Excerpt © Reprinted by permission. All rights reserved. Excerpt from part of Chapter 10: The Extraterrestrial Hypothesis DOES ET KNOW WE''RE HERE? What are the steps needed for a civilization to search for other worlds via interstellar space travel? The very first step is to identify potential planets orbiting distant stars. Humanity has already taken this step. We are very early in the process, but our abilities are advancing rapidly. As previously discussed, we have discovered over 6,000 exoplanets. This number will balloon into tens of thousands of planets and more as we develop techniques that allow us to see Earth-size planets orbiting at Earth-like distances from their star. Today, we could not detect our Earth if it was ten light-years distant from us.
It is too small and too far from the sun to detect with our current detection methods. Soon that will change as our technologies advance. A more advanced civilization would already have that ability and Earth would be among its catalog of planets. The second step is to look for planets that have signs of intelligent life. ET would begin by looking for the building blocks for life, assuming they were carbon-based like us. They would examine a planet''s reflected light to look for oxygen, water, carbon dioxide, methane, and other chemicals to determine if a carbon-based life could exist. (Humanity is just now taking its first baby steps in this area.) Like us, an extraterrestrial race would be examining planets in their catalog that not only have the right chemical ingredients but that also have signs of intelligent life.
These planets would be the ones that ET would carefully observe with their advanced telescopes and spectrometers. ET would look for changes to a planet''s atmosphere that might be caused by an advanced intelligent life. They would look for emissions in the various parts of the electromagnetic spectrum that indicate a civilization was expending large amounts of energy. Let''s use our planet as an example of how our atmosphere indicates that an intelligent civilization exists here. What would ET see if they turned their powerful telescopes toward Earth? About 200 years ago ET would have noticed large amounts of hydrocarbons were being emitted into the Earth''s atmosphere. This was driven by the coal burning of the industrial revolution in the nineteenth century. Some ET scientists might begin studying Earth as one of the more likely planets to harbor advanced intelligent life. ET would see the complexity of the emitted hydrocarbons increase in the twentieth century as we burned oils, plastics, and garbage that we released into the atmosphere.
ET scientists would know that the more complex the hydrocarbons are, the more likely that they were produced by an intelligence on Earth rather than simple vegetative fires. By the 1950s and 1960s our atmosphere contained isotopes of uranium, plutonium, and other radioactive compounds. These were created from our detonation of nuclear bombs on land and in the atmosphere. The ET scientists studying Earth might have been excited when the first detected those chemicals. There is nothing natural about those isotopes. Any civilization that analyzed our atmosphere with a high-quality spectroscope would know that intelligent life exists here. Earth''s EM emissions would also tell ET that intelligence exists on this planet. Our planet began emitting visible light into the cosmos beginning in the early 1930s, when our largest cities began to install nighttime lighting.
ET would shield their telescopes from our sun''s glare with a coronagraph and would detect our cities'' emissions of incandescent light from the dark side of Earth. They would suspect the light was not natural because of the unique frequency emitted by incandescent lights. This would pique their interest and perhaps they would dedicate a telescope to the observation of our planet. Soon ET would detect electromagnetic frequencies emitted by radio, television, and radar from Earth in the 1930s and 1940s. ET would note that our planet had revolved around its sun only a few more times before something else interesting occurred. Nuclear fission explosions had begun on this now very interesting planet. This was 1945, and ET would continue to monitor nuclear explosions on this planet for another twenty revolutions around its sun. There would no longer be any doubt that an advanced civilization was developing on the planet Earth.
The only doubt remaining with ET was whether this new civilization would destroy itself or use nuclear power peacefully. The final step in the search for extraterrestrial life is interstellar travel. Even if ET knew we were here, could they reach the Earth? Toward the end of the twentieth century no one thought interstellar travel was feasible. Most scientists didn''t think it would ever be possible. The closest star to Earth, Proxima Centauri, was four light-years away. It would take our fastest spacecraft over 17,000 years to reach a planet in that star''s system. Such a trip would be meaningless. Consequently, most scientists believed that if we could not even contemplate interstellar travel, then no one else could either.
This view rapidly changed in the twenty-first century. og of planets. The second step is to look for planets that have signs of intelligent life. ET would begin by looking for the building blocks for life, assuming they were carbon-based like us. They would examine a planet''s reflected light to look for oxygen, water, carbon dioxide, methane, and other chemicals to determine if a carbon-based life could exist. (Humanity is just now taking its first baby steps in this area.) Like us, an extraterrestrial race would be examining planets in their catalog that not only have the right chemical ingredients but that also have signs of intelligent life. These planets would be the ones that ET would carefully observe with their advanced telescopes and spectrometers.
ET would look for changes to a planet''s atmosphere that might be caused by an advanced intelligent life. They would look for emissions in the various parts of the electromagnetic spectrum that indicate a civilization was expending large amounts of energy. Let''s use our planet as an example of how our atmosphere indicates that an intelligent civilization exists here. What would ET see if they turned their powerful telescopes toward Earth? About 200 years ago ET would have noticed large amounts of hydrocarbons were being emitted into the Earth''s atmosphere. This was driven by the coal burning of the industrial revolution in the nineteenth century. Some ET scientists might begin studying Earth as one of the more likely planets to harbor advanced intelligent life. ET would see the complexity of the emitted hydrocarbons increase in the twentieth century as we burned oils, plastics, and garbage that we released into the atmosphere. ET scientists would know that the more complex the hydrocarbons are, the more likely that they were produced by an intelligence on Earth rather than simple vegetative fires.
By the 1950s and 1960s our atmosphere contained isotopes of uranium, plutonium, and other radioactive compounds. These were created from our detonation of nuclear bombs on land and in the atmosphere. The ET scientists studying Earth might have been excited when the first detected those chemicals. There is nothing natural about those isotopes. Any civilization that analyzed our atmosphere with a high-quality spectroscope would know that intelligent life exists here. Earth''s EM emissions would also tell ET that intelligence exists on this planet. Our planet began emitting visible light into the cosmos beginning in the early 1930s, when our largest cities began to install nighttime lighting. ET would shield their telescopes from our sun''s glare with a coronagraph and would detect our cities'' emissions of incandescent light from the dark side of Earth.
They would suspect the light was not natural because of the unique frequency emitted by incandescent lights. This would pique their interest and perhaps they would dedicate a telescope to the observation of our planet. Soon ET would detect electromagnetic frequencies emitted by radio, television, and radar from Earth in the 1930s and 1940s. ET would note that our planet had revolved around its sun only a few more times before something else interesting occurred. Nuclear fission explosions had begun on this now very interesting planet. This was 1945, and ET would continue to monitor nuclear explosions on this planet for another twenty revolutions around its sun. There would no longer be any doubt that an advanced civilization was developing on the planet Earth. The only doubt remaining with ET was whether this new civilization would destroy itself or use nuclear power peacefully.
The final step in the search for extraterrestrial life is interstellar travel. Even if ET knew we were here, could they reach the Earth? Toward the end of the twentieth century no one thought interstellar travel was feasible. Most scientists didn''t think it would ever be possible. The closest star to Earth, Proxima Centauri, was four light-years away. It would take our fastest spacecraft over 17,000 years to reach a planet in that star''s system. Such a trip would be meaningless. Consequently, most scientists believed that if we could not even contemplate interstellar travel, then no one else could either. This view rapidly changed in the twenty-first century.
ur atmosphere indicates that an intelligent civilization exists here. What would ET see if they turned their powerful telescopes toward Earth? About 200 years ago ET would have noticed large amounts of hydrocarbons were being emitted into the Earth''s atmosphere. This was driven by the coal burning of the industrial revolution in the nineteenth century. Some ET scientists might begin studying Eart.