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Most of the universe has no way of knowing that we exist

human radio galaxy bubble
An artist's conception of our Milky Way galaxy with the tiny red dot representing how far our radio broadcasts could have travelled. Nick Risinger/Wikimedia Commons

Most of the aliens probably have no way of knowing that humans are on Earth.

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This is a comforting thought if extraterrestrials terrify you and a disappointing one if you can't wait to find ET. It also suggests just how little we know of the vast universe — and how little it knows of us.

Seth Shostak, director of the Search for Extraterrestrial Intelligence Institute (SETI), told Tech Insider that he (and many other researchers) defines intelligent life as a being who can build a radio.

Humans only accomplished that around 1900. That means our radio signals could only have traveled up to 116 light-years away — creating a "bubble" around the Earth announcing we're here.

"If there are any aliens inside the bubble, they might know about Homo sapiens," Shostak said. "If they're outside the bubble, all they know is that there's oxygen in our atmosphere. So they know that there's photosynthesis here. That might be of interest, but I don't know that they would send a rocket to Earth just 'cause there's grass here."

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The opening scene of the 1997 movie Contact has a fantastic representation of this idea:

When we first started transmitting radio waves, though, they weren't that strong. And we certainly weren't trying to beam them to outer space. Shostak said he only counts since the development of the transistor radio during the 1940s and 50s, which makes that bubble even smaller.

Plus, as NASA Instructor and Flight Controller Robert Frost explains on Quora, radio signals get weaker the farther they go, meaning aliens probably couldn't hear the first broadcasts at the fringes of the bubble. They would probably have to be much closer in order to detect us.

For another fun visualization of this concept, visit lightyear.fm to see what songs different parts of the galaxy could be hearing now.

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All our radio signals — from last Sunday's Game of Thrones to Justin Bieber singing "Sorry" — are broadcasting our presence to the universe. But they don't go as far as you might think.

Space Radio
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