Lonely Planets

  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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  L o n e l y P l a n e t s

  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

  309

  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

  311

  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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  L o n e l y P l a n e t s

  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

  313

  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.