What is Paradoxical About ‘Fermi’s Paradox’?

Review of Milan Ćirković: The Great Silence, Oxford University Press, 2018


In this review of Milan Ćirković’s The Great Silence: Science and Philosophy of Fermi’s Paradox, we attempt to reconstruct the logic of Fermi’s paradox as understood by the author, and we critically examine the reasoning that leads to the paradox. We show that there is no plausible solution to Fermi’s paradox that can satisfy all of Ćirković’s proposed desiderata, which in turn suggests that the author’s standards for hypothesis adjudication need to be revised.

This is a preview of subscription content, access via your institution.


  1. Ćirković M (2018) The great silence: the science and philosophy of Fermi’s paradox. Oxford University Press, Oxford

    Google Scholar 

  2. Powell R (2020a) Contingency and convergence: toward a cosmic biology of body and mind. MIT Press, Cambridge

    Book  Google Scholar 

  3. Powell R (2020b) Copernicanism and its biological discontents. Q Rev Biol 95(1):59–64

    Article  Google Scholar 

Download references


Funding was provided by Templeton World Charity Foundation (Grant No. TWCF0469).

Author information



Corresponding author

Correspondence to Russell Powell.



Hypothesis Premise rejected Desideratum rejected
Fermi’s flying saucers (ETIs are already here on Earth, engaging in covert activities that make them difficult to detect; p. 109) 1a Realism
Ancient flying saucers (ETIs visited Earth in the distant past; p. 112) 1a Realism
Special creation (the origin of humans had a supernatural cause, so there is no reason to expect the emergence of other intelligent civilizations; p. 113) 4b Realism
Zoo hypothesis (Earth is located in a “zoo,” or a region of space that is set aside by advanced extraterrestrials to allow early civilizations to evolve without interference; p. 116) 2a Realism
Interdict hypothesis (planets that are likely to evolve intelligent life forms, such as Earth, have been placed under interdicts that proscribe interference by other, more advanced intelligent civilizations; p. 116) 2a Realism
Leaky interdict (although the interdict shielding intelligent life worlds from outside interference is not inviolable, violations will be extremely rare and sporadic, thereby evading our detection; p. 117) 2a Realism
Planetarium hypothesis (our observations of the universe are simulated, or projected like stars in a planetarium, by an ETI that deliberately evades detection; p. 120) 2a Realism
Peer hypothesis (a supercivilization has created our entire cosmological domain as an experiment, which is actually inhabited not just by us but by “peers,” who we cannot detect only because they are not sufficiently more advanced than we are; p. 121) 2a Realism
Simulation hypothesis (we are living in a simulation in which there are no ETIs; p. 122) 2a Realism
The paranoid style in galactic politics (we have unknowingly detected ETIs in the form of highly sophisticated encrypted signals that are undistinguishable from background radiation; p. 124) 1a Realism
Directed panspermia (the Earth’s entire biosphere, including ourselves, is extraterrestrial in origin; p. 127) 1a Realism
Bit-string invaders (ETIs exist or travel as compact bit strings that are present on Earth without our having detected them; p. 132) 1a Realism
New cosmogony (highly advanced ETIs are indistinguishable from the natural processes that we perceive as physical laws; p. 134) 1a Realism
Early great filter (at least one of the early steps required for the evolution of ETI is highly unlikely to occur; p. 153) 1b Copernicanism
Horizon to the rescue (the probability of any of the steps required for the evolution of ETI is so small as to make detection within our event horizon nearly impossible; p. 155) 1b Copernicanism
Gaian window (the planetary conditions necessary for life to emerge are extremely unlikely or insufficiently stable to prevent the regular emergence of ETI; p. 156) 1b Copernicanism
Permanence (intelligence is an inefficient trait from an evolutionary perspective, and hence it will tend to be replaced by other traits, such that at any given time the existence of detectable ETI is unlikely; p. 159) 1b Copernicanism
Thoughtfood exhaustion (intelligence is useful only so long as there is new information to be processed—once new content runs out, intelligence will disappear before we will have detected it; p. 164) 1b Copernicanism
The gigayear of living dangerously (due to some random catastrophe, the universe is nearly uninhabitable; p. 172) 3b Gradualism
Astrobiological phase transition (galactic regulation mechanisms make the emergence of early ETI much less likely than later ETI; p. 174) 3b Gradualism
Stop worrying and love the bomb (all intelligent civilizations self-destruct before we are able to detect them; p. 179) 3b Gradualism
Self-destruction, advanced version (intelligent civilizations self-destruct shortly after the discovery of post-nuclear technologies; and hence we are unable to detect them; p. 180) 3b Gradualism
Hermit hypothesis (intelligent civilizations choose to never expand beyond their home planetary system or communicate across interstellar distances, and hence we cannot detect them; p. 27). 3b Non-exclusivity
Introvert Big Brother (almost all advanced civilizations become totalitarian, drastically reducing the possibility of their contact with the rest of the universe; p. 182) 3b Gradualism
Resource exhaustion (ETIs inevitably exhaust their natural resources, leading to their extinction; p. 185) 3b Gradualism
Deadly probes (self-replicating machines released by an early ETI are programmed to destroy all sources of intelligence—although they have not reached us yet, they have destroyed all other detectable ETIs; p. 188) 3b Gradualism
Interstellar containment (advanced ETIs are coordinating to prevent less advanced ETIs from detecting one another; p. 195) 3b Gradualism
Transcendence (advanced ETIs have transformed themselves into some unrecognizable form; p. 196) 1a Gradualism
Transcension (advanced ETIs have transformed themselves into more advanced space/time/energy/matter substrates, and hence we cannot detect them; p. 198) 1a Gradualism
Red empire (ETIs tend to migrate towards dimmer, red-dwarf stars, and they have therefore avoided our solar system; p. 210) 2b Non-exclusivity
Brown empire (ETIs tend to gravitate toward brown dwarf stars or free-floating planets, and have therefore avoided our solar system; p. 211) 2b Non-exclusivity
Persistence (we happen to reside in a part of the universe that is unlikely to be colonized by ETIs for a long time; p. 213) 2b Non-exclusivity
Living on the rim (advanced ETIs are likely to migrate to the outskirts of the universe where we are coincidentally unable to detect them; p. 217) 2b Non-exclusivity
Eternal wanderers (advanced ETIs have no use for planets or planetary systems because they have built their own world-ships, so they are uninterested in visiting our solar system; p. 219) 2b Non-exclusivity
Great old ones (advanced ETIs have put themselves into a state of estivation, waiting until conditions in the universe are more conducive to information processing; p. 219) 2b Non-exclusivity
Sustainability (fast colonization is not sustainable, so any colonization attempts currently occurring are very slow and therefore have gone undetected by us; p. 221) 2b Non-exclusivity
Galactic stomach ache (all ETIs eventually degenerate due to an increase in dangerous medical conditions; p. 223) 2b Non-exclusivity

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Hepçağlayan, C., Watkins, A. & Powell, R. What is Paradoxical About ‘Fermi’s Paradox’?. Acta Biotheor 68, 469–477 (2020). https://doi.org/10.1007/s10441-020-09376-x

Download citation


  • Astrobiology
  • Copernicanism
  • Evolution
  • Extraterrestrial intelligence
  • Fermi’s paradox
  • Technological civilizations