The 1936 Berlin Olympic games broadcast was the first radio signal strong enough to leave Earth. Traveling at the speed of light, this program is the leading edge of a bubble of broadcasts racing outward through space from Earth. But that signal has managed to travel only 80 light-years from the planet.
Solomonides said advanced life elsewhere in the universe is unlikely to have arisen much before life on Earth. That's because bodies like those of humans require a mixture of the heavy elements produced over the lifetimes of stars, and it takes several generations of star formation to produce the necessary quantities. As a result, civilizations capable of communicating throughout the galaxy wouldn't have started out much earlier than happened on Earth.
Based on the assumption that life and technology on Earth should have evolved at a relatively average pace, not significantly faster or slower than for other civilizations, Solomonides calculated the communication bubbles that life would produce throughout the galaxy. He found that, as of today, only about a tenth of 1 percent of the Milky Way would be blanketed by signals. With those numbers, it's likely that Earth won't hear from other life-forms for another 1,500 years.
"There could be life everywhere in the galaxy, and we still wouldn't know it," Solomonides said.
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In fact, "if we had been contacted by another civilization, we would actually be special."
That doesn't mean humanity should stop searching for signals or cut off broadcasts (though the rise of cable to carry television signals may mean that Earth is getting quieter anyway), Solomonides said. Instead, humans should keep broadcasting and listening in order to avoid missing the historic chance of contact, he said. People simply shouldn't expect results any time in the near future.
Even if, in the next 2,000 years, humans still haven't heard from other life-forms, that won't mean life doesn't exist throughout the galaxy, Solomonides said. He pointed out that communication requires the evolution of advanced life; molecular life won't be sending out signals, and so isn't considered in the search for extraterrestrial intelligence. Other scientists have suggested alien life may have evolved but then died out.
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Another possibility is that advanced civilizations are unwilling to respond, because they'd rather avoid contact. After all, Solomnides said, Earth's first broadcast was Adolf Hitler's Olympics remarks.
"That's not really a great introduction," he said, wryly.
Originally published on Space.com.
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