In a July 2015 speech, Stephen Hawking explained "Breakthrough Listen," an initiative aimed at discovering intelligent extraterrestrial life. (Breakthrough Initiatives)
“The universe is apparently bulging at the seams with the ingredients of biology.”
So says Geoffrey Marcy, an astronomer at the University of California at Berkeley and a participant in Stephen Hawking’s $100 million search for alien life, announced on Monday.
Marcy isn’t the only person who thinks so. Frank Drake, chairman emeritus of the Search for Extraterrestrial Intelligence Institute, came up with an equation in 1961 for calculating the abundance of alien civilizations capable of communicating with us.
When he plugs modern data into the formula, the number he comes up with is 10,000. And that just includes the ones he thinks we can detect, once we have the right tools searching the right places. Researchers examining data from NASA’s Kepler space telescope (including Marcy) announced in 2013 that they believe the Milky Way may harbor billions of planets that bear liquid water — a substance integral to the emergence of living things.
[Stephen Hawking announces $100 million hunt for alien life]
But if the universe is so full of the ingredients for alien life, why haven’t we found any yet? Or, more pertinently, considering how young humans are (100,000 years) compared to the age of the universe (13.8 billion years), why haven’t any aliens found us?
This question is known as the Fermi paradox, named for Italian physicist Enrico Fermi. According to scientific lore, Fermi was sitting around chatting about extraterrestrial life with fellow researchers (you know, as one does) when he asked, “So? Where is everybody?”
In the words of a University of Oregon professor’s lecture on the subject, Fermi reasoned that any civilization with “a modest amount of rocket technology and an immodest amount of imperial incentive” could colonize the galaxy by building artificially intelligent robotic probes that would self-reproduce as they journeyed beyond their home planet. While the distances between habitable planets are much too vast to be traversed in a lifetime, the theoretical robots have had millions or even billions of years to make the journey.
An introductory video set up the announcement by Yuri Milner and Stephen Hawking of "Breakthrough Listen," a new initiative aimed at discovering intelligent extraterrestrial life. (Breakthrough Initiatives)
So far, notwithstanding the arguments of Roswell conspiracy theorists, we’ve seen no evidence of those probes. SETI experiments searching for radio signals or other broadcasts from possible alien civilizations have turned up empty.
[Do we really want to know if we’re not alone in the universe?]
There are three broad categories of explanations for Fermi’s paradox, each of which contains several of what you might call a “sub” explanation. Those range from reasonable — intelligent life is sending out signals, we just don’t know how to listen — to seemingly absurd — Earth is just a “zoo” built by aliens to hold us for their entertainment. Some come from astronomers and biologists, other from philosophers and economists. Still others seem to have more in common with science fiction than science. All of them are entertaining to think about, at least in the abstract sense.
1. We really are alone.
This could be true for any number of reasons.
Life, as scientists have learned from repeated attempts to do so in a lab, is difficult to start from scratch. It requires a spontaneous sequence of events that somehow animates simple, non-living organic compounds and organizes them into more complex molecules capable of self-replication. So far, that’s only been known to happen once — when life on Earth began.
From left: DST Global founder Yuri Milner, theoretical physicist Stephen Hawking, cosmologist and astrophysicist Lord Martin Rees, Chairman Emeritus, SETI Institute Frank Drake, Creative Director of the Interstellar Message, NASA Voyager Ann Druyan and Professor of Astronomy, University of California Geoff Marcy attend a news conference on the Breakthrough Life in the Universe Initiatives, hosted by Yuri Milner and Stephen Hawking, at the Royal Society on July 20 in London. (Stuart C. Wilson/Getty Images for Breakthrough Initiatives)
It’s possible that habitable planets like Earth are rarer than we think. Even if there are billions in the “Goldilocks zone” situated at the appropriate distance from their suns, maybe gamma rays or asteroid bombardment or other dangers from space prevented life from developing.
[One man’s quest to bury the Wild West mystery of Billy the Kid’s death]
In a 1998 essay, George Mason economics professor Robin Hanson proposed the idea of a “great filter” — something “along the path between simple dead stuff and explosive life” that is very difficult or even impossible to move beyond. If the “filter” is somewhere in the early days of life’s beginnings, that would explain why no other planet has proven capable of nurturing life.
The notion that we’re unique in the universe is what paleontologist Peter Ward and astronomer Donald Brownlee call the rare Earth hypothesis. They argue that the presence of complex life on this planet may be a once-in-a-Big-Bang occurrence.
Earthlings may have to resign themselves to the fact that we’re on our own.
2. Life is out there; we just haven’t heard from it.
That said, there’s good reason to believe that life on Earth is not unique.
First of all, we’re pretty sure that water — that essential indicator of conditions for life — is fairly ubiquitous. NASA believes that there are large quantities of water in the atmospheres of at least four other planets in our solar system and ice on countless other celestial bodies. And in April, researchers announced in the journal Nature that they’d found the first evidence of organic molecules in an infant star system.
This artist rendition provided by NASA shows the Kepler space telescope. (NASA/Associated Press)
But if we do have otherworldly company, researchers like Marcy (one of the brains tapped for Hawking’s $100 million search) want to know why we haven’t heard from them.
“The absence of strong radio beacons, television broadcasts, robotic spacecraft, obelisks on the moon — all of those absences add up to give us the suggestion that our galaxy is not teeming with technological life,” Marcy told The Washington Post in February.
Which brings us to sub-explanation number one: The other life that exists isn’t capable of reaching out. This is a popular one.
Earlier this year, NASA’s chief scientist Ellen Stofan boldly predicted that we would find indications of life beyond Earth in the next 10 to 20 years. But what we find won’t be “little green men,” she cautioned at a public panel in April.
“We are talking about little microbes,” she said, according to the Los Angeles Times.
[6 variables that determine if we’re likely to discover an alien civilization]
Another sub-explanation is that they are communicating, but either their signals haven’t reached us or they have and we don’t know how to recognize them.
Maybe, as astronomer Carl Sagan once pointed out, human brains don’t work at the right speed to comprehend an alien message — perhaps they work at a much faster pace than us, and their signals are gone in a blip, or maybe they are much, much slower, and their messages arrive at too sluggish a pace to be perceived as anything other than white noise. Or, as theoretical physicist Michio Kaku has proposed, super-intelligent aliens are out there and our brains are just too primitive to perceive them as such.
A third is that previous intelligent civilizations came and went before humans even arrived on the scene. They may have been annihilated by overpopulation or nuclear warfare or dangerous experiments or deadly disease or any number of other horrifying catastrophes. Any of these would suggest that Hanson’s great filter isn’t somewhere in our past, but rather in our future — that most civilizations destroy themselves eventually and we’re inexorably heading toward our doom.
This, as Oxford University philosopher Nick Bostrom has pointed out, is a chilling scenario, and perhaps a reason to hope that Hawking’s search doesn’t turn up remnants of any ancient alien civilizations.
“The silence of the night sky is golden,” Bostrom wrote.
[Why NASA’s top scientist is sure that we’ll find signs of alien life in the next decade]
A fourth proposal is that intelligent life is out there; it’s just smart enough to stay silent.
Humans have been cavalierly sending signals into space since before we launched the Golden Record on board the Voyager spacecraft in 1977, but it’s possible that’s a dangerous game to play. Perhaps there are vicious predator civilizations out there eager to feed on naive, idiotic species like ourselves, or even one super-advanced civilization that exterminates all competitors once they reach a certain level of intelligence. This is why many scientists — including Sagan, who orchestrated the Golden Record project — have advised against “active SETI,” or sending messages out into the unknown.
“ETI’s [extraterrestrial intelligence] reaction to a message from Earth cannot presently be known,” reads a petition signed by 28 prominent scientists and thought leaders, including Marcy and SpaceX founder Elon Musk. “We know nothing of ETI’s intentions and capabilities, and it is impossible to predict whether ETI will be benign or hostile.”
“Intentionally signaling other civilizations in the Milky Way Galaxy raises concerns from all the people of Earth, about both the message and the consequences of contact,” the petition concludes. “A worldwide scientific, political and humanitarian discussion must occur before any message is sent.”
3. They came, they saw, they conquered (or, uninterested in us puny humans, left us to our own pathetic devices).
Super-intelligent life may have already visited, but before humans were able to document it. They may even have left signs of their presence (ahem, people who believe that aliens built the pyramids). But they weren’t interested in humans for whatever reason — we’re too dumb, too useless, our planet doesn’t have resources they need — so they left Earth behind.
Or, they are here, totally in control, and we just don’t know it. Maybe we are descendants of aliens — given centuries of scientific evidence otherwise, that’s highly unlikely, but hey, you never know. Or maybe the entire concept of physical colonization is hilariously backward to a more advanced civilization, and they’re getting what they want from Earth in other ways. This could also fit with Michio Kaku’s theory that extraterrestrial intelligence operates on a higher plane than our own, limited consciousness.
[Two new exoplanets are more Earth-like than any we’ve found before]
Then there’s the unsettling “Zoo hypothesis,” proposed by researcher John Ball.
“Extraterrestrial intelligent life may be almost ubiquitous,” reads the blunt abstract to Ball’s 1973 paper, published in the journal Icarus. “The apparent failure of such life to interact with us may be understood in terms of the hypothesis that they have set us aside as part of a wilderness area or zoo.”
A bizarre theory, yes, but it’s a big universe out there, and we’ve only just made it to the edges of our solar system. You never know what’s possible.
H/T Tim Urban at WaitButWhy.com
Winston Churchill, British prime minister and one of history’s most influential statesmen, was undoubtedly a man with weighty questions on his mind. How best to save the British Empire? he must have mused. What will the postwar world look like? he surely wondered. But the legendary leader also focused his prodigious mind on less pragmatic questions. For instance: Is there life on other planets?
In fact, in 1939, Churchill penned a lengthy essay on this very topic, which was never published. Besides displaying a strong grasp of contemporary astrophysics and a scientific mind, he came to a breathtaking conclusion: We are probably not alone in the universe. The long-lost piece of Churchilliana has just floated up to the surface again, thanks to an article written by astrophysicist Mario Livio in this week's edition of the journal Nature analyzing Churchill's work.
“With hundreds of thousands of nebulae, each containing thousands of millions of suns, the odds are enormous that there must be immense numbers which possess planets whose circumstances would not render life impossible,” Churchill concluded in his essay. He wrote these words on the eve of World War II—more than half a century before exoplanets were discovered.
Until last year, Churchill's thoughts on the problem of alien life had been all but lost to history. The reason: His 11-page typed draft was never published. Sometime in the late 1950s, Churchill revised the essay while visiting the seaside villa of publisher Emery Reves, but the text still didn't see the light of day. It appears to have languished in the Reves house until Emery's wife Wendy gave it to the U.S. National Churchill Museum during the 1980s.
Last year, the museum’s new director, Timothy Riley, unearthed the essay in the museum's archives. When astrophysicist Mario Livio happened to visit the museum, Riley "thrust [the] typewritten essay" into his hands, Livio writes in Nature. Riley was eager to hear the perspective of an astrophysicist. And Livio, for his part, was floored. “Imagine my thrill that I may be the first scientist to examine this essay,” he writes in Nature.
Churchill did his homework, Livio reports. Though he probably didn't pore over peer-reviewed scientific literature, the statesman seems to have read enough, and spoke with enough top scientists—including the physicist Frederick Lindemann, his friend and later his official scientific adviser—to have had a strong grasp of the major theories and ideas of his time. But that wasn't what left the deepest impression on Livio.
“To me the most impressive part of the essay—other than the fact that he was interested in it at all, which is pretty remarkable—is really the way that he thinks,” Livio says. “He approached the problem just as a scientist today would. To answer his question 'Are we alone in the universe?' he started by defining life. Then he said, 'OK, what does life require? What are the necessary conditions for life to exist?'”
Churchill identified liquid water, for example, as a primary requirement. While he acknowledged the possibility that forms of life could exist dependent on some other liquid, he concluded that “nothing in our present knowledge entitles us to make such an assumption.”
"This is exactly what we still do today: Try to find life by following the water,” Livio says. “But next, Churchill asked 'What does it take for liquid water to be there?' And so he identified this thing that today we call the habitable zone.”
By breaking down the challenge into its component parts, Churchill ended up delving into the factors necessary to create what is now known as the “Goldilocks zone” around a star: that elusive region in which a life-sustaining planet could theoretically exist. In our own solar system, he concluded, only Mars and Venus could possibly harbor life outside of Earth. The other planets don't have the right temperatures, Churchill noted, while the Moon and asteroids lack sufficient gravity to trap gasses and sustain atmospheres.
Turning his gaze beyond our own solar system raised even more possibilities for life, at least in Churchill's mind. “The sun is merely one star in our galaxy, which contains several thousand millions of others,” he wrote. Planetary formation would be rather rare around those stars, he admitted, drawing on a then-popular theory of noted physicist and astronomer James Jeans. But what if that theory turned out to be incorrect? (In fact, it has now been disproven.)
“That's what I find really fascinating,” Livio notes. “The healthy skepticism that he displayed is remarkable.”
Churchill suggested that different planetary formation theories may mean that many such planets may exist which “will be the right size to keep on their surface water and possibly an atmosphere of some sort.” Of that group, some may also be “at the proper distance from their parent sun to maintain a suitable temperature.”
The statesman even expected that some day, “possibly even in the not very distant future,” visitors might see for themselves whether there is life on the moon, or even Mars.
But what was Winston Churchill doing penning a lengthy essay on the probability of alien life in the first place? After all, it was the eve of a war that would decide the fate of the free world, and Churchill was about to become Prime Minister of the United Kingdom.
Such an undertaking was actually quite typical for Churchill, notes Andrew Nahum, Keeper Emeritus at the Science Museum, London, because it reflects both his scientific curiosity and his recurring need to write for money. It was skill with the pen that often supported Churchill and his family's lavish lifestyle (recall that he won the 1953 Nobel Prize for Literature, with a monetary award of 175,293 Swedish Kroner worth about $275,000 today).
“One recent biography is entitled No More Champagne: Churchill And His Money,” Nahum says. “That was a phrase he put into a note to his wife about austerity measures. But he didn't know much about austerity. He liked luxury so he wrote like crazy, both books and articles that his agent circulated widely.”
That’s not to say that Churchill was simply slinging copy about aliens for a paycheck. “He was profoundly interested in the sciences and he read very widely,” notes Nahum, who curated the 2015 Science Museum exhibition “Churchill's Scientists.” Nahum relates the tale of how as Chancellor of the Exchequer, Churchill was once sent a book on quantum physics, and later admitted that it had occupied him for the better part of a day that should have been spent balancing the British budget.
He not only read scientific content voraciously, but wrote on the topic as well. In a 1924 issue of Nash's Pall Mall Magazine, Churchill anticipated the power of atomic weapons. “Might not a bomb no bigger than an orange be found to possess secret power to destroy a whole block of buildings nay, to blast a township at a stroke?” he warned. In 1932, he anticipated the rise of test-tube meat in the magazine Popular Mechanics: “Fifty years hence, we shall escape the absurdity of growing a whole chicken in order to eat the breast or the wing, by growing these parts separately in a suitable medium,” he wrote.
In 1939 he authored three essays, tackling not just extraterrestrial life but the evolution of life on Earth and the popular biology of the human body. Two were published during 1942 by the Sunday Dispatch, Nahum discovered when reading Churchill's papers at the University of Cambridge. It remains a mystery why his thoughts on alien life went unpublished.
In the rediscovered essay, Churchill admits that, because of the great distances between us and other planet-harboring stars, we may never know if his hunch that life is scattered among the vastness of the cosmos is correct. Yet even without proof, Churchill seems to have convinced himself that such a possibility was likely—perhaps by swapping his scientific mind for one more finely attuned to the human condition during the troubled 20th century.
“I, for one, am not so immensely impressed by the success we are making of our civilization here that I am prepared to think we are the only spot in this immense universe which contains living, thinking creatures,” he wrote, “or that we are the highest type of mental and physical development which has ever appeared in the vast compass of space and time.”
Seventy-five years after Churchill's bold speculations, there's still no proof that life exists on other worlds. But, as was often the case, his analysis of our own still seems prescient.
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