Key takeaways:
- Our Milky Way is vast, spanning up to 180,000 light-years across, but it’s only one of an estimated 100 billion galaxies in the observable universe, highlighting our small place in the cosmos.
- Humanity’s radio signals, representing our presence, have only spread about 200 light-years, forming a tiny “blue bubble” in the galaxy, meaning most potential alien civilizations wouldn’t even know we exist.
- The discovery of electromagnetic waves began over 200 years ago, with major advancements by scientists like Ørsted, Faraday, Maxwell, and Marconi eventually leading to radio transmission.
- Even if we assume advanced alien civilizations exist, they would likely be far beyond the reach of our earliest broadcasts, making detection of human signals by extraterrestrials unlikely.
- The SETI Institute is listening for alien signals and broadcasting messages, yet the galaxy’s scale means we may need to keep trying for tens of thousands of years to have a realistic chance of making contact.
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Our radio signals have only traveled 200 light-years—just a tiny fraction of the galaxy.
Our Milky Way galaxy may seem vast, housing an estimated 100 to 400 billion stars. However, it’s only one of about 100 billion galaxies within the observable universe, illustrating how truly small our presence is on a cosmic scale. Adam Grossman from The Dark Sky Company created a map showing that, despite over a century of broadcasting signals, human-made radio waves have barely scratched the surface of the Milky Way. The map highlights a small blue bubble, 200 light-years across, around Earth—marking the reach of our radio transmissions and emphasizing how isolated humanity remains.
The Reach and Limits of Human Radio Waves
Humans began broadcasting radio signals into space around 100 years ago, after developments in electromagnetism made it possible. Pioneers in this field included Hans Christian Ørsted, who discovered that electric currents create magnetic fields, and James Clerk Maxwell, whose theories on electromagnetism laid the groundwork for radio waves. Heinrich Hertz confirmed Maxwell’s theories in the late 19th century, and later, Guglielmo Marconi’s advancements enabled long-range radio communication. Since then, radio waves from Earth have expanded to cover a distance of 200 light-years. Yet, in the vast Milky Way, which spans roughly 100,000 to 180,000 light-years across, this coverage is minuscule.
This limited reach means any extraterrestrial civilization capable of detecting our signals would need to be within this 200-light-year bubble. Statistically, this makes the chance of any alien detection incredibly slim. If we were to throw a dart on a map of the Milky Way, symbolizing an alien civilization’s location, the odds of it landing within our signal bubble are close to zero, even with multiple attempts.
A Distant Prospect for Contact
The Search for Extraterrestrial Intelligence (SETI) Institute actively searches for signals from other civilizations, using advanced radio telescopes and occasionally sending messages. But the odds of successfully making contact remain slim, given the sheer scale of the galaxy. At the current rate, SETI would likely need to listen and transmit for tens of thousands of years for even a faint chance of a reply. And yet, even this vast timescale might be insufficient to make meaningful contact due to the cosmic distances involved.
This daunting reality reinforces Carl Sagan’s reflections on humanity’s solitude. As Sagan stated in his “Pale Blue Dot” speech, our world is “a lonely speck in the great enveloping cosmic dark,” where there is little hope that any assistance will come from the stars to “save us from ourselves.” While we may continue to explore and search, this perspective urges us to prioritize our responsibility to preserve our own world.
Source: Planetary Society
