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

Fun with Physics

Slightly edited version of my review in Wall Street Journal of Storm in a Teacup: The Physics of Everyday Life
by Helen Czerski :

Did you realize that the rumble of thunder associated with a lightning flash is actually a result of the whipcrack sound from the lightning flash taking longer to reach the ear from greater heights up the lightning bolt itself? “These sound waves are travelling at about 1,100 feet every second or 767 mph, which means they’re taking 4.7 seconds to cover a mile,” explain Helen Czerski in her entertaining new book. “What I hear just after the initial crack is the sound from slightly higher up the lightning bolt. It started as the same sound but it took longer to reach me because it had to travel along a sloping, and therefore longer, path. And then as the thunder rumbles on, I’m hearing the sound from higher and higher up that same lightning bolt.”
Dr Czerski is a British physicist with wide experience as a science popularizer both in print media and for the BBC. The emphasis here is definitely on “popular”; “Storm in a Teacup” is very much a fun book, pulling together many easily accessible accounts of how physics explains everyday phenomena, from the titular teacup whirlpools to the reason why ducks don’t freeze when swimming in icy water. Most of the stories are self-contained, so the reader can dip into the book anywhere and be pretty sure of pulling out a juicy plum; many are anecdotal, drawing on the author’s experience as a marine researcher, investigating what goes on at the boundary between sea and atmosphere. Czerski is at her best when describing her personal experiences of natural phenomena, whether this is her struggle with scientific equipment on the heaving deck of a research vessel in a storm, or something as familiar to the reader as that flash of lightning. The result is a painless way of learning how the world works, like having a friendly physicist giving you a personal fireside chat.
Although individual anecdotes are self-contained, “Storm in a Teacup” is arranged thematically, with eight chapters each jumping of from a particular phenomenon (such as the reason why popcorn pops) and developing a theme based on that everyday event (in this case, how space rockets work) with a final chapter looking at humankind’s place in the universe.
I particularly enjoyed the discussion of why coffee stains dry out to produce brown outlines, not because the explanation was a surprise to me, but because of the nod given to the pioneering microscopist Robert Hooke, whose contribution to the scientific revolution of the seventeenth century is so often overlooked. “Hooke,” she says, “hadn’t just shown the way to the world of the very small; he’d thrown open the doors and invited everyone in for a party. [His book] Micrographia inspired some of the most famous microscopists of the following centuries, and also whetted the appetite of fashionable London.” Indeed “Storm in a Teacup” whets the appetite in the same way, and the fact that there is indeed a connection between Hooke’s work and the way a puddle of coffee dries out gives you a hint of the approach used by Czerski.
One thing I learned was why ducks paddling in cold water are able to maintain their body heat. The chapter is jokingly titled “Why Don’t Ducks Get Cold Feet?” but what it actually makes clear is that their feet do indeed get cold (very cold), but thanks to some ingenious plumbing arrangements, this does not make the body of the duck cold. As the author herself says, “ducks can happily stand on the ice precisely because their feet are cold. And they don’t care.”
This otherwise excellent book did irritate me in a few small ways. A misguided attempt to interpret the English for an American audience ends up falling between two stools when we are told that the British approach to solving a problem is to “find the cookie tin and put the kettle on.” In my experience, a Britisher might have a biscuit tin, and an American might have a cookie jar. No Britisher I know has a cookie tin, but perhaps they do things differently on board ocean research vessels.
More seriously, a reference to radio waves spreading out in circle from the sinking Titanic misses the opportunity to point out that they actually spread spherically, which is relevant to the story built up from that remark. I suspect that the author meant “spherical” but wrote “circular” in a fit of absent-mindedness and never corrected it. Finally one of my pet hates is to see a physicist refer to “the Theories of Special and General Relativity.” It is the theories that are special (that is, restricted to the special case of uniform motion) or general (that is, generally applicable to any motion), not the relativity!
As these examples show, the book would have benefited from a final polish by an editor with an understanding of physics and the vernacular. But these are minor points which are unlikely to trouble the intended audience. “Storm in a Teacup” would be an ideal gift for any scientifically inquisitive person, including children and adults who retain the sense of wonder of a child. Robert Hooke would have loved it.

Aliens far and near

A double review originally written for the Literary Review

 

Aliens

Ed Jim Al-Khalili

Profile

 

All these worlds are yours

Jon Willis

Yale UP

 

 

In 1995, for the first time a planet was discovered orbiting a bright star other than the Sun. Now, several thousand “extrasolar” planets are known, some of them rocky worlds not much bigger than the Earth, orbiting their parent stars at distances which mean that liquid water could possibly exist on their surfaces. The fact that they are in the “habitable zone” does not necessarily mean that they are habitable. Venus, for example, is a roughly Earth-sized rocky planet orbiting in the habitable zone of our Sun, but that has not stopped it developing a runaway greenhouse effect, losing all its water into space, and becoming a searing hot desert. Nevertheless, the discovery of potential “other Earths” has made the subject of astrobiology respectable, even though astrobiologists do not actually have any astrobiology to study as yet. This provides fertile ground for speculation about the nature of the kind of life that might exist on other worlds, some of it more sensible than others.

Two very different books about the possibility of life elsewhere in the Universe, and how and where we might find it, cover a large part of this spectrum of ideas. Aliens is a collection of 19 short essays (plus an Introduction) squeezed into a mere 219 pages; a mixture of the good, the bad and the indifferent, but all pretty superficial. All These Worlds Are Yours is unashamedly “pop”, but tells a coherent story drawing on a lecture course given by the author, a Professor of Astronomy at the University of Victoria, British Columbia. The former includes a chapter on aliens in science fiction (good) and one on alien abductions (indifferent), which gives you some idea where it is coming from. The latter has an impressively concise and reasonably accurate account of the place of the Earth and Solar System in the Universe, then concentrates on the chances of finding extraterrestrial life among the Sin’s family of planets.

Both books address the question of how we might detect signs of life on distant planets, and point out that we are just developing the technology to identify gases such as oxygen in the atmospheres of such planets, using spectroscopy. Oxygen would be an obvious sign of life, because it is highly reactive and only persists in the atmosphere on Earth because it is constantly being manufactured by living things; if all life on Earth died tomorrow, all the oxygen would be gone in a couple of million years. But neither of them gives due emphasis (although Aliens does at least mention it in passing) to the underlying point, developed by James Lovelock, which is that life involves non-equilibrium processes, in chemical terms, graphically described as operating “on the edge of chaos”. It isn’t the presence or absence of oxygen, per se, that matters, but the presence or absence of stable chemical equilibrium. The atmosphere of Mars, for example, is a stable equilibrium (almost entirely carbon dioxide) which is a clear indication that searching for life there is a waste of time.

The worst of the bad in Aliens picks up on a silly blunder made by Fred Hoyle, who once suggested that the universe is not big enough nor old enough for complex cellular life to have been produced by chance alone. This unfortunate comment has given succour to creationists who, like Hoyle, miss the point that evolution by natural selection does not occur by chance alone (the clue is in the word “selection”), and that this operates from the moment a single self-replicating molecule appears. Many biologists have pointed this out, and Jim Al-Khalili should be ashamed to have allowed the howler to pass his editorial inspection.

On a happier note, Jon Willis gives due emphasis to the discovery that many complex molecules, the precursors of life, exist in clouds of gas and dust in space, and in comets. Indeed, one of the last observations made by the comet probe Rosetta revealed the presence in a comet of amino acids, which are the building blocks of proteins. Such molecules must have rained down on the early Earth, and it is also now clear that bubbles analogous to the membrane walls of living cells form spontaneously from solutions containing certain simple chemicals. A proto “cell” containing proto life molecules could (and probably did) emerge almost as soon as the Earth cooled. The rest is simply a matter of reproduction and natural selection. But as Matthew Cobb points out in Aliens, while it is highly likely that life exists elsewhere in the universe, it is highly unlikely that there is our kind of intelligence “out there”. There are two many so-called bottlenecks (such as the kind of impact that did for the dinosaurs) on the road from single cells to people like us.

But even if we restrict our ambitions to the search for life, discarding our ambitions of making contact with alien civilizations, if the cosmic rain led to life on Earth, why not on the other planets and moons of the Solar System? It turns out that moons are the best bet, not least because a few of them have abundant water, and the meat of Willis’ book deals with the prospects of finding life on the moons Europa, Enceladus and Titan, which orbit giant planets in the outer reaches of the Solar System. If he had a budget of $4 billion, Willis says, he would spend most of it on a probe to bring back samples of water from the moon Enceladus, where jets of water are “constantly vented into space, and the technology exists to sample it and return [it] to Earth”. Where does the figure of $4 billion come from? It is, says Willis, the amount the world spends on so-called defence each day. “Defense from what? One another”. If our priorities were right, we could tackle the question of life elsewhere with ease. Which makes it a pity that he used a quote from Arthur C. Clarke for his title. David Bowie would be more apposite. We could be heroes — just for one day.

 

 

Dr John Gribbin is a Visiting Fellow in Astronomy at the University of Sussex, and author of The Reason Why: The miracle of life on Earth (Penguin)

 

Quantum Entanglement

Quantum entanglement has been in the news (again), and in response to several puzzled enquiries, here is my attempt to disentangle the subject.  Adapted from various bits of my previous writings, including Q is for Quantum, Schrödinger’s Kittens, and Science: A History in 100 Experiments.  I also recommend George Musser’s book Spooky Action at a Distance.

Common sense tells us that if I hit a cricket ball on a playing field in England, this has no effect on a cricket ball in Australia, even if the two balls were manufactured in the same batch in the same factory and once nestled together in the same box.  But does the same common sense apply to things in the quantum world, like photons and electrons? Bizarre though it may seem, in the twentieth century quantum physics proved  by experiment that the answer is “no”.
It all started in 1935, when Albert Einstein and his colleagues Boris Podolsky and Nathan Rosen presented a puzzle (sometimes known as the “EPR Paradox”) in the form of a thought experiment.

Faster than light?
By 1935, Einstein was settled in Princeton, at the Institute for Advanced Study.  He had been working with two younger colleagues, Boris Podolsky (1896-1966) and Nathan Rosen (1909-1995), and together (led by Podolsky on this occasion) they had come up with what seemed to them an unarguable refutation of the nonsense (as they saw it) inherent in the idea of collapsing wave functions and the Copenhagen Interpretation.  This is the bizarre idea (still widely, but incorrectly, taught as the best way to understand the quantum world) that nothing is real until it is measured.  An electron for example, exists (according to the Copenhagen Interpretation) as an indeterminate superposition of waves until someone looks at it, when it “collapses” into a point, before spreading out as waves again as soon as you stop looking.  Their paper describing what became known as the “EPR Paradox”, even though it is not really a paradox, appeared under the title “Can quantum mechanical description of physical reality be considered complete?” in the journal Physical Review in May 1935.  They described the puzzle in terms of measurement of position and momentum, but I shall use what seems to me a simpler example involving electron spin.
Imagine a situation in which two electrons are ejected from a quantum system (such as an atomic nucleus) in different directions, but required by the laws of symmetry to have opposite spin.  According to the Copenhagen Interpretation (largely devised by the Dane Niels Bohr, hence the name), neither of the electrons possesses a definite spin until it is measured; each exists in a 50:50 superposition of spin up and spin down states, until it is measured.  Then, and only then, the wave function collapses into one or the other state.  But in this example the laws of symmetry require the other electron to have the opposite spin.   This is fine when both electrons are in the superposition of states, but it means that at the instant one electron is measured, the other electron, which might by now be far away (in principle, on the other side of the Universe) collapses into the opposite state at the same instant.  How does it know to do this?  It seems that what Einstein called a “spooky action at a distance” links the two particles, which communicate with one another faster than light.  And all quantum entities (which means everything) must be linked  in the same way.
It is a key tenet of the theory of relativity, which has passed every test ever applied to it, that no signal can travel faster than light, so Einstein, in particular, saw this as a complete refutation of Bohr’s ideas.  The EPR paper concluded that this makes the reality of properties of the second system “depend upon the process of measurement carried out on the first system, which does not disturb the second system in any way.  No reasonable definition of reality could be expected to permit this.”
The alternative that Einstein favoured is that there is some kind of underlying reality, an invisible clockwork which controls the workings of the Universe and gives the appearance of uncertainty, collapsing wave functions and so on, even though “in reality” each of the electrons, in this example, always has a well-defined spin.  In other words, things are “real”, not in a superposition of states, even when we are not looking at them.  The idea that the Universe is composed, even at the quantum level, of real things that exist whether or not we observe them, and that no communication can travel faster than light, is known as “local reality”.
It is, perhaps, jut as well Einstein did not live to see a series of beautiful experiments carried out in the 1980s which proved that local reality is not a good description of the Universe; more of this later, but the implication is that we are forced to abandon either the local bit (allowing communication faster than light) or reality (invoking instead collapsing wave functions).  But nobody knew this in 1935, and Erwin Schrödinger in particular was delighted when he saw the EPR paper.  He wrote at once to Einstein, commenting that “my interpretation is that we do not have a q.m. that is consistent with relativity theory, i.e, with a finite transmission speed of all influences”, and in a paper published in the Proceedings of the Cambridge Philosophical Society later that year  said “it is rather discomforting that the theory should allow a system to be steered or piloted into one or the other type of state at the experimenter’s mercy in spite of his having no access to it.”  This was the genesis of Schrödinger’s famous cat, and also introduced the term “entanglement” into the quantum story.

The truth about the cat in the box
The ideas encapsulated in the famous “thought experiment” involving Schrödinger’s cat actually came in no small measure from Einstein, in the extended correspondence between the two, triggered by the EPR paper, and preserved in the Einstein Archive at Princeton University.  Einstein introduced the idea of two closed boxes and a single ball, “which can be found in one or the other of the two boxes when an observation is made” by looking inside the box.  Common sense says that the ball is always in one of the boxes but not the other; the Copenhagen Interpretation says that before either box is opened a 50:50 wave function fills each of the boxes (but not the space in between!), and when one of the boxes is opened the wave function collapses so that now the ball is in one box or the other.  Einstein continued “I bring in the separation principle.  The second box is independent of anything that happens to the first box.”
In a later letter, Einstein came up with another reductio ad absurdum.  He suggested to Schrödinger the idea of a heap of gunpowder that would “probably” explode some time in the course of a year.  During that year, the wave function of the gunpowder would consist of a mixture of states, a superposition of the wave function for unexploded gunpowder and the wave function for exploded gunpowder:
In the beginning the -function characterises a reasonably well-defined macroscopic state.  But, according to your equation, after the course of a year this is no longer the case at all.  Rather, the -function then describes a sort of blend of not-yet and of already-exploded systems.  Through no art of interpretation can this -function be turned into an adequate description of a real state of affairs  .  .  .  in reality there is just no intermediary between exploded and not-exploded.
Stimulated by the EPR paper and his correspondence with Einstein, Schrödinger wrote a long paper, published in three parts in the journal Die Naturwissenschaften later in 1935, summing up his understanding of the theory he had helped to invent.  It was titled “The Present Situation in Quantum Mechanics”, and it introduced to the world both the term entanglement and the cat “paradox” that (like the EPR “paradox”) is not really a paradox at all.  An excellent English translation of the paper, by John Trimmer, appeared in the Proceedings of the American Philosophical Society in 1980, and can also be found in the volume Quantum Theory and Measurement edited by John Wheeler and Wojciech Zurek.  Many garbled accounts of the cat in the box “experiment” have appeared over the years, but it is best to go back to this source and Schrödinger’s own words (as interpreted by Trimmer) to get the puzzle clear:
One can even set up quite ridiculous cases.  A cat is penned up in a steel chamber, along with the following diabolical device (which must be secured against direct interference by the cat): in a Geiger counter there is a tiny bit of radioactive substance, so small, that perhaps in the course of one hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer which shatters a small flask of hydrocyanic acid.  If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed.  The first atomic decay would have poisoned it.  The -function of the entire system would express this by having in it the living and the dead cat (pardon the expression) mixed or smeared out in equal parts.
It is typical of these cases that an indeterminacy originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then be resolved by direct observation.
In other words, according to the version of quantum mechanics that was generally taught and widely (but not universally) accepted for the rest of the twentieth century, the cat is both dead and alive (or if you prefer, neither dead nor alive) until somebody looks inside the chamber and by the act of observation “collapses the wave function”.  But there is nothing in the equations about collapsing wave functions.  This collapse business is an entirely ad hoc idea, introduced by Bohr, with no basis in reality.  That is the single most important message to take away from Schrödinger’s thought experiment (which, I stress, is indeed “all in the mind”; nobody has ever done anything like this to a real cat).  Although the “cat-in-the-box” idea did not generate widespread interest in 1935, Einstein at least fully appreciated the importance of Schrödinger’s puzzle; Schrödinger described the idea to him in a letter, before his paper was published, and Einstein replied:
Your cat shows that we are in complete agreement concerning our assessment of the character of the current theory.  A [wave]-function that contains the living as well as the dead cat just cannot be taken as a description of a real state of affairs.
Schrödinger was right to point out the nonsensical nature of the concept of the collapse of the wave function, and there are much better ways to understand the workings of the quantum world – the most intriguing of which Schrödinger himself later came close to developing (my own preferred explanation, which involves the Many Worlds Interpretation; but that is anther story).
The EPR puzzle itself was later refined by David Bohm, and later still by John Bell.  In its later form, the puzzle concerns the behaviour of two photons (particles of light) ejected from an atom in opposite directions.  The photons have a property called polarization, which can be thought of as like carrying a spear pointing either up, down or at any angle across the direction of travel; the key feature of the puzzle is that the photons must have different polarization, but correlated in a certain way.  For simplicity, imagine that if one photon is vertically polarised the other must be horizontally polarised.
Now comes the twist.  Quantum physics tells us that the polarization of the photon is not determined – it does not become “real” – until it is measured.  The act of measurement forces it to “choose” a particular polarisation, and it is possible (indeed, straightforward) to set up an experiment which measures a photon to decide if it vertically polarised, or horizontally polarised.  The essence of the EPR “paradox” is that according to all this, measuring one of the pair of photons and forcing it to become, say, vertically polarised instantaneously forces the other photon, far away and untouched, to become horizontally polarised.  Einstein and his colleagues said that this is ridiculous, defying common sense, so quantum mechanics must be wrong.
After John Bell presented the puzzle in a particularly clear form in the 1960s, the challenge of testing the prediction was taken up by several teams of experimenters, leading up to a comprehensive and complete experiment carried out by Alain Aspect and his colleagues in Paris in the early 1980s.  Although such experiments have since been refined and improved, they always give the same results that emerged from the Aspect experiment itself.
The key feature of the experiment is that the choice of which polarisation will be measured is made automatically and at random by the experiment, after the photons have left the atom.  At the time the photon arrives at the polariser, there has not been long enough for any signal, even travelling at the speed of light, to have reached the other side of the experiment.  So there is no way that the detector used to measure the second photon “knows” what the first measurement is.
It would be very difficult (just about impossible with present technology) to do the experiment literally with pairs of photons, two at a time; but in the Aspect experiment and its successors very many pairs of photons are studied, with more than two angles of polarisation being investigated, and the results analysed statistically.  John Bell’s great contribution was to show that in this kind of analysis if one particular number that emerges from the statistics is bigger than another specific number, common sense prevails and there is no trace of what Einstein used to call “spooky action at a distance”.  This is what Bell expected to happen, and it is known as Bell’s Inequality.  But the experiments show that Bell’s Inequality is violated.  The first number is smaller than the second number.  Experiments are somehow particularly convincing when they prove the opposite of what the experimenters set out to find – it certainly shows that they were not cheating, or unconsciously biased by their preconceptions!  And as Richard Feynman pithily summed up the essence of science, “if it disagrees with experiment, then it is wrong”.  So Einstein was wrong.  But what does it mean?
The pairs of photons really are linked by spooky action at a distance, confounding “common sense”, in the state quantum physicists call entanglement.  What happens to photon A really does affect photon B, instantaneously, no matter how far apart they are.  This is called “non-locality”, because the effect is not “local” (specifically, it occurs faster than light}.  But (and it is not just a big “but” but an absolutely crucial “but”) it turns out that no useful information, such as the result of the 3.30 race at Newmarket, can be transmitted faster than light by this or any other means).  The polarizations of the photons are determined at random.  Measuring the polarization of photon A determines the polarization of photon B, but someone who can only detect photon B still sees a random choice of polarization.  It might be different random choice from the one that would have occurred if photon A had been affected differently, but it is still random.  The only way to extract useful information from studying photon B is to send a message (slower than light) from A to B informing the observer what was done to photon A.  Nevertheless, the Aspect experiment and its successors show that the world is non-local.  And this strange property even has practical implications, in the rapidly developing world of quantum computing.  This may not be a “reasonable definition of reality”, but it is the way the world works.
Feynman was particularly delighted by this definitive experimental evidence of the way the quantum world works.  “I’ve entertained myself always,” he said, “by squeezing the difficulty of quantum mechanics into a smaller and smaller place, so as to get more and more worried about this particular item.  It seems to be almost ridiculous that you can squeeze it to a numerical question that one thing is bigger than another.  But there you are.”
Don’t worry, though if you do not understand how the world can be like that.  As Feynman also wrote, in The Character of Physical Law, “I think I can safely say that nobody understands quantum mechanics  .  .  .  Do not keep saying to yourself, if you can possibly avoid it, ‘But how can it be like that?” because you will go ‘down the drain’ into a blind alley from which nobody has yet escaped.  Nobody knows how it can be like that.”