Space Chronicles: Facing the Ultimate Frontier (7 page)

And don’t get me started on the 1996 blockbuster
Independence Day
. Actually, I find nothing particularly offensive about evil aliens. There would be no science-fiction film industry without them. The aliens in
Independence Day
are definitely evil. They look like a genetic cross between a Portuguese man-of-war, a hammerhead shark, and a human being. But while they’re more creatively conceived than most Hollywood aliens, why are their flying saucers equipped with upholstered high-back chairs with armrests?

I’m glad that, in the end, the humans win. We conquer the
Independence Day
aliens by having a Macintosh laptop computer upload a software virus to the mothership (which happens to be one-fifth the mass of the Moon), thus disarming its protective force field. I don’t know about you, but back in 1996 I had trouble just uploading files to other computers within my own department, especially when the operating systems were different. There is only one solution: the entire defense system for the alien mothership must have been powered by the same release of Apple Computer’s system software as the laptop computer that delivered the virus.

L
et us assume, for the sake of argument, that humans are the only species on Earth to have evolved high-level intelligence. (I mean no disrespect to other big-brained mammals. While most of them cannot do astrophysics, my conclusions are not substantially altered if you wish to include them.) If life on Earth offers any measure of life elsewhere in the universe, then intelligence must be rare. By some estimates, there have been more than ten billion species in the history of life on Earth. It follows that, among all extraterrestrial life-forms, we might expect no better than about one in ten billion to be as intelligent as we are—not to mention the odds against the intelligent life having an advanced technology and a desire to communicate through the vast distances of interstellar space.

On the chance that such a civilization exists, radio waves would be the communication band of choice because of their ability to traverse the galaxy unimpeded by interstellar gas and dust clouds. But we humans have had command of the electromagnetic spectrum for less than a century. To put that more depressingly: had aliens been trying to send radio signals to earthlings for most of human history, we would have been incapable of receiving them. For all we know, the aliens may have tried to get in touch centuries ago and have concluded that there is no intelligent life on Earth. They would now be looking elsewhere. A more humbling possibility is that aliens did become aware of the technologically proficient species that now inhabits Earth, and drew the same conclusion.

Our Copernican perspective regarding life on Earth, intelligent or otherwise, requires us to presume that liquid water is a prerequisite to life elsewhere. To support life, a planet cannot orbit its host star too closely, or else the temperature would be too high and the planet’s water content would vaporize. Also, the orbit should not be too far away, or else the temperature would be too low and the planet’s water content would freeze. In other words, conditions on the planet must allow the temperature to stay within the 180°F range of liquid water. As in the three-bowls-of-food scene in “Goldilocks and the Three Bears,” the temperature has to be just right. (Once when I was interviewed about this subject on a syndicated radio talk show, the host commented, “Clearly, what you should be looking for is a planet made of porridge!”)

While distance from the host planet is an important factor for the existence of life as we know it, a planet’s ability to trap stellar radiation matters too. Venus is a textbook example of this “greenhouse” phenomenon. Any visible sunlight that manages to pass through its thick atmosphere of carbon dioxide gets absorbed by Venus’s surface and then reradiated in the infrared part of the spectrum. The infrared, in turn, gets trapped by the atmosphere. The unpleasant consequence is an air temperature that hovers at about 900°F, which is much hotter than we would expect, given Venus’s distance from the Sun. At that temperature, lead would swiftly become molten.

The discovery of simple, unintelligent life-forms elsewhere in the universe (or evidence that they once existed) would be far more likely—and, for me, only slightly less exciting—than the discovery of intelligent life. Two excellent nearby places to look are beneath the dried riverbeds of Mars (where there may be fossil evidence of life that thrived when waters formerly flowed) and the subsurface oceans that are theorized to exist under the frozen ice layers of Jupiter’s moon Europa, whose interior is kept warm by gravitational stresses from the Jovian system. Once again, the promise of liquid water leads our search.

Other common prerequisites for the evolution of life in the universe involve a planet in a stable, nearly circular orbit around a single star. With binary and multiple star systems, which make up more than half of all stars in the galaxy, orbits tend to be strongly elongated and chaotic, which induces extreme temperature swings that would undermine the evolution of stable life-forms. We also require sufficient time for evolution to run its course. High-mass stars are so short-lived (a few million years) that life on Earthlike planets in orbit around them would never have a chance to evolve.

T
he set of conditions needed to support life as we know it is loosely quantified through what’s known as the Drake equation, named for the American astronomer Frank Drake. The Drake equation is more accurately viewed as a fertile idea rather than a rigorous statement of how the physical universe works. It separates the overall probability of finding life in the galaxy into a set of simpler probabilities that correspond to our preconceived notions of suitable cosmic conditions. In the end, after you argue with your colleagues about the value of each probability term in the equation, you are left with an estimate for the total number of intelligent, technologically proficient civilizations in the galaxy. Depending on your bias level—and your knowledge of biology, chemistry, celestial mechanics, and astrophysics—your estimate may range from at least one (ours) up to millions of civilizations in the Milky Way alone.

If we consider the possibility that we may rank as primitive among the universe’s technologically competent life-forms—however rare they may be—then the best we can do is to keep alert for signals sent by others, because it is far more expensive to send than to receive. Presumably, an advanced civilization would have easy access to an abundant source of energy, such as its host star. These are the civilizations that would be more likely to do the sending.

The search for extraterrestrial intelligence (affectionately known by its acronym, SETI) has taken many forms. Long-established efforts have relied on monitoring billions of radio channels in search of a radio or microwave signal that might rise above the cosmic noise. The SETI@home screensaver—downloaded by millions of people around the world—enabled a home computer to analyze small chunks of the huge quantities of data collected by the radio telescope at Arecibo Observatory, Puerto Rico. This gigantic “distributed computing” project (the largest in the world) actively tapped the computing power of Internet-connected PCs that would otherwise have been doing nothing while their owners went to the bathroom. More recently, improvements in laser technology have made it worthwhile to search the optical part of the electromagnetic spectrum for pulses of laser light a few nanoseconds in duration. During those nanoseconds, an intense, directed beam of visible light can outshine the light of nearby stars, allowing it to be detected from afar. Another new approach, inspired by the optical version of SETI, is to keep a lookout across the galaxy, not for sustained signals, but for brief blasts of microwaves, which would be relatively cost-efficient to produce on the other end.

The discovery of extraterrestrial intelligence, if and when it happens, will impart a change in human self-perception that may be impossible to anticipate. My only hope is that every other civilization isn’t doing exactly what we are doing—because then everybody would be listening, nobody would be sending, and we would collectively conclude there is no other intelligent life in the universe.

Even if we don’t soon find life, we will surely keep looking, because we are intellectual nomads—curious beings who derive almost as much fulfillment from the search as we do from the discovery.

• • •
CHAPTER FOUR

EVIL ALIENS
^*

Interview with Sanjay Gupta, CNN

Sanjay Gupta
: Here’s a question: Do you believe in UFOs? If so, you’re in some pretty impressive company. British astrophysicist Stephen Hawking, arguably one of the smartest people on the planet, thinks there’s a good chance that alien life exists—and not exactly the friendly ET kind. In fact, Hawking envisions a far darker possibility, more along the lines of the movie
War of the Worlds
. In a documentary for the Discovery Channel, Hawking says the aliens will be big, bad, and very busy conquering planet after planet. He says they might live in massive ships, and he calls them nomads who travel the universe conquering others and collecting energy through mirrors. Mirrors; massive ships; giant, mean aliens: is it all possible? Let’s go up close with Neil deGrasse Tyson, director of the Hayden Planetarium in New York and, like Hawking, an astrophysicist.

I’ve been fascinated by this since I was a kid, given the fact that there are hundreds of billions of galaxies, with hundreds of millions of stars in each galaxy.

Neil deGrasse Tyson
: Hundreds of
billions
in each galaxy.

SG
: Hundreds of billions of stars—even more. And that probably means there’s life out there somewhere.

NDT
: Indeed.

SG
: But this idea that aliens will be evil—Hawking paints a picture that is far less ET and far more
Independence Day
—is this speculation?

NDT
: Yes, but it’s not blind speculation. It says more about what we fear about ourselves than any real expectations of what an alien would be like. In other words, I think our biggest fear is that the aliens who visit us would treat us the way we treat each other here on Earth. So, in a way, Hawking’s apocalyptic fear stories are a mirror held back up to us.

SG
: That’s a very different perspective than what Carl Sagan put out there. He was literally giving away Earth’s location.

NDT
: Exactly. Sagan provided the return address on a plaque on the Voyager spacecraft. He wanted to say, “Here’s where we are!”

SG
: So why would aliens do what Hawking proposes they’ll do? Some sort of vengeance?

NDT
: Like I said, no one knows how aliens will behave. They will have different chemistry, different motives, different intentions. How can we extrapolate from ourselves to them? Any suspicion that they will be evil is more a reflection of our fear about how
we
would treat an alien species if we found them than any actual knowledge about how an alien species would treat
us
.

SG
: We’re listening for them right now. My understanding is that we’ve been listening for a long time—for anything—and we haven’t heard a peep from out there. Do you think they’re listening to us right now?

NDT
: Possibly. The big fear, it seems to me, is that we announce our presence and then the aliens come and enslave us or put us in a zoo. Some entertaining science-fiction stories have captured just those themes.

SG
: I never thought to imagine us as living in an alien zoo.

NDT
: That’s the fear factor. But what are
we
doing? We’re mostly listening. We have giant radio telescopes pointing in different directions, with highly sophisticated circuitry that listens to billions of radio frequencies simultaneously to see if anybody is whispering on any one of them anyplace in the universe. That’s different from sending signals out. We’re not sending signals out on purpose; we’re sending them out accidentally. The expanding edge of our radio bubble is about seventy light-years away right now, and on that frontier you’ll find broadcast television shows like
I Love Lucy
and
The Honeymooners
—the first emissaries of human culture that the aliens would decode. Not much reason there for aliens to fear us, but plenty of reason for them to question our intelligence. And, rumors to the contrary, we have not yet heard from aliens, even accidentally. So we’re confronting a vacuum, ready to be filled with the many fears we harbor.