The SETI League, Inc., a membership-supported, non-profit {501(c)(3)}, educational and scientific organization Searching for Extra-Terrestrial Intelligence

Ask Dr. SETI ®

Chapter 1: Astrophysics

Oort Cloud as a Faraday Cage

Dear Dr. SETI:
Why has no radio astronomer ever managed to pick up any artificial extra terrestrial radio signal? Our solar system is equipped on its side - at the utmost border - with a huge sphere which nothing else but a gigantic spherical field, commonly called Oort Cloud, within which hundreds of thousands comets, asteroids, meteorites, and stellar fragments of all sorts and shapes orbit.

This Oort Cloud is actually a natural barrier and but for it life wouldn't have been on Earth. Why? Simply because this cloud takes on the role of - what we call in French Cage de Faraday. (Faraday cage), that protects us from noxious Supernovas' rays. However, this natural Cage de Faraday could very easily stop extra-terrestrial radio signals from entering our solar system, and prevent our own signals from going beyond it.

I hope that this very rational explanation will be the beginning of an answer from you.

Sincerely yours,
Belkhir (via email)

The Doctor Responds:
This is an intriguing theory, Belkhir, but it overlooks some important observational counter-evidence. Consider that a true Faraday cage would block all electromagnetic radiation. Starlight is electromagnetic radiation. So is the cosmic microwave background. So are all natural astrophysical emissions from the stars and interstellar space. So are the microwave beacons aboard the Pioneer and Voyager spacecraft, which are by now beyond the Oort cloud and still detectable on Earth. And, a Faraday cage cannot distinguish between natural and artificial electromagnetic radiation. So, if your hypothesis were correct, we could not see starlight, or receive our most distant space probes, and our radio telescopes would not detect galactic noise, cosmic background radiation, hydrogen emissions, or other natural astrophysical radiation.

Yet, optical astronomy and radio astronomy do indeed work from Earth! Thus, we must conclude that the Oort cloud is not an effective Faraday cage. Since it is not blocking starlight or natural emissions, it stands to reason that neither is it blocking ETI transmissions, if in fact they exist -- and we must therefore consider alternative explanations for the lack of confirmed SETI signals to date.

Click to email the Webmaster
| Home | General | Memb Svcs | Publications | Press | Technical | Internet | Index |
entire website copyright © The SETI League, Inc.; Maintained by Microcomm
this page last updated 8 August 2009
Click for top of page
Top of Page