As I first learned at a dinner table surrounded by new acquaintances, questioning
people’s belief in extraterrestrial intelligence (ETI) is like questioning their
religious faith. Doubts are met with gasps. The fierce stares say not just,
"We disagree," but "You have blasphemed."

Don’t get me wrong. I have nothing against curing cancer, heart disease, and
AIDS, which advanced aliens could presumably do. I’d be fascinated to hear an
alien’s perspective on the meaning and purpose of life. I’m all for immediate
solutions to our war/crime/ poverty problems, which a mature society is supposed
to have solved. I even think that receiving all these blessings from above may
follow logically from contact with a civilization that’s survived for millions
of years. But I also think that astronomers are now in a position to know that
our chance of achieving such contact is very small.

Nothing drives ETI faith like the Copernican Principle, the idea that we do
not occupy a privileged position in the universe. Many regard this as a necessary
axiom for the continued success of the scientific enterprise. The practice of
science begins, we are told, with the assumption that we are typical, not exceptional.
We can’t scientifically study a sampling of one, after all. Moreover, history
suggests that Copernicus began an unstoppable progression: the world’s greatest
modern thinkers proposed and then proved that the Earth is not the center of
the universe, that the Sun is not the center, that our galaxy is not the center,
and finally, that there is no center.

Copernicus gave us the theory to take the first step, and Galileo demonstrated
its truth. Einstein gave us the theory to take the last steps, and Edwin Hubble’s
observations of distant galaxies convinced the world.

Astronomer Robert Jastrow, founder of NASA’s Goddard Institute, calls Hubble’s
achievement "the last great step in the revolution of thought regarding
mankind’s place in the cosmos that had been initiated by Copernicus." But
today’s Copernican Principle proposes, not only that the universe does not revolve
around the Earth, but that the universe does not revolve around us, either
literally or figuratively.

Having proved that our planet, sun, and galaxy are typical, science has yet
to settle the question about whether we ourselves are typical. We lack absolute
certainty that we are not, in the most important sense, the center—until someone
confirms the existence of intelligent beings elsewhere in the universe.

Yes, if you put it that way, Robert Jastrow agrees: the final step in
the Copernican revolution has yet to be taken. But in my talks with him during
the 1990s, he insisted that we are on the verge of taking it.

"I think that mankind is on the threshold of entering a larger, cosmic
community," he told me during a visit to his home and then to California’s
Mt. Wilson Observatories, where he serves as Director. His words carried a kind
of ecclesiastical authority, seeming to reverberate from the seven-story dome
above him, the observatory he calls a "cathedral dedicated to mankind’s
quest for understanding of the Cosmos." Less loftily, he added, simply,
"We’ll be hearing from those guys soon."

Taking a seat on the wicker chair that Edwin Hubble had sat upon almost eighty
years before, I pondered this possibility—and then promptly forgot it while
playing with the controls that split open the ceiling to the night sky, that
slued the 100-ton telescope across the room, that spun the entire cavernous
structure around me.

Sitting there a mile above Los Angeles at the focus of the world’s largest
telescope, positioned at the helm of the entire scientific enterprise, Hubble
felt tremendous power. Oddly, he was simultaneously struck with a sensation
of puniness, of being the first to fully understand how diminutive our place
is in this enormous universe. While tweaking the controls over hundreds of cold
nights through the early 1920s, Hubble provided photographic proof that our
galaxy is but one of many. The nebulas, then understood to be wisps of gas among
the Milky Way’s stars, turned out to be more distant galaxies containing billions
of stars of their own.

Now, having entered a new millennium, we’re poised to make the final test of
the Copernican Principle. And why should Robert Jastrow think our generation
will be the lucky one to finally make contact, aside from the fact that his
generation of astronomers can’t die in peace until it happens? For one thing,
new SETI (Search for Extra-Terrestrial Intelligence) telescopes and computers
are being built with greatly enhanced sensitivity and coverage.

But Dr. Jastrow was thinking more about the signals we’ve been sending than
those we hope to receive. "We’re a very conspicuous part of the universe
right now," he explained. "The TV and FM broadcasts—and the radar
from our defense installations—are sending out a signal that there is life on
this planet."

The SETI Institute’s Robert Arnold agreed, saying: "These electromagnetic
artifacts of daily commerce, entertainment, and defense give the Earth a distinct
radio frequency signature that is brighter than the Sun."

According to Jastrow, "That started in intensity, at the million-watt
level, about thirty years ago, in the 1960s." Jack Parr and I
Love Lucy are at a wave front, he said, that’s spreading out into the cosmos.
"Within thirty light-years there are some dozens of stars. And if they
got the word thirty years ago, they would be sending a reply back to us. And
those who are only fifteen light-years away will have sent a message back fifteen
years ago, which should just about be reaching us today."

Other astronomers belonging to Dr. Jastrow’s generation recall the same kind
of enthusiasm, but new concerns have since dampened it. "I used to rather
enjoy thinking that the early civilizations would have set up an intercommunicating
system," said Senior Astronomer Emeritus Eric Carlson of Chicago’s Adler
Planetarium. "Maybe laser beams or something full of information about
all the other civilizations in the past history of the galaxy, and that this
is all circulating . . . from star to star around the galaxy, and all we have
to do is tap into it."

The actual likelihood that we’ll hear back from anyone that close, of course,
depends upon just how densely packed our galaxy is with civilizations—and upon
how long those civilizations last. Today Carlson frets about what might happen
to any civilization in the course of a ten-billion-year-old galaxy. What will
be left of human culture in a billion years, or even a million? "I tend
to get this sense of a galaxy as being sort of like a garden," says Carlson.
"You have the early spring flowers, and then you have the late spring flowers
and so on, and you have life with consciousness springing up here and there
for a while. And whether it’s ever in contact at the same time, I just don’t
know."

The next generation of cosmologists might still say that the existence of extraterrestrial
civilizations is "extremely likely," as cosmologist George Smoot (Lawrence
Berkeley Laboratories) told me. "But I think the chances of there being
life near to us is pretty low," he cautioned, "and whether
there’s life in our own galaxy, besides ourselves, I don’t know."

Among the youngest astronomers to make a name for himself is Charles Steidel,
the Caltech leader of an international team to discover ways of viewing thirteen-billion-year-old
baby galaxies. His thoughts reflect the addition of twenty-first-century biological
understanding to the equation: "The chance of there being life with which
we would be capable of communicating, I think, is fairly low, because there
are so many ways that things could develop."

Even Robert Jastrow, who has proved more relentlessly upbeat about alien civilizations
than any other astronomer with whom I’ve spoken, appears to have had some second
thoughts. When I was about to go to press with a book on modern cosmology, he
asked me to make a small addition to a statement he had made in my chapter about
SETI. Instead of saying, "We’ll be hearing from those guys soon,"
he wanted me to change it to, "If life is common, we’ll be hearing
from those guys soon."

Most people are oblivious to recent evidence bearing upon the ETI question,
both pro and con. But the Copernican principle is firmly embedded in popular
culture, understood in terms of "the awful waste of space" if aliens
aren’t out there. Any chatty taxi driver can tell you that there are billions
of galaxies and billions of stars within each. The sheer numbers demand that
there be millions of habitable planets in our galaxy alone, even if the percentage
of tenantable star systems is small. To say otherwise is to expose one’s lack
of scientific education.

Contact is assumed to be not a matter of if, but when. Our movies
have given us progressively better special effects to prepare us for a day when
the Earth will stand still, when we’ll experience Close Encounters of the
Third Kind, or when SETI will help us make Contact. Generation X
and following have been entertained by more extraterrestrials than cowboys,
Indians, and soldiers combined. It’s probably not an overstatement to say that
no movies have had greater influence on men under age thirty-five than the Star
Wars films.

Infatuation with extraterrestrials further increased in the last decade. The
Rockford Files became The X-Files. Mob-fighting Untouchables turned
into alien-fighting Men in Black, also spun into a children’s cartoon series.
The biggest hit in late night radio is a national show that frequently features
guests offering firsthand accounts of their close encounters with aliens or
their spacecraft.

For some people, real life is apparently taking too long to catch up to their
media-led expectations—and they aren’t going to wait any longer. During the
1990s, psychologists estimated that in the U.S. alone 900,000 people claimed
to have been abducted by aliens, and the trend was increasing. In his book Close
Encounters of the Fourth Kind, C. D. B. Bryan reported "the emergence
of a new psychological disorder," observed in people who have been conditioned
to look to "alien saviors" who might give them the fulfillment they
aren’t finding on terra firma.

Theoretical physicist Paul Davies claims that people are looking to extraterrestrials
as "a conduit to the Ultimate." For many, the prospect of ETI has
come to meet a need once met by religion. Even the SETI scientists say they
are motivated by a nobler goal than the mere search for intelligence. Imagine,
they say, the boost in knowledge, in morality, and maybe even in spirituality,
to be gained from a billion-year-old civilization.

Robert Jastrow imagines what it might do to our present religions. "When
we make contact with them, it will be a transforming event," he says. "I
do not know how the Judeo-Christian tradition will react to this development,
because the concept that there exist beings superior to us in this universe,
not only technically, but perhaps spiritually and morally, will take some rethinking,
I think, of the classic doctrines of Western religion."

Any signals we detect, according to SETI astronomer Jill Tarter, will come
from long-lived civilizations. This fact, combined with the fact that religions
cause so many wars on this planet, means that our first detected signals will
come from beings "who either never had, or have outgrown, organized religion,"
she said at a recent science/religion meeting sponsored by the Templeton Foundation
and held in the Bahamas.

Other scientists and theologians at the Nassau meeting thought that pantheistic
religions could survive an alien encounter, but most assumed that Western religion
would certainly meet its fate when meeting extraterrestrials. Science historian
Steven Dick called SETI "a religious quest" that might help to reconcile
science and religion. But he assumed this would occur at the expense of Christianity,
which could not accommodate the implications of ETI.

It strikes me that today’s scholars may be too quick to pronounce last rites
over the faith that actually engendered most early ETI enthusiasts. Throughout
the Middle Ages, well-read people believed that a "plurality of worlds"
was impossible, following Aristotle’s arguments. In 1277, a council of bishops
in France condemned this position, officially opening the way for many to take
other worlds seriously.

Whether encouraged or discouraged by their churches, prominent Christians became
the most prominent ETI promoters. These included Giordano Bruno and Nicholas
of Cusa (fifteenth century), Johannes Kepler (sixteenth century), American Puritan
divine Cotton Mather (seventeenth century), and Yale president/minister Timothy
Dwight (eighteenth century).

Whether aliens will deliver a knockout blow to any particular religion depends,
of course, upon exactly what aliens have to tell us about God. Materialists
have traditionally assumed that Jews, Christians, and Muslims, believing in
a transcendent God, will receive bad news. And the Christian belief in Jesus’
death for human sin seems particularly problematic to them. How could we reconcile
Jesus’ death for all with the existence of other intelligent creatures in the
universe?

Christian ETI enthusiasts, however, have a variety of responses to the skeptics:

1. Jesus’ atoning sacrifice was a one-time event that covers aliens too. Oxford
   cosmologist E. A. Milne suggested that missionaries will eventually be preaching
   the good news to far-flung galaxies.




2. Other civilizations may not have fallen into sin and so don’t require salvation.
   Oxford don C. S. Lewis wrote science fiction fantasies about such alien societies.




3. God has become incarnate in the form of alien flesh in as many places where
   His creatures have fallen into sin. Scholars and rock singers have taken this
   position. And in the words of hymn writer Sydney Carter:

Who can tell what other cradle,

High above the Milky Way,

Still may rock the King of Heaven

On another Christmas Day?

Most ETI believers remain blissfully foggy about the best evidence to support
their faith. Here are some of the recent scientific discoveries and trends I’d
be sure to mention if I were to argue for the existence of ETI at my next dinner
party.

• Exoplanets. The Copernican Principle came through once again by predicting
that we should find planets orbiting Sun-like stars. Waiting all their lives
for this discovery, astronomers finally received word of it in 1995.

Until very recently, no extrasolar planet had been observed directly, but rigorous
measurements of the wobble in their host stars assured planet-hunters of their
presence. The first exoplanets discovered appeared to belong to freakish solar
systems, not only because the pinpointed planets were huge—as expected, since
these are easiest to measure—but also because they were orbiting close to their
parent stars, which was very unlike our expectation of finding solar systems
like ours, with large, gaseous planets farther out. Our solar system is beginning
to look like the freakish one.

Astrophysicist Virginia Trimble (University of California, Irvine) typified
the consensus before these discoveries, writing: "It is not a coincidence
that the solid-surfaced, terrestrial planets are close to the Sun and warm enough
for liquid water, while the jovian (gas-giant) planets are in the outer, frigid
reaches of the solar system." Using "common sense and computer models,"
she calculated that "the Milky Way probably still contains at least 1010
[that’s ten billion] stars that could have harbored habitable, terrestrial planets
for more than five billion years." Our actual observation of unexpectedly
different planetary systems now forces us to rethink our views on the commonness
of earthlike planets.

Exobiologists have dubbed the habitable belt where water can exist in liquid
form around a star "the Goldilocks zone," because it’s neither too
hot nor too cold for life. Those exoplanets that have been observed spending
any time in the Goldilocks zone merely pass through it. Their orbits are extremely
elliptical, meaning surface temperatures fluctuate from hotter than Venus to
colder than Mars. The very fact that these massive planets cut through the habitable
zone in their elongated orbits ensures there can be no smaller, more hospitable
planets in this system, since the giants would destabilize their orbits.

Teachers and students learned from Science News: "Recent discoveries
of giant planets orbiting within spitting distance of their stars have upset
a central tenet of astronomers—that Earth’s solar system, where large planets
orbit far from the Sun, provides the model for planetary development everywhere."

Of course, it’s too early to tell by these methods just how rare our earth
is. The technique is not yet refined enough to find smaller planets. Over the
next two decades, NASA’s Origins Program will be developing a series of space-based
telescopes, hoping not only to detect the wobble produced by small, Earth-sized
planets (2009’s Space Interferometry Mission), but to measure the chemical signature
of life itself (2012’s Terrestrial Planet Finder).

In short, exoplanet discoveries probably provide the most important scientific
gain in recent years to favor ETI existence, but this good news came at a price:
the Copernican Principle cannot be applied so neatly to our own star system.
Our solar system does not appear to be typical, and those that permit life,
if they exist, must be the exception, not the rule—even among Sun-like stars.

• SETI Strides. New search instruments coming on line in the near future
may dwarf all previous attempts to pick up signals from distant civilizations.
The argument can be made that earlier searches just didn’t have the coverage
required—either in sensitivity, frequencies, or number of examined stars. And
these shortcomings will shortly be remedied with instruments that are making
great leaps in capability.

The SETI Institute of Mountain View, California, calls its main search Project
Phoenix, the best-funded search ever. Unlike others, this project carefully
searches star by star, listening only to the likeliest candidates within a radius
of two hundred light-years. Project Phoenix has shuttled its Targeted Search
System back and forth between the largest radio dishes in the world.

In September 2000, Microsoft’s cofounder Paul Allen and his associate Nathan
Myhrvold pledged $12.5 million dollars to the SETI Institute for the development
of the Allen Telescope Array (ATA), a specially designed radio telescope that
will be dedicated to the search for ETI. A small prototype is complete, and
the full ATA, comprised of hundreds of backyard-type satellite dishes working
together, is scheduled to come online in 2005. In the time it now takes Project
Phoenix to survey 1,000 stars, ATA will examine 100,000, and might eventually
scrutinize a million stars a year, looking out to 1,000 light-years or
more.

"This telescope will do it," SETI astronomer Seth Shostak told me.
According to Shostak, the ATA will scan so many stars with such speed that "even
if we use the most conservative estimates about the number of civilizations
out there, I think we’ll find their signals within the next couple of decades."

Not wanting to wait that long, over three million volunteer enthusiasts are
also partaking in the pursuit, either by joining a "distributed computing"
network called SETI@Home, or by building their own radio telescopes as members
of the amateur SETI League.

"It gets the heart pounding," says Shostak, anticipating the fact
that we may soon be listening to alien wisdom. It’s an experience several Silicon
Valley legends are giving tens of millions of dollars to have. And amateurs
are giving tens of millions of hours to try to bring us the experience sooner.

Some analysts of SETI projects argue that Project Phoenix is wasting its considerable
resources on an outdated strategy. Nathan Cohen and Robert Hohlfeld, scientists
at Boston University, point out that targeted search strategies assume that
ET civilizations are much more abundant than recent observations allow. They
favor scanning larger, star-rich areas of the sky, betting on the numbers rather
than the long-shot chance of finding ETIs via nearby, star-by-star searches.

"Unless ETs truly infest the stars like flies (very unlikely)," write
Cohen and Hohlfeld, "the first signals we can detect will come from very
rare, very powerful transmitters very far away. The 1971 model, which lent too
much weight to nearby stars, turns out to be a naive case, the best that could
be calculated at the time."

• Slow Strides in Space Travel. Each new problem for space travel is
a problem solved for SETI enthusiasts. Easy progress in our ability to zip around
the solar system might imply our eventual ability to travel between the stars—and
the ability of advanced aliens to do so. In that case, we shouldn’t have to
go looking for them; they should already be here.

But here we are, already past 2001, the year when, according to Arthur C. Clarke’s
trend-setting classic of science fiction, humankind would make contact with
more highly evolved beings (or at least one of their artifacts). At the very
least, by this time we were supposed to be doing manned missions to Jupiter’s
moons. Clarke’s expectation in the 1960s was not unrealistic, considering the
fact that our new space program went from putting the first man in orbit to
the first man on the moon in just seven years.

So why was that first small step for man the last great leap to be made in
twentieth-century space exploration? Each passing year that delays the planning
of a manned Mars mission reminds us of the exponentially greater distances—and
difficulties—as we try to reach objects beyond our Earth-Moon system. And so
these difficult-to-cross distances may explain why we haven’t been visited.

If the public knows little about the best reasons to believe in intelligent
extraterrestrials, it knows even less about the new reasons to doubt.

• Fermi’s Paradox—Back in Style. Fermi’s Paradox, a SETI-challenge
that was tried and found wanting in the 1950s, has been given a retrial. This
time, expert witnesses on propulsion technologies have been called in, claiming
that if life sprung up in our galaxy many millions of years ago, then our galaxy
should have been entirely colonized by now.

It all started over a Los Alamos lab lunch in the summer of 1950, when renowned
Italian physicist Enrico Fermi had one of those napkin-scribbling epiphanies.
His conclusion stemmed from the indisputable premise that there are billions
of stars in our galaxy that are older than our sun, and that life routinely
develops under favorable conditions.

Exhausted planet resources and dying stars would provide good motives for exploration
and homesteading. Some cultures, like our own, would find other motives for
colonizing, and it would only take one enterprising population to begin exponential
expansion. Fermi showed that, even assuming modest speeds, every habitable star
system in the galaxy should have been colonized within mere millions, not billions,
of years. Complete colonization could take place in the relative twinkling of
a cosmic eye, many times over, in a ten-billion-year-old galaxy like the Milky
Way. "So," asked Fermi, "where are they?"

Astronomers immediately developed solutions to the paradox, but as the years
passed, each of these explanations has become problematic. Some suggested that
perhaps the distances between stars are just too great for biological creatures
ever to cross. But today, while still in our space age’s infancy, physicists
and engineers at NASA envision propulsion strategies that should reach 10 to
20 percent of the speed of light, making trips to the stars feasible, even for
short-lived biological beings like us.

Figuring on a cruising speed of 10 percent that of light and periods of four
hundred years’ settling time between migrations, astronomers say it would take
just five million years for one colonizing group to reach every star system
across the Milky Way’s 100,000 light-years.

In the 1970s, four astrophysicists—Michael Hart, David Viewing, Frank Tipler,
and Ronald Bracewell—independently published studies concluding that the Fermi
Paradox was difficult to escape. Today, as NASA lays the groundwork for new
propulsion strategies, the thought that older cultures should have developed
these long ago lends added weight to Fermi’s argument. "The implication
is clear," wrote British astronomer Ian Crawford last year: "The first
technological civilization with the ability and the inclination to colonize
the galaxy could have done so before any competitors even had a chance to evolve."

In the past, alien defenders turned to sociological factors that might have
prevented interstellar travel. Perhaps aliens just don’t like traveling. Perhaps
civilizations routinely blow themselves up after achieving nuclear capabilities.
Or perhaps, according to the "zoo hypothesis," our solar system has
been set aside as a primitive nature preserve, not to be touched.

But even SETI Institute astronomer Seth Shostak is skeptical about these scenarios,
writing in his book Sharing the Universe: "It isn’t that we can
resolve the Fermi paradox by arguing that most alien societies self-destruct
or lose interest in expansion. Every single one of them must do so, for
otherwise representatives of at least one society would be in our neighborhood."

Some of them, if not all, would have ample motivation to move when their host
stars ran out of hydrogen and died. Hundreds of millions of solar-type stars
in our Milky Way have already suffered this fate, turning any surrounding paradises
into hells by puffing up into red giants or compacting into white dwarfs.

What are SETI proponents to do? Most have returned to pointing out the physical
challenges of interstellar trekking. During the 1950s, astronomer Frank Drake
decided that energy costs might make interstellar travel not just high-priced,
but impossibly so. There’s no guarantee that better propulsion systems are physically
possible or that less costly energy sources can be tapped for higher speeds.

It’s exactly here that believers in advanced ETI exacerbate the paradox. They
invariably assume that the space-travel technology and energy resources of advanced
technological civilizations will also be highly developed. After all, Carl Sagan
and other SETI pioneers classified these advanced civilizations according to
their abilities to harness the power of entire stars or galaxies. It doesn’t
sound like insufficient energy production would be the thing to hold back such
societies from powering greatly increased transit speeds. In our own history,
the cost of raw materials and fuels, relative to wages, has been dropping exponentially
for the past 150 years. In 1983 Carl Sagan himself predicted that this trend
would likely continue for another millennium.

• New Analysis of SETI Results. Recent analyses of radio search findings
have only tended to put severe constraints on the numbers and types of possible
alien civilizations.

At the first SETI conference in 1961, Frank Drake proposed a list of factors
to quantify the technological populations expected to inhabit our galaxy. Drake’s
associates assigned values to the rate of star formation, the fraction of stars
with planetary systems, the number of planets suitable for life, the fraction
of planets where life develops, and the fraction where technological civilizations
develop. By multiplying the terms together, they determined that there should
be about one million societies using radio waves in our galaxy. The scientists
assumed, conservatively, that perhaps 1 percent of the civilizations would not
blow themselves up shortly after achieving nuclear capabilities. Others have
since assigned higher values to this and other factors, and have arrived at
an even higher number.

Drake’s first project to search for extraterrestrial radio signals became the
forerunner of more than seventy grander radio searches by teams around the world,
using the world’s largest radio telescopes and most sophisticated computer programs
to analyze the data.

However, after what has now been forty years of null SETI results, astronomers
are reexamining each of the factors making up the Drake Equation, concerned
that the values of some may have been grossly overestimated. Charting the distances
and radio powers that SETI projects have checked to date, Massachusetts physicist
Andrew LePage has already determined which kinds of civilizations can be ruled
out. These include nearby civilizations slightly more advanced than ours (called
type I), as well as those at greater distances that are yet more advanced (called
types II and III). "These are not trivial results," writes LePage.
"Before scientists began to look they thought that type II or III civilizations
might actually be quite common. That does not appear to be the case."

• The Rare Earth Equation. Today the Drake Equation is being superseded
by the Rare Earth Equation, as it was named by geologist Peter Ward and astronomer
Donald Brownlee, both at the University of Washington in Seattle. Since the
Drake Equation depends upon the number of Earth-like planets orbiting Sun-like
stars, Ward and Brownlee used the latest data to revise previous estimates concerning
both—and to add many once-neglected factors, now known to be critical, to the
equation.

These include the fraction of stars in a galaxy’s habitable zone, the fraction
of metal-rich planets, the fraction of planets with a large moon, the fraction
of planets where complex animals arise (as opposed to bacteria or algae), and
the fraction of planets with a critically low number of mass extinction events.
In their 2000 book, Rare Earth—Why Complex Life Is Uncommon in the Universe,
Ward and Brownlee remind their readers: "When any term of the equation
approaches zero, so too does the final result." And they conclude: "It
appears that Earth indeed may be extraordinarily rare." Here’s why:

• Special Gas Giant. Jupiter-like planets that orbit close to their
host stars, or that orbit eccentrically, refuse to politely share their space
with smaller, life-harboring planets. Habitable planets need to make circular
orbits within the "Goldilocks zone." Gas giants making eccentric orbits
will eject smaller neighbors out of the system or send them crashing into their
sun.

Well-behaved gas giants, like Jupiter and Saturn, keep circular orbits at a
respectful distance. In that position, they actually serve the necessary function
of cosmic vacuum sweeper, drawing comets and asteroids to themselves, rather
than allowing them to hit us (as when Comet Shoemaker-Levy 9 struck Jupiter
in 1995). George Wetherill of the Carnegie Institution of Washington calculated
that without Jupiter, comets would strike Earth between 100 and 10,000 times
more frequently than they do, meaning that "we wouldn’t be here."

• Large Moon. Habitable planets, it turns out, need to be members of
a double-planet system, as some astro nomers call our Earth-Moon system. Most
people don’t realize that our Moon is huge compared to the relative sizes of
other moons in the planet-moon systems of our solar system. The Moon’s mass
creates a stabilizing anchor for the Earth, preventing the Earth from undue
attraction to the Sun or to Jupiter, which would cause the Earth to tilt too
far on its spin axis.

Discovering this, astronomer Jacques Laskar wrote: "We owe our present
climate stability to an exceptional event: the presence of the Moon." Without
an extra-large moon orbiting at the right distance from us, scientists predict
that Earth would be subject to a runaway greenhouse effect, as on Venus, or
a permanent ice age, as Mars would experience if it had more water.

Worse, most astronomers now think that the presence of the Earth’s Moon is
the result of a freak accident, perhaps a one-in-a-million shot, when a smaller
planet hit the forming Earth with a glancing blow that allowed the mantles of
each planet to combine and end up in orbit around Earth. "To produce such
a massive moon," write Ward and Brownlee, "the impacting body had
to be the right size, it had to impact the right point on Earth, and the impact
had to have occurred at just the right time in the Earth’s growth process."

• Galactic Location. As in the real estate business, location is everything.
Stars located much farther from the galaxy’s center than our Sun contain lower
concentrations of heavy elements, necessary to form rocky planets like Earth.
Stars much nearer the center of a galaxy reside in a denser neighborhood, exposing
any orbiting planets to lethal radiation. Stars within a spiral galaxy’s arms
have the same problem. Most stars traveling between the spiral arms won’t stay
there, but our Sun is unusual for its circular orbit around the galaxy.

• Plate Tectonics. A hospitable planet needs a critical amount of radioactive
elements, such as uranium, to produce the heat that generates a magnetic field.
Without our magnetic field, the atmosphere would soon drift out into space.
The radioactive core also fuels plate tectonics, the movement of the planetary
crust across its surface. Of all our solar system’s planets, such movement is
found only on Earth.

Plate tectonics is crucial for life, and a string of other improbable factors,
in turn, prove critical to the generation of plate tectonics. These include
not only a radio active core, but a crust of the right thickness and a mantle
of the right viscosity, or flexibility.

• Just-Right Crust. A fortuitous assemblage of two kinds of crust are
necessary, with different densities, in order to allow one to slide over the
other, and to allow the lighter one to maintain itself above the water to produce
stable continents.

• Timing the Warm-up. Exobiologists point out the ne cessity of a just-right
host star, called a main sequence star. But main sequence stars increase their
energy output over time, creating obvious problems for orbiting planets. In
Earth’s case, we now know that the era when the Sun heated up was timed to coincide
with the era in which Earth’s atmosphere gradually shifted from mostly greenhouse
gases to the cooler mixture we enjoy today.

• Biological Contingency. Even if we assume that there are plenty of
planets in our galaxy that meet the right conditions, and that life develops
routinely on them, the most important question remains: How many of them will
develop intelligent life? The majority of biologists and paleontologists
say that evolution works without direction or a "ladder of progress."
Instead, the history of life on Earth shows that the path of evolution depends
upon a series of unpredictable events.

What were the odds that dinosaurs would be wiped out by an asteroid impact
sixty-five million years ago, paving the way for us? What are the odds that
the Cambrian explosion, when all the modern body plans appeared on our planet
within a short interval, will happen on other planets?

Rare Earth’s Ward and Brownlee conclude that, though microbial life
may be common in the universe, complex life (even as complex as a flatworm)
is not. The Cambrian explosion of forty new, widely separated complex animal
groups, they believe, didn’t have to happen. Darwinism doesn’t predict such
an event. And the fact that no new major animal groups (called phyla) have evolved
in the 530 million years since should give us pause.

Harvard paleontologist Stephen Jay Gould views the intelligence of Homo
sapiens "as an ultimate in oddball rarity." The fact that only
one species out of an estimated fifty billion developed it on this planet after
3.8 billion years of life suggests that high intelligence may not be the most
natural result in the course of evolutionary events.

"If intelligence has such high value," says Gould’s Harvard colleague
Ernst Mayr, "why don’t we see more species develop it?" The list of
leading biologists and paleontologists on record for defending this position
is impressive, including George Gaylord Simpson, Theodosius Dobzhansky, Francois
Jacob, and Francisco Ayala. British astronomer John Barrow notes that "there
has developed a general consensus among evolutionists that the evolution of
intelligent life, comparable in information-processing ability to that of Homo
sapiens, is so improbable that it is unlikely to have occurred on any other
planet in the entire visible universe."

Younger professionals in astronomy-related fields have also joined the trend.
After writing an overview of what he calls the "bottlenecks on the road
to intelligence," Astronomy magazine editor Robert Naeye concludes:
"On Earth, a long sequence of improbable events transpired in just the
right way to bring forth our existence, as if we had won a million-dollar lottery
a million times in a row. Contrary to the prevailing belief, maybe we are special."

Ward and Brownlee tell us that if they’re right about the rarity of complex
life, then "there will be societal implications, or at least some small
personal implications." They close their book with an appeal for Earthlings
to stop causing extinctions, since we may be eliminating species, not only from
our planet, but from the entire galaxy. An editor at the Chicago Tribune
dutifully closes his review of their book with the question: "If we really
are all alone in the universe, why aren’t we taking better care of each other
and this place?" So there’s the moral to the story.

But what about those "personal implications"? Sure, it’s fun to kick
around speculations about aliens. But if intelligent life is so odd, the bigger
question is, Why are we here?

In his book on extraterrestrials, British cosmologist and ETI enthusiast Paul
Davies wrote that we have just three options when deciding why we’re here: we
either owe our existence to a very rare fluke, to unknown laws that make life
a cosmic imperative, or to a miracle.

Davies rejects the fluke idea as the ultimate "just-so story." He
rejects the miracle possibility out of hand, and warms up to the cosmic imperative
notion. This gives him, he says, "a universe in which we’re not alone."
He hopes that perhaps we’ll even find a billion-year-old society that will teach
us how to solve all our problems. But if the evidence now points more plainly
to the idea that we’re not as common as flies, then it seems unwise to put our
trust in a cosmic imperative.

In sum, we have no trustworthy principle to tell us what to believe about aliens.
Worse, all three of our options for explaining life—laws, fluke, or miracle—require
a leap of faith. This inference is a slap in the face to those who have put
their faith in science.

The conviction that intelligent life is a cosmic im perative is not a scientific
one, as we have seen, since actual data point in the opposite direction. Neither
biologists nor astronomers see anything imperative about the many contingencies
that had to be met, against all odds, for us to be here. Even Davies admits
that the idea of laws slanted toward life and mind is "enough to make most
biologists shudder," since it represents "a fundamental challenge
to the existing scientific paradigm."

Though it strains our credulity, belief that we are a fluke at first seems
more in line with modern science—until we realize that it runs directly against
science’s revered Copernican grain. What would Copernicus or Hubble say? Actually,
Copernicus would not have subscribed to the principle that bears his name, since
he remained unabashedly anthropocentric while believing that the Earth orbited
the Sun. And Edwin Hubble should be credited, not only for taking the final
step in the Copernican Revolution, but for putting the kibosh on it. Shortly
after discovering that our galaxy is one of many, he discovered that all the
galaxies are fleeing from one another, demonstrating an expanding universe.
Scientists had preferred to think of our epoch in time as a typical slice out
of a changeless eternity, but their eventual acceptance of the big bang meant
that our universe has changed over time. Our era turns out to be a special one
that permits carbon life, contradicting the Copernican Principle that there
should be nothing special about our time or place.

In their classic book The Anthropic Cosmological Principle, astrophysicists
John Barrow and Frank Tipler call this discovery "the first failure of
the Copernican Principle." And as we’ve seen, the Copernican Principle
failed again by predicting that our solar system would provide a model for most
others.

The principle Barrow and Tipler prefer, of course, is their Anthropic Principle,
which doesn’t try to explain away our privileged place or time, but instead
says that the features of the universe are constrained by the need to permit
observers like us. The less delicate way to put this is to say that the universe
appears to have been finely tuned in its fundamental force strengths, particle
mass ratios, etc., for our benefit.

Most scientists dislike the direction the Anthropic Principle points them,
not just because it implies God as an easy answer, but because, once again,
it commits heresy against Copernican dogma. "It seems to me a sort of hubris
to think that God made the universe just for us," said cosmologist George
Smoot. "It seems to me, I’d just make the universe full of life."

Theoretical physicists such as Stephen Hawking have spent much of their energies
looking for better explanations for the many anthropic "coincidences,"
seeing red flags go up with each violation of the Copernican Principle. But
surely there must be a deeper reason for choosing one principle over another.
Hoping to learn it, I asked Stephen Hawking himself. What disturbs him most
about the Anthropic Principle? "The human race is so insignificant,"
he told me, "I find it difficult to believe the whole universe is a necessary
precondition for our existence."

Maybe that’s all there is to it: his fundamental lack of belief in our significance.
Such disbelief comes easy for most people trained in science. We can’t be that
important. Why waste all that space? The movie Contact had its characters
raise this favorite SETI point three times. After all, we Earthlings don’t need
all those other galaxies. "Clearly the solar system is necessary,"
continued Hawking, "and maybe our galaxy, but not a hundred billion other
galaxies."

However, Barrow and Tipler point out that we little Earthlings actually do
require all that extra legroom. They argue that the universe has to be as large
as it is to host even one lonely outpost of life. Why? A stable universe with
gravity must be expanding, or it will collapse. An expanding universe naturally
becomes huge during the time required for stars to slowly cook the heavier elements
necessary to constitute life. By the time the first stars finish their life
cycle, making life’s ingredients available through supernovas, the cosmos will
necessarily be huge, whether it houses one population or billions.

As long as George Smoot and Paul Davies brought the possibility of God into
this, what about that "miracle" option? "Miracle," as I
take it, doesn’t have to mean magical or instantaneous—but the word is up front
about its demand for a nonphysical explanation. As Edwin Hubble’s protégé,
astronomer Alan Sandage, told me: "We can’t understand the universe in
any clear way without the supernatural."

Physicist James Trefil concluded his book about extraterrestrials and the conditions
for life with the statement: "If I were a religious man, I would say that
everything we have learned about life in the past twenty years shows that we
are unique, and therefore special in God’s sight." Not being a religious
man, apparently, he declined to make the leap.

Personally, I’ve never thought of myself as making a leap of faith,
at least, not a leap that was any greater than the alternatives. If we do take
this confluence of just-right conditions the way they sound, like someone had
us in mind all along, then we don’t need aliens to keep us from being alone.
Two-way communication with an Extraterrestrial Intelligence may indeed be available
in our lifetime. Even better than appreciating our rarity, contact with our
Superintelligent Creator could truly motivate us to take "better care of
each other and this place."

Theistic believers have the same options as everyone else. Their alternatives
are not restricted to faith in aliens or faith in God. If both exist, then the
real question about aliens reduces to: Did God want separated creature groups
to communicate with each other, or did He set them up so that they would develop
independently?

Pleading ignorance but desiring knowledge, all of us can and should remain
open to these various possibilities. But given what we can know for now, we
have little reason to hope for answers from ETI in our lifetime. We’ll have
to solve our problems with war, crime, and poverty for ourselves, while also
making up our own minds about the purpose of life and seeking another "conduit
to the ultimate."

Fred Heeren is a science journalist and author of Show Me God—What the Message
from Space Is Telling Us About God.