But particle physicist Stephen Webb collected many more such theses, in a book published in 2002, If the Universe Is Teeming with Aliens … WHERE IS EVERYBODY?: Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life (2002). A revised edition was published by Springer, a big science publisher, in 2015, offering 75 hypotheses.
“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,” the Search For Extraterrestrial Intelligence (SETI) Institute in Mountain View, California, said on its website. “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 with the age of the galaxy, which is roughly ten thousand million years. Colonization of the Milky Way should be a quick exercise.”Elizabeth Howell, “Fermi Paradox: Where Are the Aliens?” at Space.com (April 27, 2018)
Webb, quite sure that, in the immensity of the universe, they must exist, set out to look at as many reasons we might not see them as he could find, trying to avoid partiality to any one hypothesis. As one science writer puts it,
Many of Webb’s collected hypotheses suggest that aliens live where we’re not looking, talk how we’re not listening or resemble something we haven’t sought out. Maybe the aliens like to send messages or signals using neutrinos, nearly massless and barely-there particles that don’t interact with normal matter much, or tachyons, hypothetical particles that fly faster than light. Maybe they use the more-conventional radio or optical transmissions but at frequencies, or in a form, astronomers haven’t sought out. Maybe a signal is sitting on data servers already, escaping notice. Maybe the extraterrestrials subtly alter the emissions of their stable stars, or the blip-blip-blip pulsations of variable stars. Maybe they put something big — a megamall, a disk of dust — in front of their sun to block some of its light, in a kind of anti-beacon. Maybe their skies are cloudy, and they consequently don’t care about astronomy or space exploration. Or — hear Webb out — perhaps they drive UFOs, meaning they are here but not in a form that scientists typically recognize, investigate, and take seriously.Sarah Scoles, “The lonely universe: Is life on Earth just a lucky fluke?” at Astronomy
It’s enough to make hopeful skywatchers angry, and sometimes that shows a bit:
Given the fact that there are perhaps 400 billion stars in our Galaxy alone, and perhaps 400 billion galaxies in the Universe, it stands to reason that somewhere out there, in the 14-billion-year-old cosmos, there is or once was a civilization at least as advanced as our own. The sheer enormity of the numbers almost demands that we accept the truth of this hypothesis. Why, then, have we encountered no evidence, no messages, no artifacts of these extraterrestrials?Sarah Scoles, “The lonely universe: Is life on Earth just a lucky fluke?” at Astronomy
A new study from the Future of Humanity Institute (FHI) at Oxford University, aptly titled “Dissolving The Fermi Paradox,” suggests that humanity is alone in the observable universe, putting a dampener on the theory that there is intelligent life outside of Earth.
“When the model is recast to represent realistic distributions of uncertainty, we find a substantial ex ante probability of there being no other intelligent life in our observable universe, and thus that there should be little surprise when we fail to detect any signs of it,” the study’s abstract reads.
“This result dissolves the Fermi paradox, and in doing so removes any need to invoke speculative mechanisms by which civilisations would inevitably fail to have observable effects upon the universe.”Chris Ciaccia, “It’s likely that we are alone in the universe, depressing study finds” at News.com
They tried reducing it to numbers:
The new study uses a distribution of probabilities to capture the most likely scenarios, rather than assign a single value.
The authors found that the chance humanity stands alone among intelligent civilizations in our galaxy is 53%–99.6%, and across the observable universe is 39%–85%.
‘We should not actually be all that surprised to see an empty galaxy,’ the authors, Anders Sandberg, Eric Drexler, Toby Ord, wrote.Mark Prigg, “We are alone in the universe: Fermi Paradox study claims there is a ‘substantial probability’ there is not intelligent life elsewhere” at Daily Mail
But that, of course, is a pretty wide spread: 39% to 85%. In any event, one cannot very easily prove a negative of any kind. So in the end, Search for Extraterrestrial Intelligence (SETI) goes on searching and we go on listening.
You may also enjoy these accounts of why we do not see the aliens:
1.Are the Aliens We Never Find Obeying Star Trek’s Prime Directive? The Directive is, don’t interfere in the evolution of alien societies, even if you have good intentions. Assuming the aliens exist, perhaps it’s just as well, on the whole, if they do want to leave us alone. They could want to “fix” us instead…
2.How can we be sure we are not just an ET’s simulation? A number of books and films are based on the idea. Should we believe it? We make a faith-based decision that logic and evidence together are reasonable guides to what is true. Logical possibility alone does not make an idea true.
3.Did the smart machines destroy the aliens who invented them? That’s the Berserker hypothesis. A smart deadly weapon could well decide to do without its inventor and, lacking moral guidance, destroy everything in sight. Extinction of a highly advanced civilization by its own lethal technology may be more likely than extinction by natural disaster. They could control nature.
4.Researchers: The aliens exist but they are sleeping… And we wake them at our peril. The Aestivation hypothesis is that immensely powerful aliens are waiting in a digitized form for the universe to cool down from the heat their computers emit.
5.Maybe there are just very few aliens out there… The Rare Earth hypothesis offers science-based reasons that life in the universe is rare. Even if life is rare in the universe, Earth may be uniquely suited to space exploration, as the Privileged Planet hypothesis suggests.
6.Does science fiction hint that we are actually doomed? That’s the implication of an influential theory as to why we never see extraterrestrials. Depending how we read the Kardashev scale, civilizations disappear somewhere between where we are now and the advanced state needed for intergalactic travel.
7.Space aliens could in fact be watching us. Using the methods we use to spot exoplanets. But if they are technologically advanced, wouldn’t they be here by now? The Hart-Tipler conjecture (they don’t exist) is, of course, very unpopular in sci-fi. But let’s confront it, if only to move on to more promising speculations.
8.Is the brief window for finding ET closing? According to some scenarios, we could be past our best-before date for contacting aliens. Of course, here we are assuming a law of nature as to how long civilizations last. Can someone state that law? How is it derived?
9.What if we don’t see aliens because they have not evolved yet? On this view, not only did we emerge during a favorable time in the universe’s history but we could end up suppressing them. The Firstborn hypothesis (we achieved intelligence before extraterrestrials) lines up with the view that humans are unique but sees that status as temporary.
10.The aliens exist—but evolved into virtual reality at a nanoscale. That’s the Transcension Hypothesis, the latest in our series on science fiction hypotheses as to why we don’t see extraterrestrials.
On this view, after a Singularity the ETs become virtual intelligences, exploring inner space at an undetectably small scale