Dec 22, 0212
It’s difficult to not be pessimistic when considering humanity’s future prospects. Many people would agree that it’s more likely than not that we’ll eventually do ourselves in.
And in fact, some astrobiologists theorize that all advanced civilizations hit the same insurmountable developmental wall we have. They call it the Great Filter. It’s a notion that’s often invoked to explain why we’ve never been visited by extraterrestrials.
But there is another possible reason for the celestial silence. Yes, the Great Filter exists, but we’ve already passed it. Here’s what this would mean. Before we can get to the Great Filter hypothesis we have to appreciate what the Fermi Paradox is telling us.
The so-called “Great Silence” is the contradictory and counter-intuitive observation that we have yet to see any evidence for the existence of aliens. The size and age of the Universe suggests that many technologically advanced extraterrestrial intelligences (ETIs) ought to exist — but this hypothesis seems inconsistent with the lack of observational evidence to support it.
Despite much of what popular culture and sci-fi would lead us to believe, the fact that we haven’t been visited by ETIs is disturbing. Our galaxy is so ancient that it could have been colonized hundreds, if not thousands, of times over by now. Even the most conservative estimates show that we should have already made contact either directly or indirectly (such as from dormant Bracewell communication probes).
The Fermi Paradox and the Great Silence
Some skeptics dismiss the Fermi Paradox by suggesting that ETI’s have come and gone, or that they wouldn’t find us interesting.
Unfortunately, most solutions to the FP don’t hold for a number of reasons, including the realization that a colonization wave of superintelligent aliens would likely rework the fabric of all life in the cosmos (e.g. uplifting), or that these solutions are sociological in nature (i.e. they lack scientific rigor and don’t necessarily apply to the actions of all advanced civilizations; all it would take is just one to think and behave differently — what astrobiologists refer to as the non-exclusivity problem).
There have been many attempts to resolve the Fermi Paradox, including the herculean attempt by Stephen Webb in his book, Fifty Solutions to Fermi’s Paradox and the Problem of Extraterrestrial Life.
But one solution stands out from the others, mostly on account of its brute elegance: The Great Filter.
Conceived in 1998 by Robin Hanson, the GF is the disturbing suggestion that there is some kind of absurdly difficult step in the evolution of life — one that precludes it from becoming interstellar.
And like the immutable laws of the universe, the GF is a stumbling block that holds true across the board; if it applies here on Earth, it applies everywhere.
The Great Filter
Many look upon the GF as evidence that we’ll destroy ourselves in the future. The basic idea is that every civilization destroys itself before developing space-faring technologies. Hence the empty cosmos. Given our own trajectory and the ominous presence of apocalyptic weapons, this scenario certainly seems plausible. We’re not even close to going interstellar, yet we’re certainly capable of self-annihilation. But that doesn’t mean this interpretation of the GF is the correct one. Rather, it’s quite possible that human civilization has already passed the Great Filter. Should this be the case, it would be exceptionally good news. Assuming there’s no other filter awaiting us in the future, it means we might be the first and only intelligent civilization in the Milky Way.
It’s a possibility, however, that demands explanation. If the filter is behind us, what was it? And how did we manage to get past it? Interestingly, there are some excellent candidates.
First and foremost there’s the Rare Earth Hypothesis (REH), the suggestion that the emergence of life was extremely improbable for a confluence of reasons. The theory essentially suggests that we hit the jackpot here on Earth.
This argument, which was first articulated by geologist Peter Ward and astrobiologist Donald E. Brownlee, turns the whole Copernican Principle on its head. Instead of saying that we’re nothing special or unique, the REH implies the exact opposite — that we are freakishly special and unique. What we see here on Earth in this solar system and in this part of the Galaxy may be a remarkable convergence of highly unlikely factors — factors that have resulted in a perfect storm of conditions suitable for the emergence of complex life.
It’s important to note that Ward and Brownlee are not implying that it’s one or two conditions that can explain habitability, but rather an entire array of happy accidents. For example, stars might have to be of the right kind (including adequate metallicity and safe distance from dangerous celestial objects), and planets must be in a stable orbit with a large moon. Other factors include the presence of gas giants, plate tectonics, and many others. But even with all the right conditions, life was by no means guaranteed. It’s quite possible that the Great Filter involved the next set of steps: the emergence of life and its ongoing evolution.
Indeed, in addition to all the cosmological and chemical prerequisites for life, there were at least three critical stages that could all be considered candidates for the Great Filter: (1) the emergence of reproductive molecules (abiogenesis and the emergence of RNA), (2) simple single-celled life (prokaryotes), and (3) complex single-celled life (eukaryotes).
Chemists and biologists are still not entirely sure how the first self-replicating molecules came into existence. Unlike its big brother, DNA, RNA is a single-stranded molecule that has a much shorter chain of nucleotides. Moreover, it usually needs DNA to reproduce itself — which would have been a problem given the absence of DNA in those early days.
That said, scientists know that RNA is capable of reproducing through autocatalysis. It does this by storing information similar to DNA, which allows it to become its own catalyst (a ribosome). This so-called RNA World Modelsuggests that RNA can function as both a gene and an enzyme — a pre-DNA configuration that eventually became the basis for all life.
Given that we’ve never detected life elsewhere, it’s difficult to know how difficult this initial step was. But that said, this form of life emerged super-early in the Earth’s history — about a billion years after its formation, and immediately after the cooling of rocks and the emergence of oceans.
But what we do know is that the next few steps — the leap from single-celled life to complex single-celled life — was exceedingly difficult, if not highly improbable. The process of copying a genetic molecule is extremely complex, involving the perfect configuration of proteins and other cellular components.
The improbability of life
Here’s how it likely happened: Once a self-replicating molecule emerged, the presence of RNA allowed for the formation of protobionts, a theoretic precursor to prokaryotic cells. These tightly bound bundles of organic molecules contained RNA within their membranes — which could have evolved into proper prokaryotic cells. And here’s where it gets interesting. After the formation of prokaryotes — about 3.5 billion years ago — nothing changed in the biological landscape for the next 1.8 billion years. Life in this primitive form was completely stuck. Imagine that — no evolution for almost two billion years. It was only after the endosymbiosis of multiple prokaryotes that complex single-cell life finally emerged — a change that was by no means guaranteed, and possibly unlikely.
And it’s this highly improbable step, say some scientists, that’s the Great Filter. Everything that happened afterward is a complete bonus.
Now that said, there may have been other filters as well. These could include the emergence of terrestrial organisms, hominids, and various civilizational stages, like the transition from stone age culture to agricultural to industrial. But unlike the first primordial stages already discussed, these are porous filters and not terribly unlikely.
So, if the GF is behind us, it would do much to explain the Fermi Paradox and the absence of extraterrestrial influence on the cosmos. Should that be the case, we may very well have a bright future ahead of us. The Milky Way Galaxy is literally ours for the taking, our future completely open-ended.
More filters ahead?
But before we jump to conclusions, it’s only fair to point out that we’re not out of the woods yet. There could very well be another GF in the future — one just as stingy as the filters of our past. The universe, while giving the appearance of bio-friendliness, may in reality be extremely hostile to intelligent life.
Before Its News March 16, 2011
If the latest theory of Tom Weiler and Chui Man Ho is right, the Large Hadron Collider – the world’s largest atom smasher that started regular operation last year – could be the first machine capable of causing matter to travel backwards in time.“Our theory is a long shot,” admitted Weiler, who is a physics professor at Vanderbilt University, “but it doesn’t violate any laws of physics or experimental constraints.” One of the major goals of the collider is to find the elusive Higgs boson: the particle that physicists invoke to explain why particles like protons, neutrons and electrons have mass. If the collider succeeds in producing the Higgs boson, some scientists predict that it will create a second particle, called the Higgs singlet, at the same time. According to Weiler and Ho’s theory, these singlets should have the ability to jump into an extra, fifth dimension where they can move either forward or backward in time and reappear in the future or past. “One of the attractive things about this approach to time travel is that it avoids all the big paradoxes,” Weiler said. “Because time travel is limited to these special particles, it is not possible for a man to travel back in time and murder one of his parents before he himself is born, for example. However, if scientists could control the production of Higgs singlets, they might be able to send messages to the past or future.” The test of the researchers’ theory will be whether the physicists monitoring the collider begin seeing Higgs singlet particles and their decay products spontaneously appearing. If they do, Weiler and Ho believe that they will have been produced by particles that travel back in time to appear before the collisions that produced them. Weiler and Ho’s theory is based on M-theory, a “theory of everything.” A small cadre of theoretical physicists have developed M-theory to the point that it can accommodate the properties of all the known subatomic particles and forces, including gravity, but it requires 10 or 11 dimensions instead of our familiar four. This has led to the suggestion that our universe may be like a four-dimensional membrane or “brane” floating in a multi-dimensional space-time called the “bulk.” According to this view, the basic building blocks of our universe are permanently stuck to the brane and so cannot travel in other dimensions. There are some exceptions, however. Some argue that gravity, for example, is weaker than other fundamental forces because it diffuses into other dimensions. Another possible exception is the proposed Higgs singlet, which responds to gravity but not to any of the other basic forces. When a pair of protons collide in the Large Hadron Collider, the resultant explosion may create a special type of particle, called a Higgs singlet, that is capable of traveling forward and back in time. It would do so by leaving familiar three-dimensional space to travel in an extra dimension. Weiler began looking at time travel six years ago to explain anomalies that had been observed in several experiments with neutrinos. Neutrinos are nicknamed ghost particles because they react so rarely with ordinary matter: Trillions of neutrinos hit our bodies every second, yet we don’t notice them because they zip through without affecting us. Weiler and colleagues Heinrich Päs and Sandip Pakvasa at the University of Hawaii came up with an explanation of the anomalies based on the existence of a hypothetical particle called the sterile neutrino. In theory, sterile neutrinos are even less detectable than regular neutrinos because they interact only with gravitational force. As a result, sterile neutrinos are another particle that is not attached to the brane and so should be capable of traveling through extra dimensions. Weiler, Päs and Pakvasa proposed that sterile neutrinos travel faster than light by taking shortcuts through extra dimensions. According to Einstein’s general theory of relativity, there are certain conditions where traveling faster than the speed of light is equivalent to traveling backward in time. This led the physicists into the speculative realm of time travel. Ideas impact science fiction In 2007, the researchers, along with Vanderbilt graduate fellow James Dent, posted a paper titled “Neutrino time travel” that generated a considerable amount of buzz. Their ideas found their way into two science fiction novels. Final Theory by Mark Alpert, which was described in the New York Times as a “physics-based version of The Da Vinci Code,” is based on the researchers’ idea of neutrinos taking shortcuts in extra dimensions. Joe Haldeman‘s novel The Accidental Time Machine is about a time-traveling MIT graduate student and includes an author’s note that describes the novel’s relationship to the type of time travel described by Dent, Päs, Pakvasa and Weiler.
Radio guest Patrick Henningsen is a writer, pr/communications consultant and Managing Editor at 21st Century Wire.Contact: firstname.lastname@example.org