Fermi's Paradox

At a dinner party conversation about ETs in Los Alamos, New Mexico, while working on the atomic bomb, Nobel Prize winning physicist Enrico Fermi asked his fellow scientists the simple question: Where are they?, a query, now part of ET lore, that is still much discussed today.

The gist of the question is that if advanced extraterrestrials exist anywhere in our galaxy, they should be here on Earth. Both SETI Chief Astronomer Seth Shostak and SETI icon Jill Tarter agree with the premise that ET should be here (see below), but argue that just because they aren’t here, and there is no “indisputable physical evidence” that they have ever been here, they don’t exist. This debate has been going on for decades without being resolved.


Dr. Jill Tarter on Fermi’s paradox (Note: she disagrees with the conclusion):

  1. If extraterrestrial civilizations have existed elsewhere and “elsewhen” in our galaxy,

  2. and if interstellar travel/colonization/migration is inevitable for at least one of them,

  3. then simple calculations indicate that an expanding wave of colonization will fill the galaxy on a time scale short compared to the lifetime of the galaxy,

  4. but we do not “see” them here.

  5. Therefore, (1) is wrong; there has never been another technological civilization anywhere or “anywhen” in our galaxy except the earth.”

Dr. Tarter’s point 4, a reference to the absence of indisputable physical evidence of ETs on Earth, is no longer true, thanks to the discovery of the Sagan Signal.

This is what discoveries can do. For years, scientists were certain that the coelacanth, a prehistoric fish, was extinct, because all we had were fossil remains. Then, in 1938, a fishermen off the coast of South Africa pulled a living one up in his net. Since then, dozens more have been caught.

 Indisputable physical evidence.

For decades, scientists have been equally certain that ETs have never been to Earth. Then the Sagan Signal was discovered.

Indisputable physical evidence.


Dr. Seth Shostak’s essay on Fermi’s paradox:

“Is there obvious proof that we could be alone in the Galaxy? Enrico Fermi thought so – And he was a pretty smart man. Might he have been right?

It’s been a hundred years since Fermi, an icon of physics, was born (and nearly a half-century since he died).


He’s best remembered for building a working atomic reactor in a squash court. But in 1950, Fermi made a seemingly innocuous lunchtime remark that has caught and held the attention of every SETI researcher since. (How many luncheon quips have you made with similar consequence?)

The remark came while Fermi was discussing with his mealtime mates the possibility that many sophisticated societies populate the Galaxy. They thought it reasonable to assume that we have a lot of cosmic company. But somewhere between one sentence and the next, Fermi’s supple brain realized that if this was true, it implied something profound. If there are really a lot of alien societies, then some of them might have spread out.

Fermi realized that any civilization with a modest amount of rocket technology and an immodest amount of imperial incentive could rapidly colonize the entire Galaxy. Within ten million years, every star system could be brought under the wing of empire. Ten million years may sound long, but in fact it’s quite short compared to the age of the Galaxy, which is roughly ten thousand million years. Colonization of the Milky Way should be a quick exercise.

So what Fermi immediately realized was that the aliens have had more than enough time to pepper the Galaxy with their presence. But looking around, he didn’t see any clear indication that they’re out and about.

This prompted Fermi to ask what was (to him) an obvious question: “Where is everybody?”

This sounds a bit silly at first. The fact that aliens don’t seem to be walking our planet apparently implies that there are no extraterrestrials anywhere among the vast tracts of the Galaxy. Many researchers consider this to be a radical conclusion to draw from such a simple observation. Surely there is a straightforward explanation for what has become known as the Fermi Paradox. There must be some way to account for our apparent loneliness in a galaxy that we assume is filled with other clever beings.

A lot of folks have given this thought. The first thing they note is that the Fermi Paradox is a remarkable strong argument. You can quibble about the speed of alien spacecraft, and whether they can move at 1 percent of the speed of light or 10 percent of the speed of light. It doesn’t matter. You can argue about how long it would take for a new star colony to spawn colonies of its own. It still doesn’t matter. Any halfway reasonable assumption about how fast colonization could take place still ends up with time scales that are profoundly shorter than the age of the Galaxy. It’s like having a heated discussion about whether Spanish ships of the 16th Century could heave along at two knots or twenty. Either way they could speedily colonize the Americas.

Consequently, scientists in and out of the SETI community have conjured up other arguments to deal with the conflict between the idea that aliens should be everywhere and our failure (so far) to find them. In the 1980’s dozens of papers were published to address the Fermi Paradox. They considered technical and sociological arguments for why the aliens weren’t hanging out nearby. Some even insisted that there was no paradox at all: the reason we don’t see evidence of extraterrestrials is because there aren’t any.”

[Note: After introducing a few explanations, such as “too costly,” the “zoo hypothesis,” and “they are here but they are too exotic for us to detect,” Shostak continues]:

“These explanations, and a bushel-basket more, have been proffered to deal with the Fermi Paradox. Any of them might be true. Nonetheless, some scientists find them too contrived, too unlikely to work in every case. Will all the aliens find colonization too costly? Will they all run out of empirical steam? Are we so special that someone has really gone to the trouble to put us behind invisible bars?

Or is there a much simpler explanation?

The presence of aliens on Earth would neatly solve the Fermi Paradox.

But while this (UFOs) is a prevalent idea among the public, the evidence for alien visitation has failed to sway most scientists. To convince researchers, who are inherently skeptical, unambiguous and repeated detection of flying objects by satellites or ground-based radar would be required. Better yet would be indisputable physical evidence, such as the landing lights from an alien craft. In other words, something better than witness testimony is necessary, since such testimony isn’t good enough, no matter how credible the witness. It’s all a bit perplexing, but in fact there’s hope. SETI experiments offer the promise of relegating the Fermi Paradox to the dustbin of historical curiosities by proving that other intelligence is out there. So while it’s interesting and instructive to consider the pros and cons of galactic colonization, we should also make sure that we do some careful observing. In science, speculation is desirable, but experiment is definitive." (bold mine).

Dr. Shostak writes that the best evidence is “indisputable physical evidence.” After fifteen years of vetting, there is no dispute – like the living coelacanth caught in the fishermen’s net, this is what the Sagan Signal is.

Dr. Tarter, Dr. Shostak, here’s the breaking news: The Sagan Signal has been tested and confirmed by the Center for Inquiry and the verdict is unanimous: ET has been here! The Sagan Signal is the answer to Fermi’s paradox.

Indisputable physical evidence.

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