20.06.2018
Ein weiteres Salzkorn in die Wunde der Ufologen kommt mit der Aussage der Oxford University;
Stop looking for ET: modelling suggests we’re alone in the universe
Oxford University researchers run the numbers and conclude intelligent life beyond Earth is highly unlikely. Andrew Masterson reports.
Despite the small matter of lack of evidence, most astrophysicists and cosmologists today are persuaded that extra-terrestrial intelligent life must exist.
The logic behind the assumption seems compelling. There are billions of galaxies in the universe, each containing billions of stars, around a proportion of which orbit billions of planets. Given the vastness of those numbers, it would be statistically perverse to suggest that intelligent life evolved only once in the entire system.
But what, however, if the startlingly improbable is nevertheless the truth? What if Homo sapiens is, in fact, the only species ever in the entire history of the universe to invent radio, build an X-ray observatory, and send a ship into space?
What if – the existence of exoplanets coated in blue-green slime notwithstanding – we are utterly on our own?
That’s the contention of physicists Anders Sandberg, Eric Drexler and Toby Ord, all of the Future of Humanity Institute at Oxford University in the UK. In a paper lodged on the pre-print server Arxiv, and thus still awaiting peer review, the trio model what happens when two touchstones of astrobiology – the Fermi Paradox and the Drake Equation – are combined and subjected to mathematical rigour.
The results, it must be said, aren’t good, at least for people hopeful that somewhere, out there, at least one alien civilisation is bubbling along.
Existing calculations for the probability of extra-terrestrial intelligent life, they report, rest on uncertainties and assumptions that lead to outcomes containing margins for error spanning “multiple orders of magnitude”.
Constraining these, as much as possible, by factoring in models of plausible chemical and genetic mechanisms, results, they conclude, in the finding “that there is a substantial probability that we are alone”.
The Fermi Paradox is named after physicist Enrico Fermi, who noted in 1950 that there are so many stars, just in the Milky Way, that given the age of the universe even a small probability that intelligent life has evolved would mean that their existence should be plain to humanity by now.
Yet, he continued, in terms of evidence, we have squat, which, given the probability of intelligent life emerging, is odd. Hence the paradox. “Where are they?” he asked.
The Drake Equation, formulated by American astronomer Frank Drake in 1961, attempts to place an analytical framework around Fermi’s contention, by estimating the number of intelligent civilisations that exist in the universe, regardless of the fact that we can’t see them.
Drake’s work can be expressed thus: N = R ∗ fp ∗ ne∗ fl ∗ fi ∗ fc ∗ L
In the equation, N represents the number of civilisations within the Milky Way capable of emitting detectable electromagnetic signals. The number is determined by the other factors in the model, which express the rate of suitable star formation, the fraction of those stars with exoplanets, the number of those planets suitable for life and the number on which life actually appears.
That total is then further reduced by adding in other refinements – the number of life-bearing planets on which intelligence emerges, the number of those that produce technology capable of emitting signals into space, and the number of those that actually go ahead and do so.
It’s all very impressive, but “sciencey” rather than scientific. Sandberg, Drexler and Ord gleefully quote US astronomer Jill Tarter, who described the Drake Equation as “a wonderful way to organise our ignorance”.
The problem with the way the equation is usually wielded, the researchers argue, is that the parameters assigned to most of the various elements represent simply best guesses – and those guesses, furthermore, are heavily influenced by whether the person making them is optimistic or pessimistic about the chances of intelligent life existing. The result, they note, often involves well-estimated astronomical numbers multiplied by ad hoc figures.
They quote another US astronomer, Steven J. Dick: “Perhaps never in the history of science has an equation been devised yielding values differing by eight orders of magnitude ... each scientist seems to bring his own prejudices and assumptions to the problem.”
Dick, they note, was being nice. Many outcomes from Drake Equation calculations yield probabilities that range over hundreds of orders of magnitude.
In a not altogether unrelated sidebar, the researchers acknowledge a recent calculation by Swedish-American cosmologist Max Tegmark, estimating the chances of intelligent civilisations arising in the universe.
Tegmark assumes there is no reason two intelligent civilisations should be any particular distance from each other, and then argues that – given the Milky Way is a minuscule fraction of the observable universe, which is itself only a tiny part of the universe beyond what we can see – it is unlikely that two intelligent civilisations would arise in the same observable universe. Thus, to all intents and purposes, we are very probably alone.
Sandberg, Drexler and Ord use a different approach in their modelling, incorporating current scientific uncertainties that produce values for different parts of the equation ranging over tens and hundreds of orders of magnitude. Some of these concern critical questions regarding the emergence of life from non-living material – a process known as abiogenesis – and the subsequent likelihoods of early RNA-like life evolving into more adaptive DNA-like life.
Then there is the essential matter of that primitive DNA-like life undergoing the sort of evolutionary symbiotic development that occurred on Earth, when a relationship between two different types of simple organisms resulted in the complex “eukaryotic” cells that constitute every species on the planet more complicated than bacteria.
The results are depressing enough to send a thousand science-fiction writers into catatonic shock. The Fermi Paradox, they find, dissolves.
“When we take account of realistic uncertainty, replacing point estimates by probability distributions that reflect current scientific understanding, we find no reason to be highly confident that the galaxy (or observable universe) contains other civilizations,” they conclude.
“When we update this prior in light of the Fermi observation, we find a substantial probability that we are alone in our galaxy, and perhaps even in our observable universe.
“‘Where are they?’ — probably extremely far away, and quite possibly beyond the cosmological horizon and forever unreachable.”
Quelle: COSMOS
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Update: 24.06.2018
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But, Seriously, Where Are the Aliens?
Humanity may be as few as 10 years away from discovering evidence of extraterrestrial life. Once we do, it will only deepen the mystery of where alien intelligence might be hiding.
Enrico Fermi was an architect of the atomic bomb, a father of radioactivity research, and a Nobel Prize–winning scientist who contributed to breakthroughs in quantum mechanics and theoretical physics. But in the popular imagination, his name is most commonly associated with one simple, three-word question, originally meant as a throwaway joke to amuse a group of scientists discussing UFOs at the Los Alamos lab in 1950: Where is everybody?
Fermi wasn’t the first person to ask a variant of this question about alien intelligence. But he owns it. The query is known around the world as the Fermi paradox. It’s typically summarized like this: If the universe is unfathomably large, the probability of intelligent alien life seems almost certain. But since the universe is also 14 billion years old, it would seem to afford plenty of time for these beings to make themselves known to humanity. So, well, where is everybody?
In the seventh episode of Crazy/Genius, a new podcast from The Atlantic on tech, science, and culture, we put the question to several experts, including Ellen Stofan, the former chief scientist of nasa and current director of the Smithsonian National Air and Space Museum; Adam Frank, a writer and astrophysicist at the University of Rochester; Anders Sandberg, a scientist and futurist at the University of Oxford; and Tim Urban, the science essayist at Wait But Why.
Proposed solutions to Fermi’s Paradox fit into three broad categories.
One: They’re nowhere—and no-when. Aliens don’t exist, and they never have. This scenario might have seemed more likely in the universe imagined by Aristotle and Ptolemy—a small assortment of celestial orbs spinning around a singular Earth. But that isn’t the universe anybody lives in. After searching the skies for Earthlike planets for centuries, cosmologists have, in the last two decades, broken open the cosmic piñata. Today they estimate as many as 500 billion billion sunlike stars, with 100 billion billion Earthlike planets. The more we learn about the universe, the more absurd it would seem if all but one of those bodies were bereft of life. To my mind, this is both the least likely answer to Fermi’s Paradox and the only one that fits all the evidence currently available to astrophysicists.
Two: Life is out there—but intelligence isn’t. Ellen Stofan predicts that we’ll find evidence of simple life on Mars or a faraway moon within the next 10 to 30 years. But she’s imagining something more like microbes or algae, not underwater cities in the liquid-methane lakes of Titan. This shifts the question from “Where is everybody?” to a more sophisticated query: What precisely is keeping an infinitude of dumb molecules from assembling to form an abundance of intelligent life?
Think about all the factors that add up to the creation of a human. First the spark of life, followed by the creation of simple cells, then complex multicellular organisms, then the formation of organs like brains. If humanlike intelligence is rare, one of these steps must be quite insurmountable. For example, it’s notable that Earth has several million species of life, but only one has produced a civilization—that we know of. The relative silence of the universe suggests some kind of “Great Filter” that is restricting the creation of more intelligent beings. More ominously, some scientists think it’s possible that this Great Filter isn’t in our distant past, but rather in our future; so, it’s not that intelligent life is rare, but rather that it pops into existence for a few thousand years before getting wiped out of existence for mysterious reasons.
Three: Intelligent life is abundant—but quiet. This possibility, known as the zoo hypothesis, invites some of the strangest speculation. Maybe humanity is still so basic and primitive that advanced civilizations don’t think we’re worth talking to. Or maybe those other civilizations have learned that broadcasting their existence leads to extermination at the hands of violent, intergalactic colonizers. Or maybe our solar system just happens to be located in a quiet, exurban cul-de-sac of the universe, an accident of cosmic geography. But none of these theories hold a candle to my favorite conjecture of all: slumbering digital aliens. To understand why intelligent life might prefer to be based in a computer or cat-napping through the Anthropocene, check out the episode.
Quelle: The Atlantic
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Update: 27.06.2018
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Aliens may not exist – but that’s good news for our survival
A new study suggests that we could well be on our own in the universe. Yet loneliness might have its advantages
In 1950 Enrico Fermi, an Italian-born American Nobel prize-winning physicist, posed a very simple question with profound implications for one of the most important scientific puzzles: whether or not life exists beyond Earth. The story goes that during a lunchtime chat with colleagues at the Los Alamos National Laboratory in New Mexico, the issue of flying saucers came up. The conversation was lighthearted, and it doesn’t appear that any of the scientists at that particular gathering believed in aliens. But Fermi merely wanted to know: “Where is everybody?”
His point was that, since the age of the universe is so great and its size so vast, with hundreds of billions of stars in the Milky Way alone, then unless the Earth is astonishingly special, the universe should be teeming with life. This might include intelligent species advanced enough to have the knowledge and technology necessary for space travel. They ought to have colonised the entire galaxy by now. So where are they all?
More recently, the late Stephen Hawking argued along similar lines. He said, “To my mathematical brain, the numbers alone make thinking about aliens perfectly rational.” Hawking was articulating the same popular argument as Fermi – that the sheer vastness of the universe all but guarantees we have company.
In recent years, scientists have begun to take the subject more seriously again. One of the most exciting areas of research in astronomy has been the discovery of extra-solar planets, worlds orbiting stars other than our sun. Many of them even appear to be Earth-like in size and climate. Astronomers now believe there are billions of these other worlds, many of which will have conditions suitable for life. The probability of life, maybe even intelligent life, existing on at least one of them must surely, therefore, be overwhelming.
Now however, scientists at the wonderfully named Future of Humanity Institute in Oxford have poured cold water on Hawking’s and others’ optimism. They have carried out a thoughtful statistical analysis by dissecting a mathematical relation known as the Drake equation, which allows us to calculate the probability of extraterrestrial life based on the combined probabilities of all the ingredients for life being in place.
Let me make clear at the outset that the Drake equation is not very scientific, for the sole reason that some of the factors that need to be fed into it are pure guesswork at this stage. Not the least of these is the big question: given all the things we believe are necessary for life (a source of energy, liquid water and organic molecules), how likely is it that life will emerge?
The authors of the new study offer two insights, one pessimistic and the other more cheery. The first is that Fermi’s paradox is easy to resolve. The reason we have not had any messages from ET is because, well, there is no ET out there. They calculate the probability we are alone in the universe to be in the range of 39%–85% and the probability that we are alone in our own galaxy to be between 53% and 99.6%. Basically, don’t hold your breath.
Biologists, of course, hate all this silly speculation. They quite rightly point out that we still do not properly understand how life originated here on Earth, so how can we possibly have any confidence in anticipating its existence or nonexistence elsewhere? There are some who argue that life on Earth appeared pretty quickly after the right conditions emerged almost 4bn years ago, which was when our planet had cooled sufficiently for liquid water to exist. Doesn’t that mean it could easily appear elsewhere too? Actually, no. A statistical sample of one tells us nothing. It is quite possible that biology is a freak local aberration, the product of a chemical fluke so improbable that it didn’t happen anywhere else in the observable universe.
So where do we stand? Well, there are reasons to believe that we may have an answer in the coming decade or two, one way or the other. Astrobiologists are about to search exoplanets for the gases produced by microbial life using sophisticated next-generation space telescopes. There is also the possibility of finding microbial life closer to home, under the ice of several of the moons of Jupiter and Saturn.
I did say that the study also provided some cheer. Some have claimed we have not found ET yet because intelligent life (including us) always annihilates itself before it can successfully develop the technology for interstellar travel or communication. But maybe the silence is simply because no such alien civilisations exist. So, as the authors put it, pessimism about our own future is therefore unfounded. We may be alone, but we may just survive.
• Jim Al-Khalili is professor of physics and professor of the public engagement in science at the University of Surrey