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everyone is only set to receive signals and no one is beaming, would SETI be doomed to fail? Not necessarily. Even as we speak, our daily weather reports and reruns of I Love Lucy are streaming into space at the speed of light. Our radio and television signals fill a growing bubble of our galaxy, now extending more than 50 light-years from Earth--far enough to encompass hundreds of other stars. Although these broadcasts are much weaker than an intentionally beamed message would be, they might register in sensitive telescopes on the planet Grok, and vice versa.

Our species has taken some baby steps to communicate with our possible neighbors. In 1974 Drake and his colleagues used the giant Arecibo radio telescope in Puerto Rico to beam a three-minute message toward a cluster of stars. The message, encoded as a binary sequence, contained basic information about our planet, our solar system, and the biology of humans. Four of our planetary explorers--Pioneer 10, Pioneer 11, Voyager 1, and Voyager 2--carry greetings as well. Each Pioneer has an engraved plaque about us, while each Voyager features a gold-plated phonograph record with sounds and audio-encoded images from Earth. But these efforts are symbolic, not practical. For instance, the Arecibo signal will reach its target in 24,000 years. Even if a civilization there sent a reply, we wouldn't get it until the year 50,000.

Another approach to SETI relies not on radio waves but on visible and infrared light. Think of spotting the light from a handheld laser pointer across a football stadium. Even with all the light entering your eyes from the stadium lights, the playing field, and other sources, you'd probably notice the laser pointer right away. All its energy is concentrated into the familiar red laser color, and its beam remains intense as it crosses the field. In a similar way, powerful single-color lasers directed into space by a large telescope would be visible across great stretches of the galaxy. Brief but energetic pulses of laser light could outshine the parent star within that part of the color spectrum. Some SETI researchers have adapted their equipment to watch for such pulses.

It's fascinating to ponder the possible outcomes of SETI. If the project succeeds, our awareness of the universe will undergo a far greater upheaval than Copernicus caused by displacing Earth from the center of all things. If SETI fails after many years, our descendants would confront this challenging question: Despite the rich interactions between matter and energy throughout the cosmos, are we indeed alone?

Symbolic Greetings from Earth

In 1972 and 1973, Pioneer 10and Pioneer 11headed toward the outer planets and interstellar space carrying plaques (left) describing the solar system, Earth, and humankind. In 1977, Voyager 1 and Voyager 2 set off on similar journeys, bearing a recording (above) of the sights and sounds of Earth.

Where Did the UNIVERSE Come From?

Long before humans wondered whether other beings lived among the stars, they questioned the origin of the universe itself. Cultures invented creation myths and passed them down through generations, forming the richest of all stories for anthropologists to decipher. Modern Western culture has devised a story of universal creation as well. This particular story goes beyond myth because we can back it up with scientific data.

The modern creation story is called the Big Bang. It is grounded in Edwin Hubble's discovery of the expanding universe in 1929. The American physicists Ralph Alpher and George Gamow were the first to propose the theory seriously, in 1948. According to Alpher and Gamow, the universe began with a burst of nuclear fusion from which all elements arose. Astrophysicists later learned that giant stars forge most elements heavier than helium, but the nugget of the idea was in place. It appeared the universe had an explosive birth and is still flying apart after billions of years, like a fireworks blast that literally fills all of space.

For a time, proponents of the Big Bang waged an intellectual war with supporters of another theory of the universe, called the steady-state theory. In this view, the universe obeyed the "perfect cosmological principle"--it had always and would always (continued)