Adam Grossman / Nick Risinger

Carl Sagan's famous line from his 1990 speech about the Pale Blue Dot image—"Our planet is a lonely speck in the great enveloping cosmic dark"—is an understatement. We might consider our Milky Way, with its estimated 100 to 400 billion stars, a significant fixture in the cosmos. But there are some 100 billion galaxies just like it in the observable universe. It's a daunting reality to consider when we're thinking about the possibility of making contact with any intelligence that might be out there.

This map designed by Adam Grossman of The Dark Sky Company puts into perspective the enormity of these scales. The Milky Way stretches between 100,000 and 180,000 light-years across, depending on where you measure, which means a signal broadcast from one side of the galaxy would take 100,000 years or more to reach the other side. Now consider that our species started broadcasting radio signals into space only about a century ago. That's represented by a small blue bubble measuring 200 light-years in diameter surrounding the position of the Earth. For any alien civilizations to have heard us, they must be within the bubble.

The very first experimentation with electromagnetic radiation was conducted some 200 years ago, when Danish physicist and chemist Hans Christian Ørsted discovered that electric currents create magnetic fields. This research was expanded by scientists including Michael Faraday, and it eventually resulted in James Clerk Maxwell's theory of electromagnetism outlined in 1865 and demonstrated by German physicist Heinrich Hertz's experiments more than two decades later. Even then, it wasn't until Italian inventor and electrical engineer Guglielmo Marconi developed long-range radio transmission technologies around the turn of the 20th century that our species really started broadcasting its existence out into the void.

Even if you threw 100 darts, it's a near certainty that none would land in the little blue bubble of our radio waves

If we are optimistic, and we assume an advanced extraterrestrial species has the technological capabilities to detect humanity's very first radio waves (and distinguish them from the general background noise of the universe), we can estimate our farthest signals are a little more that 100 light-years away. If you threw a dart at the map of the Milky Way, and wherever that dart landed is where an advanced alien species resides, there would be a cosmically small probability that they live close enough to be aware of our existence. Even if you threw 100 darts, it's a near certainty that none would land in the little blue bubble of our radio waves.

The search for extraterrestrial intelligence (SETI) institute is constantly listening with our most capable radio telescopes, and they are broadcasting messages from us as well. But given the sheer size of the galaxy, SETI will likely have to listen and transmit for tens of thousands of years at least to have a chance of making contact with another intelligent species—and even that might not be long enough. Perhaps, in the meantime, we should contemplate Carl Sagan's next line in his Pale Blue Dot speech:

"In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves."

Source: Planetary Society

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