Fermi paradox is paradox made mainly by Enrico Fermi and what it asks is basicly: “Why are there no signs of other civilizations?”
That´s a question!
It is based on few things:
Our home star The Sun is quiet normal star which is not rare in our galaxy so lot of them should be here.
Next thing is that you must assume that the Earth is normal planet and lot of those stars will have similar rocks around itself in the right distance.
And civilization would develop on this planet and it would send some signals or travel through Galaxy.
There are really tons of stars like Sun and probably even similar planets but still we are not apparently hearing anything from space… lets see some solutions to this problem.
1) Civilizations are not common because either there is life on other planets but it is not developed or it is much rarer to survive through what is so called: Great Filter it is some event which would erase us, like meteorite or gamma burst.
2) There have to be much more specific things on planet. Without great source of energy it would probably not be able to send signals or even colonize other planets. Moon is very important for Earth since it stabilize its axis (which is important for normal seasons).
3) It is normal that life destroys itself when it has got enough good technology, nuclear war, lot of trash. OR it is normal that life destroys other lifes which means there would be some first great civilization which would keep Universe clean.
4) Another thing is that we are not sending signals really long time or listening really long time plus we are listening only to part of sky and only to some kind of signals. Maybe post-modern civilizations dont need to use our kind of communication but for example neutrino rays or something very different. AND what kind of radio signals we are using right now is not really long lasting for civilizations that would be thousands light years away.
5) Another thing is that maybe all civilizations are listening but none are sending which would cause in SETI-paradox. Or other civilizations do not want to interact because it is too dangerous.
So those are some ideas that I found, feel free to share yours!