The human radio-broadcast bubble

“Space… is big. Really big. You just won’t believe how vastly, hugely, mindbogglingly big it is” (quote from The Hitchhiker’s Guide to the Galaxy)

There is a “bubble” of radio waves radiating outwards from the Earth at the speed of light over the past 139 years since they were first intentionally produced by humans (by Marconi) in the 1880’s. See Wikipedia’s History of radio

These radio waves radiating away from the Earth are illustrated in the image below. Created by science blogger Adam Grossman, the illustration shows the radio waves as a tiny blue dot in the bottom right corner zoomed in section. You can see just tiny the blue dot is compared to the galaxy.

The human radio-broadcast bubble compared to Milky Way galaxy.

That tiny blue dot has a radius of 139 light-years with the Earth at its center and expands another light-year each year.

Tiny blue dot is actually an enormous sphere with a radius of 139 light-years and the Earth at its center!

The blue dot is very small compared to the Milky Way and even smaller when compared to the universe.

The Milky Way stretches between 100,000 and 180,000 light-years across. This vast scale means that a signal broadcast from one side of the galaxy would take at least 100,000 years or more to reach the other side. In this context, the human radio broadcast bubble, despite its impressive 200 light-year span, is just a tiny fraction of our own galaxy’s size.

The distance from Earth to the edge of the observable universe is 46 billion light-years Wikipedia: Universe and the observable universe contains about 200 billion galaxies according to latest Hubble observations Nasa: Hubble.

Feeling small yet? Even though that blue dot is arguably the biggest thing humans have created, its 139 light-year radius about 331 million times smaller than the 46 billion light-year distance to the edge of the observable universe.

It’s important to note that the signal from our radio and TV broadcasts becomes so attenuated by the 100-light-year boundary as to be undetectable except by some kind of highly advanced alien technology. This means that while the bubble is a significant marker of human presence, it’s unlikely that these signals are still coherent or detectable at great distance. But, perhaps somewhere out there, aliens within 139 light-years of the Earth who have magic technology and are entertaining themselves by listening to human radio and tv broadcasts, air traffic controllers, police and EMT calls, and cell phone conversations. Nice thought .. scary thought?

Also this image has been used often without attribution to its creators. This blog post gives more history of the creation of this image in 2011 by Adam Grossman and Nick Risinger. The original blog post by Adam Grossman can be found archived on and it was featured on YCombinator’s Hacker News here.




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