Lonely Planets
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1977, Big Ear detected a strong signal from a point within the constel-
lation of Sagittarius. The astronomer on duty, Jerry Ehman, circled the
signal on the readout and wrote, in the margin, “Wow! ” The signal
only lasted for seventy-two seconds. Everything about it is consistent
with an alien technological source.
The “Wow!” signal has entered the lore of science, and science fic-
tion, as the best candidate yet for an actual alien signal. It is a favorite
topic among those who are convinced that aliens have contacted us and
the government is suppressing this information.†
The Wow! signal winked out quickly and has never reappeared,
though hundreds of attempts have been made to find it. In 2001,
astronomers used the multiple dishes of the Very Large Array in New
Mexico to conduct the most powerful hunt ever for a signal in the
Wow! direction. Not a peep. Obviously, Wow! was not a continuous
radio beacon, but it might have been a real signal, perhaps a snippet of internal communication between some alien ships. This tantalizing
hint has helped SETI scientists maintain their enthusiasm over recent
decades.
Today, there are about a dozen active radio search programs. In addi-
tion, there is a growing amateur SETI movement, led by electrical engi-
neer (and jovial singer of geeky folk songs) Paul Shuch. His SETI
League enlists enthusiasts who want to set up a dish in their backyard.
Although the sensitivity of amateur instruments is much lower, there is
strength in numbers. Together they can look in more directions at once,
so they could detect a strong signal that comes in when the big dishes
are pointing elsewhere. The SETI League’s Project Argus is trying to
link up five thousand radio dishes around the world to continuously
monitor the entire sky. As of this writing, they are up to 120.
The power and sensitivity of searches has improved by a factor of
Drake wrote, “Fortunately for the history of astronomy, no one discovered the error until construction was well under way and it was too late to change the size.” Drake once calculated that the giant Arecibo dish could hold 357 million boxes of cornflakes.
*Way to go, Ohio.
†The Wow! signal was even mentioned in an episode of The X-Files in 1994, which means that anyone within nine light-years knows about it by now, if they get the Fox network.
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more than 100 trillion since the days of Project Ozma. Still, the stars
remain silent.
F U R T H E R
The newest development in SETI is called SETI@home (SETI at home).
Anyone with a computer hooked up to the Internet can participate. Just
download the free software and then, while you are sleeping or goofing
off, the computers do the rest. The mother machine at Berkeley auto-
matically sends your computer a packet of data gathered at Arecibo.
When your PC is through searching for the telltale regularities that
might indicate an actual signal, it sends back its analysis and waits for
the next batch of bytes. The graphic design is almost as smart as the
concept. The twenty-third-century Federation-style aesthetic looks
much cooler than most software actually used for scientific research.
The project began in May 1999, and by its fourth anniversary more
than 4.4 million PC users from 226 countries* had joined, with thou-
sands more volunteering each day. In effect, the SETI@home project
has become the world’s largest supercomputer. It has already performed
nearly a million years of combined processing time and is currently
racking up more than a thousand years per day.
Why is this global supercomputer spontaneously self-assembling so
quickly? Because SETI is inspiring. It taps into the dreams of a species
beginning a new millennium and wondering if there is more to the uni-
verse than meets the eye. SETI@home finds fertile ground among the
netizens of the rapidly evolving global cybernation. Now that small
talk with distant pals we’ve never actually seen is our daily reality, the
idea of a galactic network of distant communicating civilizations does
not seem quite so far-fetched.† It is fitting that the search for our inter-
stellar neighbors should involve as many residents of Earth as possible.
SETI@home represents a new kind of populist science, as multitudes
participate in humanity’s effort to find the all-important signal in the
noise of the universe.
*As of May 2003, participants included 59 people from Vanuatu, 433 from Zimbabwe, 37 from Laos, 78 from Iraq, and 59 from the Gaza Strip. The United States, at 1,855,456, has the most participants, and Liberia, with 20, has the least.
†No instant messaging, though. That’s precluded by the laws of physics. No IM with ET
unless we discover new laws (or have them taught to us by ET) or learn to slow ourselves down so that centuries pass like instants.
SETI: The Sounds of Silence
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The search goes on. Bigger instruments, fully dedicated to SETI, will
soon come on-line, looking farther and listening to more frequencies
with better signal detection equipment. The most ambitious of these
comes courtesy of Paul Allen, the Microsoft zillionaire and longtime
SETI supporter, who is buying a stairway to heaven.*
Located at the Hat Creek Observatory 290 miles northeast of San
Francisco, the Allen Telescope Array (ATA) will be made of 350 indi-
vidual dishes, each similar to the satellite dishes you see in backyards
around the world. Starting in 2004 or 2005, the ATA will expand the
volume of space that we can listen to by a factor of a thousand over
Project Phoenix. If radio contact with an alien civilization merely
awaits our listening a bit farther out into the galaxy, it will happen
within the next decade.
SETI has had a bumpy ride. Humans have trouble committing to proj-
ects that may require centuries to succeed. It requires a commitment to
future generations that is in short supply these days. But, if astrobiology
proves to be a sustained movement and not just a breaking wave, maybe
SETI can go along for the ride. At the Second Astrobiology Science
Conference, at NASA/Ames in April 2002, I heard Jill Tarter declare to
an enthusiastic audience that the time was right for the U.S. government
to restore generous public funding for SETI.
*Allen has contributed $11.5 million out of an estimated development and construction cost of $26 million.
Fermi’s Paradox
19
I know perfectly well that at this moment the whole
universe is listening to us, and that every word we
Image unavailable for
say echoes to the remotest star.
electronic edition
—JEAN GIRAUDOUX,
The Madwoman of Chaillot
Image unavailable for
electronic edition
He’d like to come and meet us but he thinks he’d
blow our minds.©
—DAVID BOWIE, “STARMAN”
A B S E N C E O F E V I D E N C E
In 1952 the composer John Cage produced his most minimalist of all
scores, entitled 4′33″, which directs a pianist to play nothing for four
minutes and th
irty-three seconds. Some regard this as a pretentious
intellectual game. Others see a statement about stillness, and the
sounds we hear inside our own heads when given space to listen.
What is the significance of the more than forty years of silence heard
by SETI? Researchers rightfully point out that the search is just begin-
ning, that we have listened to only a tiny fraction of the stars in our
galaxy. Success would mean everything. Failure means little. Or does it?
One of SETI’s sayings is “Absence of evidence is not evidence of
absence.”* In fact, there is no possible evidence of absence. How could
we ever prove that the aliens aren’t out there? Yet, cumulatively, the
silence is a kind of evidence. If the galaxy was thick with signals,
*Also recently invoked by Donald Rumsfeld to justify attacking a country for harboring weapons that we cannot be sure are not there.
Fermi’s Paradox
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swarming with radio-noisy species, we would know it by now. We can
rule out the most optimistic end of the range of possibilities permitted
by the Drake Equation.
Let’s face it: the Drake Equation is so loosely constrained that you
can conclude whatever you want and prop it up with a mathematical
crutch. Sometimes, I think of it as a way for nerds to justify our religion
with an equation.
Rationally, I know that it’s a big universe, and we’ve only sniffed
around in our front yard. Still, I find myself noticing the four decades
of silence and wondering. Oh, I don’t doubt that they’re out there, but
perhaps they are not on the airwaves. The question of the existence of
intellectually advanced aliens has, in my mind, become more detached
from the question of our achieving radio contact. I am hopeful by con-
stitution. But, my “adolescent optimism” has morphed into a more
detached cosmic optimism. I still see the universe evolving toward a
state of more fully developed intelligence and self-understanding, but
I’m no longer sure the human experiment is a part of that process.
We should keep listening for the next thousand years, message or no
message. If we succeed in doing that, whether or not we find anyone
else, then we’ll be well on the way to bringing to fruition the cosmic
intelligence that we seek. If we get our act together to the point where
we can commit to anything on such long timescales, then eventually
there will be messages blasting loudly through our galaxy. Let’s make
sure and include some Bob Marley.
So, yes, let’s get billionaires to spend millions, or taxpayers to spend
pennies, to build huge radio arrays. Let’s scan all the stars we can in
any way we can think of, for as long as we can. Because you never
know. Still, after more than forty years, you do start to wonder:
Where are they?
E V I D E N C E O F A B S E N C E
In 1943, physicist Enrico Fermi was having lunch with some colleagues
at the Los Alamos National Laboratory, and the topic of alien life came
up. Fermi, like most scientists with some kind of grasp on what a uni-
verse with 100,000,000,000,000,000,000,000 stars implies, was a firm
believer in extraterrestrial life. But, he asked, if life and intelligence are
likely to evolve on even a fraction of other planets, why aren’t the signs
more obvious? Why haven’t we been visited or contacted? “Where are
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they?” With this simple question, he encapsulated a major problem for
SETI. Today it is known as Fermi’s Paradox.
The question might not seem that profound, but Fermi had a deep
and subtle point in mind. Thinking like a physicist, he simplified the
problem to one of particles starting from a single point, and jumping
randomly from place to place. If alien populations moving about the
galaxy are pictured as particles spreading through a room, we can ask
how long it should be before they fill the room—and calculate an
answer.
However conservatively you work the numbers in the Drake
Equation, it’s hard to avoid the conclusion that we live in a widely
inhabited galaxy, even if stars with living worlds are only one in a mil-
lion. Fermi thought that, by this same logic, we should already have
been visited. What if, in addition to developing radio technology for
communications, advanced species also develop interstellar travel and
decide to explore or migrate to planets around other stars? Then, isn’t a
search for their presence in our own solar system just as valid as a radio
search for their distant messages? How, then, are we to interpret the
fact that, as yet, we have found no scientifically accepted evidence for
the past or present visitation of intelligent aliens? Can’t we conclude
that they do not exist and save ourselves the trouble of searching for
signals?
This logic was largely ignored during the first two decades of experi-
mental SETI. Fermi’s Paradox had been discussed—and quickly
dismissed—at the international SETI conference at Byurakan in 1971.
The stars, it was decided, are too far away from one another, so interstel-
lar travel does not make sense. The only known way to reach other stars
within a human lifetime is to travel near the speed of light and use “rela-
tivistic time dilation.” According to Einstein’s theory of special relativity,
as you approach the speed of light, time slows down. If you go fast
enough, you could theoretically cross the whole galaxy within your life-
time. But time would not slow down on the planet you left behind, and
when you returned home, all your loved ones would be long dead and you
would be Rip Van Loser.* Further, the faster you go, the more energy it
takes to reach your destination. If you calculate how much energy it takes
to travel to the stars at relativistic speeds (including the energy it takes to
slow down when you arrive), you will probably decide to stay home.
*But, as Dan Hicks sings, “Hell, I’d go!”
Fermi’s Paradox
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Relativity is a real gas guzzler. If you had a superefficient nuclear engine,
you would still need to bring something like a billion pounds of fuel for
each pound of ship. The energy barrier to interstellar travel was widely
accepted within the SETI community, so Fermi’s Paradox was not consid-
ered a serious worry.
H A R T ’ S A N S W E R
In the 1980s Fermi’s Paradox came back with a vengeance. Several sci-
entists used it as the basis for sophisticated arguments concluding that
SETI would not succeed. Astronomer Michael Hart led the charge with
his 1975 paper “An Explanation for the Absence of Extraterrestrials on
Earth.” Hart showed a flaw in the arguments, made by Drake, Sagan,
and others, against interstellar travel. Sagan was always keen to point
out the ways that our thinking may be limited by our laughably limited
experience with life. In his seventies’ parlance, he advised that we
should always be on the lookout for “chauvinisms.” At Byurakan he
discussed water chauvinism, liquid chauvinism, planetary chauvini
sm,
and temperature chauvinism. Yet Sagan was guilty, along with the rest,
of a kind of temporal chauvinism. Why assume all of these trips
between the stars have to be made within a human lifetime?
Hart showed that the stars can be reached using much less energy. If
you allow for centuries, instead of decades, then the energy needs are
much more modest. Traveling at one-hundredth the speed of light, you
reach the nearest stars in a few centuries, without a fuel tank a billion
times larger than your vehicle. Assuming that interstellar colonies
sometimes spawn their own colonies, a migrating species crosses the
galaxy in only a few million years.
Now, a few million years sounds like a long time to you and me. Hell,
I get bored driving from Tucson to Phoenix. But it’s just a fraction of a
percent of the 10-billion-year age of our galaxy. Thus, Hart argued, the
absence of evidence is evidence of absence. Radio SETI was doomed to
failure and maybe not worth the investment. Fermi’s Paradox, reinvigo-
rated, came to be called, by some, the Fermi-Hart paradox.
The argument is far from trivial. Radio SETI stands a good chance of
succeeding only if the galaxy is either (a) richly endowed with advanced
civilizations, so that there is a transmitter within a few hundred light-
years of Earth, or (b) inhabited by at least a few extremely advanced
(Type II or III) civilizations, with beacons that we could see clear across
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the galaxy. In either case, is it reasonable to think that no one has ever
ventured out between the stars? Hart argued that technological intelli-
gence capable of radio communication would also be certain to spread
throughout the galaxy on a short timescale. His answer to Fermi’s
“Where are they?” was “Since they’re not here, they’re not anywhere.”
By the early 1980s, Hart’s arguments had become accepted by many,
and the SETI debate was polarized. Some argued that intelligence must
be spread liberally throughout the galaxy. Others, swayed by Hart’s
arguments, held that human civilization stands alone, or nearly alone,
in our galaxy.
The timing of this new movement was unfortunate, as it coincided
with the SETI-gutting efforts of faux-frugal budget-cutters in Congress.