Galaxy Simulations Offer a New Solution to the Fermi Paradox


Astronomers claim in a new paper that star motions should make it easy for civilizations to spread across the galaxy, but still we might find ourselves alone.

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As far as anyone knows, we have always been alone. It’s just us on this pale blue dot, “home to everyone you love, everyone you know, everyone you ever heard of,” as Carl Sagan so memorably put it. No one has called or dropped by. And yet the universe is filled with stars, nearly all those stars have planets, and some of those planets are surely livable. So where is everybody?

The Italian physicist Enrico Fermi was purportedly the first to pose this question, in 1950, and scientists have offered a bounty of solutions for his eponymous paradox since. One of the most famous came from Sagan himself, with William Newman, who postulated in a 1981 paper that we just need patience. Nobody has visited because they’re all too far away; it takes time to evolve a species intelligent enough to invent interstellar travel, and time for that species to spread across so many worlds. Nobody is here yet.

Other researchers have argued that extraterrestrial life might rarely become space-faring (just as only one species on Earth ever has). Some argue that tech-savvy species, when they arise, quickly self-destruct. Still others suggest aliens may have visited in the past, or that they’re avoiding us on purpose, having grown intelligent enough to be suspicious of everyone else. Perhaps the most pessimistic answer is a foundational paper from 1975, in which the astrophysicist Michael Hart declared that the only plausible reason nobody has visited is that there really is nobody out there.

Now comes a paper that rebuts Sagan and Newman, as well as Hart, and offers a new solution to the Fermi paradox that avoids speculation about alien psychology or anthropology.

The research, which is under review by The Astrophysical Journal, suggests it wouldn’t take as long as Sagan and Newman thought for a space-faring civilization to planet-hop across the galaxy, because the movements of stars can help distribute life. “The sun has been around the center of the Milky Way 50 times,” said Jonathan Carroll-Nellenback, an astronomer at the University of Rochester, who led the study. “Stellar motions alone would get you the spread of life on time scales much shorter than the age of the galaxy.” Still, although galaxies can become fully settled fairly quickly, the fact of our loneliness is not necessarily paradoxical: According to simulations by Carroll-Nellenback and his colleagues, natural variability will mean that sometimes galaxies will be settled, but often not — solving Fermi’s quandary.

The question of how easy it would be to settle the galaxy has played a central role in attempts to resolve the Fermi paradox. Hart and others calculated that a single space-faring species could populate the galaxy within a few million years, and maybe even as quickly as 650,000 years. Their absence, given the relative ease with which they should spread, means they must not exist, according to Hart.

Sagan and Newman argued it would take longer, in part because long-lived civilizations are likelier to grow more slowly. Faster-growing, rapacious societies might peter out before they could touch all the stars. So maybe there have been a lot of short-lived, fast-growing societies that wink out, or a few long-lived, slowly expanding societies that just haven’t arrived yet, as Jason Wright of Pennsylvania State University, a coauthor of the new study, summarized Sagan and Newman’s argument. But Wright doesn’t agree with either solution.

“That conflates the expansion of the species as a whole with the sustainability of individual settlements,” he said. “Even if it is true for one species, it is not going to be this iron-clad law of xenosociology where if they are expanding, they are necessarily short-lived.” After all, he noted, life on Earth is robust, “and it expands really fast.”

 

David Kaplan explores the best ways to search for alien life on distant planets.

Video: David Kaplan explores the best ways to search for alien life on distant planets.

Filming by Tom Hurwitz and Richard Fleming. Editing and motion graphics by Ryan Griffin. Other graphics and images from NASA, the European Southern Observatory and Creative Commons. Music by Podington Bear.

In their new paper, Carroll-Nellenback, Wright and their collaborators Adam Frank of Rochester and Caleb Scharf of Columbia University sought to examine the paradox without making untestable assumptions. They modeled the spread of a “settlement front” across the galaxy, and found that its speed would be strongly affected by the motions of stars, which previous work — including Sagan and Newman’s — treated as static objects. The settlement front could cross the entire galaxy based just on the motions of stars, regardless of the power of propulsion systems. “There is lots of time for exponential growth basically leading to every system being settled,” Carroll-Nellenback said.

But the fact that no interstellar visitors are here now — what Hart called “Fact A” — does not mean they do not exist, the authors say. While some civilizations might expand and become interstellar, not all of them last forever. On top of that, not every star is a choice destination, and not every planet is habitable. There’s also what Frank calls “the Aurora effect,” after Kim Stanley Robinson’s novel Aurora, in which settlers arrive at a habitable planet on which they nonetheless cannot survive.

When Carroll-Nellenback and his coauthors included these impediments to settlement in their model and ran many simulations with different star densities, seed civilizations, spacecraft velocities and other variations, they found a vast middle ground between a silent, empty galaxy and one teeming with life. It’s possible that the Milky Way is partially settled, or intermittently so; maybe explorers visited us in the past, but we don’t remember, and they died out. The solar system may well be amid other settled systems; it’s just been unvisited for millions of years.

Anders Sandberg, a futurist at the University of Oxford’s Future of Humanity Institute who has studied the Fermi paradox, said he thinks spacecraft would spread civilizations more effectively than stellar motions. “But the mixing of stars could be important,” he wrote in an email, “since it is likely to spread both life, through local panspermia” — the spread of life’s chemical precursors — “and intelligence, if it really is hard to travel long distances.”

Frank views his and his colleagues’ new paper as SETI-optimistic. He and Wright say that now we need to look harder for alien signals, which will be possible in the coming decades as more sophisticated telescopes open their eyes to the panoply of exoplanets and begin glimpsing their atmospheres.

“We are entering an era when we are going to have actual data relevant to life on other planets,” Frank said. “This couldn’t be more relevant than in the moment we live.”

Seth Shostak, an astronomer at the SETI Institute who has studied the Fermi paradox for decades, thinks it is likely to be explained by something more complex than distance and time — like perception.

Maybe we are not alone and have not been. “The click beetles in my backyard don’t notice that they’re surrounded by intelligent beings — namely my neighbors and me,” Shostak said, “but we’re here, nonetheless.”

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Is Virtual Reality the Surprising Solution to the Fermi Paradox?


“If the transcension hypothesis is correct, inner space, not outer space, is the final frontier for universal intelligence. Our destiny is density.”

–John Smart

Only decades into our “age of cosmology” — the moment when we earned the technological rights to peer deep into our cosmic home — we’ve learned that we live in a mega-palace of a universe. And we’ve also found something odd. We seem to be the only ones home! Where are the aliens? Was it something we said?

Within just a single generation, powerful telescopes, satellites, and space probes have given us tools to explore the structure of our universe. And the more we find; the more we discover how fine-tuned it could be for life. At least in our own solar system, organic compound-glazed comets drift everywhere. Some scientists suggest that one of these life-triggering ice balls crashed into Earth billions of years ago, delivering the conditions for chemistry and biology to take root. If the rest of the universe is similarly structured, we should be inside a life-spawning factory of a universe.

Stars scattered like grains of sand in the Andromeda galaxy.

Just consider the mind-boggling numbers.

Even the most conservative NASA estimates say our universe has 500 billion billion stars like our own, and orbiting those suns are another 100 billion billion Earth-like planets. That is 100 habitable planets for every grain of sand on Earth. That’s trillions of opportunities for some other planet to grow life.

For argument’s sake, if even just a tenth of a percent of those planets capable of supporting life harbored some version of it, then there would be one million planets with life in the Milky Way Galaxy alone. A few might even have developed civilizations like our own, and cosmically thinking, if even just a handful of alien civilizations have advanced beyond our current level of technological progress, humanity should be waking up to a universe like the world of Star Trek.

But so far, no Ferengi, Klingons, Vulcans, Romulans—nobody.

Enrico Fermi, an Italian physicist, pointed out all of this weirdness in an observation that was later named for him: “the Fermi Paradox.” The paradox highlights the contradiction between the high probability that life would emerge in our universe, and the utter lack of evidence that advanced life exists anywhere else.

And it’s not just SETI signals we’re after — the paradox highlights that some advanced civilization that predates us has had enough time to fill our galaxy with spacecraft and other forms of blinking lights.

So, it should seem strikingly weird that we haven’t spotted anyone else.

There are no shortage of theories seeking to account for the Fermi Paradox. Entire lists of would-be explanations exist and if you have the time to spend down that rabbit hole (it’s a fun one), a recommended brain vacation is this excellent summary at Wait But Why.

But let’s focus on another emerging contender of a theory — virtual reality is to blame.

To address the Fermi Paradox, futurist John Smart proposes the fascinating “transcension hypothesis” theorizing that evolutionary processes in our universe might lead all advanced civilizations towards the same ultimate destination; one in which we transcend out of our current space-time dimension into virtual worlds of our own design.

According to Smart, as a species moves into its technologically advanced stage of progress, it develops virtual environments that exist on computers infinitely smaller than the ones we use today. Advanced species don’t colonize outer space — an idea they’d find archaic — but instead colonize inner space.

Smart proposes that our current efforts to explore parts of our solar system and beyond are just the adolescent stages of a technologically young species. We may continue to send space probes, satellites, and even courageous members of our own species into parts of our galaxy, but eventually those efforts are overwhelmed by the allure of infinite possibilities inside worlds of our own creation.

gargantua-black-hole-1Our virtual future may lie in “black-hole-like” environments that our computationally advanced descendants will build.

Computers of 40 years ago were the size of buildings, yet today we carry far more powerful ones in our pocket. Our tendencies to compress computation into smaller and smaller environments leads Smart to propose that eventually we’ll create near-infinitely small computers far more powerful than today’s.

How these infinitely small computers function is still a matter of theoretical physics and computer science, but Smart points out that there is a “vast untapped scale” of reality below the level of the atom far more broad than the plane of reality we fleshy pieces of biology inhabit. Inner space engineering, as Smart calls it, may take place in the femtoscales of reality currently out of reach by today’s tools of technology. Eventually Smart theorizes that an advanced species may even harness the spooky weirdness of black hole physics to harness their event horizons for computational density that could process entire universes of virtual realities.

If recent advancements in computing make the transcension hypothesis a little more palatable, the recent and sudden wave of progress in virtual reality adds a touch more plausibility. And combining the two: Perhaps, it’s reasonable to assume that over time, our virtual worlds will become indistinguishable from our current reality.

Soon, we won’t visit the Internet from the glass window of our computer screens, but rather walk around inside it as a physical place. Philip Rosedale, the creator of Second Life, recently announced plans for a bold new virtual universe with a potential physical game map as large as the landmass of Earth. Essentially, he’ll create a virtual world with its own laws of physics, and once he’s pressed play, a newly formed universe will have its own “let there be light” creation moment.

Where we go from there will be stunning to watch.

As we continue our plunge into virtual spaces, the validity of the transcension hypothesis will come into sharper focus. If technology trends toward a world of microscopic computers with infinitely complex realities inside, this might explain why we can’t see any alien neighbors. They’ve left us behind for the digital wormholes of their own design.

Of course, there are holes to be poked in any far-reaching theory about our place in the cosmos, and for now much of this speculating requires generalized conclusions based on a limited understanding of reality. We don’t have enough data yet, and for now we’re settled into the discomfort of “we just don’t know.”

In the meantime, and until science can catch up with our imagination — it’s fascinating to ponder a future living inside virtual realities of our own choosing.

Of course, it’s also possible that we’re already there.

Earth Bloomed Early: A Fermi Paradox Solution?


Innumerable Earth-Like Planets

An artist’s impression shows innumerable Earth-like planets to come into existence over the next trillion years in the universe.

What Is the Fermi Paradox?


The Fermi Paradox seeks to answer the question of where the aliens are. Given that our star and Earth are part of a young planetary system compared to the rest of the universe — and that interstellar travel might be fairly easy to achieve — the theory says that Earth should have been visited by aliens already.

As the story goes, Enrico Fermi (an Italian physicist) first came out with the theory with a casual lunchtime remark in 1950. The implications, however, have had extraterrestrial researchers scratching their heads in the decades since.

“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) said on its website.

Strange Discovery on Titan Leads to Speculation of Alien Life

“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.”

Plentiful planets

It is true that the universe is incredibly vast and old. One estimate says the universe spans 92 billion light-years in diameter (while growing faster and faster). Separate measurements indicate it is about 13.82 billion light-years old. At first blush, this would give alien civilizations plenty of time to propagate, but then they would have a cosmic distance barrier to cross before getting too far into space.

The sheer number of planets that we have found outside of our solar system, however, indicates that life could be plentiful. A November 2013 study using data from the Kepler Space Telescope suggested that one in five sun-like stars has an Earth-size planet orbiting in the habitable region of its star, the zone where liquid water would be possible. That zone is not necessarily an indication of life, as other factors, such as the planet’s atmosphere, come into play. Further, “life” could encompass anything from bacteria to starship-sailing extraterrestrials.

A few months later, Kepler scientists released a “planet bonanza” of 715 newly discovered worlds, pioneering a new technique called “verification by multiplicity.” The theory essentially postulates that a star that appears to have multiple objects crossing its face or tugging at it would have planets, as opposed to stars. (A multiple star system at such close proximity would destabilize over time, the technique postulates.) Using this will accelerate the pace of exoplanet discovery, NASA said in 2014.

Our understanding of astrobiology (life in the universe) is just at a beginning, however. One challenge is these exoplanets are so far away that it is next to impossible for us to send a probe out to look at them. Another obstacle is even within our own solar system, we haven’t eliminated all the possible locations for life. We know from looking at Earth that microbes can survive in extreme temperatures and environments, giving rise to theories that we could find microbe-like life on Mars, the icy Jovian moon Europa, or perhaps Saturn’s Enceladus or Titan.

All of this together means that even within our own Milky Way Galaxy — the equivalent of the cosmic neighborhood — there should be many Earth-size planets in habitable zones that could host life. But what are the odds of these worlds having starfarers in their bounds? [Countdown: 13 Ways to Hunt Intelligent Aliens]

Life: plentiful, or rare?

The odds of intelligent life are estimated in the Drake Equation, which seeks to figure out the number of civilizations in the Milky Way that seek to communicate with each other. In the words of SETI, the equation (written as N = R* • fp • ne • fl • fi • fc • L) has the following variables:

N = The number of civilizations in the Milky Way galaxy whose electromagnetic emissions are detectable.

R* = The rate of formation of stars suitable for the development of intelligent life.

fp = The fraction of those stars with planetary systems.

ne = The number of planets, per solar system, with an environment suitable for life.

fl = The fraction of suitable planets on which life actually appears.

fi = The fraction of life bearing planets on which intelligent life emerges.

fc = The fraction of civilizations that develop a technology that releases detectable signs of their existence into space.

L = The length of time such civilizations release detectable signals into space.

None of these values are known with any certainty right now, which makes predictions difficult for astrobiologists and extraterrestrial communicators alike.

There is another possibility that would dampen the search for radio signals or alien spacecraft, however: that there is no life in the universe besides our own. While SETI’s Frank Drake and others suggested there could be 10,000 civilizations seeking communications in the galaxy, a 2011 study later published in the Proceedings of the National Academy of Sciences suggested that Earth could be a rare bird among planets.

It took at least 3.5 billion years for intelligent life to evolve, the theory by Princeton University researchers David Spiegel and Edwin Turner said, which indicates it takes a lot of time and luck for this to happen.

Other explanations for the Fermi paradox include extraterrestrials “spying” on Earth, ignoring it altogether, visiting it before civilization arose, or visiting it in a way that we can’t detect.