Carl Sagan: Life on Other Planets?
Dr. Carl Sagan on CAMERA THREE in New York City on January 27th, 1974.
At a time when there is so much provocative nonsense around, it’s nice to encounter some provocative sense. Carl Sagan’s reputation as a brilliant astronomer with a gift for plain talk began around 1965 with the appearance of Intelligent Life in the Universe, a book he co-authored with the Soviet astronomer Iosef Shklovskii. Though never a best seller, Intelligent Life soon came to be known as one of the most exciting nontechnical science books ever written.
In a burst of energy following his work on the Mariner project (which put a satellite full of cameras into orbit around Mars), Sagan has written or contributed to five more books, all due out this year. Most of these center on his speciality, exobiology, the emerging science that concerns itself with life beyond the earth.
Trained in astronomy, physics, biology and genetics, Sagan lives with his wife and three children in Ithaca, New York, where he is director of Cornell University’s Laboratory for Planetary Studies. In that laboratory we sat down one snowy January morning to talk.
“…the Dead Planet.” “Now we know that there is no life on Mars,” and so forth. And the most recent Mariner mission — which provided an extraordinary opportunity to observe climate on another planet — was widely described as a disappointment, because dust at first obscured the surface of Mars. Is it discouraging to you that this opportunity for people’s consciousness to be expanded has been treated by the press as an opportunity instead to do the opposite?
Yeah, it is a disappointment. But I’ve thought about this precise business a lot and those early reports about “The Dead Planet” are kind of interesting. Their logic is the kind of logic nobody would use in any other area.
For example, Mariner IV flew by Mars on Bastille Day 1965 and got 20 pictures of the planet with the finest detail one kilometer across. Now you take 20 pictures of the earth at one kilometer resolution, there’s no chance of finding life here. If there were kilometer-long elephants cheek by jowl covering the entire planet, they would have been excluded. And yet people say, “Well, I didn’t see anything alive on that planet, it must be a dead planet.” What terrible logic. How come everybody’s using that?
The New York Times in 1965 ran an editorial called “The Dead Planet,” and the argument was that a magnetometer on board — which you know measures magnetic fields — didn’t find any magnetic field, therefore the planet is geologically dead. Now we know from these pictures that Mars is not geologically dead. Then they went on to say geologically dead is dead, so there’s no life on the planet; it’s a lifeless planet.
There seemed to be almost a passion to do it.
Well, I think a keen insight into how a lot of people think about this was provided by Lyndon Johnson, who said — this is more or less an exact quote — “As one of that generation of Americans who had the pants scared off of them by that Orson Welles invasion from Mars broadcast in 1938, I’m glad to hear that there isn’t any life on Mars.” I think Lyndon Johnson was speaking for many Americans then, as he may not have done on other issues.
Some people, at least, are disturbed about the idea that there might be life elsewhere; even simple forms of life. And the idea that there might be civilizations more advanced than ourselves elsewhere upsets a lot of people. I’m not a psychologist but I have spoken to a lot of people on the subject and I think that there is a sense of “let’s keep the idea of where we are in the universe tidy.” It gets very complicated if you imagine that we’re only one kind of life where there are millions of other kinds, some of them much more advanced than us. That is precisely a mind-expanding experience, and some people are not interested in having their minds expanded.
I think it also bumps into people’s religious prejudices. The sophisticated representatives of all the major religions have stated that there’s no test of faith involved, that it expands the range of God’s activities if he made life on other planets and all that. But still I think there is a kind of fundamentalist malaise about the idea of life elsewhere.
An opposite emotional predisposition also exists: People desperately want to believe there’s life elsewhere. That comes up in a lot of the UFO enthusiasts and you can find it in a lot of 18th-century popular writing on the planets, where every planet had a different kind of being: The Mercurians were mercurial, the Venusians were amorous, the Martians fought a lot and the Jovians were jolly.
It seems to me an important issue whether there is life elsewhere. On important issues, you shouldn’t make a decision until you have the evidence. But some people find it difficult to withhold judgment until the data is in. It’s unsettling. I once wrote a book for Time/Life, a popular book on planets, and I would say, “Here’s the relevant data; some people think this is the explanation, some people think that is the explanation.” The editors of Life would come back to me and say, “Look, don’t confuse our readers with the alternatives; just tell us what’s right.” I would say, “I don’t know what’s right. There are several possibilities and we have to withhold judgment.” They would say, “Well, just pick one. Whichever you like the best.” I have the feeling that the editors of Life are in keen attunement with the way a lot of people think — with an intolerance for ambiguity.
The Barnard star situation is interesting. What you have is a residual in the apparent motion of the star. That is, here’s a nearby star and you can plot very accurately its position in the sky relative to more distant stars that aren’t moving. It’s close and it’s moving fast, so it has a large apparent or what we call proper motion. Superimposed on that proper motion there are little wiggles which are difficult to measure but have been measured over a period of decades and are certainly there. Now, the wiggles are due to a dark companion or companions, gravitationally on one side of the star and then on the other side, pulling the star one way or another. As to how many companions there are and what orbits they’re in and masses they have, there is a range of possible solutions.
The original solution referred to in Intelligent Life in the Universe, and proposed by Peter Van De Kamp of Swathmore Observatory, was a single dark planet about one and a half times the mass of Jupiter, in a highly stretched-out elliptical orbit. Now he finds that he can match the data a lot better if he assumes two planets in circular orbits, like the orbits of our planets. They have just about the mass of Jupiter, but they’re in a bit closer to their star than ours is. If you wanted to assume, say, 11 planets, you could fit the data even better. The main point is not that he has uniquely found two versus one, but that far and away the most likely explanation of this motion of Barnard’s star is planets of roughly Jovian mass.
Would someone, say at the distance of Barnard’s star or the star Sirius, observing the sun with equipment similar to that which we have now, be able to observe perturbations of the sun’s motion or in some other fashion discover the existence of our planets?
The remarkable thing is that even from the nearest star the sun is extremely unspectacular. For example the constellation Cassiopeia is in our northern skies and it’s a kind of “W.” Well, if you were in the vicinity of Alpha Centauri, the nearest star to our little one, four light years away, and you looked in the direction of Cassiopeia, you would see a “W” OK, but then there would be a final jog down. There would be one more star there, just about as bright as any of the others in Cassiopeia: That’s us. That’s the sun.
You know, our sun looks just like thousands of other stars in the sky. You’d never guess that there are planets going around it, and that one of those planets has people who consider themselves very intelligent. There would be no way of knowing that.
Here on the earth if you go and look up some clear night you can see a few thousand stars. How do you know that they don’t all have planets and guys standing around thinking that they are the smartest guys in the universe?
As far as detecting the earth by gravitational perturbations, even from the vantage point of the nearest stars you can’t do it. The earth is just not massive enough. It’s just too insignificant a planet. You could probably detect Jupiter and Saturn from the distance of the nearest stars with techniques not much more advanced than what we have today. But you’d never detect the earth gravitationally from that distance. And if you went to any greater distance, you would not even be able to detect Jupiter and Saturn.
Are those star maps in existence?
Yes. We’re thinking of making a children’s book with pictures, called The Sky from Elsewhere.
I want to ask you about the conference on communication with extraterrestrial intelligence you attended in Armenia.
This is something that a couple of us and a couple of Soviet astronomers tried for some years to get organized. It’s not very easy to have an interdisciplinary meeting on such a speculative subject that involves two nations as much at odds as the US and the Soviet Union. So merely holding the meeting represented something of a victory.
We had astronomers, physicists, chemists, biologists, anthropologists, archeologists, linguists, historians and one or two people who I’d call philosophers, plus people in computer sciences and electrical engineering. It was a remarkably diverse group and the quality of people was extremely high. We met for about five days at the base of Mt. Ararat, on which Noah’s Ark is said to be beached.
The main conclusion was that it is not unlikely there are civilizations in advance of our own elsewhere in the galaxy and that we have means currently at our disposal to detect them. This doesn’t mean that the conference committed itself to guaranteeing the existence of extraterrestrial intelligence, just that we cannot exclude the possibility. Some people think it’s likely, some people think it’s not very likely, but nobody can exclude it.
The Russians announced that for the last four years they have been doing a small project to examine the closest stars which are like the sun at two frequencies in the radio spectrum to see if there are any intelligible signals. The answer so far has been no. Even though that’s a reasonably modest program, I think it is of interest that the Soviets have made such a sustained effort.
The thing that impresses me is that we have a capability with existing radio-telescopes for tuning in to an enormous number of stars, and we’re not doing anything at all in the United States. For example, the world’s largest semi-steerable telescope is Cornell’s Arecibo Observatory in Puerto Rico. It’s getting resurfaced and it has a set of new receiving equipment.
Let’s imagine Arecibo used one percent of its time to listen for some other civilization’s signals, and imagine there to be another civilization just at our level of development, so they also have an Arecibo instrument to use as a transmitter. How far away could that other Arecibo be for us to detect it? The answer is, that except for obscuration and dust in certain places, it could be anywhere in the galaxy and we would pick up the signals. That means at least one hundred billion stars that you can listen to for signs of extraterrestrial intelligence. In the United States we’ve listened to just two, back in 1960. The Russians have listened to something like a dozen.
So the situation is not that we have to build some vast and expensive new instrument to listen. We already have at hand the instrumentation necessary to muster such a search and we’re not utilizing it.
When you put it that, way, it seems astonishing that we’re not.
That’s right. I’m hopeful that in the next few years the situation will turn around and astronomers will be willing to spend a small fraction of their time on a regular basis searching for signs of extraterrestrial intelligence.
However, it’s likely to be a very long search. You can’t expect that you’re going to go out and spend a few weeks and find it, because even under optimistic assumptions only something like one in one hundred thousand stars should have a civilization that we can communicate with. It may be much less than that, but I don’t know anybody who thinks the chances are much better than one in one hundred thousand stars. So you’ve got to look at one hundred thousand stars, under optimistic assumptions, to have a good chance of picking one up.
In your book you talk about how inconspicuous the earth would seem from other stars. In Isaac Asimov’s phrase, the solar system consists of the Jovian planets — Jupiter, Saturn, Uranus, Neptune — and debris. We are part of the debris; if you looked at the solar system from another star you wouldn’t even notice us. Except, you point out, if you used a radio telescope, because ordinary radio and TV broadcasts in the past 30 years have suddenly made the earth, in radio wavelengths, “brighter” than the sun itself.
Well, the enormous amount of radio energy that we’re pouring out today is due to three sources. One is the high frequency end of the AM broadcast band, another is just ordinary domestic television, the third is the radar defense networks in the United States and the Soviet Union. Those are the only signs of intelligent life detectable on earth from a distance. It’s pretty sobering. It’s often asked, if there is extraterrestrial intelligence how come they don’t come here? Now we know. Just listen to what we’re sending out.
There’s a lot of soul music up at that end of the AM band, though.
Yes, and WQXR is at that end. There’s a wide range of things at that end of the radio spectrum. But television and radar are the dominant thing.
Anyway, only for a brief moment in earth’s history have we had broadcasting. We’re now going to cable television, the reason being that broadcasting wastes all that energy out into space when you’re trying to talk to people on this planet. So soon we may be sending it all along various pipelines with nothing leaking out. And I could even imagine, if we don’t destroy ourselves, our living with each other sufficiently happily that we are no longer constantly scanning for each other’s missiles. Therefore it’s possible that advanced civilizations don’t leak out any radio energy.
It is much harder to detect the leakage that a civilization uses for its own purposes than it is to detect a signal that they are aiming at us for us to detect. When I was talking about there being a hundred billion stars within range of our hearing, that was under the assumption that some of those stars are sending a signal in our direction. If none of them are sending to us and they’re just talking to themselves, then it is necessary to construct a very large array of radio telescopes in order to pick them up. That’s called eavesdropping.
But remember, we’re using a set of very restrictive conditions — namely that those guys are only transmitting as much power as we can transmit. We are the baby civilization in the galaxy, because we’ve just developed radio techniques in the last few decades. It’s not likely that anybody else we can communicate with would be that backward. So anyone we can tune in on must be much smarter than us and therefore much more capable.
Just in talking about civilizations having progressed beyond ours, we may be victims of such assumptions: J.B. Bury wrote a book called The Idea of Progress, the thesis of which is that the whole concept of progress has existed only within the last couple of centuries of human thought. You suggest at one point that technological civilization itself may prove to be only a fleeting manifestation of intelligent life, possibly because it tends to quickly destroy itself. Doesn’t it keep you awake at times just trying to trace some of these threads back, trying to get your thinking onto as solid a foundation as you can?
Yes. It’s a very important issue. I don’t spend most of my time on these issues, largely for the reason that you’ve just very well stated — Because it’s not experimentally well-based yet. It remains in a very speculative arena. I spend some fraction of my time trying to make people aware that this is a very important question, but I don’t pretend that the issue is solved at all. I think it’s perfectly possible that there are few or conceivably no other civilizations in our entire galaxy of 250 billion stars. It’s not out of the question at all.
But I can’t imagine a more important scientific question, and we have in our hands the tools to approach it. I just can’t understand why we’re not doing it.
The general question that you ask is in the area which I like to call chauvinism. There’s carbon chauvinism, water chauvinism — you know, people who say that life elsewhere can only be based on the same chemical assumptions as we are. Well, maybe that’s right. But because the guys making that statement are based on carbon and water, I’m a little suspicious. If they were based on something else I’d give much more credence to it.
I must confess I’m a carbon chauvinist. Having gone through the alternative possibilities, I find that carbon is much better suited for making complex molecules, and much more abundant than the other things that you might think of. The standard science fiction business of silicon replacing carbon just doesn’t work well at all. The only circumstances in which it works are circumstances in which there is much more carbon, and so it always comes out second. I’m not that much of a water chauvinist. I can imagine ammonia, or mixtures of hydrocarbons, which are not all that cosmically rare, playing the role of water.
Then there are G-spectral-type chauvinists, who say that you can only have life around stars that are like our own; most stars are very different from our own. Planetary biology chauvinists say that life can only happen on planets, not for example in stars or in the interstellar medium. I’m a planetary biology chauvinist; there seem to be good reasons why life can only happen on planets.
The extreme chauvinist says, “If my grandmother would be uncomfortable in that environment, then life there is impossible.” You come upon that pretty often. The phrase that you hear a lot, “life as we know it,” is based exactly on that. It depends on who the “we” is. There are many exotic microorganisms on the earth which do well in solutions of hot concentrated sulphuric acid, and so on. If you don’t know about them, you figure nobody could live in such an environment, but there are bugs that love it.
I think one of the great delights of exobiology is that it forces us to confront the provincialism in our assumptions about biology. All life on earth is essentially the same; chemically we’re identical to bacteria or begonias. It’s as though you said to a physicist, “You’re going to study gravity now, but you can’t go out of this room, and you can’t look at anything that has a gravitational influence except what’s within this room. Here are two big lead spheres. Measure how much they attract each other and try to devise a general theory.” Well, that’s very difficult. Newton did it not by being in a laboratory, but by looking at the motion of our moon and the moons of Jupiter and so on, and things on the earth as well. By making those connections he was able to make a general law of gravitation. Well, the biologists have mighty few general laws, and that’s because they have mighty few cases — like one.
When you look at speculation about possible other forms of life, it seems to me a lot of it is on one hand simply too fanciful. You mentioned, for example, that huge creatures with bone skeletons on an earth-like planet cannot exist because beyond a certain size bones don’t have the strength to do it. The skeleton would have to be steel. And enormous insects in an earth-like environment are likely to exist only in human fantasy, because insects breathe by virtue of diffusion, which is not efficient enough to keep a big creature alive.
That’s why motion pictures like Mothra are flawed.
I haven’t either, but I understand it’s a very large insect. Maybe I’m wrong. If it’s not a large insect then I don’t object to it.
So on one hand, speculation can be too fanciful. On the other hand a lot of it is too conservative — that’s the consequence of limited imagination. In what ways can people on either side open up their thinking and realize the great variety of real possibilities without just slipping over into opposite errors?
The only way is experimental. I just don’t think you can sit down and think and get rid of all that accumulation of prejudices and fantasies. The way our minds think is the result of millions of years of evolution — hunting and gathering food, shinnying up trees, mating, building fires and all the rest of it. The way we think hasn’t been optimized for confronting intelligence elsewhere, because we’ve never had to. So I just don’t expect that we’re going to make much progress by pure thought. The way we make the progress is to make the confrontation. Let’s get the extraterrestrial message and then very carefully and very slowly try to come to grips with it.
The first part of your question brought to mind Mars. Mars has had the fanciful elements — Lowell’s canals and all that — and it’s had the almost fussy chauvinistic approach — “Oh, it’s just like the moon.” That second argument went, “The moon has craters, the moon is lifeless. Mars has craters therefore Mars is lifeless.” Aristotle would turn over in his grave if he heard a syllogism like that.
Well, what’s the reality as revealed by Mariner IX? We don’t see any canals with liquid water running through them, but we do see things that look for all the world like dried-up rivers. We don’t see a planet that’s like the moon either; we see something just different. It’s just fantastically different than anybody guessed. And I think that’s where the reality is going to be in the search for extraterrestrial intelligence. It’s not going to conform to our fantasies and it’s not going to conform to our chauvinism.
Is the scientific method changing from a purely deductive, rational method to a more creative activity which tests itself against coherent data? And is our conception of the universe changing from seeing it as entropic and random to a view that it is essentially unified, and that the things that science treats are only part of a greater unity? Is that actually going on?
I don’t think science has ever been all that deductive. The cutting edge of science is always following the wild hunches, tracking out the clues, and that sort of thing. It differs from art only in that it makes a different sort of confrontation with reality. There’s a test of whether a scientific theory is right or wrong: Namely, does it correctly predict all the things I can measure? That’s different from the test of the success of a work of art. But I think that the kind of internal excitement motivating the scientist is very artistic. It’s that same kind of searching for order and meaning, a quest for how the universe is put together.
I think we’re constrained in how far we can go. Not by the scientific method; it seems to me the only reasonable approach, the one that confronts the data. Otherwise how would you ever know if a view were right or wrong? I think we’re constrained by our minds. For the reason I mentioned before, our minds are put together the way they are because of the needs of a very different sort of existence in which human beings evolved — a hunter-gatherer society — and now we’re asking that sort of brain to approach quite different circumstances.
It’s remarkable that it does as well as it does. The thing that I find astonishing is that we are able to invent simple rules and constructs which are able to predict quantitatively a wide range of natural phenomena. I mean, how is it that we can have one little simple equation which describes pretty closely how bodies fall, no matter where on earth they fall or where you throw them or what their shapes are. You know, it’s just a couple of little equations which are taught in high-school physics. Why is the world put together in such a way that we are able to construct these little equations which explain such a wide variety of phenomena? That’s the astonishing thing.
The answer to that may be merely that things falling were pretty important to our ancestors, who lived in trees or something, so our minds evolved in such a way that things falling was something we had to understand. Those guys that couldn’t understand it all fell out of the trees and broke their necks. We’re not their descendants. We’re the descendants of the guys who could understand how things fell.
But on the other hand, understanding how things fall here gives us a law of gravitation which happens to describe how two galaxies orbit each other. That’s pretty fascinating…. Einstein said he found that the most astonishing thing of all is that we’re able to understand as much as we can. He was not astonished that there were some things that we couldn’t understand; that of course is what you’d expect.
Now there is a kind of dichotomy that a lot of people draw between rational and mystical. I’m not sure that that’s a real dichotomy. For example, the thing that’s described under the drug experience is to be one with the universe. Of course it’s also described in non-drug religious experience. Eastern religions, Christianity, all have something like it. If you ask somebody who’s had such experiences what he means by “one with the universe,” well, of course there’s great difficulty in converting it into words because it’s a highly nonverbal experience. But I haven’t found anybody who, while having that experience, was able to test it out.
You know, “Terrific, here I am, one with the universe, now I’m going to ask a question which nobody on the earth knows.” OK? In detail. And come out of the experience, and say, well, “That was really a fabulous experience, and incidentally if you will perform the following experiment, with deuterons into a vanadium target, you’re going to get the following result.” Everybody says nonsense, but you do it and it turns out that you were right. If that happened then I’d be much more willing to believe we were synched up to something we don’t now understand.
So while not at all taking away from the ecstasy of such an experience, I’m skeptical about whether it really makes contact with the way in which the universe is put together. I think it makes contact with the way our skulls are put together, which is a different thing. I think mystical experiences may be excellent ways to find out about ourselves, at least it seems to me that would be the case, but I don’t think we find out what’s outside of ourselves that way.
The so-called rational approach seems to me, for all its shortcomings, to be the only way that works. I don’t mean by that to justify at all the kind of mindless rationalism in which people say, “Don’t ask me what happens to these poison gas canisters, I’m just doing my job.” That’s not what I’m talking about at all. Rationalism is not the suspension of ethical judgments. We’re talking about finding out about the universe. I think that the rational approach, or if you want to call it that, the scientific method, is the way to go. The thing I stress is that it’s driven by strong emotions. It’s not dispassionate. The scientist — the real scientist, not the drudge — is a guy who is strongly motivated to find out about things around him and who would do it even if he wasn’t making some money or recognition off it.
Have you been reading more or have you turned up more evidence about the possibility that we have already been involved in interstellar communications? There is an argument that recorded history may make up only a small and not particularly important portion of man’s real history. William Irwin Thompson suggests that, as he puts it, “Something has been communicating with us through the epochs of our civilization.” He holds to the idea that communication historically could have been going on over periods so long that only mythology provides a vessel durable enough to accumulate any of the information.
In your book you include material gathered from Sumerian archeology. And of course there are many legends other than the Sumerian which are striking because you find such widely separated civilizations sharing a seemingly common mythology — a belief that civilization was derived from some high order of beings who passed it along to some sort of a priestly class of people and then disappeared. So my question is whether that seems to you a profitable avenue to pursue.
Yes, I pursue that because one, it’s a logical possibility, and two, it seems silly to spend a lot of money looking for life elsewhere if we have the evidence right here on earth. The conclusion I came to is that you’ll never prove anything by legend alone. There are just too many possibilities. Even with very similar legends, there are two classic possible explanations. One is that they in fact had contact among themselves. There was a huge amount of cultural diffusion in primitive time; even though it took a long time to traverse from Europe to Asia, those traverses were being made.
Secondly, there’s a possibility that some kinds of things are wired into us. After all, birds have wired into them how to build nests, fly south for the winter and so on. There may be certain images that are wired into human beings, in our genetic material. Therefore human beings in very different places may have similarities in their thinking. I don’t consider that a bizarre idea at all.
The only situation in which such a legend would be believable would be if it was remarkably detailed: The gods gave us information, and we didn’t understand what they were talking about, but in the 13th century Irish monks copied it down, and in the 16th century somebody cataloged it and noted what was in there but he didn’t understand what it was about either; and now it turns out to be details for the construction of a transistor radio. Well, such a legend I’d be willing to consider extremely seriously. But it’s never anything like that. It’s, “They came down and taught us how to write, do agriculture and regulate our behavior.” That seems to me to have many other possible explanations.
The other possibility of course is to find the artifact; to find a sample of extraterrestrial technology that could not have been created by human beings because we weren’t technologically up to snuff at that time. Those two cases I would certainly consider worth paying a lot of attention to. But the usual sort of legends about beings that lived in the sky and were not human beings — there are just too many other ways of understanding that for me to think they are serious clues to extraterrestrial intelligence.
Is it realistic to think that there might not only be planets on which the environment is too hostile to life to exist, but also planets on which life is too comfortable for intelligence to derive? I’m thinking of the suggestion that the Ice Age may have had to do with the genesis of civilization on earth, and on the other side Arthur C. Clarke’s suggestion that the chief difference between men and dolphins may be simply that at a point in evolution, the ancestors of the dolphin turned around and went back into the ocean and we didn’t. They seem to be having a good time and we have civilization. Is that a meaningful question?
Oh, yes, it’s a meaningful question. Unfortunately there are no meaningful answers. The Ice Age suggestion is Toynbee’s idea of challenge and response. I think there is some aspect in which that is right. But as to the question of what are the accidental rare factors necessary to make an intelligent being by slow evolutionary process, and what are the factors that develop a civilization, nobody knows. The reason nobody knows is first that you can’t do experiments on it — apart from ethical questions it would just take too long — and secondly, the one technical civilization that’s developed on this planet has the awkward tendency to wipe out all the other civilizations that haven’t yet achieved technical expertise. We never find out what would have happened to Aztec civilization if we had left it alone.
If that tendency proved to be inherent in technological civilizations generally, it would be an awfully good argument for our not broadcasting anything.
Yeah, this argument comes up many times. The main point to bear in mind there is that it’s too late. We’ve already broadcast. A wave front of electromagnetic radiation is spreading out from the earth at the speed of light, and contained in it are arias by Enrico Caruso, the 1924 election returns, the Scopes Trial…. We’ve sent it, to say nothing of other things we’ve been talking about like television and the semi-paranoid radar defense networks of the major technical powers. So, it’s just too late to say we shouldn’t send. We have sent.
But my guess is that’s not where it’s at. The spaces between the stars are just enormous, and it’s so difficult to do an interstellar journey that we cannot pose any threat to another civilization hundreds of light years away, and that distance between civilizations is an optimistic assumption. Even at the speed of light it would take hundreds of years to get there, and we certainly can’t travel anything close to the speed of light. So there’s a kind of imposed quarantine, at least at our level of civilization. There is no way in which we can pose a threat to any other civilization and they must know it.
As for the other kind of paranoid fantasies — that they’ll find out we’re here and come and eat us because we’re so tasty or something — that doesn’t work because the freightage is too expensive. If you found human beings had a particularly tasty sequence of amino acids in their proteins, you’d take home one human being and synthesize the protein and artificially mass-produce it. The gourmets on some other planet would then eat stuff that was made on that planet.
No, I think that this is the result of just not thinking the implications through carefully enough. I don’t think anybody poses that kind of threat to us, and the sort of threat we might pose to somebody else is constrained by the vast distances between the stars. Also, mankind is getting better.
One thing about those vast distances, though, is that in your writing it sometimes begins to seem easy to traverse them. For example, you mentioned that if we could build a spaceship able to maintain an acceleration close to the force of gravity on earth, we could travel to the center of the galaxy — 30,000 light years away — in only 21 years measured on board the ship, owing to Einstein’s time dilation.
But that’s for a technology that we’re nowhere near obtaining, if it’s possible at all. That starship capable of accelerating at 1g reaches 99% the speed of light as time goes on. It never reaches the speed of light because of the fundamental restrictions of special relativity. We must be at least centuries away from having such devices.
For example, a spacecraft called Pioneer F is on its way to Jupiter. It will get a big acceleration when it passes Jupiter, like the whip at the county fair, so much so that it will become the first man-made object to leave the solar system. At the speed it’s going, how long before it gets to the distance of the nearest star? About a hundred thousand years.
That serves to calibrate the difference between the kind of 1g constant acceleration starship that I was talking about and where we really are at. We don’t know if it is possible to have such a 1g starship. But if it is, we’re certainly a huge way from having it. Some other guys may have it, but even if they do, I suspect it’s extremely expensive and they don’t just go tooling around for Sunday drives.
It appears that we’re also hundreds of years away from holding a dialogue with another civilization. You estimate that the average distance between intelligent civilizations, based upon a chain of conjecture, is maybe a hundred to a thousand light years.
Yeah, say 300 light years. So that means that they send a signal that says “Hello, how are you?” and we send back saying “Fine, thank you,” and that takes 600 years or something.