Dis-closures can be distracting.
The question of import to me seems to be less "Are we alone" and more "How do we get along." Whatever is sharable is the information that gets spun into the web of life, giving us more stuff that dreams are made of.
Everybody is receiving notice regarding the upcoming CSETI disclosure, and listening for the bells and whistles of it like it was the end of a season ball game. Well, I'm not going to play ball in the dark.
First of all, when I look up at the night sky, I do not feel "alone" or even a need to conquer rationally what all is up there. I see a vast screen of a great movie. The star dust matter in my physical being spins as they spin, kind of a quantum knowingness that, when heard, speaks volumes about history and science and biogenesis in languages all their own. Hmmm. Maybe it's a different drummer thumping out in star beats; not the sound of some boys whacking fences in a vacant lot behind the power station. Course, you could tell those boys to quit arguing, or stop whacking the fence, get out of the vacant lot, go play in an open field somewhere, play until after the sun sets when you can't see the dumb ball anymore. Then look up and see the stars. Feeling "alone" is tantamount to not being able to get along with others, whether alien or human. I think some of us learned how to get along better after we couldn't see the ball anymore.
The key to harmony lies in the variation of chance that is choice. In a harmonic relation, these two chords smack of the same logic. The following discussion of DNA codes and information and the ultimate conspiracy is interesting in light of the pending ball game. It also provides some metaphorical insight into the nature of information and anti-information (my odd concept of dis-information). Some 4 little codes, those.
Is anybody out there?
By Paul Davies
Is life inevitable? Maybe, just maybe, but we need a whole new branch of science to know one way or the other.
Are we alone in the Universe? When I was a student in the 1960s I was convinced that the answer was "no". This put me at odds with the prevailing scientific view. The orthodox position at that time was summed up by the French biologist Jacques Monod when he wrote of the "unfeeling immensity of the Universe", and declared that we had emerged from it alone and by pure chance. It was an opinion echoed by many other leading scientists. American palaeontologist George Gaylord Simpson, one of the giants of modern biology, described attempts to search for life elsewhere in the Universe--especially intelligent life--as "a gamble of the most adverse odds in history".
Thirty years on, there has been a remarkable U-turn. Take Christian de Duve who, like Monod, is a Nobel prizewinning biologist. In his book Vital Dust, published in 1995, de Duve suggests that life is "a cosmic imperative" bound to arise wherever conditions allow. His stance is shared by many at NASA, whose astrobiology programme is dedicated to seeking out alien life forms. Meanwhile, a team of enthusiastic astronomers sponsored by the SETI Institute in California is sweeping the sky with radio telescopes in the hope of stumbling across a message from ET. Journalists, Hollywood producers and schoolchildren likewise assume that the Universe is teeming with life.
This shift in opinion has little to do with advances in understanding. True, we now have concrete evidence of planets in other star systems, but most astronomers believed all along that they were there. Biochemists have inched forward in their attempts to synthesise the building blocks of life, but creating life in a test tube remains a distant dream. We may soon discover evidence for past life on Mars, but if so it will almost certainly have arrived there from Earth, in rocks blasted off our planet by large asteroid impacts (New Scientist, 12 September 1998, p 24).
Yet the question of whether life is widespread in the Universe is important. Researchers are making plans to search for Earth-like planets around other stars, chiefly because they hope to find alien life there (see p 32). The assumption that life should arise inevitably given Earth-like conditions is known as biological determinism. But it is hard to find any support for it in the known laws of physics, chemistry or biology. If we relied solely on these laws to explain the workings of the Universe, it would be reasonable to conclude like Monod that life can only have arisen by sheer good luck--and that it is therefore exceedingly unlikely to be found elsewhere. But those hoping to encounter aliens need not despair: an exciting new field of research may yet justify the theory of biological determinism, and thereby boost our chances of finding neighbours somewhere in the cosmos.
The idea of biological determinism received a fillip in 1953, when Harold Urey and Stanley Miller at the University of Chicago tried to recreate in a test tube what they believed to be the conditions of primeval Earth. They found that amino acids--the building blocks of proteins--were part of the chemical sludge formed when electricity was discharged through a mixture of gaseous methane, ammonia, water vapour and hydrogen. The Miller-Urey experiment was hailed as the first step towards the creation of life in the laboratory: many chemists envisaged "destination life" to lie at the end of a long road down which a chemical soup zapped with energy would be inexorably conveyed by the passage of time.
But this idea did not stand up to scrutiny. Making the building blocks of life is easy--amino acids have been found in meteorites and even in outer space. But just as bricks alone don't make a house, so it takes more than a random collection of amino acids to make life. Like house bricks, the building blocks of life have to be assembled in a very specific and exceedingly elaborate way before they have the desired function. To form proteins, many amino acids must link together in long chains in the right order. In energy terms that is an "uphill" process.
In itself this is not a problem as there were plentiful energy sources on the early Earth. The problem is that simply throwing energy willy-nilly at amino acids will not create delicate chain molecules with highly specific sequences, but a tarry mess--in the same way that putting a stick of dynamite under a pile of bricks won't make a house. Somehow the energy has to be fed into the system in a contrived and particular manner. In a living organism this step is under the control of the cell's molecular machinery, with its intricate specifications, but in a jumbled prebiotic chemical soup, the amino acids would have to take pot luck. So while amino acids are written into the laws of nature, large and highly specialised molecules such as proteins are certainly not.
We now know that the secret of life lies not with the chemical ingredients as such, but with the logical structure and organisational arrangement of the molecules. So DNA is a genetic databank, and genes are instructions for making customised proteins and, indirectly, other biological molecules. Like a supercomputer, life is an information-processing system, which implies a special sort of organised complexity. It is the information content, or software, of the living cell that is the real mystery, not the hardware components.
Nothing better illustrates the computational prowess of life than the genetic code. All known life is based on a deal struck between nucleic acids and proteins--two classes of molecule that from a chemical point of view are scarcely on nodding terms. The nucleic acids DNA and RNA store instructions, and proteins do most of the work. Together these molecules perform life's many miracles, but on their own they are helpless. To manufacture proteins, nucleic acids employ a clever intermediary to form a coded information channel. It works like this. DNA, the famous double helix, is built like a ladder with four different kinds of rung. The information is stored in the sequences of these rungs, just as an instruction manual records information in sequences of letters. Proteins are built from 20 different amino acids, and the right protein is made only if the amino acids are linked together in the right order.
To translate from the four-letter alphabet used by DNA into the twenty-letter system used by proteins, all Earth life uses the same code. The key question when it comes to the inevitability--or otherwise--of life is how this ingenious system of coding emerged? How did stupid atoms spontaneously write their own software, and where did the very peculiar form of information needed to get the first living cell up and running come from?
Nobody knows, but scientists have traditionally divided into two camps on the issue. In one group are those who believe it all happened by chance--that life is the result of a stupendous chemical fluke. That was Monod's view. It is easy to work out the odds against a random chemical mixture just happening to shuffle the appropriate molecules into the elaborate arrangement needed. The numbers are breathtakingly huge. If life as we know it arose by chance, it will have happened only once in the observable Universe.
By contrast, biological determinists assume that chance is secondary, and that the right sorts of molecule obligingly form as a result of the laws of nature. American biogenesis pioneer Sidney Fox, for example, claimed that chemistry prefers to link up amino acids in precisely the right combinations to make them biologically functional. If so, it is as if there is an in-built bias--even a conspiracy--in nature to create life-encouraging substances. But is it credible that the laws of physics and chemistry contain a blueprint for life? How would the crucial information content of life be encoded in those laws?
To address this question, we need to think more carefully about the nature of the information that underpins living things. One important observation is that a structure that is rich in information tends to lack patterns. This property is illustrated most clearly by a branch of mathematics known as algorithmic information theory, which seeks to quantify the complexity of information by treating it as the output of a computer program, or algorithm. Consider the binary sequence 10101010101010101010 . . . This can be generated by the simple command "Print 10 n times." The input instructions are far shorter than the output sequence, reflecting the fact that the output contains a repeating pattern, which is easy to describe compactly. For this reason, the output has very little information content. By contrast, an apparently random sequence such as 110101001010010111. . . cannot be condensed into a simple set of instructions, so it has a high information content. If the job of DNA is to store information efficiently, it had better not contain too many patterns in the sequence of "rungs", since patterns represent informational redundancy. Biochemists confirm this expectation. The genomes of organisms that have been sequenced so far mostly look like random jumbles of the four constituent letters.
The higgledy-piggledy nature of genome sequences runs counter to biological determinism. The laws of physics can be used to predict ordered structures, but not random ones. A crystal, for instance, is simply a regular array of atoms with a periodic structure, like the repeating binary sequence given above, and is thus almost devoid of information. The construction of crystals is built into the laws of physics, as their periodic forms are determined by the mathematical symmetries inherent in those laws. But the random sequences of amino acids in proteins, or the series of "rungs" in the DNA ladder, cannot be "in" the laws of physics, any more than houses are.
Nor can it be "in" the laws of chemistry. A direct illustration of this fact comes from examining the structure of DNA. Each rung of the ladder is made up of two segments, which couple together snugly like a lock and key. Ultimately, chemistry determines the nature of the bonds that hold together the segments, and also the forces that attach them to the sides of the ladder. However, there are no chemical bonds between successive rungs. Chemistry doesn't care about the order of the rungs, and life is free to change them on a whim. Just as the sequence of letters in an instruction manual is independent of the chemistry of the paper and ink, so the "letters" in DNA--which make up the information--are independent of the chemical properties of nucleic acid. It is this ability of life to free itself from the strictures of chemistry that bestows upon it such power and versatility. Biological determinism would imply a chemical straitjacket that would serve only to inhibit, not enhance, biological creativity.
If life represents an escape from chemistry, we cannot appeal to chemistry to explain life. But where else might an explanation lie? Life is ultimately about complex information processing, so it makes sense to seek a solution in the realm of information theory and complexity theory. Since biological information is not encoded in the laws of physics and chemistry (at least as currently known), where does it come from? There seems to be agreement that information cannot come into existence spontaneously (except perhaps in the big bang), so the information content of living systems must somehow originate in their environment. Although there is no known law of physics able to create information from nothing, there might be some sort of principle that could explain how information can be garnered from the environment and accumulated in macromolecules.
One way to do this is by Darwinian evolution. Life on Earth started with simple organisms possessing short genomes with a relatively low information content. More complex organisms have longer genomes storing more information. The added information has flowed from the environment into the genomes by the process of natural selection: whenever a selection among alternative genomes is made--according to the degree of "fitness" they confer on their owners--information is gained. So Darwinism can explain how organisms acquire information. But Darwinism kicks in only when life is already under way. How can we appeal to natural selection in the prebiotic phase?
Some biochemists believe that a form of molecular Darwinism is the answer. They envisage replicating molecules in some sort of chemical soup. Although bare replicating molecules may not satisfy most people's intuitive definition of life, they can still undergo a type of Darwinian evolution if they are subject to variation and selection. Proponents of this Darwinism-all-the-way-down theory suppose that the first replicator molecule was simple enough to form purely by chance.
The trouble is that the only experience we have of replicating molecules is of those used by life. It is extremely unlikely that DNA would form by chance. Even its simpler cousin, RNA, is hard to make in long enough strands to be biologically potent. And shorter nucleic acid molecules tend to make more errors when replicating. If the error rate gets too high, information leaks away faster than selection can inject it, and evolution grinds to a halt. Far from accumulating information, an error-prone molecule will shed it.
So for molecular Darwinism to work, nature must obligingly provide replicators simple enough to form by chance, deft enough to replicate accurately and with a huge range of variants--which are also good replicators--for selection to act upon. These need not be nucleic acids, but to explain life as we know it they would eventually have to make nucleic acids and hand over the replicating function to them. In effect, molecular Darwinism still smuggles in biological determinism. Not only must the laws of nature imply the existence of molecules possessing all the above properties, but the evolutionary pathway that the population of replicators follows must also lead to nucleic acids. Otherwise life as we know it would still be a tremendous fluke.
So should we concede that life is the result of an exceedingly unlikely chemical accident, a chance event unique in the entire Universe? Not necessarily. A type of biological determinism may still be true, even if life isn't written into the familiar laws of physics, chemistry and evolutionary theory. It may be that these laws can account for life's hardware, that is, the raw materials, but the vital software, or informational component, derives from the laws of information theory.
The concept of "information" is admittedly rather woolly, though this is usual when a subject is in its infancy. Two centuries ago, energy was an equally vague notion. Scientists intuitively recognised it as significant in physical processes, but it lacked mathematical rigour. Today, we accept energy as a real and fundamental quantity, because it is well understood. Information remains bewildering, partly because it crops up in different guises in so many scientific fields. In relativity theory, it is information that is forbidden to travel faster than light. In quantum mechanics, the state of a system is described by its maximum information content. In thermodynamics, information falls as entropy rises. In biology, a gene is a set of instructions containing the information needed to execute some task.
What we know about information comes mainly from the realm of human discourse. A landmark study in information theory was an analysis of
communication over noisy radio channels conducted by American electrical engineer Claude Shannon during the Second World War. But nobody has yet written down the equivalent of Newton's laws for informational dynamics. Scientists can't even agree on whether information is invariably conserved in physical processes. For years, debate has raged over what happens to the information in a star when it collapses to form a black hole, which subsequently evaporates. Is the information irreversibly lost, or does it somehow get back out again?
One new area of research, however, offers a tantalising pointer. Until recently, biochemists treated life's molecules as little blocks that stick together. In reality, molecular structure and bonding are subject to quantum mechanics. Now physicists have extended the concept of information to the quantum domain, and made some extraordinary discoveries. One of these is the ability of quantum systems to process information exponentially faster than classical systems--a property that lies behind the quantum computer.
The riddle of biogenesis is essentially computational in nature--discovering a very special type of molecular system from among a vast decision tree of chemical alternatives, most branches of which represent biological duds. Could it be that the key initial steps in "informing" matter and setting it on the road to life lie in the offbeat realm of quantum physics? If so, biological determinism might at last receive a convincing theoretical underpinning, justifying the popular belief that we inhabit a bio-friendly Universe in which we are not alone.
From New Scientist, 18 September 1999
© Copyright New Scientist, RBI Limited 2001