Those aliens better be nearby.

Key takeaways

  • The Milky Way contains up to 400 billion stars, and there are about 100 billion galaxies in the visible universe.
  • Our radio signals have traveled only about 100 light-years, forming a tiny bubble in the vast galaxy.
  • Humanity began broadcasting radio waves into space just over a century ago, starting with early radio technology.
  • The chance of alien civilizations being within our signal bubble is extremely small.
  • The SETI Institute listens and broadcasts continuously, but connecting with alien life may require thousands of years of effort.

Carl Sagan’s famous comment from his 1990 talk on the Pale Blue Dot image—”Our planet is a lonely speck in the great enveloping cosmic dark”—is an understatement. We may think of our Milky Way, with its estimated 100 to 400 billion stars, as an important feature in the universe. However, there are around 100 billion such galaxies in the visible universe. It’s a difficult truth to ponder when considering the idea of making contact with any intelligence that may exist.

This map, created by Adam Grossman of The Dark Sky Company, illustrates the vastness of these sizes. The Milky Way is 100,000 to 180,000 light-years wide, depending on where you measure, therefore a signal sent from one side of the galaxy would take 100,000 years or more to reach the other. Consider that our species began sending radio messages into space only about a century ago. That is illustrated as a tiny blue bubble 200 light-years in diameter that surrounds the Earth. For alien civilizations to hear us, they must be inside the bubble.

Around 200 years ago, Danish physicist and chemist Hans Christian Ørsted discovered that electric currents generate magnetic fields. This study was advanced by scientists like as Michael Faraday, and it eventually led to James Clerk Maxwell‘s theory of electromagnetic, which was published in 1865 and confirmed by German physicist Heinrich Hertz‘s tests more than two decades later. Even yet, it wasn’t until Italian scientist and electrical engineer Guglielmo Marconi invented long-distance radio transmission technology around the beginning of the twentieth century that our species truly began broadcasting its existence into the universe.

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 assume that an advanced extraterrestrial species has the technological capabilities to detect humanity’s first radio waves (and distinguish them from the universe’s general background noise), we can estimate that our farthest signals are slightly more than 100 light-years away. If you tossed a dart at the Milky Way map and it landed somewhere where an advanced extraterrestrial race lives, there’s a cosmically minuscule chance that they’re aware of our existence. Even if you shot 100 darts, it’s almost probable that none would land in the little blue bubble of our radio waves.The SETI Institute is continually listening with our most powerful radio telescopes, and they are also transmitting communications from us. However, given the vast breadth of the galaxy, SETI will most likely need to listen and broadcast for tens of thousands of years to have a chance of establishing contact with another sentient species—and even that may not be enough. Perhaps, in the interim, we could consider Carl Sagan’s following remark 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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