SHARKS! IN! SPAAAAAAAACCCCE!

XKCD is a bit disturbing today. 

It is disturbing on a multiple levels, because it makes you ask some questions that you may not want to know the answer to. 

First and foremost, you might ask, what IS the Fermi paradox?  Good question! That’s why I love you so, dear reader!  You ask the best questions! 

The Fermi paradox (or Fermi's paradox) is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilization and humanity's lack of contact with, or evidence for, such civilizations.^[1] The basic points of the argument, made by physicists Enrico Fermi andMichael H. Hart, are:·         The Sun is a young star. There are billions of stars in thegalaxy that are billions of years older;
·         some of these stars probably have Earth-like planets^[2]which, if the Earth is typical, may develop intelligent life;
·         presumably, some of these civilizations will develop interstellar travel, a technology Earth is investigating even now, such as that used in the proposed 100 Year Starship;
·         at any practical pace of interstellar travel, the galaxy can be completely colonized in a few tens of millions of years.

Got it?  The Fermi paradox is simply an expression of confusion with the fact that most scientists believe that it is absolutely inevitable that Earth is not the only life-bearing planet in the universe, and that given the sheer number of planets, that Earth is almost certainly not the only one to support intelligent life, and that given that our sun is not that old in the grand scheme of things, it is almost just as certain that there are civilizations out there that are much more advanced than ours. 

So why haven’t we made contact with them yet, or them with us?  If nothing else, why have we been unable to find any evidence of them at all? 

There are many different, competing and complimentary hypotheses about why, but the XKCD comic today presents what is possibly the most disturbing:

All other advanced civilizations, who would otherwise incidentally emit evidence of their existence, are deliberately concealing those emissions, and therefore the evidence of their existence, for reasons of survival, in the same way that a flounder is colored like the ocean bottom to avoid being eaten by sharks. 

So what, one might ask, are they hiding from?