What's stopping humans from living in space? The problem isn't just a loss of political will to finance human space flight. Rocket science turns out to be rocket science - not easy, and constrained by some very real limitations dictated by material science, the physics of acceleration, and the unwieldy economics of interstellar propulsion. Until a real-life Zefram Cochrane comes along to invent a practical warp drive, we may not be sightseeing on any Class M planets anytime soon. One of the best briefings on the state of the art of interstellar exploration is Lee Billings' essay "Incredible Journey." Famed science journalist Steve Silberman recently interviewed Billings on his blog Neurotribes about when we'll be living among the stars. Here's what he found out.


Image of the Milky Way's galactic core via NASA, ESA, SSC, CXC, and STScI.

Like many geeks of the post-Sputnik generation, I grew up hoping that space travel would be common by the time I reached middle age. Weaned on a youthful diet of speculative fiction by the likes of Ray Bradbury and Arthur Clarke, raised on Star Trek and The Outer Limits, and thrilled by real-life hero Neil Armstrong's "one small step" onto the gravelly surface of the Moon when I was in elementary school, it never occurred to me that humankind's manifest destiny in the stars would be undone by changing political winds, disasters like the Challenger explosion, and a mountain of debt to pay for misguided military adventures like the War in Iraq.

It's true that, in some ways, we're living in a new golden age for space nerds. Bard Canning's gorgeously enhanced footage of Curiosity's descent to Mars - made instantly available by the global network we built instead of a Hilton on the Moon - certainly beats grainy snippets beamed down from Tranquility Base. A newly discovered exoplanet that "may be capable of supporting life" seems to make headlines every few months. Cassini's ravishing closeups of Saturn regularly put the fever dreams of ILM's animators to shame. But wasn't I supposed to be "strolling on the deck of a starship" by now, as Paul Kantner's acid-fueled hippie space epic Blows Against the Empire promised me when it was nominated for a Hugo award in 1971?


One of the best briefings on the state of the art of interstellar exploration is Lee Billings' essay "Incredible Journey," recently reprinted in a wonderful new anthology called The Best Science Writing Online 2012, edited by Scientific American's Bora Zivkovic and Jennifer Ouellette. I'm very honored to have a piece in the anthology myself: my NeuroTribes interview with John Elder Robison, author of the bestselling memoir of growing up with autism, Look Me in The Eye, and other books. When SciAm's editors suggested that each author in the book interview one of the other authors, I jumped at the chance to interview Billings about his gracefully written and informative article about the practical challenges of space flight. Billings is a freelance journalist who has written for Nature, New Scientist, Popular Mechanics, and Seed. He lives outside New York City with his wife, Melissa.

Silberman: Several times a year now, we hear about the discovery of a new exoplanet in the "Goldilocks zone" that could "potentially support life." For example, soon after he helped discover Gliese 581g, astronomer Steven Vogt sparked a storm of media hype by claiming that "the chances for life on this planet are 100 percent." Even setting aside the fact that the excitement of discovering a planet in the habitable zone understandably seems to have gone to Vogt's head at that press conference, why are such calculations of the probability of life harder to perform accurately than they seem?

Billings: The question of habitability is a second-order consideration when it comes to Gliese 581g, and that fact in itself reveals where so much of this uncertainty comes from. As of right now, the most interesting thing about the "discovery" of Gliese 581g is that not everyone is convinced the planet actually exists. That's basically because this particular detection is very much indirect - the planet's existence is being inferred from periodic meter-per-second shifts in the position of its host star. The period of that shift corresponds to the planet's orbit as it whips from one side of the star to the other; the meter-per-second magnitude of the shift places a lower limit on the planet's mass, but can't pin down the mass exactly. So that's all this detection gives you - an orbit and a minimum mass. That's not a lot to go on in determining what a planet's environment might actually be like, is it?


Now, get up and walk around the room. You're moving at about a meter per second. Imagine discerning that same rate of change in the motion of a million-kilometer-wide ball of plasma, a star many light-years away. Keep in mind this star's surface is always moving, in pounding waves and swirling eddies, in rising and falling convection cells, in vast plasmatic prominences arcing above the surface, often at many kilometers per second. At any particular moment, all that stellar noise can swamp the faint planetary signal. Only by building up hundreds or thousands of careful measurements over time can you get that crucial periodicity that tells you what you're seeing might be a planet. So the measurement is quite statistical in nature, and its interpretation can change based on the statistical assumptions being used. This is further complicated by the fact that planets are rarely singletons, so that any given stellar motion may be the product of many planets rather than one, requiring careful long-term study to tease apart each world's contribution to the bulk signal. It's also complicated by the instability of astronomical instruments, which must be kept carefully, constantly calibrated and stabilized lest they introduce spurious noise into the measurements. In the case of Gliese 581g, not everyone agrees on the putative planetary signal actually being caused by a planet, or even being real at all - the signal doesn't seem to manifest equally in the handful of instruments purportedly capable of detecting it.

So it's very difficult to just detect these things, and actually determining whether they are much like Earth is a task orders of magnitude more difficult still. Notice how I'm being anthropocentric here: "much like Earth." Astrobiology has been derisively called a science without a subject. But, of course, it does have at least one subject: our own living planet and its containing solar system. We are forced to start from what we know, planting our feet in the familiar before we push out into the alien. That's why we, as a species, are looking for other Earth-like planets - they probably offer us the best hope of recognizing anything we might consider alive. It's not the strongest position to be in, but it's the best we've got. Calculating the probability of life on an utterly alien world outside the solar system for which we know only the most basic information - its mass, its orbit, maybe its radius - is at this stage a very crude guess. The fact is, we still don't know that much about how abiogenesis occurred on Earth, how life emerged from inanimate matter. There are very good physical, chemical, thermodynamic reasons to believe that life arose here because our planet was warm, wet, and rocky, but we really don't yet know all the cogent occurrences that added up to build the Earth's earliest organisms, let alone our modern living world. A warm, wet, rocky planet may be a necessary but not a sufficient condition for life as we know it to form and flourish.

This is really a chicken-and-egg problem: To know the limits of life in planetary systems, we need to find life beyond the Earth. To find life beyond Earth, it would be very helpful to know the limits of life in planetary systems. Several independent groups are trying to circumvent this problem by studying abiogenesis in the lab - trying to in effect create life, alien or otherwise, in a test tube. If they manage to replicate Earth life, the achievement could constrain just how life emerged on our own planet. If they somehow manage to make some single-celled organism that doesn't use DNA, or that relies on silicon instead of carbon to build its body, or that prefers to swim in liquid ethane rather than liquid water, that gives us a hint that "Earth-style" biologies may only be one branch in a much larger and more diverse cosmic Tree of Life.



Silberman: Going deeper than the notion of the cosmos feeling "less lonely" – as well as the fact that we all grew up watching Star Trek and Star Wars and thinking that aliens are frickin' cool (as long as they're not the mama alien from Alien) - why do you think people are so motivated to daydream about extraterrestrial life? What need in us do those dreams fulfill?

Billings: I don't really think most people are necessarily motivated to daydream about just any sort of extraterrestrial life. It will probably take more than a microbe or a clam to excite most of our imaginations, even if that microbe happens to be on Venus or that clam happens to be on Mars.

I do think humans are motivated to daydream about extraterrestrial intelligence, and, to put a finer point on it, extraterrestrial "people." They are motivated to dream about beings very much like them, things tantalizingly exotic but not so alien as to be totally incomprehensible and discomforting. Maybe those imagined beings have more appendages or sense organs, different body plans and surface coverings, but they typically possess qualities we recognize within ourselves: They are sentient, they have language, they use tools, they are curious explorers, they are biological, they are mortal - just like humans. Perhaps that's a collective failure of imagination, because it's certainly not very easy to envision intelligent aliens that are entirely divergent from our own anthropocentric preconceptions. Or perhaps it's more diagnostic of the human need for context, affirmation, and familiarity. Why are people fascinated by their distorted reflections in funhouse mirrors? Maybe it's because when they recognize their warped image, at a subconscious level that recognition reinforces their actual true appearance and identity.


More broadly, speculating about extraterrestrial intelligence is an extension of three timeless existential questions: What are we, where do we come from, and where are we going? The late physicist Philip Morrison considered SETI, the search for extraterrestrial intelligence, to be the "archaeology of the future," because any galactic civilizations we could presently detect from our tiny planet would almost certainly be well more advanced than our own. It's unlikely that we would ever receive a radio message from an alien civilization in the equivalent of our past Stone Age, and it's unlikely Earth would ever be visited by a crewed starship that powered its voyage using engines fueled by coal or gasoline. Optimists consider this, and say that making contact with a superior alien civilization could augur a bright future for humanity, as it would suggest there are in fact solutions to be found for all the current seemingly intractable problems that threaten to destroy or diminish our species. It's my opinion that most people think about aliens as a way of pondering our own spectrum of possible futures.

Silberman: Continuing that thought, how likely is it that, if we ever make contact with life on other planets, they will be the type of creatures that we could sit down and have a Mos Eisley IPA or Alderaan ale with - even if, by then, we've worked out the massive processing and corpus dataset problems inherent in building a Universal Translator that works much better than Google? And if we ever did make contact, what social problems would that meeting force us to face as a species?

Billings: Outside of the simple notion that complex intelligent life may be so rare as to never allow us a good chance of finding another example of it beyond our own planet, there are three major pessimistic contact scenarios that come to mind, though there are undoubtedly many more that could be postulated and explored. The first pessimistic take is that the differences between independently emerging and evolving biospheres would be so great as to prevent much meaningful communication occurring between them if any intelligent beings they generated somehow came into contact. Indeed, the differences could be so great that neither side would recognize or distinguish the other as being intelligent at all, or even alive in the first place. An optimist might posit that even in situations of extreme cognitive divergence, communication could take place through the universal language of mathematics.



The second pessimistic take is that intelligent aliens, far from being incomprehensible and ineffable, would be in fact very much like us, due to trends of convergent evolution, the tendency of biology to shape species to fit into established environmental niches. Think of the similar streamlined shapes of tuna, sharks, and dolphins, despite their different evolutionary histories. Now consider that in terms of biology and ecology humans are apex predators, red in tooth and claw. We have become very good at exploiting those parts of Earth's biosphere that can be bent to serve our needs, and equally adept at utterly annihilating those parts that, for whatever reason, we believe run counter to our interests. It stands to reason that any alien species that managed to embark on interstellar voyages to explore and colonize other planetary systems could, like us, be a product of competitive evolution that had effectively conquered its native biosphere. Their intentions would not necessarily be benevolent if they ever chose to visit our solar system.

The third pessimistic scenario is an extension of the second, and postulates that if we did encounter a vastly superior alien civilization, even if they were benevolent they could still do us harm through the simple stifling of human tendencies toward curiosity, ingenuity, and exploration. If suddenly an Encyclopedia Galactica was beamed down from the heavens, containing the accumulated knowledge and history of one or more billion-year-old cosmic civilizations, would people still strive to make new scientific discoveries and develop new technologies? Imagine if solutions were suddenly presented to us for all the greatest problems of philosophy, mathematics, physics, astronomy, chemistry, and biology. Imagine if ready-made technologies were suddenly made available that could cure most illnesses, provide practically limitless clean energy, manufacture nearly any consumer good at the press of a button, or rapidly, precisely alter the human body and mind in any way the user saw fit. Imagine not only our world or our solar system but our entire galaxy made suddenly devoid of unknown frontiers. Whatever would become of us in that strange new existence is something I cannot fathom.

The late Czech astronomer Zdeněk Kopal summarized the pessimist outlook succinctly decades ago, in conversation with his British colleague David Whitehouse. As they were talking about contact with alien civilizations, Kopal grabbed Whitehouse by the arm and coldly said, "Should we ever hear the space-phone ringing, for God's sake let us not answer. We must avoid attracting attention to ourselves."

Silberman: You're currently working on a book with the marvelous title Five Billion Years of Solitude. What's it about, and what excites you most in writing it? Has the research or writing process inspired you to change your mind about anything?


Billings: When people ask about the book at cocktail parties and the like, I simply say that it's about the search for other Earth-like planets, which is true, but not the whole truth. The whole truth is that the book is about the unique moment of time in which we now find ourselves, this unprecedented period in the history of our civilization and our entire planet during which we can rationally hope to discover that we are not alone in the universe. It's a book less about other Earth-like planets, and more about the Earth itself, viewed in a cosmic context that informs whether or not our world and our time might in any way be privileged or special. Most importantly, it's a book about people, and the mysterious forces that drive us, individually and collectively, to search for meaning in our everyday lives by gazing up into the heavens.

What excites me the most about writing this book is the time I get to spend with some of the scientists who are so heavily invested in this search, and the privilege I have in talking with them and telling some of their stories. If life as we know it is in fact relatively common in the universe - and I suspect it is – some of them may be remembered as the first who found other inhabited planets, other living worlds, elsewhere in the cosmos.


The book's title, Five Billion Years of Solitude, is actually a subtle nod to some things I've changed my mind about in the course of my research. It's a reference to the longevity of Earth's biosphere. Earth's life emerged shortly after the planet itself formed some 4.5 billion years ago, and current estimates suggest our world has a good half-billion years left until its vibrant biosphere of diverse, complex multicellular life begins sliding back to microbial simplicity. When I first began planning this book, I believed that we would eventually find clear signs of life beyond our solar system, and suspected that contact with other cosmic civilizations was just a matter of time, for they were probably common throughout our galaxy. I believed that humans had a future, a destiny, beyond the Earth, and that our discoveries of other habitable or inhabited worlds would galvanize society to strive to voyage to the stars. I no longer hold these beliefs as foregone conclusions. My optimism for humanity's long-term prospects has dimmed.

I now believe that while life may be widespread in the universe, creatures like us are probably uncommon, and technological societies are vanishingly rare, making the likelihood of contact remote at best. I am less confident than I once was that we will find unequivocal signs of life in other planetary systems within my lifetime. I believe that, when seen in the fullness of planetary time, our modern era will prove to have been the fulcrum about which the future of life turned for, at minimum, our entire solar system. I believe that we humans are probably the most fortunate species to have ever arisen on Earth, and that those of us now alive are profoundly privileged to live in what can objectively be considered a very special time. Finally, I would guess that though we possess the unique capacity to extend life and intelligence beyond Earth into unknown new horizons, there is a better-than-even chance that we will fail to do so. The human story may end as it began - in nasty, brutish, and short isolation on a lonely, solitary planet. The book in part is my attempt to explain and come to terms with these beliefs, beliefs that I would very much like to be proved wrong.


Silberman: As much as I enjoyed reading your piece in The Best Science Online 2012, the bad news it conveyed was inescapable: The chances of us even being able to launch a little football crammed with sensors and CPUs anywhere near a potentially habitable planet anytime soon are very slim. What would be the one innovation that could potentially be a game-changer that would make interstellar travel practical?

Billings: We really must dramatically reduce the cost of hauling payloads into orbit, which would allow Earth's economic sphere to extend into the rest of the solar system.

Right now reaching low-Earth orbit generally comes at a cost somewhere between $5,000 to $10,000 per kilogram, depending on which launch vehicle is used. This creates an enormous barrier to making profitable ventures in space or building major space-based infrastructure. It also engenders further high costs in the design, fabrication, and testing of most spaceflight hardware, which due to the high cost to orbit must be made as lightweight and reliable as possible. Launch costs of $1,000 per kilogram appear within reach using current chemical rocket technology, and proposals exist for various non-rocket launch systems such as magnetic launchers or beam-based propulsion that could potentially reduce launch costs to hundreds of dollars per kilogram. The shift from government to commercial launch providers could be a very powerful force to drive costs down and spur innovation, and should perhaps be further encouraged through government subsidies until a more robust market develops.


If launch costs fall well below $1,000 per kilogram, a host of economic activities that were previously prohibitively expensive should at a stroke become cheap enough to be readily profitable. Space tourism would no longer be solely the provenance of multi-millionaires. Asteroid mining and space-based solar power production would no longer be the stuff of science fiction. Space stations, interplanetary missions, and enormous space-based communications networks and astronomical observatories would become significantly cheaper and more numerous. Humanity would become a more mature space-faring civilization, and as our space-based infrastructure bloomed, the resources and technical expertise required to mount more practical forays into interstellar space would grow.

Silberman: What practical investments on Earth could we be making now to increase the chances of our great-great-great-great-grandchildren being able to exchange Instagrams from Mars?


Billings: Pardon the rant, but I feel very passionate about this. More than anything else, the citizens of democratic nations that are wealthy enough to maintain space programs must hold their political leaders accountable and make space a major, legitimate voting issue to be taken very seriously. That's the investment that needs to be made.

I'm an American citizen, so I will focus my comments on the American space program and the American political system. I'm sad to say that in this country, the most powerful nation presently on the planet, space science, exploration, and development are treated as fringe issues at best. Too many politicians, if they consider these issues at all, treat them in one of two ways: Dismissively, as things to be joked about, or cynically, as little more than pork-barrel job programs for their districts, things to be defended purely for the status quo and only given token lip-service when absolutely necessary.


And who can blame them? Look at what happens to politicians when they try to talk seriously and ambitiously about space today. They are lampooned and ridiculed by the media and by their political opponents as starry-eyed idealists who are disconnected from everyday realities. American politicians and voters alike view space programs as luxuries when in fact they should be seen as necessities. The truth is, the USA doesn't really spend that much on space - less than half a penny of each federal dollar goes to NASA each year. NASA has a budget of about $17 billion. That is indeed a lot of money, but Americans collectively spend more each year on almost any mundane thing you can imagine: Pet food, pizza, sports equipment, video games, cosmetics, pornography, you name it. Some people say money spent on space is wasted, as if NASA stuffs sheaves of US dollars into rockets and then launches them into the Sun. Of course, all that money is spent right here on Earth, where it can provide good jobs and abundant spin-off technologies that indirectly benefit society. It really should be an easy sell, and the fact that so few Americans are buying in makes me worry very much for our future.

Americans seem to have forgotten that NASA is their space program, that it works for them. They're steering the ship but don't seem to realize their hands are on the wheel. The agency takes its orders and directions from the Congress and from the President that voters elect, but its course has become increasingly erratic and wastefully rudderless. Too few Americans possess the same sense of ownership over NASA's future as they do for NASA's past. So, if you are of voting age and you think space science and exploration is cool and important, let your voice be heard! Vote. Call your Congressperson. Organize groups of like-minded voters. Push back against the blithe cynics who say this stuff doesn't matter. As far as I can tell, this sort of grassroots enthusiasm and engagement is the only way you or your descendants will ever again have a space program that is truly worthy of a great nation. It's really up to you.

Steve Silberman is an award-winning investigative reporter, a contributing editor of Wired magazine, and a blogger for the Public Library of Science. His articles have appeared in Wired, the New Yorker, Technology Review, and many other national publications. His book "NeuroTribes: Thinking Smarter About People Who Think Differently" will be published in 2013 by Avery Books/Penguin.