split my answer for this question up into two posts.
a) What is
the basis of the Fermi Paradox and explain the close connection it has to the
13.6 billion years old 1. 100 000 light years in diameter 2. Hundreds
of billions of stars.
The Milky Way is a pretty big place.
Given that the Earth is relatively young (only 4.54 billion years old 3) and
we have intelligent life, shouldn’t the night sky should be teeming with other lifeforms
from older, more advanced civilizations?
Where are they all?
This contradiction between the idea that there should be many intelligent
extraterrestrials and the lack of evidence for them is what forms the basis of the
Fermi Paradox 4.
It suggests that the reason why we haven’t come into contact with
extraterrestrials is either because 4, 5 & 6:
There are actually none (or very few) exist in our galaxy. In
other words, the answer to the Drake equation is 0 (or an extremely small
There are factors that affect the possibility of communicating with
extraterrestrials which we have not taken into account in the Drake equation.
For those who are not yet aware of the Drake equation, it the
theoretical formula in Image 1 that estimates the number of communicative extraterrestrial
civilisations there are in the Milky Way galaxy 6. To understand what each term
in the Drake equation represents in more detail, and what their numerical
values might be, I strongly advise that everyone reads Ziyi’s answer to another
question that someone else posted before continuing. (https://moodle.telt.unsw.edu.au/mod/forum/discuss.php?d=643404).
Now, the Fermi Paradox implies that instead of having
to hypothesise inputs for the Drake equation, one can just look at the empirical
evidence that supports the existence of intelligent extraterrestrials 8. If
there were any intelligent technological civilizations in the Milky Way, they should’ve
been capable of colonize a large majority of the entire Milky Way by now. According
to the mathematicians Duncan Forgan and Arwen Nicholson, even at the modest
velocity of 10% the speed of light, the whole galaxy should be accessible
within 10 million years 9.
However, we are yet to find any kind proof that
suggests communicative aliens exist. Thus, why the Fermi Paradox implies that either
none exist (and the Drake equation’s answer is 0) or there is some unknown
factor that we haven’t taken into account (missing variable from Drake