Fermi’s Paradox and Stephen Hawking

In the summer of 1950, while having lunch with colleagues who were chatting about recent reports of “flying saucers” in the news, nuclear physicist Enrico Fermi suddenly blurted out, “Where is everybody?” [Web2002, pg. 17-18]. Behind his question was the following line of reasoning: (a) There are likely many other technological civilizations in the Milky Way galaxy; (b) It is highly likely that other technological civilizations are many thousands of years more advanced than us (since if they are less advanced by even a few decades they would not be technological); (c) In a few million years, they could have explored or even colonized many distant planets, certainly encompassing the Milky Way; (d) So why don’t we see any evidence of extraterrestrial civilizations?

Clearly the question of whether other civilizations exist is one of the most important questions of modern science. And any discovery of a distant civilization, say by analysis of microwave data or observation of laser-like signals, would certainly rank as among the most significant and far-reaching of all scientific discoveries [Davies2010]. Back in 1961, Frank Drake encapsulated the issues involved in his eponymous equation:

N = R* fp ne fl fi fc L

N = number of civilizations in our galaxy that can communicate

R* = average rate of star formation per year in galaxy
fp = fraction of those stars that have planets
ne = average number of planets that can support life, per star that has planets
fl = fraction of the above that eventually develop life
fi = fraction of the above that eventually develop intelligent life

fc = fraction of civilizations that develop technology that signals existence into space

L = length of time such civilizations release detectable signals into space (before dying).

The values originally estimated by Drake in 1961 were R = 10, fp = 0.5, ne = 2, fl = 1, fi = 0.01, fc = 0.01, L = 10,000, so that N = 10 (other estimates vary widely).

In the ensuing decades since 1961, numerous leading scientists have examined Fermi’s paradox and have proposed solutions. These range from presuppositions that there is a galactic pact not to disturb nascent civilizations like us (preferred by astronomer Carl Sagan), to the stark conclusion that there are no other technological civilizations in the Milky Way, or even in the entire universe! Here is a brief listing of some of the proposed “solutions,” and common rejoinders [Web2002, pg. 27-231]:

  1. They are nearby observing us, but are under strict orders not to disclose their existence. Rejoinder: It just takes one member of the extraterrestrial community to break the pact. Given our experience with human society, it seems utterly impossible to impose such uniformity on a vast civilization.
  2. They exist, but are too far away. Rejoinder: Once a civilization is sufficiently advanced, it could send “von Neumann probes” to distant stars, which could scout out suitable planets, land, and then construct additional copies of themselves, using the latest software beamed from earth. Simulations suggest that the entire Milky Way galaxy could be explored within a few million years (an eyeblink in galactic time).
  3. They exist, but have lost interest in interstellar communication and/or transportation. Rejoinder: As with item #1, this explanation requires that each and every civilization forever lacks interest in communication and transportation, which seems very dubious.
  4. They are calling, but we do not recognize the signal. Rejoinder: The current Search for Extraterrestrial Intelligence (SETI) project has designed their equipment with the assumption that the remote civilization is making some effort to signal their existence in a way simple enough for us to detect and understand.
  5. Civilizations like us invariably self-destruct. Rejoinder: This is the L term in Drake’s equation. From our experience we have survived at least 100 years of technological adolescence, and have not yet destroyed ourselves in an nuclear, biological or environmental apocalypse. Besides, within a few decades we will have colonized the Moon and Mars, and then our long-term existence will be impervious to potential calamities on earth.

Recently the well-known physicist Stephen Hawking entered into the fray by declaring, in a documentary aired on the Discovery Channel, that it is highly “risky” for us to attempt to contact alien civilizations. Hawking warned that aliens might be seeking new resources to commandeer, and thus be hostile to us in the same way that Europeans were hostile to New World natives. Many news outlets immediately reported his comments (see for instance [Hawking2010]).

However, it appears that Hawking’s enormous grasp of physics does not extend into the realm of exobiology. As mentioned above, many scientists have studied this topic in detail. Most see little if any risk in attempting to contact these civilizations, if they exist [Yam2010; Tarter2010]. Besides, it is too late — we have already been beaming TV signals and the like for decades. As pointed out in a Scientific American rejoinder [Yam2010],

A species that masters the difficulty of space travel would certainly seem to have the brain power to mine its own resources without having to travel tens of light years (at least) to ravage our home. … Earth as a nice place to colonize is perhaps the strongest argument for hostile aliens, and that’s not a very strong argument. The odds that Earth’s biosphere safely matches that of the alien’s home planet is low.

Similarly, Jill Tarter, a veteran scientist with the Search for Extraterrestrial Intelligence (SETI) project, explains:

Can we be certain that their magic would do us harm? I would hope that Hawking would agree that a large value for L [in Drake’s equation] (a requirement for that magical, star-spanning technology) could also mean that their distant civilization had found a way to stabilize itself in order to survive and grow old. That might require outgrowing any aggressive and belligerent tendencies that may have characterized their youth.

Physicist Paul Davies, in a recently published book on the subject [Davies2010], similarly dismisses the possibility that aliens pose any threat to us. He is more concerned that we might appear threatening to them! So the real question is this: Why did Hawking’s speculations commandeer such a large audience? Why didn’t those journalists who quoted Hawking’s remarks immediately seek responses from other scientists who have studied this topic in greater detail?

This episode seems to us to be a clear example of a major structural weaknesses in the worldwide enterprise of science — the need for journalists in the field who: (a) are themselves significantly knowledgeable in modern science and how it operates, so as to comment accurately on research; and (b) who can recognize when a scientist may be speaking outside his/her expertise and thus seek a reasonable balance of informed views.

As one of the editor’s of the National Post said to one of us a few years ago, “we cover conflict.” In other words, the press is structurally biased to running controversial items, not feel good or informative stories. And the growing dominance of online media in the news cycle has exacerbated this. Careful science is a big loser in such a milieu. Also, the boundary between news and entertainment is so degraded that anything a “star” or “celeb” says is bound to be covered whether that star is Stephen Hawking or Angelina Jolie.


  1. [Davies2010] Paul Davies, The Eerie Silence: Renewing Our Search for Alien Intelligence, Houghton Mifflin Harcourt, New York, 2010.
  2. [Hawking2010] [no author], “Stephen Hawking: Human, alien interaction ‘risky’ business,” Associated Press, available at Online article.
  3. [Tarter2010] Jill Tarter, “Should we fear space aliens?”, CNN, 27 Apr 2010, available at Online article.
  4. [Ward2000] Peter D. Ward and Donald Brownlee, Rare Earth: Why Complex Life Is Uncommon in the Universe, Copernicus Books, New York, 2000.
  5. [Webb2002] Stephen Webb, If the Universe Is Teeming with Aliens… Where Is Everybody? Fifty Solutions to Fermi’s Paradox and the Problem of Extraterrestrial Life, Copernicus Books, New York, 2002.
  6. [Yam2010] Philip Yam, “Alien horror: Stephen Hawking hawks Stephen King,” Scientific American, 28 Apr 2010, available at Online article.

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