a sudden the scene shifts and he vanishes. What's happened here was that he used the trans-warp effect to transport himself immediately from Earth to the main planet in the Klingon Empire. When I was watching this movie a couple of things started going through my head at this point. First of all, I want to repeat the issue here, science fiction doesn't mean, a science fiction story does not have to adhere to all the laws of science. It can't or it wouldn't be fiction, it wouldn’t be science fiction. But I will make this point that I think we have to expect the authors of the story, the writers of the story to play fair. We must expect them, if they introduce something like this trans-warp effect, to think about the implications that it has for the rest of the story.
Now there here a couple things that came to my mind when I was thinking about this transwarp effect here. The first one, and this is because I'm a physicist, is the issue of precision. He just trans-warped himself across the distance of light years, many light-years through another star system and distance is like that. In miles, we are talking about something like 50 or 60 trillion miles assuming that the Klingon star system is one of the nearest ones to our own Sun.

Stars are light-years apart; there are trillions of miles apart, and he trans-warped there with a precision of a few feet, a few feet over the course of trillions of miles. By my estimation that's about one part in 50 quadrillion accuracy in terms of doing that. If you think about that knowing the earth’s diameter the same precision would be knowing it to the precision of the diameter of an atom. So he's trans-warped, now this is not to mention any of the other problems associated with the idea okay, well the two planets are moving, we have to match distances, things like that, but that's really big accuracy. That's really a high degree of accuracy.
Let's move on from there. Now another part of this is of course the Federation has starships. If you can do this why do you need a starship? If you can transport yourself instantly through anywhere in known space you don't need a starship. Starships are big and expensive-looking and they’re slow at least compared to this, this looked like it happened right at once. If you can do that why do you need starships to begin with? Why isn't just everyone going everywhere using this trans-warp device?
And of course a large part of the plot of this is hinged on the idea that they had to send the
Enterprise out there to retrieve this guy Harrison because he trans-warped the Klingon Empire and they’re worried that the Enterprise is going to get involved with the Klingons and start a war because they're worried about the Klingons. Well given the trans-warp thing, this transwarp effect, you do not need to worry about a war with the Klingons. If you have this device and the Klingons don't and the Klingons start making problems you immediately trans-warp an antimatter bomb to their planet and you’ve solved the problem. If the Klingons have it as well that’s a little bit different, but still, it didn't make a whole lot of sense. And so I think that the movie is bad science fiction in that sense. Science fiction is supposed to be literature of imagination; the idea of what happens when we apply advanced scientific ideas to the ideas of the literature, but again, the authors have to play fair.
One of my favorite science fiction authors and the man to whom this book is dedicated was
Poul Anderson, a quote, unquote Golden age science fiction writer. He wrote the same time as
Heinlein did, Isaac Asimov, things like that. He wrote an essay called How to Build a Planet, which this book would not have been written without actually, without my having read this essay before; and in the book he made a point: the process of designing a world serves up innumerable story points. The essay was essentially on how to design a real, a scientifically realistic planet for the settlement of alien life. If you can find the essay, it’s not easy to find anymore, I would highly recommend reading it. The point, however, is that if you can restrain yourself to be self-consistent and to work with science that's at least kind of plausible it makes for a much stronger storyline than if you kind of get away from all of that. And the best science fiction writers pay attention to these ideas.

Now, I will say one thing however, not all the laws of nature are equivalent to one another.
Scientists tend to kind of rank them. And I would make the following statement that if you look at the ranking of the laws of nature the ones that come at the top and the ones that science fiction writers tend to stress the most and pay attention the most to in their stories are what I would call the great conservation laws, the conservation of mass energy, the conservation of momentum, the second law of thermodynamics as well and the principles of relativity, although science fiction writers tended to bend them to be able to go off to distant star systems relatively quickly; but I would say the great conservation laws are the really, the ones at the top of the list that science fiction writers who are paying attention to the science will tend to focus on.
And so for the next section of the talk I'm going to actually just focus on one of them. My book goes through more of them. I call this section, for reasons that will become obvious in a second, Harry Potter and the great conservation laws. Now I like taking a look at fantasy as well. Right up there you have the most famous formula in all of physics, E equals MC squared.
It is a statement that mass is a form of energy. Mass is equivalent to energy. And so we can convert energy into mass or vice versa.
Now if we look at the conservation of mass energy we run into some interesting issues. We want to look at say the Harry Potter films. Mass, let's say we’re looking at the scene from the first film where Professor McGonagall goes from cat, Professor McGonagall in the Harry Potter books is an Animagus. She can turn herself from a human being into a cat and back and back again. Cats weigh a lot less than human beings. I’ve know some who were kind of an exception to that, but most cats weigh a lot less than most human beings do. And so if we think about this issue of Professor McGonagall turning herself into a cat, E equals MC squared basically says that for every kilogram of mass there's a lot of energy involved here. If we look at the amount of energy that it takes, that she will liberate by turning into a cat we arrive again fairly E equals
MC squared, simple formula to do, we get that she liberates something like 50 H-bombs worth of energy every times she turns from an human into a cat. Hogwarts, boom, right? At that point. Now this is fantasy, so maybe we'll get a little more leeway to Ms. Rowling because it's fantasy, it's maybe not quite so nice although there are some fantasy writers who actually do pay attention to the conservation of mass in fantasy stories, Poul Anderson being one of them.
But we'll let her slide on this one.
But when we go back to science fiction there are actually a couple of things I would like you guys to consider for a second. We know that the Starship Enterprise has, is powered by matter, antimatter reactions. And we look at that, well, antimatter is kind of hard to find. It doesn't really occur in the real universe in very large quantities. If we want to make antimatter out of

nothing which can be done, we do this in reactors all the time, as we just flash by there the energy cost is 90,000 trillion joules per kilogram of antimatter.
So we want to make this, we get a big power plant, we run in on some sort of accelerator, we started generating the antimatter. We’ll worry later about how we can fine it. Okay, so we do this. At current energy costs that's 3 billion dollars per kilogram, 3 billion dollars per kilogram if we could do it at 100 percent efficiency. We cannot do it 100 percent efficiency. At best, the laws of physics will let you do it 50 percent efficiency. But in fact, realistic studies have been done. Robert Forward actually did some studies about it and came to the conclusion that if we, at current technology you could do it at an efficiency of about one tenth of a percent to one percent, so we are actually talking about energy production costs thousands of times larger than that, hundreds to thousands of times larger than that for realistic technologies available today. So maybe in the future the world of the Federation will bring into down. But it's still going to be a costly thing, and the Enterprise is going to need a lot more than one kilogram of antimatter to power it, possibly thousands of kilograms or even more than that.
Another issue comes up though concerning this. If we go to Star Trek: The Next Generation, probably my favorite version of the show, if you remember there was this thing called the replicator, I think it was called that, where Captain Picard would stand next to this little box in his office and say, tea, Earl Grey, hot. And somehow a glass of hot tea would be beamed in into this little box sitting there. Now presumably this an offshoot of transporter technology or something like the holodeck where the holodeck materializes these things. And so presumably you're materializing a cup of tea from pure energy.
We've discussed the issues of energy costs in the last, but I want to point out one other thing though which is that there is no technology that is 100 percent efficient. Technologies always involve a little bit waste heat. So let's assume that the technology behind this device is 99.9 percent efficient which is much, much, much, much, much better than any available technology on the face of the earth. If we do that, assuming 99.9 percent efficiency we find that okay, we materialized this, we've got a lot of waste heat being generated, enough to brew 2 billion cups of tea with the waste heat generated by creating one cup of tea from this replicator device.
You know, I'm not sure why we're doing this way in the first place. I guess it looks cool, but still.
Now you may say that okay, well you’re spoiling all the fun of these stories; why are you doing this, man? And the thing I’ve got to say back is that this is all part of playing the game. If you look at, people do a lot of literary criticism of novels. What I'd like to talk about is the scientific critique of science fiction. It doesn't spoil the story to have these things in there, well, I will say the Star Trek: Into Darkness kind of spoiled because of the other issues, but it doesn't have to spoil the story not worrying about the science here. On the other hand, I would say it adds an extra dimension to the story to actually think about the science here and whether it's

scientifically plausible or not. But things in the story that are possible and aren't plausible I think it adds an extra fun to the story and it also I think gets you thinking about this sort of far out science and things like that.
So, going on. I like doing it. It's fun for me to do it; I hope everyone else finds it fun as well.
Moving on from here. Let's talk about this issue about the Enterprise is of course concerned with going out, seeking out new civilizations, finding advanced life forms. So let's talk about this issue in science fiction of space travel. It is pretty clear that if you read science fiction, if you go back far enough back to the 1950s through the 1980s perhaps, the future as envisaged by science fiction writers is not much like what we actually got today.
Here is a book cover from Robert Heinlein's 1949 juvenile novel Rocketship Galileo which is a great book. I love the book. It’s a book based around the first trip to the moon back in 1949.
And it's actually fairly, it's a fun read. It has in it Boy Scouts who build this spaceship to go to the moon, it has an atomic powered spaceship in it, the Galileo, and they end up finding Nazis who have made it to the moon before them. You know what, what's not to like about this?
The Nazis have actually made it to the moon before them, they've established this moon base, they’re going to bomb the rest of the planet back into the Stone Age because they lost the second World War.
But our future today looks nothing like what Heinlein posited. We’ve put people on the moon of course. We put them back in the 1960s, but we haven't really gone back there since the early 70s and Heinlein and most of the other writers like him assumed back in the 1950s to the
1970s, and you can actually see essays they rode talking about this, that in the future world of the 1980s through 2000 people would be routinely involved in space travel. Space travel would be cheap and easy, lots of people would out in space. If you've seen the movie in 2001, Space
Odyssey, you get the idea of what all this is going about.
So what the heck happened? Why did we not get this future with a cheap, easy space travel?
Well, I think if you look at it what happened was that there's an interesting combination of things that the science fiction writers got right but also got wrong. What they got right was the science. If you look at Rocketship Galileo and other works around the same era and other works by science fiction writers the science is pretty darn good. Heinlein paid attention to the science. He was what is called a hard science fiction writer. He paid attention to the science; he made the Rocketship scientifically plausible. He anticipated the atomic energy rocket program by 20 years. The US had a rocket, had an atomic powered rocketship program called
NERVA which ran from 1972 to 1975. They originally considered putting up a rocket for the
Apollo program but they decided on chemical engines at that point. So it was good science. He understood the physics of getting a rocket from the Earth to the Moon.

However, it was bad accounting. Heinlein and other science fiction writers like him made the assumption that the ultimate costs for space travel were going to be the costs involved in the fuel. The fuel costs were going to be the driving costs for the mission. And if you look at that, even today if you look at the space shuttle missions, space shuttle missions costs something like
400 million dollars per mission, fuel costs for the missions were only something like one percent to 10 percent of the total cost of the missions. They were not the driving costs. The accounting that took place, the bad accounting that when involved here was that the science fiction writers really grotesquely underestimated the other costs associated with it. The overhead costs, the fact that for any mission going out into space you need to buildings, you need trained personnel, you need to hire engineers and computer programmers, you need to hire people who are going to train the astronauts for their missions, you need a huge support program to actually support people going off into space which they completely ignored when they actually looked at the fuel costs. The fuel costs are just kind of the minor point of it.
But what they also ignored was another issue as well which is almost uniformly science fiction from this era has no computers or at least the computers that they have in this era, well, if you remember back to 1960s computers were these big machines that you had in rooms. My father was a computer programmer for the State Department; I visited him there, and again, my impression of a computer back then were these big machines that were in rooms that you typed on teletype machines to communicate with. No one back then anticipated the million fold shrinkage in computers and technology which is a very common part of life today. People expected that science fiction writers expected that manned programs and space would be the most important part of the space program. Scientifically speaking they are not. They're actually a fairly minor part of the space program because it is infinitely easier to put a computer up there than it is to put a person up there. You don't have to keep them alive among other things. The overhead costs for people are probably 100 times higher than putting a computer up there and there are very few things that a computer can do, I'm sorry that a human can do that a computer cannot in space. This is why, in fact, most of the more really important scientific missions have all been computer-driven.
Okay. Now of course, let me back up for a second. I think that if you look at it right now as far as human space travel goes, I'm not saying that there's no role for humans in space, but what I will say is that as far as human space travel goes we are something like where Charles Babbage was. Charles Babbage was the inventor, one of the first people to try to invent computers back in the early 1800s. And he built, he had these designs for this huge machine, the analytical engine which was this computer that would work off of steam. A steam powered mechanical computer. And he had these designs and it didn't quite work. It was marginally a workable operation. It was never built. It was very, very expensive, but he was not able to see the revolution that we had in terms of the electronic revolution, first the revolution of transistors

and chips and things like that have gone on to make the world that we know today. I think that in terms of space travel we're somewhere like that right now. We don't have manned space travel except for the extraordinarily rich. People pay, people can shell out about 20 million dollars apiece for space tourism today, but it’s not going to come down until something like that happens.
Now one of the truly audacious ideas that has been proposed for actually bringing the cost of the space travel down is the space elevator. It is exactly what it says on the box. People have had this idea of building an elevator into space. The idea being, it's this very straightforward idea, it actually gets back to the 1880s; it's a lot older than people think. You put a satellite in orbit around the Earth in a geosynchronous orbit, like our dish network satellites or whatever for satellite TV, stays in the same place over the earth, rotates around the Earth once every 24 hours the same as the rotation period as the earth. You then start you elongating it. You start pulling part of it down and pulling the other part of it up so that the center of gravity stays in the same point always. And you pull one end of it so far down that that and touches the earth, the other one extends more than twice as far out up going the other direction. And people have proposed this as a means both of lowering fuel costs and lowering other types like administrative overhead costs for this.
Now I am a space elevator agnostic. I will make that statement right now. I think it would be wonderful. I would love to do it. But I want to point out a couple things about it. The book actually addresses some of the materials problems. You don't have any materials. We are kind of border-line on having materials that could actually build a space elevator nowadays. People want to build them out of these carbon nana-fibers, but no one's been able to actually make really long lengths of them yet. They are material that are really, really strong and really light.
You're talking about a 150,000 mile-long structure here so it’s got to be really strong and really light.
But I do want to make a point though about building a structure like this. The enthusiasts want to build it in the next 30 years. Okay. Well, through ancient times up to around the year 1900, the tallest structures in the world were about 100 meters high, 300 feet high, roughly speaking.
And that's because of the materials that were available, stone. Try to build something much larger than that out of stone you run into problems. In 1900, around 1900, Eiffel constructed the Eiffel Tower which effectively doubled the size of all buildings ever built up to that point by building it out of steel. Steel structures are better than stone structures in terms of their strength to weight ratios and things like that. And so he built this very high structure, the Eiffel
Tower, which was basically twice as large as any other building built up to that point. And we've gotten better than that. Our structures today stand maybe twice, the tallest structures in the world today stand, I think it’s about twice the height of the Eiffel Tower, maybe more than

that. I'm not 100 percent sure. But they are two or three times that height of the Eiffel Tower.
Not a whole lot bigger than that.
Well, the space elevator would be 150,000 times larger than the largest structure on earth. The issue is we have to go from structures which are something, structures which are like the skyscrapers, structures as tall as the skyscrapers to things that are 150,000 times larger in 30 years. I think it is safe to say that we actually do not understand the engineering problems involved in constructing a structure like that. If we tried to build a structure like that we're going to run into problems we have no concept of today. Not to mention that the space elevator would represent a structure unique on the planet today. If you think about it, structures on earth, all structures resting on the Earth are structures which are built either in compression, being pushed down, or intention, being pulled out. Okay? Steel structure, stone structures are mostly built to withstand compression. Steel structures are built as a combination of both, to resist both compression and tension. The space elevator is only in tension. It does not rest on the earth. In order to stay in the heavens basically the part that hangs down from it gravity overwhelms centrifugal force and so it gets pulled out. The part above the center point centrifugal force overwhelms gravity and it again gets stretched out.
We have never built any structure like this for that reason as well, and so I tend to think that it’s going to present a lot of interesting issues. It’s a wonderful design to think about, but I think it's going to present a lot of interesting problems if we actually ever try to make this structure. And again, like I said, I think it's kind of on the borderline of possibilities, but I'm not entirely sure which side of the border it’s on.
Okay. Let's keep on going. People have called for, President Obama and the other past administrations have called for a manned to Mars, I think the timeline is something like 30 years out now, of that order. I want to discuss a little bit about what that would involve with present technology. People have called for, we've landed unmanned missions on Mars, by the way, that's a quote from one of Rodman William’s albums; I just love it there. People have called for manned missions on Mars in the next 30, 40 years, something like that.
Now I would like to discuss some of the issues involved with a man landing on Mars. We put people on the Moon, right, so how hard could Mars be? Well, I want you to think about the scale here. The Moon was 230,000 miles away, 240,000 miles away from the Earth. Mars, at its closest approach is 78 million miles, so hundreds of times farther away. The point is that, and that’s at its closest approach, the point is that if we were to spend a spacecraft out there today we would actually not have Mars at its closest approach when we sent the spacecraft out. The reason being is that when we actually start talking about trips beyond low Earth orbit or trips beyond the moon or things like that fuel costs do start to get very expensive, and so we want to look at the orbits that take the minimal amount of fuel. The orbit that takes the minimal

amount of fuel essentially would be sending the spacecraft into orbit around the sun so it would be in orbit around the sun just like another planet orbiting the sun which follows the same laws of orbital dynamics that the Earth did. It turns out that the minimum energy orbit, let me just demonstrate what that looks like here, the minimum energy orbit starts when the earth is in one side of the Sun and stops when Mars is on the opposite side of the Sun. It's called a Hohmann Transfer Orbit from the German engineer who first thought of it, and it turns out that this is the orbit which takes the minimum amount of energy that it requires to travel between these two planets.
Now the issue here of course though because it is in orbit around the Sun just like another planet around the Sun one can use the principles of orbital dynamics to work out how long it takes. It's actually pretty easy. I won't go through the details, but if you actually work out the case for Earth and Mars it takes about seven tenths of a year, 250 days or so. This, we've done it before; we’ve put spacecraft onto Mars, unmanned ones though. If you think about the problems involved in putting human beings out to Mars you start thinking, oh well, you know they're going to do be in space for 250 days going out there but they can't come back immediately because Earth and Mars are in the wrong position. If you want them to come back well you have to wait by my calculations something like another six months before you can actually send them back to Earth. And of course you have to store all the fuel you're going to need, well, actually I think people have talked about putting fuel along the way, but the fuel costs are pretty big especially for bringing human beings back.
To give you an example when you talk about fuel you typically talk about mass ratios. The fuel in the spacecraft is usually a lot more than the mass of the payload. For example, the mass of the rockets, the mass of the shuttle engines I think is something like, this mass of the shuttle propulsion is something like 20 times the payload mass that the space shuttle was. So for Mars let’s say we are talking about the same thing, 20 times the ratio, it's going to be bigger than that, but let's just say for the sake of argument that is that way. So 20 times the payload mass goes into fuel, that's for the trip out, the problem is that in order to take all that fuel out with you, that's for the trip back, if you want to come back your payload mass is going be 20 times your thing. So you're getting back from Mars, your spacecraft initially starts out 20 times the mass that’s actually to get back to the Earth. The issue is that to get out there you need to actually bring the spacecraft out with all the fuel you're going to need to get back, so the payload mass has to be multiplied by another 20. The payload mass suddenly becomes 400 rather than 20 because you’ve got to get these people back.
Of course there have been calls for people to colonize Mars, go out on a one-way trip. There are some people I suspect who would be willing to do that. My own feeling about that it's probably more like a slow form of suicide than almost anything else. I don't think that one

could actually do that in good conscience to people who are wanting to go out there. I will say this though, if we could build spacecraft which were not limited by these fuel costs then the universe is our oyster.
Let me give you one example. Very simple, straightforward thing to calculate here. If you were somehow to be able to build a spacecraft that could accelerate with 1g acceleration, you're on the spacecraft, you're traveling through space, the spacecraft is continually traveling faster and faster and faster, if you could build one that could travel with the same acceleration as the acceleration of gravity so that every second you’re moving 32 feet per second faster than the last second you were moving in, so keeps on speeding up and speeding up and speeding up, you have to keep the fuel, you have to keep the accelerator on all the time but okay, we'll worry about that later, if you could do that how long does it take to get to Mars? It takes 250 days in the last calculation. If you could just accelerate there all the way out with an acceleration equal to the acceleration of gravity anyone can do that. If you can stand up, you can survive that trip, how long does it take? It took a few months for the other trip. Does it take a month? A week? Amazingly enough, at constant 1g acceleration to get to Mars at its closest approach, two days. If you can accelerate at 1g continually for a long time, by the way that calculation assumed that we flip around somehow and decelerate to slow down and stop by the time we get there, if we can do that that then only takes a few years to actually get out to the nearest stars.
Now if we start doing that of course we run into this one problem which is that as far as we know the speed of light is the ultimate limiting speed for the entire universe. And so when you keep on accelerating like that you're going to be pushing light speed fairly quickly after a year or so. When you start getting close to the speed of light you have to take into account things like the theory of relativity. It turns out that it's good for you though because the theory of relativity tells us that our clocks aboard the spacecraft started ticking away more slowly than they would on Earth. Because of this you can do this amazing calculation which basically tells you that constant 1g acceleration you can actually get to the edges of the universe within a human lifetime. It takes about 40 years, as measured by your clock on the ship, to travel about
1 billion light-years. I find that just incredible. I love relativity. I think it's one of the neatest things in the world. If you could do that you could get anywhere in the universe within a human lifetime, or at least most, a lot of interesting places within a human lifetime if you can do that. Yes.
>>: [inaudible] universe expands?
>> Charles Adler: Well, all right. Yeah. I'm not worrying about that right now. Yeah, it would keep on expanding while you're going out, so maybe not anywhere but-

>>: Will everyone you know be dead?
>> Charles Adler: Oh, yeah. Everyone you know would be dead. It would be, billions of years would pass on Earth, yes. Billions of years would pass on Earth while you went out gallivanting like this. There are science fiction writers who've written about this. Poul Anderson, again, wrote a neat book called Tau zero which is basically premised on that idea that essentially the spacecraft has to keep on, I'll go into it later on, basically the same idea there, but yeah.
Everyone you know is long, long, long, long, long dead. But, yes. But if you want to go out exploring I can see the appeal of it.
There is one little problem though. In 1961 a physicist named Edward Purcell did a quick calculation of how much power a spacecraft like that would take when it took off. You run into a problem which is that if you take off anywhere near the Earth you basically are irradiating the
Earth with the same amount of radiation that the Sun illuminates the Earth with but all in the form of high-energy gamma rays. You would essentially sterilize the planet. This is for fairly reasonable sizes of spacecraft here. It's actually a very fairly straightforward calculation to do.
And so you can't take off with the spacecraft anywhere near the Earth because you basically destroyed the Earth by taking off.
I'm going to make a point about this though which is I think something you should consider one's watching science fiction movies. Anyone here remember the science fiction movie
Avatar, came out five, six years ago, something like that? At the end of Avatar the Na’vi are triumphant, they have won the war over the human beings, they send them all back to Earth on their spacecraft. That was a very bad idea. Larry Niven was the first science fiction writer to point out that any spacecraft, any starship, sorry, because of the enormous energies implicit in its design makes a darn good weapon. The Earth people, merely by turning on their starship’s engines, their starship can travel two thirds of the speed of light, by turning on their starship’s engines can sterilize the planet. They can go back and get all the unobtainium they want after that point. And the Na’vi, who are a Bronze Age culture, can't do anything about it. They can't get access to the spacecraft. So I think these points are interesting because when you start thinking about these things there's no way the Na’vi should've actually let them get anywhere near that spacecraft after they won the war on the planet.
All right. Of course, if we want to build spacecraft like this we have to have actually some reason for building spacecraft like this. And so that's kind of forms a natural way to get into the next section of the talk, which is of course one of the big reasons for going out there, is the issue of the communication with alien life. We live in the Golden Age of exoplanet discovery.
One of the problems of writing this book was that I expected that any time I would write anything down about discoveries of planets outside of our own solar system it would be outdated in a week. We are, there are scientific programs right now that are continually finding

new planets outside of our solar system. The planets in our solar system are now in the minority by a huge margin, 40-1 at least. We know now 40 times at least as many planets outside of our own solar system than we know inside of it. And of course the golden ideal here is to find an exoplanet with life on it. That's what we really want to do, find an exoplanet with life on it.
All right. So the question is what are our criteria for life on another planet? To start out with
I'm going to talk about this in terms of a physics sense. I'm going to talk about the physics involved here. I'm going to go through what I in the book somewhat modestly called Adler's mantra which is something I tell all of my astronomy students the first day of class. The mantra goes like this: all as stars are the same. This does not mean that all stars in the universe are like our Sun. But what it does mean is that all the stars in the universe, all their properties really depend only on one thing, their mass. The mass of the star determines its surface temperature, its lifetime, the amount of light that it emits, almost any property you want to know about the star is essentially implicit in that one parameter, its mass. The stars are very, very, very similar objects to one another.
Planets, on the other hand, are a chaotic mess. The issue of planets, planets are kind of the shmutz[phonetic] left over when solar systems form. The little dandruff left over once the stars form. The star, of course, is a something like 99 plus percent of the mass of the entire system.
When the planets form they form essentially out whatever is left over and they form, there are common features that the planets have but they are diversity I would say is actually, at least from the point of view of talking about life on other planets, their diversity is at least as great as their commonalities. For example, Earth is the only known the planet in the universe, to the best of my knowledge at least, which has plate tectonics. There is evidence that Venus had plate tectonics at some point in the distant past but it probably doesn't have it anymore. Mars, there are a lot of things that determine what a planet is like, geological history, history of impacts, things like that, that actually make all planets strikingly different from one another.
What I'm going to state, however, is a third thing which is an unproved hypothesis on my part which is that when we actually find life on Earth-like planets they're all going to resemble one another in a fairly, in a large number a fairly striking ways. A lot of them, in fact, a lot of criteria we actually probably don't know ahead of time. This is what I would call, sorry not what I call, this is an example of what Jared Diamond, a sociologist at UCLA, calls the Anna Karenina
Hypothesis. The opening line of the novel Anna Karenina stated that all happy families are the same, all unhappy families are very different from one another. The issue here that he made was that all happy families have to get a lot of things right in order to be a happy family. No money troubles, parents who love each other, kids don't talk back, things like that. All unhappy families mess up in one or two of these areas, but there are a lot more ways to mess up then to

get it perfectly right. What I would say is that for Earth-like life to be on another planet, Earth is in some sense I would say a cosmic lottery winner. In order for earth-like life to be on a planet you probably have to get a lot of factors correct, and if any one of those screws up, you're probably not going to see life on the planet. And again, but we probably don't know all the criteria that are involved.
Now the most important point I would say, from a physics standpoint, is that the planet needs to be neither too hot nor too cold. This is basically called placing the planet within the habitable zone, a zone basic of life near the star which is neither too close nor too far from the star. So let me discuss a little bit about what's involved in finding a planet within the habitable zone. Oh, darn it, let me back up a second. All right. This is an example of Earth. The issue is the habitable zone is dependent on the amount of light the star puts out, the luminosity of the star. If the star is like our Sun, I’ll call the luminosity of our Sun equal to one in the distance of
Earth from the Sun equal to one as well, the average distance. If the luminosity is one we want the planet to be about the same distance as Earth is from its star in order to see the same illumination from the star. And the illumination in some sense is going to determine how cold or how hot the planet is. It's actually a pretty straightforward issue if you want to actually find out how far planets need to be in order to get the same illumination that Earth gets. If we want the planet twice as far away from the star the star should be two times two brighter than our
Sun is, a luminosity of four. It should be four times as bright as the Sun. If we want the planet twice as far away from, if we want the Earth-like planet twice as far away from the star. The rule is again very simple, if you want the luminosity to be the same take the distance of the planet from the star and square it and that’s your star’s luminosity. It goes that way because the illumination of light drops off as the inverse of the square of the distance from the star.
Again, three times as far, nine times as bright.
Except you run into some complications involved here in that illumination isn't the only thing.
This is a picture of the planet Venus. The planet Venus, because it has an atmosphere primarily composed of carbon dioxide, while Venus might have been marginally within the habitable zone of our solar system the problem is that because it has, its atmosphere is 95 percent carbon dioxide there is a runaway greenhouse effect on its surface which makes the surface hot enough to melt lead. So there are complications that run in here. Now the other issue of course is that placement inside the habitable zone, well, there seems to be a feedback effect here going on for Venus. Venus started out with carbon dioxide in the atmosphere, it goes a little closer to the sun, it heated up a little bit more driving more carbon dioxide out, more carbon dioxide in the atmosphere led it to further heating leading to more carbon dioxide being driven into the atmosphere and a weird feedback effect is going on there. It seemed to have gone on there to make Venus in fact that hot.

There are actually further complications as well. And again, there are more criteria than that, there are further complications as well. If we look at the position of the Sun within the Milky
Way galaxy some astrophysicists have speculated that in fact there's a habitable zone inside the galaxy as well. The issue here of course is that if you get too far away from the center the stars are low metallicity[phonetic] meaning that they're mostly hydrogen and helium, they don't have as many metals as our Sun does and having quote, unquote metals is actually favorable for planet forming. Get in too close there are too many supernovas forming these higher element of materials and the radiation may be too intense for life to form. Again, we don't know. People actually do not know whether that is a correct hypothesis or not. But again, there may be all sorts of different criteria for this, and again, we probably don't know all the ones.
Now the one issue here of course is we actually want to find intelligent aliens. We want to talk with the other guys. Even if we can't go out there we can actually communicate with them via radio. You can actually detect radio signals from Earth probably over a distance of order several light years. I think maybe even as much as 100 light years away. However, our technological civilization has had radio for the last 100 years meaning that we would not be able to communicate with anyone or no one would be able to detect us at least whose farther than 100 light years away from us. Well, 100 years is not very a long time in terms of the history of the cosmos. The history of the cosmos runs billions of years back. Intelligent life could have formed any time within that period. A miss is as good as a mile here. If they evolved and then stopped having a technological civilization 100 million years ago we would never learn about them because we were too late. If our civilization ends 1000 years from now and intelligent aliens evolve 10,000 years from now in another star system they will never hear of us because we evolved. We went out of existence too early.
To give you an analogy about this, if you are, imagine being in a dark field on a warm summer's night, everything around you dark and you look at fireflies coming through here and you watch the fireflies wink in and wink out you'll see one, there aren't that many fireflies around, you'll see one wink in, wink out, a little while later another will wink in, wink out. Occasionally two wink in and wink off at the same amount of time in the same time. But a lot of the time you’ll see one flickering on and flickering off. This is I think the situation which we are with respect to alien life in the cosmos. If the lifetime of the civilization isn't long enough, if the lifetime of a technologically advanced civilization isn't long enough then there is very little hope of actually detecting other intelligent alien life. We don't know what that is of course. People like Frank
Drake and his famous Drake Equation have actually tried to estimate this. I would say that if you actually look at the geometry of the Milky Way Galaxy that if a civilization is not going to last for several thousand years at a very, very, very base minimum than there's probably almost

no hope of different alien races communicating with one another. It's kind of a depressing thought, but I suspect that that's actually probably a fairly decent minimum idea.
Now the question of course, that does beg the question of course, how long can in fact an intelligent civilization last? And let me just discuss that very briefly, an advanced technological civilization last. There are of course obvious problems going on in the world today. Right now we face major problems with our civilization. Over the next century we're going to have to deal with the issues of both resource depletion and global climate change. These are going to be pretty serious problems facing us. They could in fact mean the end of our technological civilization. If we make it that far, make it for a few thousand more years of course we have to worry about the next Ice Age, really the next period of glaciation. The last glaciers retreated something like 20,000 years ago; and if you look at all of human history, the last 5000 years is from far beyond the point, recorded human history from 5000 years ago is far beyond the point that the glaciers retreated. Agriculture developed when the glaciers retreated probably because people had a fairly nice relatively stable climate to grow crops in. When the next Ice
Ages come back in 20,000 years or so will human civilization survive them if we are still around at that point? I hope so, but it’s going to be a big change. We had glaciers covering I think a mile thick in Wisconsin in the last one.
If we go beyond that we of course have to start thinking really long-term, and making the civilization last even longer term than that we have to start thinking about things like well, 65 million years ago an asteroid impacted the Earth destroying all the dinosaurs. They happen once every 50 to 100,000,000 years. Maybe we have to worry about those if we actually survive long enough. But if we get past those ideas what do we start doing at that point? If we talk about, if we worry about civilizations, really advanced civilizations what do we start doing what we get out to that point, if we actually survive for a few hundred million years? What do we start thinking about at those points?
Well Dyson suggested, Freeman Dyson, a physicist of Princeton, suggested that if we really needed that much energy we could just start taking the planet apart and build a shell around the Sun to capture all of the Sun’s energy for use of our really advanced technological civilization at that point. It's called, I will make a point here actually, it's called a Dyson Sphere in most literature but is actually not a solid sphere. It's actually a network of satellites orbiting the Sun at the same distance that Earth is blocking out most but not all the light. A shell could not be built for some fairly good reasons but people actually think of it as a shell, as a solid shell even though that's clearly not what Dyson meant in his first paper. If we don't build a Dyson shell though in 1 billion years we’re going to start worrying because the Sun's luminosity is going to start increasing. The Sun’s luminosity will increase about 10 percent in 1 billion years probably making life on earth impossible at that point, maybe, maybe not, certainly in several

billion years the Sun will swell into a red giant hundreds of times its current luminosity, we'll have to move the Earth away 10 times farther away from the Sun than it is right now at least in order to keep life on there. Well, people have speculated about how to do that. It's kind of the inverse problem of impacting giant comets on the Earth. People have actually speculated on taking big things like asteroids, passing them close by the Earth, and deflecting the Earth's orbit so that it actually moves out farther away from the Sun. It takes a lot of energy. We would effectively need all the energy that the Earth receives from the Sun on average over the next billion years to do this, so I think we better start early, but people have actually speculated on this being possible.
We make it past a billion years; a few billion years from now the Sun will die out. It will swell into a red giant, die out in about 5 billion years or so, four and a half to 5 billion years. We moved to another star system then, right? But in 1 trillion years all the stars are going to die off. What do we do at that point? Well, I think what we have to do at that point is basically the only things left in the universe by that point are going to be the black holes. Black holes are not of course all-devouring monsters. You can actually get energy out of them. If you toss things into them you actually, they're actually very efficient at extracting energy out of objects you toss into them. In principle you can actually get half of the rest mass energy, one half of MC squared out of any object tossed into the black hole through either heating the accretion disc or through gravitational waves or through weirder processes like the Blandford-Znajek Process; things like that, so we can power the civilization with black holes until all of them evaporate roughly speaking a googol years from now, 10 to the hundredth years from now is when the largest ones in the universe are going to evaporate away.
So, my posit is if we work hard and start right now maybe the human race can last a googol years. Thank you very much. I would like to acknowledge everyone who has helped me with this before I sign off: Vickie Kearn, my editor, Quinn Fusting and Jessica Pellien at Princeton
University Press, the students who took the class that this book was eventually based off of, the science fiction writer Larry Niven, who very graciously let me use the quote that begins the book out, and of course all of my hosts at Microsoft here and at the bookstore sponsoring
[inaudible]. So thank you all very much for coming. I'll take any questions. Yes.
>>: So what science fiction it do you particularly like? Do like the stories where the writer takes a law, breaks it, but then remains consistent with the remaining laws of however, whatever laws they decided to write?
>> Charles Adler: Yes. Actually, that's exactly what I like. David Gerrold, the science fiction writer who is the author of the Star Trek episode, The Trouble With Tribbles, wrote that if you look at stories, good science fiction stories will typically involve one example of what he called bolognium[phonetic], one of place where the writer breaks the laws of science fiction. And

beginning authors should just put one example of bolognium[phonetic] in their stories.
Experienced authors can use two, but only the greatest grandmasters can actually put three pieces of bolognium[phonetic] in a story and expect it to be still decent science fiction. So I agree with that. That's actually kind of the criteria I also used when writing the book as well.
So, yeah. I absolutely feel that if you actually vary one of the physical laws, let's say people invent a way to travel faster than the speed of light, you should probably respect the other ones because varying one is going to give you enough for story ideas. Yeah.
>>: I particularly like Futurama. Do you see a lot of breaking the science laws in that show?
>> Charles Adler: Futurama. Only 10 or 12 per episode, I think. I love Futurama. I mean look, again please don't make the mistake of thinking that I'm going to insist that every piece of science fiction must be scientifically accurate, there are a lot of science fiction and fantasies that I like that is not particularly accurate. I happen to like the stories best that don't vary a whole lot, but Futurama is an interesting example. I mean someone's paying some attention because you actually do see some interesting scientific ideas presented in it, but they basically bend them to make the stories funnier. I mean that's really what they do there. And I've got no problems with that. Yes.
>>: What do you think about wormholes and dimensional travel?
>> Charles Adler: Wormholes and dimensional travel. That's the piece of bolognium[phonetic]
I put in the book. My gut feeling is that faster than light travel is not possible simply because faster than light travel always involves time travel back into the past, at least from somebody's point of view. You also have to have this weird form of unobtanium[phonetic] called exotic matter in order to thread the wormholes through. I tend to think that they're probably not possible, and even if they are possible they’re so far beyond what I can imagine our civilization doing that it’s going to be a long time before we can actually even think about things like them, but I would say not proven to be impossible, certainly not proven to be impossible. If there is any way of traveling faster than light it’s probably doing something like using a wormhole to do that. They seem to be on the very borderline of what the general theory of relativity allows as I understand it. But again, which side of the borderline they fall on is kind of I think probably anyone's guess. Hawking doesn't believe in them, doesn’t believe in the fact you can actually use them for faster than light travel. But again, I don't know where most of the physicists actually fall on this particular case. I'm not a relativist, so I'm not a specialist in the general theory of relativity, so it's hard for me to state with certainty what most people think about that. Yeah.
>>: So, sorry. So building on what you were saying about the general theory of relativity, a lot of our most classic robot science fiction stories tend to [inaudible] maybe try to treat in the

sense that well okay, all of our viewers are [inaudible] to get enough some form of like suspension of disbelief, Star Wars, Star Trek anything like that. So anyway, what I'm getting at is, I'm sort of interested in your take on why we are so enamored with this idea of how applying some of the things that we see in our observable world, inn our energy world to this broader scale where that's completely impossible.
>> Charles Adler: That's a very good question actually, why we actually want to do these things.
I think it's because we like stories to be human-sized if I had to make a statement about that. If you look at most science fiction stories, most science fiction stories center around things like interstellar discoveries. The Mote in God’s Eye, for example, is a very good story about the first contact between humans and aliens called Motes. So there's a story there, basically it’s a very good novel. It's a great novel, but it involves essentially this kind of Napoleonic era intrigue involving humans discovering these aliens and the aliens hiding a big secret from them and trying to figure out diplomatically what the aliens are going to do, what the humans are going to do with the aliens and vice versa, whether they're going to get involved in a war or not.
That's what I mean by I guess human-sized stories. We tend to think of these dramatic stories as ones involving warfare or people in falling in love with each other or jealousy or things like that.
The cosmological stage is pretty large when you want to set stories like that up against it. If we want to have stories involving humans then we have to posit things like, if you want to involve stories involving humans interacting with each other then we have to have things like faster than light travel in order for us to be able to actually get out there and interact with the aliens on that level. I will state that not all science fiction writers actually fall along that track. There are writers like Stanislaw Lem, or my personal favorite scientific science-fiction writer of all time, Olaf Stapledon, who wrote back in the 1920s who actually adopt a much broader view of what the potentials of science fiction are.
Olaf Stapledon, for example, wrote a novel called Last and First Men in which he views the entire history of the human race from the present time to an era billions upon billions of years in the future in fairly broad swatches, and he talks about these issues involved with science.
And Olaf Stapledon knew his science. He was a journalist, but he actually understood the science of his day pretty well, in particular, one of the greatest discoveries of that time which was the issue of the expansion of the universe. So he knew his science very well, and he incorporated fairly accurate astronomy and cosmology into these stories to make these stories set against a real cosmic backdrop. And so he's one of the people actually that did kind of these very much larger than sort of human scale stories. But I think the reason we want to do these things is so we can actually present stories that in some sense people are sympathetic with, that we can actually kind of understand people's motivations in there. Because when you're

talking about things that go on for millions of years it may not be that possible. That's my take on it at least why people tend to do that. Yeah.
>>: [inaudible] quite a bit of time on travel and movement through space, one of my favorite authors is Card, and he had this interesting notion in the Ancible and the idea of communication. So while he tries to respect these ideas around travel and relativity and those kinds of things he has this concept of some of that can be defeated through more instant and much more scalable forms of communication across great, great distances. What you think about stuff like that? Do you address those sort of those things in your book?
>> Charles Adler: I do, actually. I do actually talk about the Ancible, which both Ursula Le Guin and Orson Scott Card use in their books. As I understand it, the Ancible is based upon the idea of wave function collapse, the idea that if you make a measurement, backtrack for a second here. In quantum mechanics, quantum mechanics have systems of correlated particles. If we have a system which has net spin zero and if we have a particle which has spin zero and it decays into say two other particles which both have spin associated with them because you need to conserve angular momentum one particle will have spin up, the other particle will spin down. And they go off in different places. One particle must have spin up, the other particle must have spin down. And if you have an observer here who measures one that has spin up he knows that the other observer in Alpha Centauri, when he measures it four years later, is going to measure spin down. Or if you base this and use a cross, let’s have someone in the middle here, you send it to someone a light year that way and a light year that way with your particles the guy over there when he measures the particle being spin up he knows immediately that the other particle’s got to be spin down because he's made the measurement. Now that will be okay if they had an assigned spin beforehand, but quantum mechanics tells you that in fact until you actually make the measurement the spin doesn't have a good value. And so somehow by making the measure over here you've caused the spin to have that value over there instantaneously, whatever that word means. Instantaneously is a dirty word in physics because it doesn't mean to the same thing to everyone.
Ursula Le Guin had this idea of using this effect for her communicator. I don't know if it's original to her or to Card or who actually first thought it up, but in any event, the problem with that is that the measurement that you make there's no way of actually putting a value onto the spin. It's completely indeterminate. It could be either up or down. If you make the measurement then you know the other guy’s measurement is either up or down, but in a physics sense no information has actually been sent because what you're receiving is if you look at these, if you make repeated measurements you’re receiving a random set of ones and zeros, call one spin up zero, spin down, you’re receiving a random set of bits here and there's actually no way to send an actual intelligible signal using that.

This is actually a stuff which is at the forefront of atomic physics right now, my own field of study, because correlated systems you can actually do pretty neat things with correlated systems. Quantum computation, for example, is based around these ideas. But it does not appear to be able to transfer information faster than the speed of light. Yes.
>>: Did you consider anything when you're talking about like [inaudible] in space travel, so
[inaudible] speed in different problems?
>> Charles Adler: Sure. I did not actually consider that in the book. If I ever write another book
I'll probably actually include that in there. It was one of those things where the book was getting a certain length and at some point you have to say that's it for it. Yeah. You could actually put people in suspended animation for, well, maybe you can put people in suspended animation for very long periods of time. You’re talking about, however, if you're talking about any sorts of reasonable speeds you're talking about periods of time which are much, much, much longer than recorded history.
If you look at the speed, for example, the Voyager Spacecraft I think that people said they'll get to the distance of Alpha Centauri and they’re not heading in that direction but they'll get out that distance, the nearest star system something like 40,000 years. So it's a possibility. I mean the issue, one issue with all of these projects is that as someone who's funded by the government you have to worry about funding for projects like this because if you're talking about a project that's going to have, even talking about projects that have payoffs in 20 years is kind of dicey as far as getting, as far as actually funding these. So you actually have to posit a very different society than the one that we live in. As far as I know there's nothing intrinsically impossible about that. I may be wrong because I'm not a biologist, but as far as I can think of there's nothing intrinsically impossible about long-term suspended animation. Yes.
>>: I guess a lot of science fiction in early years inspired some of the innovations like Heinlein inspired our trip to the moon. I think maybe replicators inspiring 3D printing. What ideas do you think could be inspired in the next generation of technology?
>> Charles Adler: Sure. I don't know the historical pathways involved. It's a good point in that I think that, I think the most directed example of this is that Arthur Clarke had the idea for the communication satellite back in the, I think 1948, this idea of putting satellites around the Earth in geosynchronous orbits to do satellite communications. He actually refused to patent the idea basically as a present to mankind, but he had this idea, he actually printed it up in a paper, and I think that's a very direct inspiration for this is idea for communication satellites that he had. I don't, the path between other things like that I think is not quite as clear. If you look at, again, I don't know the history of the space program well enough to say how much of it was inspired by science fiction , how much of it was inspired by scientists who were not initially

inspired by it, well, I take that back. Wernher von Braun of course was actually, his main statement was that he was actually directly inspired by Jules Vernon and HG Wells; so I think there's actually a lot of the value in what you just said. I think that in fact science fiction can actually serve as a great inspiration even if the scientific ideas are particularly good ones. I think actually there was one, I saw a TV program once where the guy who invented the MP3 format for music playing said that he was actually inspired by Star Trek: The Next Generation where they would actually call up a bit of music or something like that and play it from the computer; and he was basically inspired to develop this because it looked like a great idea that no one had done this. So I think that's a very good point though.
>>: I think we're out of time.
>> Charles Adler: Well, thank you again.