Interview with Paul Davies

February 23, 2007


CI:      I’m gobsmacked that you’ve written more than two dozen books. How do you do it?

PD:    People often ask how I manage to write so many books and do other things as well. I write about the things I’m thinking about anyway, in particular the topics of my research projects. Research is useful for writing a “popular” book—I like to think of it more as public outreach than popularization. It’s a good way to really understand something. If I can explain it in simple sentences, I’m probably on top of the subject.

CI:      That’s similar to the reason some people teach outside of their discipline—you’re explaining it to students, who ask obvious and direct questions.

PD:    You’re fast to get to the core issue, exactly. I also write fairly quickly, if it’s a subject I know something about. I can do a three-thousand-word article on black holes in an afternoon, whereas some people might struggle over it for several days. A short book on a topic I know well may take no more than a week or two. As anyone who’s written a book knows, the easy part is the creative part, getting the core content down. Most of the labor goes into the many edits, tracking down references, getting people’s names spelled correctly, artwork, index, all those things. But those peripherals can be done in spare moments, on planes and trains.

CI:      What about the issue of popularization in general? There’s a mixed reaction among senior scientists as to whether it’s a good or a bad thing to do. There was a famous story of Carl Sagan not being elected a member of the National Academy of Sciences because of his popularization.

PD:    So I gather. When I started this game in the seventies, a work colleague and friend said, “Stop writing these popular books, it’ll seriously damage your career.” There was a rule of thumb then in theoretical physics that for every popular book you wrote, you subtracted ten papers from your publication list.

Then a couple of things changed, in particular for popular physics books. Students turned away from physics in the seventies and eighties in quite a big way. Universities realized that the subject was going to die unless young people could be enthused. Suddenly, most university administrations became supportive of people who were prepared to communicate with the wider public, particularly with young people, and to encourage them to come into what were perceived as difficult subjects—physics, mathematics—by giving them some sex appeal.

That was one thing that changed. The other was the Stephen Hawking phenomenon; Brief History of Time outsold just about every other book—it was on the London Sunday Times bestseller list for over four years. A lot of people felt, “If it’s all right for Hawking, then it’s all right for me, I can write a popular book.” Everybody charged through the gap. Almost every distinguished scientist you meet today has written one or two popular books. Now it’s okay to be a popularizer, but it’s been a long, hard struggle.

CI:      Do you think there’s been an impact on science literacy? Surveys imply a stubbornly low level of science literacy, however you want to define it.

PD:    I just saw the result of a new survey that was truly awful. It’s not hard to get examples. My wife teaches science communication at Arizona State University. She had her students, who mainly have an arts background, go around the campus and ask some basic questions—for example, “Is it true or false that the father determines the sex of a child?” About a third of the students thought it was false. [Laughs] So I would not like to claim that the plethora of popular science books over the last twenty years have significantly improved science literacy; that’s probably not the case.

Most of the people who enjoy reading these books are people who have some scientific background, or at least training in a discipline that requires a certain amount of ordered thinking. A lot of people write to me with the start line: “I know no science, but…” Lawyers and medical doctors will often have much in the way of basic science. Another group of people, who might be regarded as dreamers, people of a mystical frame of mind, think science—particularly physics—is so weird and wonderful that it must hold all the secrets of the universe; for them it’s a substitute religion. They look to scientists, particularly people working in fundamental physics, to point the cosmic way for them.

Do young people learn any real science from these books? I’m a bit doubtful. To put it unkindly, we have to dumb it down so much that what’s left is an indication that certain subjects are exciting and important and have a lot of things happening in them. I have a go at teaching concepts they need to know—my most recent book is about the unification of physics, so I’ve had to go into areas like string theory, the different fundamental forces, and symmetry breaking and its application to the early universe. I’ve found ways to explain those things. But the average high school student isn’t going to be doing symmetry breaking in gauge field theories; they’re not going to be learning about wormholes or even black holes. They may go into a little razzmatazz on that, but they’re going to be struggling with Newton’s equations, things as basic as defining energy. I’m not sure these popular science books help with that. The best thing they can do is to show that science doesn’t stop with Newton’s equations. There’s a wonderland that lies beyond. But you’ve got to put in some work if you’re going to get to the forefront of the field; it’s a hard slog, but the view from the summit is breathtaking.

CI:      Do you have an archetypal reader in mind? Do you pitch your writing at a particular audience?

PD:    I don’t have any particular person in mind. What I usually say is that the reader needs no specialist background knowledge in physics or cosmology, but that I’d expect them to have a strong interest in science and to have followed the key developments. It helps if they know what’s going on.

There’s always this problem of which words you can get away with. My wife is a great help because she’s a radio science journalist, so she knows you can’t use words like “isotopes.” You can use “atom” and “black hole,” and increasingly you can talk about DNA, even though most people wouldn’t have a clue what the letters stand for; but there are certain other words and concepts that are off-limits, so there’s always this problem of steering in and out of things. I regard these as the words or concepts that have currency, even though they’re not understood; they’re like little pegs upon which you can hang other things.

For example, time travel is a fun topic to imagine. How do we do it? It may not be possible at all, but one possible way is a wormhole. The concept of a wormhole in space requires the general theory of relativity and an understanding of differential geometry and topology. These things are all way beyond what ordinary people are going to understand. But I can say, ”You’ve all heard of black holes. A black hole is a one-way journey to nowhere, you fall into it and you can’t get out again. Imagine something like a black hole, but with an exit as well as an entrance. It would be like a stargate or a shortcut between two points in space a long way apart. Imagine going through it and coming out somewhere else suddenly.” So I can play off those things, but the people who would be happy to accept “black holes” as currency couldn’t give you an explanation of what a black hole is. And yet we’ve heard so much about them. Same thing with an atom—everyone’s heard of atoms. What are they? Ask people to tell you the architecture of an atom or how it’s held together—they wouldn’t have a clue.

CI:      Astrobiology’s a tricky example because, at least in this country, the slate is not clean. People have been inculcated by the popular culture to believe not only that aliens exist, but that they’ve visited. Getting back to a scientific reference point for astrobiology is even harder than in physics, where people may have some dim, vestigial memory of their only physics course.

PD:    That’s quite true. It’s even worse in the subject of SETI, which is the speculative end of astrobiology by anybody’s standards, and yet to be sharply distinguished from alien abductions and UFO stories. It is tricky. The difficulty is that we like to play off that intrinsic fascination—as a teenager I was blown away by these stories, thinking that we’re not alone, and we’re surrounded by advanced alien beings. It’s a thrilling concept, and it’s unfortunate that when we look at the scientific evidence, all that stuff melts away. Yet there’s still this sense that trying to find out whether we’re alone in the universe, trying to locate a second genesis of life—even if it’s only microbial life—is a wonderfully compelling goal. It’s what drives us on. The question is, how do we keep the public on our side without giving them the impression that we’re looking for little green men? They seem disappointed when we say, “Oh no, it’s just microbes.” [Laughs]

CI:      As we exceed the first few hundred extrasolar planets, we have pictures of essentially none of them. We can’t tether to the visual impact of the beautiful Hubble pictures. Astrobiology research, when it’s represented for the public, is sometimes disappointing—the “little green men” expectation is one part of it, but there’s also, “Show me! We can’t see all these things you’re talking about.” Spectra don’t set a deep hook in a public audience.

PD:    It would take a very significant discovery to turn that around; perhaps if somebody saw chlorophyll in a spectrum from an extrasolar planet, but we’re a long way from being able to do that. The search for Earth-like planets elsewhere in the galaxy could be made the focus of an international movement. Searching for other places like home out there has uplifting appeal. It’s not inconceivable that, decades ahead, we could have instruments with the capability of imaging entire planets to a resolution where we could look at pictures and say, “Wow, there’s another Earth out there.” A lot of people could get behind the idea of exploring the cosmos beyond the now-familiar retinue of planets in the Solar System.

CI:      Even if we don’t promise it, Earth-clones at least offer the possibility of companionship.

PD:    That’s the way NASA always seems to present it. That’s a bit shameful, given that, since Viking, there has been no astrobiological package. All of the missions—particularly those to Mars, which is the best hope for life—are clearly relevant to the astrobiology program, but nobody’s actually gone and searched.

CI:      There’s the Mars Science Lab.

PD:    Yes, it’s the next mission. Finally, that will happen. There was the ill-fated British mission, Beagle 2, which was going to be the first since Viking to attempt to do biology on the surface of another planet. Every time I read the description of another mission, the possibility of life is brought up. It’s always cast in the context of looking for life elsewhere, but mostly the scientists are not looking for life elsewhere, they’re looking for other things. The subject has great propaganda value in tying all of planetary astronomy to some quest for life. Evidently the public likes that idea. How can we best capitalize on that, given that it may be a long time before we get any concrete evidence?

CI:      It’s the expectations game—you don’t want to overpromise or people will lose interest. I’m going to use discipline to not ask you about cosmology and other areas; I’ll keep to astrobiology. You had a series of parallel interests for a long time. When did you first start getting interested in astrobiology at a research level? What were the issues that attracted you?

PD:    I’ve often wondered how I got into this game. The interest goes back a long way, to my early teens and reading those UFO stories. When I was a student in the sixties, no scientist wanted to talk about life beyond Earth; it was regarded as absolutely inconceivable that there was any life out there. For me, a turning point was a Cambridge conference in 1983—organized by Martin Rees, who’s now President of the Royal Society—in which a number of astronomers and cosmologists and biologists were brought together. It was called “From Matter to Life.” My serious interest in the subject can be traced to that time. I realized there were whole subject areas that could be investigated. Freeman Dyson was there, and he also traces his interest to that point; he wrote Origins of Life as a result of that meeting.

I had read Schrödinger’s book, What is Life? as a young post-doc at Cambridge. To a physicist, life looks like a miracle. [Laughs] I think physicists are much more intrigued by life than biologists. Biologists take it for granted—“Of course it’s living!”—because that’s all they study. But it really does blow physicists away. I’ve always been fascinated by what it takes to make a living organism. What’s the physics going on there? The other half of the question is, at what stage did stupid atoms start doing such clever things?

A couple of things came together for me in Australia. One was meeting Duncan Steele, who is an expert on asteroid and comet impacts; he had done work with micrometeorites and was particularly interested in organics in meteorites. I learned this whole dimension of astrobiology from him, that the Solar System is full of organic material—although the word “organic” has to be used carefully: it doesn’t mean the detritus of once-living things, it means it’s a building block that we find in life. Duncan Steele had told me about asteroid and comet impacts, and Tommy Gold, who was at the conference, had wacky ideas about trying to find hydrocarbons in the deep subsurface of the Earth, which led to the discovery of life under the ground. Putting two and two together, as did Jay Melosh independently here at University of Arizona: clearly, if rocks could be traded between planets, maybe microorganisms could as well. In the early nineties I wrote about and lectured on the possibilities of transport of life between Earth and Mars by this mechanism, but I couldn’t find anyone who would believe me. I’m sure Jay would have done, but we hadn’t discovered each other at that time.

CI:      Now the paradigm has shifted to the point where everyone says, “Sure, there’s a conveyor belt.”

PD:    Exactly. That all turned around. Why? Bill Clinton stood on the White House lawn in 1996 and proclaimed that NASA had evidence for life on Mars, based on the Allan-Hills meteorite. Most of that evidence has gone away, but it brought to public attention to the idea that a Mars rock could come here with pieces of microfossils, and maybe it could come with live microorganisms. The whole subject changed.

This little bit of agitation had come to the attention of Malcolm Walter, who as geologist-paleobiologist works with microfossils in western Australia, the oldest convincing traces of life on Earth.

CI:      They’re stromatolites?

PD:    Stromatolies and microfossils. They’re about 3.5 billion years old. It’s looking pretty convincing. That’s the place to go if you want to see the oldest traces of life. I was asked to help set up the Australian Center for Astrobiology, which was founded about the year 2000. I’ve spent five or six years getting that up, getting to know people working in all aspects of astrobiology. I keep saying, “I’m just a physicist trying to make sense of this stuff—I blundered into this field from the outside.”

CI:      In the history of biology, there have been some interesting perspectives brought by physical scientists.

PD:    You don’t have to convince me that physics is the one discipline that can illuminate everything.

CI:      Let me go to the speculative edge of the panspermia idea. Maybe not in an environment like the Sun’s, but in other stellar environments, transfer between planetary systems might be possible if organisms could go into a hibernation state for sufficiently long. Is that a plausible idea?

PD:    Statistically, what’s favorable is transfer between neighbor planets. It’s easier to go from Mars to Earth, because of the lower surface gravity of Mars, but it can go the other way as well. Getting off Venus is hampered both by the higher gravity and the thick atmosphere. But, with big enough impacts, you could splatter rocks off any of these bodies. Some of those rocks will be ejected from the Solar System by Jupiter. Then it boils down to two things. Could microorganisms survive long enough to travel interstellar distances? The answer to that seems to be: maybe. But that’s not the real issue. Much more significant is the question of the chances that a rock blasted off Earth would ever hit another Earth-like planet in another star system. The statistics for that are incredibly unfavorable; it’s exceedingly unlikely. So this rocky panspermia works well within a planetary system, but works very badly between planetary systems.

That’s not to say it’s never happened. It clearly is possible with very favorable statistics, or an early phase during which a lot of planetary systems were forming fairly close together. If perchance one of them had early life, it’s not inconceivable that it could have spread to the others, and then those star systems moved apart. But these are odds and ends, special factors. Generally speaking, life isn’t going to spread across the galaxy this way.

There is another panspermia theory that is quiet different—they’re often confused. The original one goes back to ancient Greece, but was popularized by  Svante Arrhenius about a hundred years ago. It suggests that microorganisms could waft naked across the galaxy, propelled by the pressure of sunlight and starlight. Microbe-sized, bacteria-sized particles can certainly get across the galaxy that way, but they’re almost certainly going to be dead on arrival because they’re exposed to the harsh conditions of outer space, in particular ultraviolet radiation. UV radiation from the Sun is absolutely, totally deadly. You’re stone dead in next to no time if you’re exposed to that. It’s easy to screen out—a small rock will do it—but a truly naked microbe isn’t going to make it. The advantage of naked microbes is that they can be blown around in countless trillions among trillions, so the statistics are much more favorable. But they’re all going to be dead when they get there.

CI:      One of the dichotomies I’ve encountered talking to physicists and life scientists about life in the universe is that the biologists seem to be less sanguine about widespread and even microbial life; they view a lot of the contingencies or special conditions as being determining, whereas most of the physical scientists say, ”Come on, there are a few hundred million habitable places in the galaxy, more if you include moons of outer planets as well as terrestrial planets—how could all those hundreds of millions of Petri dishes be dead?” The statistical game seems to be compelling to most physical scientists.

PD:    Right. But the flaw in this argument is that you have to decide right at the outset: did life form just from the random shuffling of the building blocks? We know it’s easy to make building blocks out of amino acids—it’s dead easy, you could make that in any high school lab. It’s the next step—putting them together in the exceedingly elaborate, highly specific, complex structures that we would recognize as an autonomous, living thing—that gets tricky. We may be living in a universe that has ten to the twentieth potential Earthlike planets within the body of space that we can see. But ten to the twentieth is a trifling number compared to the odds against shuffling those molecules into the right formation. If it happened by chance shuffling, we’re it; it’ll have to be just us.

CI:      That’s illustrated most vividly in the Fred Hoyle comment, the assembly of a jumbo jet…

PD:    …by a whirlwind in a junkyard. It’s a compelling image. But we don’t know whether that’s the way it happened. Maybe there is something like a Judeo-Christian deity, a cosmic imperative; that is, maybe life really is built into the laws of nature in some fundamental way. Maybe there are organizing tendencies that shortcut those odds enormously. In other words, maybe life is a natural outcome of a complexification of matter, in much the same way that the formation of crystal is a natural outcome—it’s determined already by the laws of physics. This type of biology, called predeterminism, is very popular. Many astrobiologists accept it as the default assumption: that life will out, given Earthlike conditions. But it is an act of faith. In the present state of ignorance it could be anywhere on the spectrum between total chance—happened only once in the entire universe, a stupendously improbable accident—right up to being part of the natural workings of a fundamentally bio-friendly universe.

CI:      Which presumably is why going from the first example to the second example is so critical. Perhaps that second example will be the subsurface of Mars.

PD:    The frustrating thing about Mars is that we might go there, find life, celebrate it, and suddenly find that it’s good old Earth life. It got there from here or here from there, it’s just another branch on the known tree of life, it didn’t start from scratch independent of life on Earth; these two planets have been compromised by cross-contamination. To find a truly independent second genesis, we may have to go beyond the Solar System altogether.

CI:      Could we rule out the transfer idea if it were Europan life?

PD:    It’s better than Mars, although it’s hard to get through all that ice to discover what might lie beneath. But, even there, it couldn’t be ruled out—rocks have gone from Earth to Europa. It does happen. Whether it happens often enough, I wouldn’t like to say.

There is one way of getting around all of this: if it is the case that life forms readily in Earthlike conditions, shouldn’t it have happened many times over right here on Earth? In other words, if there is a cosmic imperative or life principle, we can test it by looking for evidence of multiple geneses right here. That’s something I’ve been thinking about a lot in the last year or two; my own research in astrobiology is precisely directed to looking for evidence of a second genesis right under our noses on our home planet.

CI:      As you alluded to, the nature of the evidence more than 3.5 billion years old is pretty dicey, so this is difficult empirical work.

PD:    We can’t reconstruct the events that took place at that time—many of those records have almost certainly been obliterated. A lot of people would like to identify the cradle of life—find the place where it happened, maybe a relic or trace of what happened. I think that’s inconceivable. I often get into arguments with people about whether science can explain the origin of life. We may never know, because the origin of life is an exercise in chemistry, in physics, in earth sciences, in informational processing, computation, all sorts of things. It’s also an exercise in history—there may have been certain sequences of events that were necessary for life to get going. These could have been microscopic events that happened billions of years ago, all traces of which have been lost. We may never know how it happened. That doesn’t mean it was a miracle; it just means that, like a lot of history, the record peters out if you go back far enough. That’s a hard point to get across.

I’m hopeful that we may find, right under our noses, extant organisms descended from an independent genesis. There could be microbes that are not our life, but life from some other origination event. Finding such microbes would immediately establish the cosmic imperative, the life principle. Then we would expect life all around the universe.

CI:      What might that life look like? Even if there is a tendency for chemistry to evolve into biochemistry, at the higher levels of organization it might not be that similar. Biologists are comfortable studying their one example of biology, but the alternative biologies that could be reached with similar starting points and building blocks presumably are quite diverse.

PD:    We could be limited only by the powers of our imagination. Alternative forms of life here on Earth are likely to be microbial, because we’d notice if there were alien elephants wandering around; but you can’t tell by looking at microbes what they’re made of—you have to explore their innards. The biochemical techniques used to study life as we know it are customized precisely to life as we know it, so there’s circularity: we’ll only discover life as we know it.

If there are alien microbes—not “alien” in the sense of having come from another planet, but alien in the sense of being an alternative form of life—those could differ in a large number of ways from life as we know it. It could be something as small as a different genetic code, a different sequence of amino acids or nucleotides. It could have opposite chirality, that is, it could be like a mirror form of known life. It could be based on a more extreme solvent than water. It could be non-chemical altogether.

CI:      Somewhere in that spectrum is that it might not need the cell as the unit of organization.

PD:    Yes. We’re obsessed with the idea that life is a little blob of something; there’s no reason that has to be the case. I often wonder whether life, even life as we know it, could have started with something large, a complicated chemical cycle that only later on became refined and microminiaturized and packaged into cells.

My old friend Graham Cairns Smith in Scotland thought of clay crystals, and that there could be clay life all around us, but it’s so boring that we’ve overlooked it. [Laughs] I suppose I have in mind something that would look like a microbe, but it wouldn’t taste like a microbe; there would be an alternative biochemistry. The challenge would be determining whether it’s a deeper branch on the known tree of life, or whether it’s a genuinely different tree. That could be difficult, but there are obvious things to look for. And the more different these alternative microbes would be, the more likely it would be that they had a different origin.

CI:      I have to ask you about anthropic principle. There’s a big distinction between recognizing fine-tuning in the physical universe and jumping to the various levels of anthropic interpretation of those physical facts. Where do you stand on those arguments?

PD:    It’s a vast topic—on which I’ve just written a book.

CI:      [Laughs]

PD:    It would be hard to give you a quick summary, but I’ll make a few points. The first is that I do take life of mind seriously. Most physicists would regard life as a bizarre aberration in the universe, not something integral to its workings; I have always thought differently, largely for philosophical reasons, not scientific reasons. I think the emergence of life and the emergence of mind are no trivial accident or byproduct; they are deeply imbedded in the workings of things, which is why I’m so interested in finding evidence that life is widespread.

Giordano Bruno was burned at the stake for many heresies; one of them was preaching the idea of alternative inhabited worlds—the Church felt it was very threatening, and that a universe with a purposeful God would not have other inhabited worlds. That’s exactly wrong; a universe throughout which life flourishes, a universe that is in favor of life, is much more congenial to the notion of meaning and purpose than a universe in which life is a bizarre statistical fluke that happened on one planet and is of no significance in the great cosmic scheme of things. By temperament, I like the idea of a biological universe and life happening all over the place.

CI:      I detect optimism on the issue of the cosmic imperative towards biology. It’s amenable towards scientific investigation, that’s the key.

PD:    That’s right. I get tired of all these arguments about the deeper aspects of science and cosmology, especially when it’s all words. I keep wanting to come back and ask, “Where is the science? How can we test this?” I’m always trying to focus in on things. For example, in the subject of emergence people often say—using lots of words—that there are certain thresholds of complexity above which we see phenomena that cannot be captured by the physics of the lower level. But what does it matter? Are these new laws of physics? We have a phenomenon of downward causation. It looks like higher levels of the system have causal efficacy over the lower levels; wholes can affect parts in a way that we can’t understand by looking at the parts on their own. But does it matter to the humble foot soldier of physics—namely, the atom? Are there any forces being deployed that we could not understand without having to see emergence? If so, what do we look for, and how do we pin it down? I always want to go beyond philosophy and words and look at real science.

CI:      Do you think the physical scientists have developed sufficient tools to address complex systems that they could apply ideas to biology and emergence?

PD:    No, I think the field of complex systems is still in its infancy. One of the reasons we don’t understand the origin of life is that we don’t understand the principles that apply to the emergence of complex organization.

CI:      It doesn’t seem amenable to computation approaches, either.

PD:    The problem with doing computation is that you often lose sight of the physics amid the welter of pictures and computer output. That’s okay; it’s a taxonomy, and it’s a bit like the time of Linnaeus. You go around, collect plants, look at their shapes and classify them and so on, but you don’t understand the principles. I’d like to know the principles that complex, organized systems have in common. If we’re to try to understand the secret of life—which we don’t, we can describe life at the molecular level in great detail but the whole package still looks like a miracle—if we’re going to understand that, we probably have to get clues from looking at nonliving systems that have organized complexity, in particular emerging complexity, to get a clue as to how the complexity of real life emerged.

CI:      Is that one of the research agendas for your Institute?

PD:    Yes. I’m running a workshop on life as an emerging phenomenon.

CI:      One last thing: by coming to live in Phoenix in a year that’s anticipated to be unusually hot, you’ve declared yourself an extremophile.

PD:    [Laughs] Everybody’s warning me about that.