The Meaning of Multiverse

In answer to a question posed by a friend:

According to the Oxford English Dictionary, the word “multiverse” was first used by the American psychologist William James (the brother of novelist Henry James) in 1895.  But he was interested in mysticism and religious experiences, not the nature of the physical Universe.  Similarly, although the word appears in the writings of G. K. Chesterton, John Cowper Powys, and Michael Moorcock, none of this has any relevance to its use in a scientific context.  From our point of view, the first intriguing scientific use of the word followed from an argument put forward by Alfred Russel Wallace, the man who came up with the idea of evolution by natural selection independently of Charles Darwin, that “our earth is the only inhabited planet, not only in the Solar System but in the whole stellar universe.”  Wallace wrote those words in his book Man’s Place in the Universe, published late in 1903, which developed ideas that he had previously aired in two newspaper articles.  Unlike Darwin, Wallace was of a religious persuasion, and this may have coloured his judgement when discussing “the supposed Plurality of Worlds.[1]  But as we shall see, there is something very modern about his approach to the investigation of the puzzle of our existence.  “For many years,” he wrote:

I had paid special attention to the problem of the measurement of geological time, and also that of the mild climates and generally uniform conditions that had prevailed throughout all geological epochs, and on considering the number of concurrent causes and the delicate balance of conditions required to maintain such uniformity, I became still more convinced that the evidence was exceedingly strong against the probability or possibility of any other planet being inhabited.

This was the first formal, scientific appreciation of the string of coincidences necessary for our existence; in that sense, Alfred Russel Wallace should be regarded as the father of what is now called “anthropic cosmology.”

Wallace’s book stirred up a flurry of controversy, and among the people who disagreed publicly with his conclusions were H. G. Wells, William Ramsay (co-discoverer of the inert gas argon), and Oliver Lodge, a physicist who made pioneering contributions to the development of radio.  It was Lodge who used the term “multiverse,” but referring to a multitude of planets, not a multitude of universes.

In scientific circles, the word was forgotten for more than half a century, then invented yet again by a Scottish amateur astronomer, Andy Nimmo.  In December 1960, Nimmo was the Vice Chairman of the Scottish branch of the British Interplanetary Society, and was preparing a talk for the branch about a relatively new version of quantum theory, which had been developed by the American Hugh Everett.  This has become known as the “many worlds interpretation” of quantum physics, with “world” now being used as a synonym for “universe.”  But Nimmo objected to the idea of many universes on etymological grounds.  The literal meaning of the word universe is “all that there is,” so, he reasoned, you can’t have more than one of them.  For the purposes of his talk, delivered in Edinburgh in February 1961, he invented the word “multiverse” – by which he meant one of the many worlds.  In his own words, he intended it to mean “an apparent Universe, a multiplicity of which go to make up the whole  .  .  .  you may live in a Universe full of multiverses, but you may not etymologically live in a Multiverse of ‘universes’.”

Alas for etymology, the term was picked up and used from time to time in exactly the opposite way to the one Nimmo had intended.  The modern usage of the word received a big boost in 1997, when David Deutsch published his book The Fabric of Reality, in which he said that the word Multiverse “has been coined to denote physical reality as a whole.”  He says that “I didn’t actually invent the word.  My recollection is that I simply picked up a term that was already in common use, informally, among Everett proponents.”  In my books, the word “Multiverse” is used in the way Deutsch defines it, which is now the way it is used by all scientists interested in the idea of other worlds.[2]  The Multiverse is everything that there is; a universe is a portion of the multiverse accessible to a particular set of observers.  “The” Universe is the one we see all around us.

[1] His emphasis.

[2] I refer any offended etymologists to the comment of Humpty Dumpty in Through the Looking Glass:  “When I use a word,’ Humpty Dumpty said, in a rather scornful tone, ‘it means just what I choose it to mean, neither more nor less.’”

Adapted from my book In Search of the Multiverse (Penguin)


Out of the Shadows

Here is a copy of a blog I provided for the Yale University Press website, in connection with my book Out of the Shadow of a Giant.  More details will be at ‎from 22 October.

Who was the first person to realise that gravity is a universal force possessed by every object in the Universe, which attracts every other object? Isaac Newton, right?  Wrong! Newton got the idea, and other insights which fed in to his theory of gravity, from Robert Hooke, a seventeenth century polymath whose work has been overshadowed by the giant figure of Newton. Hooke was both an experimenter and observer, and a theorist.  His insight about gravity came partly from his telescopic observations of the Moon.  He studied lunar craters, and noticed that they are formed of nearly circular walls, around a shallow depression.  They looked, in his words “as if the substance in the middle had been digg’d up, and throw on either side.”  So he carried out experiments, dropping bullets onto a mixture of water and pipe-clay, making miniature craters which, when illuminated from the side by a candle, looked just like lunar craters.  He realised that the material thrown up from the centre of the craters of the Moon was pulled back down by the Moon’s own gravity, independent of the Earth’s gravity.  He pointed out that apart from small irregularities like craters, the Moon is very round, so that “the outermost bounds. . . are equidistant from the Center of gravitation”, tugged towards the center by gravity, and concluding that it had ”a gravitating principle as the Earth has.”  This was published in 1665, when Newton was just completing his degree at the University of Cambridge.  Hooke went on to suggest that planets are held in orbit by an attractive gravitational force from the Sun. This was a revolutionary idea. Hooke’s contemporaries argued that the planets were whirled around in vortices in some mysterious invisible fluid, like chips of wood in whirlpools on a river. When Newton convinced them that this was wrong, and gravitational attraction was right, they remembered him and forgot who gave Newton the idea!

Hooke wasn’t the only seventeenth century scientist overshadowed by Newton. Edmond Halley, of comet fame, was another. It was Halley, in fact, who not only persuaded Newton to write his great book, the Principia, but paid for its publication! The most astonishing forgotten achievement of Halley, though, is that he was given command of a Royal Navy ship to make a scientific voyage of exploration to the southern ocean. Literally given command.  He was the captain and navigator (in Royal Navy language, Master and Commander), not a passenger. The ship, Paramore was just 52 feet long, with a crew of 24.  It sailed on 16 September 1699, and Halley took it as far south as the edge of the Antarctic ice pack, making observations of magnetism and winds long the way.  At their furthest south, 52 degrees 24 minutes latitude, they were nearly crushed by icebergs.On his return to England, Halley was lauded by Samuel Pepys as “the first Englishman (and possibly any other) that had so much, or (it might be said) any competent degree (meeting in them) of the science and practice (both) of navigation.” His navigational skills were also used by the British in secret surveying of the French side of the English channel, to make charts for use in time of war. When Halley became Savilian Professor of Astronomy in Oxford, the Astronomer Royal, John Flamsteed, complained that he “talks, swears, and drinks brandy like a sea captain.” He was indeed a sea captain, and proud of it; not your average Oxford Professor, even by eighteenth century standards.




Cosmic chemistry and the Origin of Life

Recent experiments suggesting that the origin of life may have happened in warm little pool four billion years ago made a splash in the media. The idea is relatively old, but the “news” was that precursors to life might have been brought down to Earth by meteorites and laced those ponds with the chemicals necessary to kickstart life. But all these stories missed an even more significant possibility, that life itself may have been brought down to Earth by comets. If that scenario is correct, the Universe is teeming with life. To put it all in perspective, here is an adapted extract from my book Alone (aka The Reason Why).

Carbon atoms have an unusual ability to combine strongly with up to four other atoms at a time, including other atoms of carbon. The simplest way to picture this is to imagine that a carbon atom has four hooks sticking out from its surface, and each of these can latch on to another atom to make a chemical bond. In the simplest example, each molecule of the compound methane is made of a single carbon atom surrounded by four hydrogen atoms which are attached to it by bonds – CH4. But carbon atoms can also link up with one another fore and aft to form chains, linking each carbon atom in the chain with two other carbon atoms, but leaving two bonds free to hook up with other kinds of atoms, and leaving the two carbon atoms at the ends of the chain each with three spare bonds. Or the chain may become a ring, with carbon atoms forming a closed loop, still with two bonds available for each atom in the ring to form other linkages. Even complex carbon-based molecules, including other rings and chains, can attach to other carbon chains or to other rings. It is this rich potential for carbon chemistry which makes the complexity of life possible. Indeed, when chemists first began to study the complexity of life, and realised that it involves carbon so intimately, the term “organic chemistry” became synonymous with “carbon chemistry.”
There are two key components of the chemistry of life. To non-biologists, the most widely known life molecule is DNA, or deoxyribonucleic acid. This is the molecule within the cells of living things, including ourselves, which carries the genetic code. The genetic code contains the instructions, rather like a recipe, which tell a fertilised cell how to develop and grow into an adult. But it also contains the instructions which enable each cell to operate in the right way to keep the adult organism functioning – how to be a liver cell, for example, or how to absorb oxygen in the lungs. The mechanism of the cell also involves another molecule, ribonucleic acid, or RNA. As the name suggests, molecules of DNA are essentially the same as molecules of RNA but with oxygen atoms removed.
The “ribo” part of the name comes from “ribose” (strictly speaking the names should be ribosenucleic acid and deoxyribosenucleic acid). Ribose (C5H10O5) is a simple sugar, but it lies at the heart of DNA and RNA. Each molecule of ribose is made of a core of four carbon atoms and one oxygen atom linked in a pentagonal shape. Each of the four carbon atoms in the pentagon has two spare bonds with which to link up with other atoms or molecules. In ribose itself, these attachments link the pentagon to hydrogen atoms, oxygen atoms, and one more carbon atom, making five in all, which is itself joined to more hydrogen and oxygen; but any of these attachments can be replaced by other links, including links to complex groups which themselves link up with other rings or chains. In DNA and RNA, each sugar ring is attached to a complex known as the phosphate group, which is itself attached to another sugar ring. So the basic structure of both of the life molecules is a chain, or spine, of alternating sugar and phosphate groups, with interesting things sticking out from the spine. It is the interesting things that carry the code of life, spelling out the message in what is in effect a four-letter alphabet with each letter corresponding to a different chemical group. But that is not a story to go into here; from the point of view of interstellar chemistry, it is the basic building block of DNA, the ribose molecules, that are significant.
Nobody has yet detected ribose in space. But astronomers have detected the spectroscopic signature of a simpler sugar called glycolaldehyde. Glycolaldehyde is made up of two carbon atoms, two oxygen atoms and four hydrogen atoms (usually written as H2COHCHO, which reflects the structure of the molecule), and is known, logically enough, as a “2-carbon sugar.” Glycolaldehyde readily combines, under conditions simulating those in interstellar clouds, with a 3-carbon sugar, making the 5-carbon sugar ribose. We have not yet found the building blocks of DNA in space; but we have found the building blocks of the building blocks.
The other kind of “life molecule” is protein. Proteins are the structural material of the body; they always contain atoms of carbon, hydrogen, oxygen, and nitrogen, often sulphur, and some contain phosphorus. Things like hair and muscle are made of proteins in the form of long chains, not unlike the long chains of sugar and phosphate in DNA and RNA molecules; things like the haemoglobin that carries oxygen around in your blood are forms of protein in which the chains are curled up into little balls. Other globular proteins act as enzymes, which encourage certain chemical reactions that are beneficial to life, or inhibit chemical reactions that are detrimental to life. There is such a variety of proteins because they are built up from a wide variety of sub-units, called amino acids.
Amino acid molecules typically have weights corresponding to a hundred or so units on the standard scale where the weight of a carbon atom is defined as 12, but the weights of protein molecules range from a few thousand units to a few million units on the same scale, which gives you a rough idea how many amino acid units it takes to make a protein molecule. One way of looking at this is that half of the mass of all the biological material on Earth is in the form of amino acids. But even though a specific protein molecule may contain tens of thousands, or hundreds of thousands, of separate amino acid units, all the proteins found in all the forms of life on Earth are made from combinations of just twenty different amino acids. In the same way, every word in the English language is made up from different combinations of just 26 sub-units, the letters of the alphabet. There are many other kinds of amino acid, but they are not used to make protein by life as we know it.
If a chemist wishes to synthesise amino acids in the laboratory, it is relatively easy and quick to do so by starting out with compounds such as formaldehyde (HCHO), methanol (CH3OH) and formamide (HCONH2), all of which will be to hand in any well-stocked chemical lab. With such materials readily available, it would be crazy to start out from the basics – water, nitrogen and carbon dioxide. But the chemistry lab isn’t the only place you will find such compounds. One of the most dramatic results of the investigation of molecular clouds is the discovery that all of the compounds used routinely in the lab to synthesise amino acids (including the three just mentioned) are found in space, together with others such as ethyl formate (C2H5OCHO) and n-propyl cyanide (C3H7CN). In a sense, the molecular clouds are well-stocked chemical laboratories, where complex molecules are built up not atom by atom, but by joining together slightly less complex sub-units.
There have also been claims that the simplest amino acid, glycine (H2NH2CCOOH), has been detected in space. It is very difficult to pick out the spectroscopic signature of such a complex molecule, let alone those of even more complex amino acids, and these claims have not been universally accepted by astronomers, even though amino acids have been found in rocks from space left over from the formation of the Solar System, which occasionally fall to Earth as meteorites. The claims have been bolstered, though, by the recent detection in space of amino acetonitrile (NH2CH2CN), which is regarded as a chemical precursor of glycine. But even if we take the cautious view and leave these claims to one side, that still means that, echoing the situation with DNA, with the identification of compounds such as formaldehyde, methanol and formamide, although we have not yet found the building blocks of protein in space, we have found the building blocks of the building blocks.
Complex organic molecules can only be built up in the molecular clouds because those clouds contain dust as well as gas. If all the material in the clouds were in the form of gas, even if by some unimaginable process a complex molecule such as NH2CH2CN did exist, how could it grow? You might imagine that a collision with a molecule of oxygen, O2, would provide an opportunity to capture some of the additional atoms needed to make glycine, H2NH2CCOOH. But the impact of the oxygen molecule would be more likely to break the amino acetonitrile apart, rather than encouraging it to grow. But tiny solid grains, coated with a snowy layer of ice (not just water ice, but also things like frozen methane and ammonia) provide sites where molecules can stick and be held alongside each other for long enough for the appropriate chemical reactions to take place.
Old stars swell up near the end of their lives, and eject material out into space. Spectroscopic studies show that this material includes grains of solid carbon, silicates, and silicon carbide (SiC), which is the most common solid component definitely identified in the dust around stars, although there are many as yet unidentified spectral features as well. Laboratory experiments simulating the conditions on the surfaces of such particles in space have confirmed that they provide places where the kinds of chemical reactions needed to make the kinds of complex organic molecules we detect in space can take place. Some of these studies suggest that the grains may not simply provide a surface where the reactions can take place, but that there may be chemical bonds between the molecules and the surface itself. That would explain how the molecules stick around for long enough for the reactions to take place even in relatively warm parts of a molecular cloud. As long as they do stick, there is plenty of time for the reactions to take place, because molecular clouds may wander around the Galaxy for millions – even billions – of years before part of the cloud collapses to form a group of new stars. When the grains are warmed by the heat from a newly forming star, the complex molecules can be liberated and spread through the molecular cloud, where they can be detected by our radio telescopes.
In this context, it is almost an anticlimax, but still significant, that a simple organic molecule, methane, was detected in the atmosphere of one of the hot jupiters in 2008. This was no surprise – methane is an important component of the atmosphere of Jupiter itself. But it was still regarded as a landmark event. For the record, the planet is the same one where water was identified earlier, orbiting the star HD 189733. Astronomers working with the Spitzer Space Telescope have also found large amounts of hydrogen cyanide, acetylene, carbon dioxide and water vapour in the discs around young stars where planets form. And a team from the Carnegie Institution used the Hubble Space Telescope to analyse light from a star known as HR 4796A, 270 light years away in the direction of the constellation Centaurus, to determine that the red colour of the dusty disc around the star is caused by the presence of organic compounds known as tholins. Tholins are large, complex organic molecules that are manufactured by the action of ultraviolet light on simpler compounds such as methane, ammonia and water vapour. They can be synthesised in the lab, but do not occur naturally on Earth today because they would be destroyed by reacting with oxygen in the atmosphere as fast as they formed. But their presence explains the reddish-brown hue of Saturn’s moon Titan, they are present in comets and on asteroids, and they may well have been present on Earth when it was young. Tholins are widely regarded as precursors of life on Earth, which made their discovery in the disc around HR 4796A hot news.
This is not the same, though, as finding such compounds on a planet. When planets like the Earth form by the accretion of larger and larger lumps of rock, they get hot, because of the kinetic energy released by all those rocks smashing together. A rocky planet starts its life in a sterile, molten state, certainly hot enough to destroy any organic molecules present in the material from which it formed. The importance of all the observations of organic material in space is that they tell us that there is a great reservoir of such material available to fall down on to the planets after they are cool enough for the complex molecules to survive. Life does not have to be “invented” from scratch on each new planet from the basics of water, carbon dioxide and nitrogen, any more than an organic chemist has to synthesise amino acids from the basics of water, carbon dioxide and nitrogen. In which case, every “Earth-like” planet in the Galaxy should have been seeded with life — all of it based on the same chemistry as life on Earth.

Better than Newton

An article we wrote for the Big Issue, using material from our book Out of the Shadow of a Giant.


If you remember one thing from physics lessons in school, it ought to be Newton’s First Law of Motion, which says that any object that is not “at rest” moves in a straight line at a constant speed unless it feels an outside force. The truth of this law is familiar today from video of astronauts inside the International Space Station, or at a more local level in a game of air hockey. Clever old Newton. Snag is, he didn’t think of it. The first person to realise this fundamental law of Nature was Newton’s slightly older contemporary Robert Hooke. Hooke was also the first person to realise that gravity is a force of attraction in which everything in the Universe pulls on everything else – in particular, that the Sun pulls on the planets. Newton, until Hooke pointed this out to him, thought that the planets were carried around the Sun in eddies, like chips of wood in a whirlpool, by some mysterious cosmic fluid.

So how come we don’t talk about “Hooke’s First Law of Motion” and give him the credit he deserves as a pioneering physicist? Largely beacause Newton, who was a bit of a plagiarist and somewhat flexible with the truth, outlived Hooke, and wrote him out of history as far as he coiuld. When Newton became President of the Roylal Society, after Hooke died, the only known portrait of Robert Hooke mysteriously disappeared when the Society moved to new premises – the only picture to get lost in the move.

By minimising Hooke’s contribution to science, Newton also helped to encourage the impression that Hooke’s other activities were not particularly noteworthy. History tells us that Hooke played a part in the rebuilding of London after the Great Fire of 1666, with most accounts implying that he was some kind of assistant to Christopher Wren. In fact, Hooke was essentially an equal partner in Wren’s architectural practice, and was personally responsible for laying out the streets after the fire and much of the rebuilding. About half of the “Wren” churches in London are actually Hooke’s work. And it was Hooke who discovered the technique which Wren used to make it possible to build the spectacular dome of St Paul’s.

Along the way, Hooke was a pioneering microscopist, and made a careful study of fossils, convincing himself that the Earth was much older than the religious authorities claimed, and very nearly coming up with the idea of evolution. Our book is an attempt to set the record straight, and bring his genius out from under the shadow of Newton. But, as we discovered, he was not alone in that shadow.

Edmond Halley is at least remembered, for the comet that bears his name (although he did not, contrary to widespread belief, discover that comet). But what else did he do? He carried out the first astronomical survey of the stars of the southern hemisphere, and commanded a King’s ship on the furthest voyage south up to that time, to the edge of the Antarctic pack ice, to survey the Earth’s magnetic field. “Commanded” is a key word here – Halley is still the only civilian ever to be given command of a Royal Navy vessel and crew. He was so successful that he later carried out undercover missions, details of which have never been revealed, in the English Channel and the Adriatic, making him a combination of Jack Aubrey and James Bond. He also proposed the idea of an expedition to measure a phenomenon known as a transit of Venus from the Pacific Ocean; this would happen after he was dead. The expedition was duly carried out under the command of James Cook, and after completing their astronomical observations Cook went on to discover New Zealand and make a landfall in southeastern Australia. The French reached New Zealand a little later. Without Halley’s suggestion, New Zealand would probably have become a French colony, and there might have been some squabbling over Australia.

When we set out to bring these remarkable men out from the shadow of the giant Newton, the question we had the back of our minds was whether science would have made the great leap forward it achieved in the seventeenth century if Newton had never lived. Our conclusion is that it wouldn’t have made much difference. Newton’s singular contribution was to pull a lot of ideas together in his famous book the Principia. But the ideas were “out there”, and even then, Halley suggested the idea of the book, and he both edited it and paid for its publication out of his own pocket. Without Robert Hooke and Edmond Halley, we would probably never have heard of Isaac Newton. Without Isaac Newton, we would have heard a lot more about Robert Hooke, in particular, and Edmond Halley.



Probing the Universe

The announcement of the invention of a 3-D printer that can make 3-D printers that can make 3-D printers  .  .  .     prompts me to offer this extract from my book Computing With Quantum Cats:

Like Alan Turing, the computer pioneer “Johnny” von Neumann was fascinated by the idea of artificial intelligence, although he had a different perspective on the rise of the robots. But unlike Turing, he lived long enough (just) to begin to put flesh on the bones of those ideas.

There were two parts to von Neumann’s later work. He was interested in the way that a complex system like the brain can operate effectively even though it is made up of fallible individual components, neurons. With the early computers (and many even today), if one component, such as a vacuum tube, failed the whole thing would grind to a halt. Yet in the human brain, quite apart from everyday operation, it is possible for the “hardware” to suffer massive injuries and continue to function effectively, if not quite in the same way as before. Von Neumann was also interested in the problem of reproduction. Jumping off from Turing’s idea of a computer that could mimic the behaviour of any other computer, he suggested first, that there ought to be machines that could make copies of themselves and, secondly, that there could be a kind of universal replicating machine that could make copies of itself and also of any other machine.

Both kinds of mimic, or copying machine, come under the general heading “automata”. Von Neumann’s interest in working out how workable devices can be made from parts prone to malfunction, and his interest in how complex a system would have to be in order to reproduce itself, began to grow in 1947. This was partly because he was moving on from the development of computers like the one then being built at the IAS and other offspring of EDVAC, but also because he became involved in the pressing problem for the US Air Force in the early 1950s of developing missiles controlled by “automata” that would have to function perfectly, if only during the brief flight time of the rocket.

Von Neumann came up with two theoretical solutions to the problem of building near-infallible computing machines out of fallible, but reasonably accurate, components. The first is to set up each component in triplicate, with a means to compare automatically the output of each of the three subunits. If all three results, or any two results, agree, the computation proceeds to the next step, but if none of the subunits agree the computation stops. This “majority voting” system works pretty well if the chance of any individual subunit making a mistake is small enough. It is even better if the number of voters for each step in the calculation is increased to five, seven, or even more. But this has to be done for every step of the computation (not just every “neuron”), vastly (indeed, exponentially) increasing the amount of material required. The second technique involves replacing single lines for input and output by bundles containing large numbers of lines — so-called multiplexing. The data bit (say, 1) from the bundle would only be accepted if a certain proportion of the lines agreed that it was correct. This involves complications which I will not go into here; the important point is that although neither technique is practicable, von Neumann proved that it is possible to build reliable machines, even brains, from unreliable components.

As early as 1948, von Neumann was lecturing on the problem of reproduction to a small group at Princeton. The biological aspects of the puzzle were very much in the air at the time, with several groups looking for the mechanism by which genetic material is copied and passed from oner generation to the next; it would not be until 1952 that the structure of DNA was determined. And it is worth remembering that von Neumann trained as a chemical engineer, so he understood the subtleties of complex chemical interactions. So it is no surprise that von Neumann says that the copying mechanism performs “the fundamental act of reproduction, the duplication of the genetic material.” The surprise is that he says this in the context of self-reproducing automata. It was around this time that he also surmised that up to a certain level of complexity automata would only be able to produce less complicated offspring, but above this level they would not only be able to reproduce themselves but “syntheses of automata can proceed in such a manner that each automaton will produce other automata which are more complex and of higher potentialities than itself.” He makes the analogy with the evolution of living organisms, where “today’s organisms are phylogenetically descended from others which were vastly simpler”. How did the process begin? Strikingly, von Neumann points out that even if the odds are against the existence of beings like ourselves, self-reproduction only has to happen once to produce (given time and evolution) an ecosystem as complex as that on Earth. “The operations of probability somehow leave a loophole at this point, and it is by the process off self-reproduction that they are pierced.”

By the early 1950s, von Neumann was working on the practicalities of a cellular model of automata. The basic idea is that an individual component, or cell, is surrounded by other cells, and interacts with its immediate neighbours. Those interactions, following certain rules, determine whether cell reproduces, dies, or does nothing. At first, von Neumann thought three-dimensionally. Goldstine:
[He] bought the largest box of “Tinker Toys” to be had. I recall with glee his putting together these pieces to build up his cells. He discussed this work with [Julian] Bigelow and me, and we were able to indicate to him how the model could be achieved two-dimensionally. He thereupon gave his toys to Oskar Morgenstern’s little boy Karl.
The two-dimensional version of von Neumann’s model of cellular automata can be as simple as a sheet of graph paper on which squares are filled in with a pencil, or rubbed out, according to the rules of the model. But it is also now widely available in different form that run on computers, and is sometimes known as the “game of life.” With a few simple rules, groups of cells can be set up that perform various things familiar from living organisms. Some just grow, spreadIng as more cells grow around the periphery; others pulsate, growing to a certain size, dying back, and growing again; others move, as new cells are added on one side and other cells die on the opposite side; and some produce offspring, groups of cells that detach from the main body and set off on their own. In his discussion of such systems, von Neumann also mentioned the possibility of arbitrary changes in the functioning of a cell, equivalent to mutations in living organisms.

Von Neumann did not live long enough to develop these ideas fully. He died of cancer on 28 February 1957, at the age of 53. But he left us with the idea of a “universal constructor”, a development of Turing’s idea of a universal computer — a machine which could make copies of itself and of any other machine, a self-reproducing robot. Such devices are now known as von Neumann machines, and they are relevant to one of the greatest puzzles of our, or any other time — is there intelligent life elsewhere in the Universe? One form of a von Neumann machine would be a space-travelling robot that could move between the stars, stopping off whenever it found a planetary system to explore it and build copies of itself to speed up the exploration while sending other copies off to other stars. Starting with just one such machine, and travelling at speeds well within the speed of light limit, it would be possible to explore every planet in our home Milky Way Galaxy in a few million years, an eyeblink as astronomical timescales go. The question posed by Enrico Fermi (why, if there are alien civilizations out there, haven’t they visited us?) then strikes with full force.

There’s one other way to spread intelligence across the Universe, which von Neumann was also aware of. A universal constructor would operate by having blueprints, in the form of digitally coded instructions which we might as well call programs, telling it how to build different kinds of machines. An even more efficient means to spread this information across the Universe would be in the form of a radio signal travelling at the speed of light, rather than in a von Neumann machine pottering along more slowly between the stars. If a civilization like ours detected such a signal, it would be surely be copied and analysed on the most advanced computers available, ideal hosts for the program to come alive and take over the operation of the computer. In mentioning this possibility, George Dyson makes an analogy with the way a virus takes over a host cell; he seems not to be aware of the entertaining variation on this theme discussed back in 1961 by astrophysicist Fred Hoyle in his fictional work A for Andromeda, where the interstellar signal provides the instructions for making (or growing) a human body with the mind of the machine. Hoyle though, was well aware of the work of Turing and von Neumann.


Seeds of Life?

I thought this extract from my old book Companion to the Cosmos might be of interest in the light of the news about the system TRAPPIST-1


interstellar chemistry Many molecules (more than 80 by the mid- 1990s) have been discovered in clouds of gas and dust between the stars. Although the nuclei of different elements are built up inside stars by the processes of nuclear fusion, under the conditions of heat and pressure inside a star atoms cannot combine together to make molecules. So all of the variety of molecules seen in interstellar space must have been produced by chemical reactions going on in the clouds of gas and dust where we detect those molecules today. The complexity of the reactions involved in this interstellar chemistry is indicated by the complexity of some of the molecules identified — several contain 10 or more atoms, and one is the amino acid glycine (NH2CH2COOH), an essential building block of life on Earth.

Many of the molecules found in interstellar space are made up from carbon, oxygen and nitrogen (the most abundant elements manufactured from hydrogen and helium inside stars), together with hydrogen itself (see CHON). Simple compounds made up of carbon and hydrogen (CH) and carbon and nitrogen (CN) were discovered at the end of the 1930s, using optical spectroscopy. But the first real progress towards an understanding of interstellar chemistry came in the 1960s, when suitable radio astronomy techniques were developed to identify the characteristic radiation of polyatomic molecules in space. The hydroxyl compound (OH), water (H2O), ammonia (NH3) and formaldehyde (H2CO) were soon identified.

In the 1970s, astronomers were surprised by the variety and complexity of organic molecules (that is, molecules that contain carbon atoms) found in space. These included ethyl alcohol (C2H5OH), which is present in one large complex of molecular clouds (known as Sgr B2) in sufficient quantities to make 1027 litres of vodka. As well as these complex molecules, interstellar clouds must also contain simple compounds such as oxygen (O2), nitrogen (N2), carbon dioxide (CO2) and hydrogen (H2), which are stable and form very easily from the basic atomic ingredients that are known to be present.

The key to interstellar chemistry is the presence of a large amount of carbon in the form of grains of graphite in these interstellar clouds. These show up from the way in which they absorb visible light from more distant stars, which can be explained by the presence of elongated grains about 0.1 millionths of a metre long, mostly made of carbon but with water ice and silicates present as well. It may seem odd to think of interstellar clouds as being laced with soot, but carbon is one of the most common products of nucleosynthesis inside stars, and there is a family of stars (known as carbon stars) which are shown by their spectra to have atmospheres relatively rich in carbon, and which vary regularly, puffing in and out with periods of a year or so, and ejecting material into interstellar space as they do so. The evidence suggests that many (if not all) stars go through a phase of such activity.

Most of the complex molecules are found in unusually dense clouds in space, where there is enough of the sooty dust to act as a shield, protecting the molecules from the strong ultraviolet radiation from nearby young stars, which would tend to break the molecules apart. These are exactly the clouds in which new young stars, and their associated planets, are forming. The molecules are probably built up by reactions that take place on th surfaces of dust grains, where atoms can “stick” and have a chance to interact with one another. The molecules later evaporate from the surfaces of the grains. All of this makes it extremely likely that new planets are “seeded” by quite complex molecules early in their existence; any molecules present in the interstellar clouds from which stars and planets form could easily be deposited on a planet by, for example, the impact of a large comet.

Interstellar chemistry involves not only interactions between material in gaseous form and the solid grains of dust in molecular clouds, but also interactions with the stars themselves. It is harder than you might think for such a cloud to collapse and fragment to form stars. When it starts to do so, gravitational energy is released in the form of heat, making the molecules in the cloud move faster and generating a pressure which resists further collapse. The cloud can only collapse further if this excess heat can be disposed of, in the form of electromagnetic radiation. This is produced by the molecules of compounds such as carbon dioxide and water vapour in the cloud. Then, when a young star begins to form, it produces copious amounts of ultraviolet radiation, which would tend to blow the cloud apart. Fortunately, though, the grains of carbon dust (or soot) in the cloud absorb the ultraviolet radiation and re-radiate it in the infrared part of the spectrum, at wavelengths which can escape much more easily into space. Carbon dust grains, and molecules produced by interstellar chemistry, are essential in the cooling processes without which the stars which edge the spiral arms of a galaxy like our own Milky Way would not form in such abundance.

In the early 1990s, astronomers found evidence of a complex molecule in the form of a ring in interstellar clouds. The evidence came from the NASA Ames Research Center, and concerned the detection of features interpreted as those of the spectrum of pyrene (C12H10), in which a dozen carbon atoms are joined together in a ring, with ten hydrogen atoms attached to it around the outside. This provided the first independent support for controversial claims made by Fred Hoyle and his colleague Chandra Wickramasinghe in the 1970s and 1980s.

Hoyle and Wickramasinghe have gone further than any other astronomers in claiming that some of the features seen in the radiation from molecular clouds can be explained in terms of very large organic molecules called polymers. These form chains of repeating units. The basic component of a polysaccharide chain, for example, is the so-called pyran ring, a hexagon made up of five carbon atoms and one oxygen atom (C5O). These rings link together to make a chain when one of the carbon atoms joins on to another oxygen atom, which itself joins on to the next pyran ring in the chain, and so on. Once formed, a pyran ring shows one of the fundamental properties of life — it acts as a template, encouraging the formation of more identical rings which join up in a growing polysaccharide chain.

Hoyle and Wickramasinghe have suggested that even more complex polymers such as cellulose may already have been directly revealed by their spectral signatures in radiation from these clouds (other astronomers dispute this interpretation of the data), and that molecules of life itself may be present in the clouds but not yet detected. Once, these ideas were derided as so heretical that just voicing them may have cost Hoyle the Nobel Prize he deserved for his work on nucleosynthesis. In fact, the team has an impressive track record (they were, for example, the originators of the idea that interstellar clouds contain grains of soot, an idea established now beyond reasonable doubt), and their ideas look far less extreme now that glycine and pyrene have both been identified in space.

At the very least, it is now difficult to escape the conclusion that when a planet like the Earth forms its atmosphere and oceans are soon laced with complex organic molecules. Since interstellar chemistry seems to be the same in molecular clouds across the Milky Way, this suggests that the complex chemistry of other planets would be similar to that of the Earth, and that where life has evolved from that complex chemistry it should be based on the same sort of compounds (including amino acids) that we are.


A Science Fiction Taster

I am putting together a collection of my science fiction short stories, to be published by Elsewhen Press.  This is one that will not be in the collection, because it was a collaboration with the well-known science writer Marcus Chown.  So I thought I would offer it here as a taste of things to come, with thanks to Marcus for permission to share it with you.

Survival of the Fittest

By John Gribbin and Marcus Chown



When Darwin coined his famous theory concerning evolution by natural selection, he had in mind a different kind of fitness from the benefits we gain from physical exertion.



“Don’t go too far, Jan.” Frances Reese’s warning was still ringing in Du Toit’s ears as he cut the jet pack and attempted a landfall a kilometre from the cluster of spacecraft. The terrain a hundred metres below was largely hidden, cloaked in mottled shadow, but it was unlikely, in such low gravity, that he would come to grief by dropping blind. Still, there was no sense in taking chances. He peered down into the gloom, trying to make out something as he fell in a long, leisurely arc towards the surface.

He had had to get away, get some precious solitude, and even mother-hen Reese had relented, grudgingly, when he’d told her, in all seriousness, that he was set to explode. It was true; make no mistake. He might have been the most even-tempered and phlegmatic spacer on the long flight out to the Dragon, but intolerable pressure had built up inside him like a head of steam, until he didn’t like to think what he might do to any of his crew-mates if he didn’t crack a release valve, and soon.

Of course, he had known exactly what to expect when he had volunteered for this crazy mission. But, somehow, recognising intellectually the pitfalls of overcrowding on a long interplanetary flight had not prepared him for the nerve-jangling click of Wenzel’s jaw as he munched each and every mouthful, or Finnegan’s deathly bleak depressions which infected the rest of the crew like an emotional cancer, or even the innocuous but endless chess games between Xu and Bertorelli – the board with its magnetic pieces always cluttering up the rec room table (why couldn’t they play on the computer, for God’s sake?) and never leaving enough room for a food tray.

Irritating habits, idiosyncrasies, petty selfishness magnified to enormous proportion: the old, old story. No doubt he, Du Toit, irritated the hell out of half the crew with a dozen microscopic mannerisms. He knew for sure that most of his colleagues took exception to his keep-fit routines. “Training for the Olympics, Jan?” Every time he tried to work out in the limited space available he’d get the same crack from Xu, usually followed by a remark about how humankind had reached the top of the evolutionary tree by intellectual superiority, not brute force. Maybe that was a comfort to someone who stood little more than 150 centimetres high and weighed well under sixty kilos back on Earth. But he’d never seen why being intellectually gifted gave you a license to let your body run to seed, and he didn’t care who knew his views.

Perhaps, in a myriad of small ways, he was continually getting his own back. That sadistic thought had helped him to keep sane and maintain his outward cool through all these difficult months. At least he hadn’t hit anyone, which was more than could be said for Jackson. Who would have believed they’d have to transfer meek and mild Jackson from the Hoyle to Aries II in mid-flight, with all the risks of that manoeuvre, just to get him away from Saha and prevent the first interplanetary murder?

He felt the metal claws on his boots snag the surface, and flexed his legs to take up the momentum. The Sun was directly overhead, forever at zenith now that the comet was no longer spinning, but it was still too distant and dim to illuminate the surface properly. But some detail was visible close by. Where the ice wasn’t streaked with dust it seemed to glow eerily as if from an internal light source, deep down inside. He’d seen the same ghostly effect on Earth, walking across freshly fallen snow on a starry night.

Du Toit turned off his helmet light and felt himself poised between the stars and the faint Sun and the glowing surface of the comet. He seemed to be in a valley, or at least a depression of some kind, cupped in a giant hand carrying him through space. He had to remind himself that this really was a world, with a substantial surface area, with hills and cliffs, mountains and crevasses. It was difficult to reconcile this reality with the image of a tiny speck – for that was all it had been – that he had watched for three months in the Hoyle’s 50-centimetre finder.

When he clicked the full beam of his light back on, the cone of illumination lit up a wide cleft in the ice with sheer ice walls towering on both sides of him. The wall to his right must be 50 metres away, but the left-hand wall was just a few strides from him. His gentle landing, floating down almost parallel to the ice face, could so easily have become a tumble down the nearly vertical face. Back home they’d call the feature a kloof. Du Toit’s Kloof! How about that? He would talk to Reese on his return to the ships and request that they name it after its discoverer. He had no idea how long the feature would persist in the heat of the Sun once the ice started buckling and boiling off into the vacuum, but it was the nearest he would ever get to immortality.

He began walking parallel with the ice walls – long, looping, comical strides, each of which ended in an awkward manoeuvre he had yet to perfect, in which he corkscrewed the claws of one boot into the ice to gain purchase for the next stride and to ensure he didn’t bounce off into space. All this was unnecessary. He had a jet pack and, if he floated away in the minuscule gravity of the comet, all he had to do was orient the nozzle and trigger a short burn to nudge himself back down to the surface. But that would be cheating. He wanted to walk, or at least practice what laughably passed for walking on this oversized snowball. He had spent too much time these past few months floating inside a spaceship or tethered to one or another of the vehicles, directing the burns that cancelled the angular momentum of the comet. He wanted at least the pretence of normality, and that was why he was out here, doing silly walks on a chunk of primordial ice between the planets.

In two days time Reese would order the big burn that would change the course of this ponderous iceberg of the vacuum. Only a couple of hours before, they had finished orienting the fusion engines. So Reese had given them all a much-needed forty-eight-hour break from their daily toil. And he had taken a walk in the dark rather than oblivion in his bunk. Sleep wasn’t what he needed. No, he needed a breath of fresh air. Metaphorically, of course.

The kloof had tributaries, narrow fissures which swallowed up the light of his helmet beam. Du Toit stopped and peered into one. He could see at least a hundred metres into the crack, which stretched downward into the comet, maybe to its rocky core. He would never know, since a sharp bend interrupted his line of sight. Better watch out for crevasses, he reminded himself. His quest for solitude had taken him out of radio touch with the ships. That, perhaps, was unwise. But he would be careful.

What the scientists of a century ago would have given for an opportunity like this! A human expedition to a comet, an opportunity to test out theories of the origin of the Solar System. But nobody on this expedition was interested in the scientific possibilities, whatever nonsense the Reunited Nations seemed to be feeding the news media as a cover. Wouldn’t they be getting a surprise soon! To the astronauts, the Dragon was just a missile which had to be steered in a certain direction. A ready-made, deep-frozen atmosphere, to be dumped on Earth’s Moon. But a vestige of scientific curiosity remained. We ought to make some sort of effort to send back some data on the comet, thought Du Toit, idly. After all, there won’t be another opportunity like this.

He swung his helmet out of the crack and began examining closely the wall of the kloof. It had a curious texture, looking like fabric; narrow, sinuous runnels were crisscrossed by dust veins. He pressed the palm of his glove against the wall and convinced himself that he could feel the roughness. He had a good imagination.

Thoughts of scientific investigation slid from his mind as he imagined the great bulk of the comet, a sleeping Dragon waiting to be warmed into life as it neared the Sun. This was a landscape that no other eyes would ever see, let alone investigate scientifically. He moved on, trying now to think of nothing at all, to blank out all the tedious events of the past months, using the walk to recharge his mental batteries. Breathing deeply, and leaping along rhythmically as he learned the trick of the twist in each step, he began to fall into a meditative, trance-like state, and felt fatigue seeping out of his bones. He glided to a halt, cupped in the bowl of ice, and turned slowly to see how far he had come. It was then that he felt the first, faint rumble beneath his feet.

Du Toit froze. His pulse rate and a dozen other physiological signs somersaulted off scale. What was that? Movement where there should be no movement, deep down inside the comet. The Dragon was coming to life – but much too early; it shouldn’t stir for weeks yet. For an age he stood motionless, with only the flutter of a muscle and the beating of his heart preventing the complete fusion of his awareness with the structure of the comet. He felt himself fusing with the ice, imagining layers upon layers of icy crystal plane stretching down into the cryogenic core. He felt that he could detect any microscopic slippage of these crystal planes. Poised on the knife-edge between comet and space, he felt for the heartbeat of the vacuum – but the rumble had stopped. With sudden relief, the answer came to him. The fusion engines! Reese must be testing the main drive. Of course!

Then the world fell apart. Literally. He was thrown loose from the ice and found himself floating in a shower of splinters as the comet convulsed beneath him and a great gaping canyon opened up before him, barely ten metres away along the floor of the kloof. A rising berg of ice, tens of metres across, nudged him to one side as it moved ponderously upward and out into space. Du Toit saw that he was heading for the nearest ice wall, and fast. A spacer’s instinct made him lunge at his tool belt, activate the emergency grapple line. There was no time to see whether the explosive harpoon buried itself in solid ice or powdered snow. The stars were obliterated, eclipsed by a moving mountain of ice. Then he hit, and darkness closed in.

When he awoke, he was floating. But the grapple line had held. Thank God. His head was fuzzy and his left elbow bruised and stiff. The suit had not been pierced. But when he triggered his jet pack, nothing happened. He was alive, but his principal means of propulsion was useless. He hauled in the grapple line, hand over hand, until once again he could hook his boots into the surface and ‘stand’ on ‘solid’ ice. How long had he been out? The needle on the gauge showed thirty minutes of oxygen used; given that he’d been unconscious and breathing shallowly, that meant maybe an hour had passed.

What had happened? The massive quake couldn’t have been anything to do with Reese. The Dragon, dormant since the birth of the Solar System, had hiccupped. They knew it would happen when the heat of the Sun got stronger – but not this soon. They were still out near Mars, and the Sun was too feeble to melt off even a film of surface ice. No, it had to be the fault of the expedition, somehow, with heat from the engines and the change in stresses caused by halting the comet’s spin combining to release an old pressure along a line of weakness that had been there since the dawn of time. But that was no excuse.

He began to pay out the grapple line, crawling now, not leaping, over the kloof floor. Something else was wrong. What was it? His fuddled brain tried to take stock of the surroundings. The Sun! Where had the Sun gone? It should be directly overhead; it had been before the quake. Where was the Sun? Scrabbling frantically onward, slipping and sliding on the ice, digging his toe claws into the ice to stop himself, Du Toit reached the canyon he had seen open up in the kloof floor. But it was no longer a canyon. There was nothing on the other side.

Trying hard to swallow panic, he craned over the edge, and found the Sun. It was down a sheer face of glistening ice. How could that be? How – then his brain finally understood, and Du Toit felt a cold hand seize him in its grip. Surely it couldn’t be. He closed his eyes for a moment, but when he opened them the scene was still the same.

In the light of the distant Sun he saw rubble and ice, great blocks of the stuff, occluding the stars: a flotilla of calved icebergs setting sail upon the sea of the vacuum. With him riding on one of them. Hoping against hope that it wasn’t too late, he tripped the Mayday transmitter.


What in God’s name was that?” Reese supported herself against the rec room wall as the groggy sleepers assembled. While they slept, she had been on watch, working, as always, at her desk console. Blood seeped from her nose where she had hit a support stanchion when the first big shock had struck. She pawed at the leaking droplets, but it did no good, only staining the sleeve of her tunic. As the myriad tiny droplets slowly settled and were dispersed by the air currents, she spoke through an incongruous pink haze.

Bertorelli proffered the tiny vacuum cleaner they used to clear up such messes, but she waved him aside, turning from one crew member to another as she sought an explanation of what had happened. Nobody had one. Then Finnegan, white from shock, blurted out “DuToit!” and Reese felt a sickness inside. He was out there, somewhere, a human needle in a landscape they hardly knew in the first place and which had now been twisted out of all recognition by – something. By forces they had failed to recognise or anticipate. By the unexpected – and the unexpected could mean the end for the whole mission, not just Du Toit.

“Mary, get an all-around scan working, at once. Bertorelli, see if Aries can be ready to fly. We may have to go out and find him.”


As Du Toit gazed down the seemingly endless cliff, his brain suddenly adjusted the perspective. The ‘cliff’ became a flat floor, and it no longer seemed endless. In fact, it was only a few metres across. He stood once again and ‘walked’ across to the other side. Looking over the edge, he saw the same scene repeated. He was on a small chunk of ice, a faceted, irregular lump. Secured by his clawed boots, he could roam at will over the surface, but there was virtually no gravity at all to hold him in place or give a sense of direction. In that case, he told his brain firmly, anywhere I am standing the ground is straight down beneath my feet. And don’t you forget it.

A sudden flash of light caught his eye, and he turned (slowly! carefully! this lump of ice might not be very big, but he preferred to stay on it rather than float off on his own) to look. What was it? Then another flash, slightly to one side, and he realised what was happening. The icebergs surrounding him were rotating, and like faceted jewels they were catching the light of the Sun as they did so. It was beautiful. But admiring the beauty of his surroundings wasn’t going to get him back to the safety of Dragon base. There was no reply to his Mayday, which meant that either his transmitter or his receiver were useless. Or both. He’d soon know; if Reese had heard the electronic cry for help she’d have the Aries off and running after him in a matter of minutes. After all, he couldn’t walk home.

Du Toit continued to stand quietly, watching the shifting display of glinting icebergs around him, conserving energy and oxygen. His own miniature world was also rotating, he noticed, so that the Sun had now ‘risen’ completely to the zenith and was dropping away behind him. Think! he commanded his still dazed brain. There’s no reply to my signal, and no sign of Aries, They haven’t heard me. He took a small drink of water from the tube next to his mouth and chinned the bar to release a stimtab. He’d have to pay the price of increased heart rate and higher oxygen consumption in order to clear his head. Maybe Xu was right after all. He wouldn’t get out of this hole by physical effort. What he needed was a bright idea, some intelligent scheme to signal his whereabouts to the others. C’mon, Jan, he subvocalised, show Mary you’re not just a big physical ape.

He began to feel better, physically and mentally, as the stimulants got to work. The Sun set behind him, and Du Toit saw the comet itself, the Dragon, rising high in the sky of his tiny world. So near, and yet so far. He felt colder in the dark, and, although his brain was clearing and he knew this was purely a psychological reaction, began to walk towards the horizon so that he could see the Sun again. Dig one boot in, and thrust backwards; unhook without pulling yourself to a halt; dig the other boot in, and twist; repeat indefinitely. The rhythm flowed back. And then he had an idea.


“He must be out of oxygen by now.” Bertorelli and Xu were together in the Aries II, floating free amongst the debris of the cometary convulsion. There was little doubt that Du Toit was out there somewhere, but where? Hopefully, they’d nosed among the fragments looking for a spacesuited figure, but to no avail. It was far worse than the proverbial needle in a haystack. He might be no more than a hundred metres away, but with no means of signalling his presence they’d never know, unless they struck very lucky indeed.

Xu thumbed the talkback button and spoke to Reese at Dragon base. “We’ll stay out here until we run out of air if you like. But I’d rather be carrying out an intelligent search pattern than just drifting at random.”

“There is no intelligent search pattern, Mary. He could be anywhere in the shoal of ice. It’s up to him to signal us, any way he can, and then I want you out there ready to grab him. I’ll give it another hour, then we’ll admit defeat.”

Reese turned away from the console wearily. Things could have been worse. Their main work was done; the fusion engines were mounted to shift the orbit of the comet as required, and the installation had only suffered minor damage in the quake. They could complete the mission without Du Toit. And they’d all known someone might get killed along the way. But somehow the idea of losing him on a sightseeing trip, on his day off, seemed much worse than if he had suffered an accident while working on the engine installation.

Wenzel’s head came through the hatch, followed by the rest of his long, thin body. Politely, he adjusted his attitude to match the ‘up’ of his commander.

“Boss, I’ve got something weird. I don’t know what it is, but it doesn’t make sense, and you said to watch out for anything unusual at all.”

“What is it, Chuck?” Wenzel had been monitoring the search program set upon by Xu. It was their last hope of detecting any signal Du Toit might try to make.

“Well, it’s like this. All these chunks of ice out there are rotating, and I’ve had the computer work out all their rotation rates and velocities. It’s easy to monitor them from the way they flash in the sunlight. I had a half-baked idea that I could extrapolate back to the ground zero of the breakup, and work out a search based on the probability of an object with Du Toit’s mass moving at a typical velocity having travelled a certain distance by now. But it’s no use – the search volume is still far too big.”

“So what have you found?”

“It’s one of those icebergs. Its rotation is speeding up. At first I thought it might be Du Toit, using his jetpack to increase the spin of the thing, or trying to steer it back to us. But there’s no trace of his exhaust plume in the spectrum of the thing, and anyway if he had a working jetpack he could fly right in the front door. Besides, the change is tiny – I’d never have noticed if the computer hadn’t flagged it as an anomaly. But it just isn’t natural. How can a lump of ice in space start to rotate faster all on its own?”

“I’ve no idea, Chuck, but we’re sure gonna find out. In this universe, if something doesn’t seem to be obeying the laws of physics, chances are there’s intelligence at work. I only hope it’s Du Toit.”

She turned back to the board, and flipped the toggle for Aries II.


When Xu pulled the fogged helmet off Du Toit’s shoulders, he was nearly unconscious. The suit’s air conditioning, damaged during the quake, hadn’t been able to cope adequately with his recent exertions, and his face was running with sweat. He breathed deeply, opened his eyes and smiled weakly.

“Hi, Mary. I’m glad it’s you. But I could’ve done with you getting the message sooner.”

“You big ox, Jan. You had us all worried to death, you know. But we should have guessed that superman was indestructible.”

“Indestructible, but crazy.” Bertorelli, his smile equally broad, interjected. “Who else would have tried to walk home on a piece of ice floating in space, like some demented logger floating on a Canadian river? When Reese told us that iceberg was spinning up and we drifted over to take a look, I don’t know what I expected to see. But it sure wasn’t the sight of you running over the horizon like the Seventh Cavalry charging to the rescue.”

“Just took a little intellectual effort to work it out.” Du Toit, though exhausted, was recovering fast in the oxygen-rich atmosphere of the Aries II. “Action and reaction, equal and opposite. Law of conservation of angular momentum. If I push one way to walk around the ice, the ice has to spin the other way to compensate. Faster I walk, more the ice spins. Knew you big brains would understand icebergs don’t spin faster by magic, and the shiny surface made a great mirror to signal with. Mary’s right – intelligence is the key to survival.”

“But not just intelligence,” she acknowledged. “If I’d been in your shoes I might have had the idea, but that lump of ice would never have noticed my body mass trying to make it spin up. Survival of the fittest needs brain and, brawn, and I’m glad it was you out there, not me.

“C’mon, Jan, we’re taking you home.”


© 1990 John Gribbin and Marcus Chown

First published in Aboriginal Science Fiction, Sept.-Oct. 1990