Are Alien Civilizations Technologically Advanced?

As we discover numerous habitable planets around other stars in the Milky Way galaxy, including the nearest star, Proxima Centauri, one cannot help but wonder why have we not detected evidence for an advanced alien civilization as of yet.

The surfaces of other planets might show either relics of advanced civilizations that destroyed themselves by self-inflicted catastrophes or living civilizations that are technologically primitive. Such circumstances can only be revealed by visiting those planets and not by remote observations.

Abraham Loeb
(Submitted on 18 Jan 2018)

Comments: 3 pages, published in Scientific American
Subjects: Popular Physics (physics.pop-ph); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:1801.06180 [physics.pop-ph] (or arXiv:1801.06180v1 [physics.pop-ph] for this version)
Submission history
From: Avi Loeb
[v1] Thu, 18 Jan 2018 12:24:19 GMT (111kb)
https://arxiv.org/abs/1801.06180
Astrobiology, SETI