This question already has an answer here:

So, I'm not into writing or creating any new worlds, but this question (or a set of questions) was bothering me for a while and I thought it's a good place to ask.

  1. If there exists an alien civilization in a nearby star system (i. e. Alpha Centauri) and it has a similar technology level to ours (producing the same amount of radio noise), would we be able to detect it?
  2. Are we at this point 100% sure there are no such civilizations in nearby star systems?
  3. If there's a civilization nearby with similar technology to ours (or more advanced but still scientifically plausible) do they already know that we're here?

This question asks for hard science. All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See the tag description for more information.

marked as duplicate by Morris The Cat, Ash, Measure of despare., user535733, Community Aug 5 at 15:18

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ Also worth reading: space.stackexchange.com/questions/17765/… $\endgroup$ – Morris The Cat Aug 5 at 14:22
  • $\begingroup$ Welcome to worldbuilding. We have a 1 question per post policy, while you have 3 questions here, and I am not fully sure they are about worldbuilding. Moreover, you are using the hard science tag, are you sure about it? Please take the tour and visit the help center, then narrow down your question and make it fit our scope. $\endgroup$ – L.Dutch Aug 5 at 14:22
  • $\begingroup$ Hi, thanks for the linked questions. That's basically what I've been looking for, so this one can be closed. $\endgroup$ – Przemysław Czechowski Aug 5 at 14:46
  • $\begingroup$ You should have got a notification about the duplicate. If you accept the suggestion, the question will be closed as duplicate automatically. $\endgroup$ – L.Dutch Aug 5 at 15:04