Sunday, March 27, 2011

The Myth of Terraforming

Every story about humankind’s colonization of space, as well as much of current thinking on the subject, depends on the assumption that we will either find a planet near enough like Earth that we can live on it, or we can find a suitable candidate and create Earthlike conditions by “terraforming.”

Finding a New Earth

The odds are pretty slim. Consider that we humans are exquisitely adapted through evolution to live on the planet where we evolved. Not a surprise, because all living creatures adapt and optimize their structure and chemistry to their environment.

But we can’t even live on the seventy percent of the Earth’s surface that is water unless we have support from a civilization on shore, where we evolved. We need ships or platforms, breathable air if we’re trying to colonize the seabed, and fresh water. Humans can visit the ocean. We can live there for months at a time in habitats and submarines prepared ashore. But we can’t stay without help.

We can’t live on the highest places like the Himalayan and Andean peaks, or in the deepest places like the vast caverns of Pennsylvania and New Mexico, without similar support from a surface civilization. On the peaks we die slowly from suffocation, bleeding, and dehydration. In the caverns we die from lack of light and food.

Consider that the first thing we would look for in an Earthlike world is liquid water. But even on Earth, we can only survive on a fraction of the water that’s present. If we drink from the oceans, the excess salts upset our metabolism. Our cellular functions collapse as the relatively fresher water inside the cells rushes out to dilute the saltier water outside, through the most basic process of osmosis. But neither can we drink absolutely pure H2O because it lacks the electrolytes—the salts—we’re accustomed to. With an isolated diet of distilled water or pure rainwater, our bodies would lack essential minerals. And, in sufficient quantity, chemically pure water will invade and disrupt our cells by trying to dilute the salts and nutrients inside them. No, our bodies were adapted to drink ground water that once fell as rain but has since soaked up some soluble minerals—a narrow slice of the Earth’s habitat.

In every other aspect of an environment—the air, the amount and wavelength of sunlight, the mineral mix, the supporting biosphere—we need exactly what this planet provides in both gross and subtle ways. For example, although the local bacteria are sometimes not our friends, we live symbiotically with a huge array of one-celled helpers. Without their influence in aiding our digestion, breaking down our dead skin cells, and supporting the natural decay of organic products in the world around us, we would die slowly—but much more quickly than we could adapt to an environment without them.

We will certainly colonize the Moon one day, but that will be a camping trip. For all the technology we might bring (short of programmable energy-to-matter conversion á la Star Trek), we will still need contact with and supplies from the home planet for long-term survival. Pre-civilization humans could roam our world and inhabit many climates and islands with just their bare hands and a few tools. But none ever settled Antarctica for its cold and dryness or the upper slopes of Mount Everest for their low air pressure. The Moon will be in a similar category of harshness but with even more difficult logistics.

Creating a New Earth

Things are the way they are for a reason. Over the long haul, planets acquire the conditions they have because of underlying physical causes.

The most likely and immediate object of our potential terraforming projects will be Mars. We expect to live on the Moon in pressurized tunnels and domes forever, never hoping to make an Earthlike world of that rocky ball. But Mars already has an atmosphere, soil, sunlight, and weather. How hard can it be to recreate Earth conditions on that nearby planet?

Mars is a much smaller planet than Earth, with a gravity only 38 percent—or just over a third—of that on our home world. (Compare that with the Moon, which is smaller still and has one-sixth the gravity.) What keeps an atmosphere on a planet is gravity. The lower the gravity, the more easily the jostling, bouncing molecules of its gas layer can reach escape velocity and fly off into space.1 If Mars ever had an oxygen-nitrogen atmosphere like Earth’s, it long ago dissipated into space. Mars has an atmosphere, sure, but it’s at about one percent of Earth’s air pressure. Take a jet up to about 50,000 feet and open a window: you will suddenly be breathing a Mars-rich atmosphere. However, the dominant gas on Mars is the heavy molecule carbon dioxide, because all the lighter gases have bounced away, so you won’t be breathing for long.

If you wanted to terraform Mars, you would have to find a way to release enough oxygen-nitrogen mixture to cover the 89.5 million square miles of the planet’s surface.2 That’s assuming you could find that much gas latent in the planet’s rocks and liberate it in a reasonable amount of time. But it better be a fast process, because the gas you pump in will ride up over the heavier carbon dioxide atmosphere and self-select to be among the first gases to bounce away again.

Let’s run the calculations. Assuming you could somehow remove the existing carbon dioxide atmosphere, then release 89.5 million cubic miles of new oxygen-nitrogen atmosphere, they would cover the planet to a depth of just one mile, or about 5,000 feet. That won’t give you anything like a breathable Earth environment: to create the pressure of 14 pounds per square inch we have on Earth, there’s a layer of air twenty times deeper, pressing down at full Earth gravity. Even if you could come up with the 1.8 billion cubic miles of gas to duplicate this atmosphere on Mars, you still wouldn’t have the gravity to sufficiently pressurize it. Or support it. If you piled up 100,000 feet of atmosphere above the Martian surface, the upper layers would dissipate even faster due to the lower escape velocity. Things are the way they are for a reason.

The second great difficulty with terraforming Mars is dealing with radiation from the solar wind. The core of the planet, whether molten or not—and this has been the subject of some debate—does not create the kind of magnetic field found around Earth, Jupiter, and Saturn. Without a magnetic field, the charged particles of the solar wind3 fall directly on the upper atmosphere, heating and accelerating the loss of gases. And any fast particles that aren’t stopped in the atmosphere reach the surface to ionize atoms and break up the organic molecules of living things.

Earth life in general does require a certain amount of radiation to support the rate of genetic mutation that took us collectively from single-celled bacteria to a planet rich with plants, animals, and humans. No radiation, no mutation, no evolution. But it’s a finely tuned amount we need. Too little radiation, and the various species don’t drift enough to adapt to changing environmental conditions. Too much radiation, and our molecules don’t hold together: we become sick with the resulting molecular poisons and die; or our genetic material disrupts, throwing off damaged proteins and cancers.

Once again, we were adapted for life on this planet under this sun. We might visit other Earthlike planets and breathe their atmospheres for a while and drink their strangely flavored water. We might extend our stay by taking along bottled gases, food supplements, and a long checklist of camping gear. But it’s unlikely that we’ll find a planet so close to Earth’s conditions, or create one so stable in its new pattern, that we’ll have time to take off our space helmets, walk freely in the sunshine, hunt the local game for food, mine the metals we need, and eventually evolve and adapt to what will inevitably be a changing environment.

It’s a nice dream. But I am literally not holding my breath for it.

1. The lighter molecules go first and fastest. On Earth, free hydrogen would have left the planet long ago if it didn’t have such an astounding attraction to oxygen atoms: they would rather form water molecules than escape. Helium, on the other hand, does not bond with other atoms. Most of our helium comes from natural gas wells as a residue of Earth’s formation out of the stellar cloud. We extract the helium by refrigeration for commercial purposes—now mostly festive. When you release a helium balloon, it rises into the stratosphere, bursts, and releases its cargo of fossil gas into the upper atmosphere, where the atoms continue to rise, and one-by-one eventually bounce into space. There they are widely space and so less jostled, but the even-lower gravity environment is less likely to draw them back. Finally, the flying gases encounter the solar wind and are pushed away from the planet altogether.

2. Mars has a surface area about equal to all the dry land on Earth.

3. The solar wind is made up of electrically charged protons and electrons and other atomic particles. The magnetic field catches and deflects them—most visibly to fall into our northern and southern polar regions as the colorful auroras. Fortunately for us, the sun is mostly hydrogen and helium, and so its nuclear reactions don’t kick out many fast neutrons. And the sun lacks sufficient energy to bathe us with a hard dose of gamma rays. If it did these things, the life that evolved in this system—if any—would be very different from our soft, water-soluble bodies.

Sunday, March 20, 2011

Making the Nuclear Option Work

We’ve all been watching the agony of the Japanese as they struggle to control the nuclear power stations damaged by the earthquake and tsunami. What concerns everyone, I think, is that Japan is one of two countries, along with France, that have made nuclear power really work.1 And now, it seems, even they have trouble with the resource.

Nuclear power has a bad reputation in the United States. During the 1950s, the Atomic Energy Commission and its technology supporters, seeking peaceful uses for fission, urged utilities to build nuclear power plants on the basis that the electricity would be “too cheap to meter.” Free power from rocks—what could be better? Many utilities took up the cause and built one or more nuclear plants. But the energy turned out to be anything but cheap.

For one thing, the regulatory burden on a nuclear plant is much greater than on any other energy resource. When I worked at the engineering company, we had several nuclear projects under way. Every step of design and construction is monitored, documented, and filed for future reference. To take just one example, the steel for rebar in the concrete of the containment is tracked from the steel mill to the construction site using a chain of custody—lot numbers, way bills, dates in and out of storage, final placement in the structure, with signatures all the way—very much like the provenance that follows a piece of evidence from crime scene to trial.

When I worked at the public utility, I met the sort of people who operate, maintain, and refuel a nuclear plant. These are serious, clear-eyed, methodical people. Think of a conscientious peace officer or medical technician—the sort of people you trust. The plant’s safe and efficient operating record is a major point of pride with them. They take their processes and procedures seriously. They never talk or joke about cutting corners. To get a feel for the life inside a nuclear plant, it’s as clean and orderly as a hospital, and there are signs everywhere identifying who has access to which rooms, under what conditions, with what equipment—and every sign carries the signature authorization of the plant manager or area supervisor. No one is in doubt about what he or she is supposed to do in any situation.

The 70 or so nuclear plants in the U.S. have been run successfully and mostly without incident. Today they provide more power than ever before. Improved practice has boosted their capacity—that is, the amount of time the plant actually generates electricity, as opposed to being shut down for maintenance and refueling—from about 56% in the 1980s to more than 90% currently. A safe operating record and high utilization are good things.2

But still … there is the potential for catastrophe when handling highly radioactive material. We experienced loss-of-coolant accidents at Three Mile Island in 1979 through operator error and now in Japan through a natural disaster. Although there was no release of radiation beyond the plant boundaries at Three Mile Island, and it’s unclear what releases there have been or will be in Japan, the potential for harm is there. If containment is breached, there can be widespread environmental damage and human illness, as at Chernobyl. However, it should be pointed out that the Chernobyl reactor was a completely different design, moderated by graphic blocks instead of boiling water, from the reactors in the U.S., Japan, or France. And the Chernobyl accident was attributed to a risky operating procedure that the state commissars wanted to try and the plant engineers argued against. And yet, experiencing only three notable incidents in 60-odd years of reactor operation is a pretty good record.

There was a time when the low energy ratio of nuclear power was its biggest commercial drawback. That is the ratio of energy output from the plant divided by the energy input. In the case of nuclear fuel, that input is determined by the costs of mining the uranium ore, transporting it, refining it, concentrating the fissionable U-235, making the fuel pellets, and assembling the fuel rods. With an average plant capacity factor of 56%, you don’t get enough power out of the plant to make up for the energy—usually in the form of fossil fuels—that you burned to make the fuel. The good news is that, with improved enrichment technologies that lower the cost of fuel and those higher capacity factors that spread the cost over more energy production, the energy ratio is more favorable these days.3

Still, the standard wisdom has been that nuclear energy isn’t actually profitable without completing the nuclear fuel cycle. The final steps in the cycle, which starts with mining the ore and continues through running the reactor, address reprocessing the spent fuel rods to recover the fractions of unburned U-235 and newly created plutonium for making new rods, and then disposing of the radioactive wastes. The United States halted reprocessing of nuclear fuel after an Executive Order by President Carter because he did not want to create a “plutonium economy” that might support nuclear terrorism.

Still, we have do to something with the spent fuel rods. Because we’ve also abandoned work on long-term storage at repositories like salt mines and granite caverns in the deserts of the U.S. west, American plants are now holding their spent fuel in “swimming pools”—which cool and shield the rods with filtered water—at the plant site. And those temporary storage measures are rapidly filling up. There will come a day, sometime in the next ten years, when many existing plants must shut down because they can no longer store additional rods. And there will come a day, sometime in the next 40,000 years, when humanity will have to close down the swimming pools and deal with the decaying rods.

Early on, France undertook the nuclear option in wholehearted fashion. With a single nationwide utility, the French concentrated on a single reactor design, so that everyone in the system would be familiar with its operation and maintenance. They run teams of experts who do nothing but go around the country sequentially refueling plants. And because the shutdown for refueling is also the time when every part of the plant undergoes extensive evaluation, maintenance, and rebuilding as necessary, this team is charged with overall plant health. In contrast, in the United States, each utility builds its own plants as engineering one-offs, choosing from among two different reactor designs and many options for steam supply, turbine, and control systems.4 Each U.S. utility does its own refueling and long-term maintenance, although under supervision of the Nuclear Regulatory Commission, so they each must absorb the costs of the specialized engineering teams required to perform this work.

France reprocesses its fuel to get the extra boost from recovering unburned U-235 and reactor-bred plutonium. And they reprocess fuel from Japan under contract. Reprocessing includes appropriate disposal of low-level radioactive waste from the clay and cladding of the rod bundles, and vitrification and sequestration of the high-level wastes from burned uranium.5 So at least two countries in the world are already dealing with the long-term problem of spent fuel.

With the new fear of global warming from fossil fuel use, many people want to see more nuclear power plants built in the United States. However, the last contract for a new nuclear plant in this country was signed in the mid-1970s. That was before the disasters at Three Mile Island and Chernobyl, and not long after the first commercial power reactors had come on line in the late 1960s. Clearly, even then, the utility companies were coming to understand that nuclear power—far from being “too cheap to meter”—was too expensive to operate. The fact that the later plants were built at all was a matter of engineering pride, political inertia, and the economic desire to recover money already invested.

Before nuclear power can become viable again, we have to address three conditions: a new, inherently safe, stable, and simple reactor design; facilities for long-term storage of wastes; and ideally a facility for nuclear fuel reprocessing. Without these—plus a political climate that gives the nuclear option its irrevocable and unimpeachable blessing—the energy utilities in this country won’t touch new nuclear power.

1. In 1987, at an Energy Daily conference in Washington, DC, I heard the then-president of the French national electric utility, Electricité de France, describe the nuclear option as, “France has no coal. France has no oil. France has no choice.”

2. For an overall analysis of nuclear power in this country, see the U.S. Energy Information Administration.

3. For a detailed analysis of power systems and energy ratios, see the World Nuclear Association.

4. To give just one example of the complexity that exists in the U.S. nuclear power industry, when I worked at the engineering company a group of our engineers and technical writers was put under contract with the local utility, PG&E, to help them bring the Diablo Canyon nuclear plant on line. One of our system engineers walked into the room one day shaking his head. All of the control circuits in the plant operated at 38 volts, he said. I asked if that was a problem. No, he said, the controls would work fine, but 38 volts was a hydro power standard, not the standard voltage used in nuclear plants. PG&E’s design and engineering group got their start in the hydro business, and apparently when they turned to designing their nuclear plants, they used the standards they were familiar with. It doesn’t hurt the plant, but it sure confuses anyone coming in from the outside.

5. Briefly, low-level wastes are common materials that have become irradiated and now emit alpha and beta particles and gamma rays. These are all forms of ionizing radiation and therefore dangerous to humans. But irradiated materials don’t emit fast neutrons, which alone have the power to irradiate other materials in turn and make them radioactive. (Otherwise, the whole world would gradually start to glow.) Only naturally occurring fissionable isotopes like those of uranium and radium, and their decay products like isotopes of strontium and cesium, emit neutron radiation and so they are considered high-level waste.

Sunday, March 13, 2011

SIPRE as a Way of Life

Even though I ride a high-powered motorcycle, I get very few traffic tickets.1 Maybe I’m careful or lucky. Maybe I’m invisible. But for every ticket I get, I go to traffic school in order to work off the insurance points. It was there I learned the cornerstone concept of defensive driving, SIPRE, which I’ve since come to understand is the key to achieving personal speed and safety in living as a whole.

SIPRE stands for See, Interpret, Predict, React, Execute. This chain of mental events is the basic structure by which our awareness meets a threat. They teach it as an aid to avoiding traffic accidents, but it really applies in almost any situation.

Seeing marks the brain’s first awareness of a possible situation. Maintaining an appropriate state of alertness and observation really precedes seeing; you can’t see if you don’t have your eyes open and possess a readiness to look around. In contexts other than driving, “seeing” might also reflect any of the senses. You might hear a twig snap behind you in the forest, or smell the garlicky odor of natural gas in the basement, or touch an unexpected warm body in a darkened room. The classic driving example is that something bounces into your field of vision from the side of the road.

Interpreting is the second step. The first sight, especially from the visual periphery, is of movement, or something that strikes the eye as out of the ordinary. From there, the mind interprets what the eye sees. That movement from the side of the road is the bumper of another car, or a bicycle, or a dog running, or a ball bouncing into the street.

Predicting follows interpretation, based upon knowable or guessable facts that are associated with the interpretation. If the movement is another car and driver, a human life may or may not be at stake: perhaps the driver will see your car and slam on the brakes, avoiding an accident. If he doesn’t and hits you broadside, there may be collision damage but, at normal street speeds, not much injury. If the movement is a bicyclist, his ability to stop is much less and he may hit your car, or you may hit him, and his injuries will be severe. If the object is a dog, it is unlikely to stop, or it may freeze right in your path; in either case, the dog is at risk. If object is a bouncing ball, there may be a child chasing after it. Balls you can roll over without worry; children are an entirely different matter.

Not all of these predictions will occur to you in the split second after you interpret the object. Experienced drivers have thought about these possibilities, either over time as incidents occurred or at their leisure while reliving past incidents. New and inexperienced drivers will benefit from imagining various situations and what the possibilities are in each.

Reacting is the key step in the mental chain. Reactions do not have to be wild and woolly impulses thrown out by the hind brain. Reactions can be learned: ahead of time and at your leisure, you reason about what is the right thing to do in each situation, rehearse it, think it through, get the feel of it, practice it if possible.

If a car pulls out in front of you, is it better to slam on the brakes and possibly T-Bone it, or be T-boned by it, at a decreasing rate of speed, or to swerve into the next lane—possibly into oncoming traffic—and risk a head-on collision at compounded speeds? If a bicycle or dog darts out from the right-hand side of the road, is it better to swerve to the left and try to pass ahead of it, while possibly absorbing its impact on your passenger door, or swerve to the right and try to pass behind it, while possibly hitting it dead-on because the object itself stopped or swerved? If a ball bounces out and you swerve left, you might hit it but miss the child chasing it. If you swerve right, you miss the ball but might hit the child.

You can forge a link in your mind between these strategies and the triggering interpretation: car, bicycle, dog, ball, ball-with-child. This helps makes your reaction become an informed or learned movement, rather than panicking because something unexpected happens and randomly slamming on the brakes or swerving into traffic.

Executing is the final step in the sequence, where your muscles perform the learned reaction. Reaction is the choice of how to move; execution is the movement itself.

This is all well and good, as far as it goes, for defensive driving. The five steps of SIPRE describe the split-second instances of awareness, realization, and choice that guide how you respond to a threat. But how do they relate to life itself?

I pondered this until I realized that these steps were all familiar ground. During my college years, I studied karate and graduated with a black belt as well as a bachelor’s degree.2 Karate is not actually a glamorous undertaking. You practice the same moves over and over, throwing a million practice punches and kicks during a lifetime, absorbing and building into somatic memory the nuances of moving and positioning the elbow, wrist, and fist in a punch, or the knee, ankle, and toes in a kick. You practice combinations of block and punch, step and kick, until they become automatic, two movements working as one. You spar with partners—not in order to beat them, but to build your awareness of body spacing, ranging, and timing.

The result is an ingrained reaction: see something moving, interpret it as crossing into your personal space or not, predict its trajectory, react with the appropriate combination of moves, execute with muscle memory. It was my experience with karate that told me the reaction part of the SIPRE sequence was not supposed to be just a random movement. If you can practice block-and-punch combinations to build reaction speed in self-defense, you can also practice braking and swerving to build reaction speed in driving emergencies.

So SIPRE applies to self-defense and driving, but what is the application to life as a whole? In moving through life, you operate in two ways: first, you choose to act based on your desires, goals, and plans; and second, you react to your environment, which brings you both opportunities and obstacles. SIPRE cannot tell you how to choose your goals, but it can certainly help you coordinate your responses to the environment and what it throws at you.

Any movement or change in your environment presents the alert observer with possibilities. You can evaluate and interpret the actions of friend or foe, the tremors in the ground, or the fluctuations of a stock price as either threat or opportunity. You can use your previous experience to predict the future course of that occurrence and assign to it a probability. You can apply that probable outcome to your existing plans and goals, which then form the basis for your possible reactions. And finally, you can move based on the threat or opportunity.

SIPRE becomes the basis for tactical or strategic maneuvering in the context of your short- and long-range plans. Life stops being a panic rush toward gains and flight from losses. Instead, you move with deliberation toward your goals in the context of evaluated opportunities and obstacles that the environment offers. You become an analyst and a strategic thinker.

You gain some measure of control, even when all around you is chaos.

1. Okay, ’fess up time. One ticket in 1976 was for driving 60 mph in a 55 zone. That was during our national experiment in driving slowly, and the ticket was written in Oregon. I made the state trooper’s day by being from California and letting him explain the innate environmental superiority of Oregon’s traffic laws. The second ticket was in San Francisco in 1987 for crossing the broad white line that sometimes defines a traffic lane, this time on the on-ramp to the Bay Bridge. A string of us motorcyclists routinely bypassed the eternal jam on the bridge approach by invading this forbidden zone rather than “share the lane” with the single line of cars. One day, the Highway Patrol stopped us all. Fair enough. The third ticket was in 2004 in the East Bay for driving through a stop sign that wasn’t on that intersection the last time I went that way. Also fair enough. Such is my life of crime.

2. See Isshinryu Karate.

Sunday, March 6, 2011

Where Do Aliens Come From?

First things first: I personally don’t believe that the Earth has yet been visited by intelligent beings from another planet. Not that I doubt such beings exist. In a universe of 100 billion or so galaxies, each consisting of 100 billion or so stars, anything—no, everything—is possible. But have they come here? More to the point, have they started coming here in the last sixty-odd years, since the outbreak of UFO sightings that began in the late 1940s?

These were also the years, remember, that many more airplanes were flying in the skies of this country. With advances in high-altitude and nighttime operations developed during World War II, many more airplanes—and suddenly helicopters, too, with their great whirling rotors—were moving high overhead, some leaving condensation trails, and all flashing strange patterns of landing and navigation lights. These were the years when researchers were experimenting with weather balloons and other high-flying objects like the surveillance device that came back to earth in Roswell, New Mexico.1 Advances in astronomy were feeding a growing public awareness of other planets, and science fiction writers were speculating about their alien cultures. And finally, the horrors of world war were still ringing in our heads, and the growing threat of a new Cold War was feeding a climate of suspicion and paranoia. All told, it was time for Americans to expect to see the aliens.

So why don’t I buy into the irresistible fantasy that Earth has been visited repeatedly, endlessly—practically buzz-bombed and harassed—by hairless little people with big slanting eyes riding in silver saucers?

Because they never announced themselves. They did not, to anyone’s knowledge, ever land like Klaatu in a public park2 and say “Take me to your leader.” Of course, conspiracy theorists contend that the first government they approached—ours—put them under wraps, declared them a state secret, and have been dealing with them in private ever since. But is this reasonable, considering the huge number of supposed sightings? Even though the aliens are not human and cannot be expected to have human motivations, we should be able to attribute some intention to any being we might meet and describe as intelligent.3 If there is intention, then we can also predict how an intelligent being will respond to that intention being foiled, as by a paranoid local government.

Any interstellar trip is going to take time and effort, regardless of how much energy the traveler has at his disposal. Even the starship Enterprise, with its limitless matter-antimatter conversion reactor and space-bending warp technology, represents a significant investment in shipbuilding effort in order to whisk humans from one star to another in a vessel filled with science labs, state rooms, and cocktail lounges. One undertakes the trip with a purpose in mind: curiosity and exploration in the case of Star Trek, conquest and colonization in many other scenarios.

In neither case would the traveler be likely to give up his purpose because the locals were either paranoid or hostile. Fear of a United States or Soviet Union armed with fusion bombs wouldn’t occur to any being equipped with the energy resources to travel dozens or hundreds or thousands of light years. Even if the conspiracy theorists are right and the travelers were initially bought off, warned off, or scared off, then why do they endlessly return to abduct isolated individuals and perform experiments on them?

One could theorize that these travelers have some benign intent that prefers to remain secret. Thus they would have reasons for not making formal presentations in the U.S. Congress and at the U.N. General Assembly. They might, for example, want to work behind the scenes to bring humans quietly and peacefully up to a level where we can join some kind of Council of Planets (per Klaatu’s mission). Or they might want to study us while their ethics require them to let us develop culturally and technologically in our own unique way (per the Star Trek Prime Directive). But neither intent would account for this clumsy sneaking around, creating crop circles, mutilating cattle, and leaving light sleepers with dreamlike, half-remembered episodes of abduction and rape.

The aliens as depicted by the UFO theorists are a mix of clever and stupid: clever enough not to make public demands and present hard evidence of their arrival, but too stupid to cloak and shield themselves effectively. They are also too disturbingly humanoid, with homeobox segmentation4 and tetrapod limbs, to be the product of an evolution that started out among the stars.

No, I am dissatisfied with any evidence and explanations of extraterrestrial intelligence that we’ve seen so far. There is one explanation that does fit, however, although it is even more improbable than that hairless bipeds would come thousands of light years to butcher cattle and give rectal exams to agricultural workers.

The aliens as depicted might very well be from around here, but not from this time. They might be travelers from our own distant future, come back to study their history, take samples from their ancestral genome, or influence our development. That would explain the humanoid resemblance but with differences in size and appearance: future evolution and environment suits. That would explain the secrecy: protecting the awareness of the civilization that will one day evolve into themselves. It would also explain the persistence: if you could go back and study the past, wouldn’t you do it more than once? And it might explain some of the clumsiness: if you have lots of people applying for grants and permission to travel back in time, you’re bound to have a few comedians with the urge to drop their pants and scare the locals.

Of course, travel in time is even more improbable than travel over distances of light years. We know perfectly well how to travel through space by accelerating and expending of some kind of reaction mass, whether chemical propellants or ionized particles.5 We don’t have more than a few untested theories about the structure of space and time to support notions about how a physical body might travel backwards and forwards from one timespace to another.

Personally, my bet is that all the alien sightings are attributable to weather balloons and other identifiable effects salted with human imagination, yearning, and paranoia. But that doesn’t make such a good story, does it?

1. One of the reasons I don’t believe the Roswell event represents the recovery of a crashed spaceship is that the believers usually couple it with the development of solid-state transistors in that same year, 1947. These people claim that integrated circuits were found in the crashed spacecraft and secretly exploited to create all of our marvelous modern electronics. My father was a mechanical engineer at Bell Labs at about the same time that William Shockley and other physicists were experimenting with transistors. He once brought home one of these devices that I could hold in my hand as a child: a copper cup the size of a bottle cap filled with opaque material from which three wires stuck out. The first transistors were single gates, which would conduct an electric current across two wires, or not, based on the input of current through the third wire. They operated in printed circuits just like their predecessors, the vacuum tubes. It took a while—a major developmental step, actually—for human designers to stop soldering those wires together and start integrating them as collections of gates etched directly on the silicon substrate. No alien spaceship traveling the stars would have used single transistors; they would have advanced to integrated circuits much denser than even our current models. If humans had discovered integrated circuits in the debris at Roswell, I never could have held that single bottle cap in my hand.

2. The alien hero of The Day the Earth Stood Still played by Michael Rennie in the original 1951 version and Keanu Reeves in the 2008 remake.

3. Referring to science fiction stories in which scaly or tentacled aliens try to have amorous relations with Earth females, Carl Sagan said it would be much more likely for a human to have sex with a petunia than mate with a being from another planet. At least humans and plants share the same basic organizing principle, DNA. Given the huge possibilities for other forms of entropy-reversing energy conversion, or life, out among the stars, I think that to expect aliens to have tentacles, eyes, intentions, or anything we might recognize as intelligence is pure anthropomorphizing. When we actually are visited by beings from another planet, it’s likely we won’t recognize them as life at all, let alone try to communicate with them. Their organic processes, their time scales and attention spans, and their cerebral processes may simply be too strange, in human terms, for us even to notice them.

4. The homeobox, or hobox, gene sequences define bodily segmentation during embryonic development. They are why human beings share with fish, whales, crocodiles, cockatoos, fruit flies, and wasps a body shape that generally includes a head with clusters of sensory organs, a thorax with the mechanisms of respiration and circulation, an abdomen with mechanisms of digestion and reproduction, and various articulated limbs attached to the thorax. (Think of it: your pelvis and legs attach directly to the spine which supports the ribs; your belly hangs from this structure like an afterthought separated from the lungs by the diaphragm.) Most of the advanced, DNA-based animal life on Earth shares these features. Products of an alien evolution would not.

5. More exotic technologies like warp drive—where some kind of “generator” extends a “field” that bends and compresses the “fabric” of space—are not even the stuff of physics theory. They are literature with less scientific basis than fairytales.