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)

One measure of  space is the size of a “bubble” created by radio waves radiating outwards from the Earth over the past 139 years since they were first intentionally produced by humans in the 1880’s. Wikipedia: History of radio

The image below, created by science blogger Adam Grossman, illustrates this “bubble” of radio waves as a tiny blue dot on an artist visualization of the Milky Way galaxy.

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

The visualization has an inset in the bottom-right with a close-up of the Earth’s region of the Milky Way galaxy to make the blue dot more readily visible. This shows that the blue dot is very small compared to the Milky Way.

However, that tiny blue dot is actually an enormous sphere with a radius of 139 light-years Wikipedia: light-year and the Earth at its center and the sphere’s grows another light-year every year. For the non-science people, those radio waves are travelling at the speed of light!

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 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.

Also as a final note, it is not likely that the radio-waves are actually detectable, at least not by our current technology, after travelling 139 light-years. But, perhaps somewhere out there, aliens with some magic technology 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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