• The Fermi Paradox contrasts the overwhelming lack of evidence of alien life with the high theoretical probability of observable alien life.
  • Groups such as SETI observe incoming radiation from space to search for signs of life outside Earth.
  • The cosmic microwave background radiation we observe is believed to have resulted from the Big Bang.

Could the cosmic microwave background be the result of an abundance of alien life communicating, thus solving the Fermi Paradox?
In other words, what evidence justifies or disproves the above statement?

If so, how would you explain the lack of leftover radiation from the Big Bang?

  • $\begingroup$ If you think this is too broad or too opinion based please help me by editing it. I will accept all edits that help keep this answerable. $\endgroup$
    – Zxyrra
    Nov 21, 2016 at 1:33
  • 1
    $\begingroup$ That doesn't explain why we don't see more obvious signs of them. All it takes is one species in which even a tiny minority of individuals seek colonization for the species to spread galaxy wide in an eyeblink. $\endgroup$ Nov 21, 2016 at 10:24

2 Answers 2


It's difficult to answer such questions, because there are so many unknowns. I would point to the Drake Equation as an excellent example of the extremes one has to go to quantify such a discussion. Many of the probabilities that make up the Drake Equation are truly unknowns.

However, the background radiation has a very very regular spectra. It's a very easy to recognize spectra. Because of that, it's trivial to analyze any signals from other sources and discern the difference between them and a background radiation. We regularly do analyses in multiple spectral regions, making it trivial to isolate any non-background signals. I would call it implausible that, out of all of the factors which go into the Drake Equation, background radiation would prove to be the straw that broke the camel's back.

As for your last question, abut explaining the radiation, that's a completely separate topic unrelated to Fermi or Drake, and a good topic for speculation in the physics community. You may be able to succeed with a Physics.SE question on the topic, but do be sure to do a search first. It's a popular topic, someone may have asked already!

  • $\begingroup$ Thanks for the thorough answer! Could you disprove the "regular spectra" part by saying the radiation here may be different from the radiation somewhere else, and our neighborhood just has x channels? Or is there a way we can observe that it's the same everywhere? $\endgroup$
    – Zxyrra
    Nov 21, 2016 at 2:01
  • $\begingroup$ By regular I mean the spectra is very well known (I'm pretty certain its blackbody, but I don't know for sure). This means that if you see a certain amount of background radiation in the IR band, you can calculate the expected amount of radiation that a UV sensor would detect. (although note: background radiation in those bands is REALLY low. Most background radiation is in the longer RF bands). As for detecting it everywhere, we've never flown anything to another star to check, but when we look in all directions, we see a surprisingly consistent temperature in all directions. $\endgroup$
    – Cort Ammon
    Nov 21, 2016 at 3:34
  • $\begingroup$ If radiation behaved differently in different parts of the visible universe, we'd almost certainly notice things that were strange and inexplicable. We can currently explain a great deal with our working assumption that the laws of physics are the same everywhere. That is an assumption, but it's held up well for all the time we've been doing spectroscopy. $\endgroup$ Nov 21, 2016 at 16:00
  • $\begingroup$ @JohnDallman Not necessarily radiation behaving differently, just different types of radiation (radio here, x-ray here, visible light here, etc) from different communications, which would not interfere with the laws of physics $\endgroup$
    – Zxyrra
    Nov 21, 2016 at 16:45
  • $\begingroup$ @Zxyrra We have no definitive way of scientifically proving that the radiation we see from the background radiation is not different a light year away. However, we have absolutely no reason to believe this is the case. In these situations, science shys away from such hypotheses as you put forth. That's not to say its definitively wrong, its just a topic that science cannot touch. It would also be an awefully mighty coincidence if we saw blackbody radiation (a very specific mix of radio, xray, visible, IR, etc.) here, and others saw something other than blackbody. $\endgroup$
    – Cort Ammon
    Nov 21, 2016 at 18:08

The simplistic answer would be, and this is the type of answer that easily falls over in contact with any real depth of knowledge, that was no Big Bang, and therefore, no cosmic microwave background (CMB) radiation produced as a relic.

if we were living in a Big Bang free universe this could extend infinitely in all directions of space and time. Electromagnetic radiation from all sources, not just alien civilizations, but stars, galaxies and astrophysical whatever, could have eventually mushed together into what resembles the CMB.

For good measure, the old hypothesis of "tired photons" could be tossed into the mix. In this case, assume the photons wind over time as they travel cosmological distances to a base energy level of microwave radiation photons.

An answer of this sort could pass the this is plausible enough for a certain type of science fiction story. It's doubtful if it could pass the reality test of science as she is practised in the real world.


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