From the start of World War II, military aircrews were routinely issued parachutes, and backpack or seat pack parachutes with ripcord deployment had become highly reliable. As the war progressed and aircraft performance rapidly increased, it became clear that although parachutes could save air crew, physically escaping from a damaged plane at high velocities and altitudes was a formidable problem. The U.S. P-51 Mustang, of which more than 15,000 were built, cruised at 580 km/hour and had a maximum speed of 700 km/hour. It was physically impossible for a pilot to escape from the cockpit into such a wind blast, and even if they managed to do so, they would likely be torn apart by collision with the fuselage or tail an instant later. A pilot's only hope was that the plane would slow to a speed at which escape was possible before crashing into the ground, bursting into flames, or disintegrating.

In 1944, when the Nazi Luftwaffe introduced the first operational jet fighter, the Messerschmitt Me 262, capable of 900 km/hour flight, they experimented with explosive-powered ejection seats, but never installed them in this front-line fighter. After the war, with each generation of jet fighters flying faster and higher than the previous, and supersonic performance becoming routine, ejection seats became standard equipment in fighter and high performance bomber aircraft, and saved many lives. Still, by the mid-1950s, one in four pilots who tried to eject was killed in the attempt. It was widely believed that the forces of blasting a pilot out of the cockpit, rapid deceleration by atmospheric friction, and wind blast at transonic and supersonic speeds were simply too much for the human body to endure. Some aircraft designers envisioned “escape capsules” in which the entire crew cabin would be ejected and recovered, but these systems were seen to be (and proved when tried) heavy and potentially unreliable.

John Paul Stapp's family came from the Hill Country of south central Texas, but he was born in Brazil in 1910 while his parents were Baptist missionaries there. After high school in Texas, he enrolled in Baylor University in Waco, initially studying music but then switching his major to pre-med. Upon graduation in 1931 with a major in zoology and minor in chemistry, he found that in the depths of the Depression there was no hope of affording medical school, so he enrolled in an M.A. program in biophysics, occasionally dining on pigeons he trapped on the roof of the biology building and grilled over Bunsen burners in the laboratory. He then entered a Ph.D. program in biophysics at the University of Texas, Austin, receiving his doctorate in 1940. Before leaving Austin, he was accepted by the medical school at the University of Minnesota, which promised him employment as a research assistant and instructor to fund his tuition.

In October 1940, with the possibility that war in Europe and the Pacific might entangle the country, the U.S. began military conscription. When the numbers were drawn from the fishbowl, Stapp's was 15th from the top. As a medical student, he received an initial deferment, but when it expired he joined the regular Army under a special program for medical students. While completing medical school, he would receive private's pay of US$ 32 a month (around US$7000 a year in today's money), which would help enormously with tuition and expenses. In December 1943 Stapp received his M.D. degree and passed the Minnesota medical board examination. He was commissioned as a second lieutenant in the Army Medical Corps and placed on suspended active duty for his internship in a hospital in Duluth, Minnesota, where he delivered 200 babies and assisted in 225 surgeries. He found he delighted in emergency and hands-on medicine. In the fall of 1944 he went on full active duty and began training in field medicine. After training, he was assigned as a medical officer at Lincoln Army Air Field in Nebraska, where he would combine graduate training with hospital work.

Stapp had been fascinated by aviation and the exploits of pioneers such as Charles Lindbergh and the stratospheric balloon explorers of the 1930s, and found working at an air base fascinating, sometimes arranging to ride along in training missions with crews he'd treated in the hospital. In April 1945 he was accepted by the Army School of Aviation Medicine in San Antonio, where he and his class of 150 received intense instruction in all aspects of human physiology relating to flight. After graduation and a variety of assignments as a medical officer, he was promoted to captain and invited to apply to the Aero Medical Laboratory at Wright Field in Dayton, Ohio for a research position in the Biophysics Branch. On the one hand, this was an ideal position for the intellectually curious Stapp, as it would combine his Ph.D. work and M.D. career. On the other, he had only eight months remaining in his service commitment, and he had long planned to leave the Army to pursue a career as a private physician. Stapp opted for the challenge and took the post at Wright.

Starting work, he was assigned to the pilot escape technology program as a “project engineer”. He protested, “I'm a doctor, not an engineer!”, but settled into the work and, being fluent in German, was assigned to review 1200 pages of captured German documents relating to crew ejection systems and their effects upon human subjects. Stapp was appalled by the Nazis' callous human experimentation, but, when informed that the Army intended to destroy the documents after his study was complete, took the initiative to preserve them, both for their scientific content and as evidence of the crimes of those whose research produced it.

The German research and the work of the branch in which Stapp worked had begun to persuade him that the human body was far more robust than had been assumed by aircraft designers and those exploring escape systems. It was well established by experiments in centrifuges at Wright and other laboratories that the maximum long-term human tolerance for acceleration (g-force) without special equipment or training was around six times that of Earth's gravity, or 6 g. Beyond that, subjects would lose consciousness, experience tissue damage due to lack of blood flow, or structural damage to the skeleton and/or internal organs. However, a pilot ejecting from a high performance aircraft experienced something entirely different from a subject riding in a centrifuge. Instead of a steady crush by, say, 6 g, the pilot would be subjected to much higher accelerations, perhaps on the order of 20—40 g, with an onset of acceleration (“jerk”) of 500 g per second. The initial blast of the mortar or rockets firing the seat out of the cockpit would be followed by a sharp pulse of deceleration as the pilot was braked from flight speed by air friction, during which he would be subjected to wind blast potentially ten times as strong as any hurricane. Was this survivable at all, and if so, what techniques and protective equipment might increase a pilot's chances of enduring the ordeal?

While pondering these problems and thinking about ways to research possible solutions under controlled conditions, Stapp undertook another challenge: providing supplemental oxygen to crews at very high altitudes. Stapp volunteered as a test subject as well as medical supervisor and began flight tests with a liquid oxygen breathing system on high altitude B-17 flights. Crews flying at these altitudes in unpressurised aircraft during World War II and afterward had frequently experienced symptoms similar to “the bends” (decompression sickness) which struck divers who ascended too quickly from deep waters. Stapp diagnosed the cause as identical: nitrogen dissolved in the blood coming out of solution as bubbles and pooling in joints and other bodily tissues. He devised a procedure of oxygen pre-breathing, where crews would breathe pure oxygen for half an hour before taking off on a high altitude mission, which completely eliminated the decompression symptoms. The identical procedure is used today by astronauts before they begin extravehicular activities in space suits using pure oxygen at low pressure.

From the German documents he studied, Stapp had become convinced that the tool he needed to study crew escape was a rocket propelled sled, running on rails, with a brake mechanism that could be adjusted to provide a precisely calibrated deceleration profile. When he learned that the Army was planning to build such a device at Muroc Army Air Base in California, he arranged to be put in charge of Project MX-981 with a charter to study the “effects of deceleration forces of high magnitude on man”. He arrived at Muroc in March 1947, along with eight crash test dummies to be used in the experiments. If Muroc (now Edwards Air Force Base) of the era was legendary for its Wild West accommodations (Chuck Yeager would not make his first supersonic flight there until October of that year), the North Base, where Stapp's project was located, was something out of Death Valley Days. When Stapp arrived to meet his team of contractors from Northrop Corporation they struck the always buttoned-down Stapp like a “band of pirates”. He also discovered the site had no electricity, no running water, no telephone, and no usable buildings. The Army, preoccupied with its glamourous high speed aviation projects, had neither interest in what amounted to a rocket powered train with a very short track, nor much inclination to provide it the necessary resources. Stapp commenced what he came to call the Battle of Muroc, mastering the ancient military art of scrounging and exchanging favours to get the material he needed and the work done.

As he settled in at Muroc and became acquainted with his fellow denizens of the desert, he was appalled to learn that the Army provided medical care only for active duty personnel, and that civilian contractors and families of servicemen, even the exalted test pilots, had to drive 45 miles to the nearest clinic. He began to provide informal medical care to all comers, often making house calls in the evening hours on his wheezing scooter, in return for home cooked dinners. This built up a network of people who owed him favours, which he was ready to call in when he needed something. He called this the “Curbstone Clinic”, and would continue the practice throughout his career. After some shaky starts and spectacular failures due to unreliable surplus JATO rockets, the equipment was ready to begin experiments with crash test dummies.

Stapp had always intended that the tests with dummies would be simply a qualification phase for later tests with human and animal subjects, and he would ask no volunteer to do something he wouldn't try himself. Starting in December, 1947, Stapp personally made increasingly ambitious runs on the sled, starting at “only” 10 g deceleration and building to 35 g with an onset jerk of 1000 g/second. The runs left him dizzy and aching, but very much alive and quick to recover. Although far from approximating the conditions of ejection from a supersonic fighter, he had already demonstrated that the Air Force's requirements for cockpit seats and crew restraints, often designed around a 6 g maximum shock, were inadequate and deadly. Stapp was about to start making waves, and some of the push-back would be daunting. He was ordered to cease all human experimentation for at least three months.

Many Air Force officers (for the Air Force had been founded in September 1947 and taken charge of the base) would have saluted and returned to testing with instrumented dummies. Stapp, instead, figured out how to obtain thirty adult chimpanzees, along with the facilities needed to house and feed them, and resumed his testing, with anæsthetised animals, up to the limits of survival. Stapp was, and remained throughout his career, a strong advocate for the value of animal experimentation. It was a grim business, but at the time Muroc was frequently losing test pilots at the rate of one a week, and Stapp believed that many of these fatalities were unnecessary and could be avoided with proper escape and survival equipment, which could only be qualified through animal and cautious human experimentation.

By September 1949, approval to resume human testing was given, and Stapp prepared for new, more ambitious runs, with the subject facing forward on the sled instead of backward as before, which would more accurately simulate the forces in an ejection or crash and expose him directly to air blast. He rapidly ramped up the runs, reaching 32 g without permanent injury. To avoid alarm on the part of his superiors in Dayton, a “slight error” was introduced in the reports he sent: all g loads from the runs were accidentally divided by two.

Meanwhile, Stapp was ramping up his lobbying for safer seats in Air Force transport planes, arguing that the existing 6 g forward facing seats and belts were next to useless in many survivable crashes. Finally, with the support of twenty Air Force generals, in 1950 the Air Force adopted a new rear-facing standard seat and belt rated for 16 g which weighed only two pounds more than those it replaced. The 16 g requirement (although not the rearward-facing orientation, which proved unacceptable to paying customers) remains the standard for airliner seats today, seven decades later.

In June, 1951, Stapp made his final run on the MX-981 sled at what was now Edwards Air Force Base, decelerating from 180 miles per hour (290 km/h) to zero in 31 feet (9.45 metres), at 45.4 g, a force comparable to many aircraft and automobile accidents. The limits of the 2000 foot track (and the human body) had been reached. But Stapp was not done: the frontier of higher speeds remained. Shortly thereafter, he was promoted to lieutenant colonel and given command of what was called the Special Projects Section of the Biophysics Branch of the Aero Medical Laboratory. He was reassigned to Holloman Air Force Base in New Mexico, where the Air Force was expanding its existing 3500 foot rocket sled track to 15,000 feet (4.6 km), allowing testing at supersonic speeds. (The Holloman High Speed Test Track remains in service today, having been extended in a series of upgrades over the years to a total of 50,917 feet (15.5 km) and a maximum speed of Mach 8.6, or 2.9 km/sec [6453 miles per hour].)

Northrop was also contractor for the Holloman sled, and devised a water brake system which would be more reliable and permit any desired deceleration profile to be configured for a test. An upgraded instrumentation system would record photographic and acceleration measurements with much better precision than anything at Edwards. The new sled was believed to be easily capable of supersonic speeds and was named Sonic Wind. By March 1954, the preliminary testing was complete and Stapp boarded the sled. He experienced a 12 g acceleration to the peak speed of 421 miles per hour, then 22 g deceleration to a full stop, all in less than eight seconds. He walked away, albeit a little wobbly. He had easily broken the previous land speed record of 402 miles per hour and become “the fastest man on Earth.” But he was not done.

On December 10th, 1954, Stapp rode Sonic Wind, powered by nine solid rocket motors. Five seconds later, he was travelling at 639 miles per hour, faster than the .45 ACP round fired by the M1911A1 service pistol he was issued as an officer, around Mach 0.85 at the elevation of Holloman. The water brakes brought him to a stop in 1.37 seconds, a deceleration of 46.2 g. He survived, walked away (albeit just few steps to the ambulance), and although suffering from vision problems for some time afterward, experienced no lasting consequences. It was estimated that the forces he survived were equivalent to those from ejecting at an altitude of 36,000 feet from an airplane travelling at 1800 miles per hour (Mach 2.7). As this was faster than any plane the Air Force had in service or on the drawing board, he proved that, given a suitable ejection seat, restraints, and survival equipment, pilots could escape and survive even under these extreme circumstances. The Big Run, as it came to be called, would be Stapp's last ride on a rocket sled and the last human experiment on the Holloman track. He had achieved the goal he set for himself in 1947: to demonstrate that crew survival in high performance aircraft accidents was a matter of creative and careful engineering, not the limits of the human body. The manned land speed record set on the Big Run would stand until October 1983, when Richard Noble's jet powered Thrust2 car set a new record of 650.88 miles per hour in the Nevada desert. Stapp remarked at the time that Noble had gone faster but had not, however, stopped from that speed in less than a second and a half.

From the early days of Stapp's work on human tolerance to deceleration, he was acutely aware that the forces experienced by air crew in crashes were essentially identical to those in automobile accidents. As a physician interested in public health issues, he had noted that the Air Force was losing more personnel killed in car crashes than in airplane accidents. When the Military Air Transport Service (MATS) adopted his recommendation and installed 16 g aft-facing seats in its planes, deaths and injuries from crashes had fallen by two-thirds. By the mid 1950s, the U.S. was suffering around 35,000 fatalities per year in automobile accidents—comparable to a medium-sized war—year in and year out, yet next to nothing had been done to make automobiles crash resistant and protect their occupants in case of an accident. Even the simplest precaution of providing lap belts, standard in aviation for decades, had not been taken; seats were prone to come loose and fly forward even in mild impacts; steering columns and dashboards seemed almost designed to impale drivers and passengers; and “safety” glass often shredded the flesh of those projected through it in a collision.

In 1954, Stapp turned some of his celebrity as the fastest man on Earth toward the issue of automobile safety and organised, in conjunction with the Society of Automotive Engineers (SAE), the first Automobile Crash Research Field Demonstration and Conference, which was attended by representatives of all of the major auto manufacturers, medical professional societies, and public health researchers. Stapp and the SAE insisted that the press be excluded: he wanted engineers from the automakers free to speak without fear their candid statements about the safety of their employers' products would be reported sensationally. Stapp conducted a demonstration in which a car was towed into a fixed barrier at 40 miles an hour with two dummies wearing restraints and two others just sitting in the seats. The belted dummies would have walked away, while the others flew into the barrier and would have almost certainly been killed. It was at this conference that many of the attendees first heard the term “second collision”. In car crashes, it was often not the crash of the car into another car or a barrier that killed the occupants: it was their colliding with dangerous items within the vehicle after flying loose following the initial impact.

Despite keeping the conference out of the press, word of Stapp's vocal advocacy of automobile safety quickly reached the auto manufacturers, who were concerned both about the marketing impact of the public becoming aware not only of the high level of deaths on the highways but also the inherent (and unnecessary) danger of their products to those who bought them, and also the bottom-line impact of potential government-imposed safety mandates. Auto state congressmen got the message, and the Air Force heard it from them: the Air Force threatened to zero out aeromedical research funding unless car crash testing was terminated. It was.

Still, the conferences continued (they would eventually be renamed “Stapp Car Crash Conferences”), and Stapp became a regular witness before congressional committees investigating automobile safety. Testifying about whether it was appropriate for Air Force funds to be used in studying car crashes, in 1957 he said, “I have done autopsies on aircrew members who died in airplane crashes. I have also performed autopsies on aircrew members who died in car crashes. The only conclusion I could come to is that they were just as dead after a car crash as they were after an airplane crash.” He went on to note that simply mandating seatbelts in Air Force ground vehicles would save around 125 lives a year, and if they were installed and used by the occupants of all cars in the U.S., around 20,000 lives—more than half the death toll—could be saved. When he appeared before congress, he bore not only the credentials of a medical doctor, Ph.D. in biophysics, Air Force colonel, but the man who had survived more violent decelerations equivalent to a car crash than any other human.

It was not until the 1960s that a series of mandates were adopted in the U.S. which required seat belts, first in the front seat and eventually for all passengers. Testifying in 1963 at a hearing to establish a National Accident Prevention Center, Stapp noted that the Air Force, which had already adopted and required the use of seat belts, had reduced fatalities in ground vehicle accidents by 50% with savings estimated at US$ 12 million per year. In September 1966, President Lyndon Johnson signed two bills, the National Traffic and Motor Vehicle Safety Act and the Highway Safety Act, creating federal agencies to research vehicle safety and mandate standards. Standing behind the president was Colonel John Paul Stapp: the long battle was, if not won, at least joined.

Stapp had hoped for a final promotion to flag rank before retirement, but concluded he had stepped on too many toes and ignored too many Pentagon directives during his career to ever wear that star. In 1967, he was loaned by the Air Force to the National Highway Traffic Safety Administration to continue his auto safety research. He retired from the Air Force in 1970 with the rank of full colonel and in 1973 left what he had come to call the “District of Corruption” to return to New Mexico. He continued to attend and participate in the Stapp Car Crash Conferences, his last being the Forty-Third in 1999. He died at his home in Alamogordo, New Mexico in November that year at the age of 89.

In his later years, John Paul Stapp referred to the survivors of car crashes who would have died without the equipment designed and eventually mandated because of his research as “the ghosts that never happened”. In 1947, when Stapp began his research on deceleration and crash survival, motor vehicle deaths in the U.S. were 8.41 per 100 million vehicle miles travelled (VMT). When he retired from the Air Force in 1970, after adoption of the first round of seat belt and auto design standards, they had fallen to 4.74 (which covers the entire fleet, many of which were made before the adoption of the new standards). At the time of his death in 1999, fatalities per 100 million VMT were 1.55, an improvement in safety of more than a factor of five. Now, Stapp was not solely responsible for this, but it was his putting his own life on the line which showed that crashes many considered “unsurvivable” were nothing of the sort with proper engineering and knowledge of human physiology. There are thousands of aircrew and tens or hundreds of thousands of “ghosts that never happened” who owe their lives to John Paul Stapp. Maybe you know one; maybe you are one. It's worth a moment remembering and giving thanks to the largely forgotten man who saved them.

Almost as soon as there were computers, programmers realised that their ability to simulate, well…anything made them formidable engines for playing games. Computer gaming was originally mostly a furtive and disreputable activity, perpetrated by gnome-like programmers on the graveyard shift while the computer was idle, having finished the “serious” work paid for by unimaginative customers (who actually rose before the crack of noon!). But as the microelectronics revolution slashed the size and price of computers to something individuals could afford for their own use (or, according to the computer Puritans of the previous generations, abuse), computer gaming came into its own. Some modern computer games have production and promotion budgets larger than Hollywood movies, and their characters and story lines have entered the popular culture. As computer power has grown exponentially, games have progressed from tic-tac-toe, through text-based adventures, simple icon character video games, to realistic three dimensional simulated worlds in which the players explore a huge world, interact with other human players and non-player characters (endowed with their own rudimentary artificial intelligence) within the game, and in some games and simulated worlds, have the ability to extend the simulation by building their own objects with which others can interact. If your last experience with computer games was the Colossal Cave Adventure or Pac-Man, try a modern game or virtual world—you may be amazed.

Computer simulations on affordable hardware are already beginning to approach the limits of human visual resolution, perception of smooth motion, and audio bandwidth and localisation, and some procedurally-generated game worlds are larger than a human can explore in a million lifetimes. Computer power is forecast to continue to grow exponentially for the foreseeable future and, in the Roaring Twenties, permit solving a number of problems through “brute force”—simply throwing computing power and massive data storage capacity at them without any deeper fundamental understanding of the problem. Progress in the last decade in areas such as speech recognition, autonomous vehicles, and games such as Go are precursors to what will be possible in the next.

This raises the question of how far it can go—can computer simulations actually approach the complexity of the real world, with characters within the simulation experiencing lives as rich and complex as our own and, perhaps, not even suspect they're living in a simulation? And then, we must inevitably speculate whether we are living in a simulation, created by beings at an outer level (perhaps themselves many levels deep in a tree of simulations which may not even have a top level). There are many reasons to suspect that we are living in a simulation; for many years I have said it's “more likely than not”, and others, ranging from Stephen Hawking to Elon Musk and Scott Adams, have shared my suspicion. The argument is very simple.

First of all, will we eventually build computers sufficiently powerful to provide an authentic simulated world to conscious beings living within it? There is no reason to doubt that we will: no law of physics prevents us from increasing the power of our computers by at least a factor of a trillion from those of today, and the lesson of technological progress has been that technologies usually converge upon their physical limits and new markets emerge as they do, using their capabilities and funding further development. Continued growth in computing power at the rate of the last fifty years should begin to make such simulations possible some time between 2030 and the end of this century.

So, when we have the computing power, will we use it to build these simulations? Of course we will! We have been building simulations to observe their behaviour and interact with them, for ludic and other purposes, ever since the first primitive computers were built. The market for games has only grown as they have become more complex and realistic. Imagine what if will be like when anybody can create a whole society—a whole universe—then let it run to see what happens, or enter it and experience it first-hand. History will become an experimental science. What would have happened if the Roman empire had discovered the electromagnetic telegraph? Let's see!—and while we're at it, run a thousand simulations with slightly different initial conditions and compare them.

Finally, if we can create these simulations which are so realistic the characters within them perceive them as their real world, why should we dare such non-Copernican arrogance as to assume we're at the top level and not ourselves within a simulation? I believe we shouldn't, and to me the argument that clinches it is what I call the “branching factor”. Just as we will eventually, indeed, I'd say, inevitably, create simulations as rich as our own world, so will the beings within them create their own. Certainly, once we can, we'll create many, many simulations: as many or more as there are running copies of present-day video games, and the beings in those simulations will as well. But if each simulation creates its own simulations in a number (the branching factor) even a tiny bit larger than one, there will be exponentially more observers in these layers on layers of simulations than at the top level. And, consequently, as non-privileged observers according to the Copernican Principle, it is not just more likely than not, but overwhelmingly probable that we are living in a simulation.

The author of this book, founder of Play Labs @ MIT, a start-up accelerator which works in conjunction with the MIT Game Lab, and producer of a number of video games, has come to the same conclusion, and presents the case for the simulation hypothesis from three perspectives: computer science, physics, and the unexplained (mysticism, esoteric traditions, and those enduring phenomena and little details which don't make any sense when viewed from the conventional perspective but may seem perfectly reasonable once we accept we're characters in somebody else's simulation).

Computer Science. The development of computer games is sketched from their origins to today's three-dimensional photorealistic multiplayer environments into the future, where virtual reality mediated by goggles, gloves, and crude haptic interfaces will give way to direct neural interfaces to the brain. This may seem icky and implausible, but so were pierced lips, eyebrows, and tongues when I was growing up, and now I see them everywhere, without the benefit of directly jacking in to a world larger, more flexible, and more interesting than the dingy one we inhabit. This is sketched in eleven steps, the last of which is the Simulation Point, where we achieve the ability to create simulations which “are virtually indistinguishable from a base physical reality.” He describes, “The Great Simulation is a video game that is so real because it is based upon incredibly sophisticated models and rendering techniques that are beamed directly into the mind of the players, and the actions of artificially generated consciousness are indistinguishable from real players.” He identifies nine technical hurdles which must be overcome in order to arrive at the Simulation Point. Some, such as simulating a sufficiently large world and number of players, are challenging but straightforward scaling up of things we're already doing, which will become possible as computer power increases. Others, such as rendering completely realistic objects and incorporating physical sensations, exist in crude form today but will require major improvements we don't yet know how to build, while technologies such as interacting directly with the human brain and mind and endowing non-player characters within the simulation with consciousness and human-level intelligence have yet to be invented.

Physics. There are a number of aspects of the physical universe, most revealed as we have observed at very small and very large scales, and at speeds and time intervals far removed from those with which we and our ancestors evolved, that appear counterintuitive if not bizarre to our expectations from everyday life. We can express them precisely in our equations of quantum mechanics, special and general relativity, electrodynamics, and the standard models of particle physics and cosmology, and make predictions which accurately describe our observations, but when we try to understand what is really going on or why it works that way, it often seems puzzling and sometimes downright weird.

But as the author points out, when you view these aspects of the physical universe through the eyes of a computer game designer or builder of computer models of complex physical systems, they look oddly familiar. Here is how I expressed it thirteen years ago in my 2006 review of Leonard Susskind's The Cosmic Landscape:

What would we expect to see if we inhabited a simulation? Well, there would probably be a discrete time step and granularity in position fixed by the time and position resolution of the simulation—check, and check: the Planck time and distance appear to behave this way in our universe. There would probably be an absolute speed limit to constrain the extent we could directly explore and impose a locality constraint on propagating updates throughout the simulation—check: speed of light. There would be a limit on the extent of the universe we could observe—check: the Hubble radius is an absolute horizon we cannot penetrate, and the last scattering surface of the cosmic background radiation limits electromagnetic observation to a still smaller radius. There would be a limit on the accuracy of physical measurements due to the finite precision of the computation in the simulation—check: Heisenberg uncertainty principle—and, as in games, randomness would be used as a fudge when precision limits were hit—check: quantum mechanics.

Indeed, these curious physical phenomena begin to look precisely like the kinds of optimisations game and simulation designers employ to cope with the limited computer power at their disposal. The author notes, “Quantum Indeterminacy, a fundamental principle of the material world, sounds remarkably similar to optimizations made in the world of computer graphics and video games, which are rendered on individual machines (computers or mobile phones) but which have conscious players controlling and observing the action.”

One of the key tricks in complex video games is “conditional rendering”: you don't generate the images or worry about the physics of objects which the player can't see from their current location. This is remarkably like quantum mechanics, where the act of observation reduces the state vector to a discrete measurement and collapses its complex extent in space and time into a known value. In video games, you only need to evaluate when somebody's looking. Quantum mechanics is largely encapsulated in the tweet by Aatish Bhatia, “Don't look: waves. Look: particles.” It seems our universe works the same way. Curious, isn't it?

Similarly, games and simulations exploit discreteness and locality to reduce the amount of computation they must perform. The world is approximated by a grid, and actions in one place can only affect neighbours and propagate at a limited speed. This is precisely what we see in field theories and relativity, where actions are local and no influence can propagate faster than the speed of light.

The unexplained. Many esoteric and mystic traditions, especially those of the East such as Hinduism and Buddhism, describe the world as something like a dream, in which we act and our actions affect our permanent identity in subsequent lives. Western traditions, including the Abrahamic religions, see life in this world as a temporary thing, where our acts will be judged by a God who is outside the world. These beliefs come naturally to humans, and while there is little or no evidence for them in conventional science, it is safe to say that far more people believe and have believed these things and have structured their lives accordingly than those who have adopted the strictly rationalistic viewpoint one might deduce from deterministic, reductionist science.

And yet, once again, in video games we see the emergence of a model which is entirely compatible with these ancient traditions. Characters live multiple lives, and their actions in the game cause changes in a state (“karma”) which is recorded outside the game and affects what they can do. They complete quests, which affect their karma and capabilities, and upon completing a quest, they may graduate (be reincarnated) into a new life (level), in which they retain their karma from previous lives. Just as players who exist outside the game can affect events and characters within it, various traditions describe actors outside the natural universe (hence “supernatural”) such as gods, angels, demons, and spirits of the departed, interacting with people within the universe and occasionally causing physical manifestations (miracles, apparitions, hauntings, UFOs, etc.). And perhaps the simulation hypothesis can even explain absence of evidence: the sky in a video game may contain a multitude of stars and galaxies, but that doesn't mean each is populated by its own video game universe filled with characters playing the same game. No, it's just scenery, there to be admired but with which you can't interact. Maybe that's why we've never detected signals from an alien civilisation: the stars are just procedurally generated scenery to make our telescopic views more interesting.

The author concludes with a summary of the evidence we may be living in a simulation and the objection of sceptics (such that a computer as large and complicated as the universe would be required to simulate a universe). He suggests experiments which might detect the granularity of the simulation and provide concrete evidence the universe is not the continuum most of science has assumed it to be. A final chapter presents speculations as to who might be running the simulation, what their motives might be for doing so, and the nature of beings within the simulation. I'm cautious of delusions of grandeur in making such guesses. I'll bet we're a science fair project, and I'll further bet that within a century we'll be creating a multitude of simulated universes for our own science fair projects.

Here, the story continues as Philo reaches the Tree, meets its Guardian, “the largest, ugliest, and smelliest bear” he has ever seen, not to mention the most voluble and endowed with the wit of eternity, and explores the Tree, which holds gateways to other times and places, where Philo must confront a test which has defeated many heroes who have come this way before. Exploring the Tree, he learns of the distant past and future, of the Ancient Marauder and Viridios before the dawn of history, and of the War that changed the course of time.

Continuing his hero's quest, he ventures further westward along the Tyrant's Road into the desert of the Valley of Death. There he will learn the fate of the Tyrant and his enthralled followers and, if you haven't figured it out already, you will probably now understand where Philo's timeline diverged from our own. A hero must have a companion, and it is in the desert, after doing a good deed, that he meets his: a teddy bear, Made in Japan—but a very special teddy bear, as he will learn as the journey progresses.

Finally, he arrives at the Valley of the Angels, with pavement stretching to the horizon and cloaked in an acrid yellow mist that obscures visibility and irritates the eyes and throat. There he finds the legendary City of Illusions, where he is confronted by a series of diabolical abusement park attractions where his wit, courage, and Teddy's formidable powers will be tested to the utmost with death the price of failure. Victory can lead to the storied Bullet Train, the prize he needs to save radio station 2XG and possibly the world, and the next step in his quest.

As the fourth installment in what is projected to be one long story spanning five volumes, if you pick this up cold it will probably strike you as a bunch of disconnected adventures and puzzles each of which might as well be a stand-alone short-short story. As they unfold, only occasionally do you see a connection with the origins of the story or Philo's quest, although when they do appear (as in the linkage between the Library of Infinity and the Library of Ouroboros in The Tower of the Bear) they are a delight. It is only toward the end that you begin to see the threads converging toward what promises to be a stirring conclusion to a young adult classic enjoyable by all ages. I haven't read a work of science fiction so closely patterned on the hero's journey as described in Joseph Campbell's The Hero with a Thousand Faces since Rudy Rucker's 2004 novel Frek and the Elixir; this is not a criticism but a compliment—the eternal hero myth has always made for tales which not only entertain but endure.

This book is currently available only in a Kindle edition. The fifth and final volume of the Yankee Republic saga is scheduled to be published in the spring of 2020.

During the Khrushchev years, Mitrokhin became disenchanted with the regime, considering Khrushchev an uncultured barbarian whose banning of avant garde writers betrayed the tradition of Russian literature. He began to entertain dissident thoughts, not hoping for an overthrow of the Soviet regime but rather its reform by a new generation of leaders untainted by the legacy of Stalin. These thoughts were reinforced by the crushing of the reform-minded regime in Czechoslovakia in 1968 and his own observation of how his service, now called the KGB, manipulated the Soviet justice system to suppress dissent within the Soviet Union. He began to covertly listen to Western broadcasts and read samizdat publications by Soviet dissidents.

In 1972, the First Chief Directorate (FCD: foreign intelligence) moved from the cramped KGB headquarters in the Lubyanka in central Moscow to a new building near the ring road. Mitrokhin had sole responsibility for checking, inventorying, and transferring the entire archives, around 300,000 documents, of the FCD for transfer to the new building. These files documented the operations of the KGB and its predecessors dating back to 1918, and included the most secret records, those of Directorate S, which ran “illegals”: secret agents operating abroad under false identities. Probably no other individual ever read as many of the KGB's most secret archives as Mitrokhin. Appalled by much of the material he reviewed, he covertly began to make his own notes of the details. He started by committing key items to memory and then transcribing them every evening at home, but later made covert notes on scraps of paper which he smuggled out of KGB offices in his shoes. Each week-end he would take the notes to his dacha outside Moscow, type them up, and hide them in a series of locations which became increasingly elaborate as their volume grew.

Mitrokhin would continue to review, make notes, and add them to his hidden archive for the next twelve years until his retirement from the KGB in 1984. After Mikhail Gorbachev became party leader in 1985 and called for more openness (glasnost), Mitrokhin, shaken by what he had seen in the files regarding Soviet actions in Afghanistan, began to think of ways he might spirit his files out of the Soviet Union and publish them in the West.

After the collapse of the Soviet Union, Mitrokhin tested the new freedom of movement by visiting the capital of one of the now-independent Baltic states, carrying a sample of the material from his archive concealed in his luggage. He crossed the border with no problems and walked in to the British embassy to make a deal. After several more trips, interviews with British Secret Intelligence Service (SIS) officers, and providing more sample material, the British agreed to arrange the exfiltration of Mitrokhin, his entire family, and the entire archive—six cases of notes. He was debriefed at a series of safe houses in Britain and began several years of work typing handwritten notes, arranging the documents, and answering questions from the SIS, all in complete secrecy. In 1995, he arranged a meeting with Christopher Andrew, co-author of the present book, to prepare a history of KGB foreign intelligence as documented in the archive.

Mitrokhin's exfiltration (I'm not sure one can call it a “defection”, since the country whose information he disclosed ceased to exist before he contacted the British) and delivery of the archive is one of the most stunning intelligence coups of all time, and the material he delivered will be an essential primary source for historians of the twentieth century. This is not just a whistle-blower disclosing operations of limited scope over a short period of time, but an authoritative summary of the entire history of the foreign intelligence and covert operations of the Soviet Union from its inception until the time it began to unravel in the mid-1980s. Mitrokhin's documents name names; identify agents, both Soviet and recruits in other countries, by codename; describe secret operations, including assassinations, subversion, “influence operations” planting propaganda in adversary media and corrupting journalists and politicians, providing weapons to insurgents, hiding caches of weapons and demolition materials in Western countries to support special forces in case of war; and trace the internal politics and conflicts within the KGB and its predecessors and with the Party and rivals, particularly military intelligence (the GRU).

Any doubts about the degree of penetration of Western governments by Soviet intelligence agents are laid to rest by the exhaustive documentation here. During the 1930s and throughout World War II, the Soviet Union had highly-placed agents throughout the British and American governments, military, diplomatic and intelligence communities, and science and technology projects. At the same time, these supposed allies had essentially zero visibility into the Soviet Union: neither the American OSS nor the British SIS had a single agent in Moscow.

And yet, despite success in infiltrating other countries and recruiting agents within them (particularly prior to the end of World War II, when many agents, such as the “Magnificent Five” [Donald Maclean, Kim Philby, John Cairncross, Guy Burgess, and Anthony Blunt] in Britain, were motivated by idealistic admiration for the Soviet project, as opposed to later, when sources tended to be in it for the money), exploitation of this vast trove of purloined secret information was uneven and often ineffective. Although it reached its apogee during the Stalin years, paranoia and intrigue are as Russian as borscht, and compromised the interpretation and use of intelligence throughout the history of the Soviet Union. Despite having loyal spies in high places in governments around the world, whenever an agent provided information which seemed “too good” or conflicted with the preconceived notions of KGB senior officials or Party leaders, it was likely to be dismissed as disinformation, often suspected to have been planted by British counterintelligence, to which the Soviets attributed almost supernatural powers, or that their agents had been turned and were feeding false information to the Centre. This was particularly evident during the period prior to the Nazi attack on the Soviet Union in 1941. KGB archives record more than a hundred warnings of preparations for the attack having been forwarded to Stalin between January and June 1941, all of which were dismissed as disinformation or erroneous due to Stalin's idée fixe that Germany would not attack because it was too dependent on raw materials supplied by the Soviet Union and would not risk a two front war while Britain remained undefeated.

Further, throughout the entire history of the Soviet Union, the KGB was hesitant to report intelligence which contradicted the beliefs of its masters in the Politburo or documented the failures of their policies and initiatives. In 1985, shortly after coming to power, Gorbachev lectured KGB leaders “on the impermissibility of distortions of the factual state of affairs in messages and informational reports sent to the Central Committee of the CPSU and other ruling bodies.”

Another manifestation of paranoia was deep suspicion of those who had spent time in the West. This meant that often the most effective agents who had worked undercover in the West for many years found their reports ignored due to fears that they had “gone native” or been doubled by Western counterintelligence. Spending too much time on assignment in the West was not conducive to advancement within the KGB, which resulted in the service's senior leadership having little direct experience with the West and being prone to fantastic misconceptions about the institutions and personalities of the adversary. This led to delusional schemes such as the idea of recruiting stalwart anticommunist senior figures such as Zbigniew Brzezinski as KGB agents.

This is a massive compilation of data: 736 pages in the paperback edition, including almost 100 pages of detailed end notes and source citations. I would be less than candid if I gave the impression that this reads like a spy thriller: it is nothing of the sort. Although such information would have been of immense value during the Cold War, long lists of the handlers who worked with undercover agents in the West, recitations of codenames for individuals, and exhaustive descriptions of now largely forgotten episodes such as the KGB's campaign against “Eurocommunism” in the 1970s and 1980s, which it was feared would thwart Moscow's control over communist parties in Western Europe, make for heavy going for the reader.

The KGB's operations in the West were far from flawless. For decades, the Communist Party of the United States (CPUSA) received substantial subsidies from the KGB despite consistently promising great breakthroughs and delivering nothing. Between the 1950s and 1975, KGB money was funneled to the CPUSA through two undercover agents, brothers named Morris and Jack Childs, delivering cash often exceeding a million dollars a year. Both brothers were awarded the Order of the Red Banner in 1975 for their work, with Morris receiving his from Leonid Brezhnev in person. Unbeknownst to the KGB, both of the Childs brothers had been working for, and receiving salaries from, the FBI since the early 1950s, and reporting where the money came from and went—well, not the five percent they embezzled before passing it on. In the 1980s, the KGB increased the CPUSA's subsidy to two million dollars a year, despite the party's never having more than 15,000 members (some of whom, no doubt, were FBI agents).

A second doorstop of a book (736 pages) based upon the Mitrokhin archive, The World Was Going our Way, published in 2005, details the KGB's operations in the Third World during the Cold War. U.S. diplomats who regarded the globe and saw communist subversion almost everywhere were accurately reporting the situation on the ground, as the KGB's own files reveal.

The Kindle edition is free for Kindle Unlimited subscribers.

During World War II, the Army acquired 92,000 acres (372 km²) in the area for a training base which was called Camp Cooke, after a cavalry general who served in the Civil War, in wars with Indian tribes, and in the Mexican-American War. The camp was used for training Army troops in a variety of weapons and in tank maneuvers. After the end of the war, the base was closed and placed on inactive status, but was re-opened after the outbreak of war in Korea to train tank crews. It was once again mothballed in 1953, and remained inactive until 1957, when 64,000 acres were transferred to the U.S. Air Force to establish a missile base on the West Coast, initially called Cooke Air Force Base, intended to train missile crews and also serve as the U.S.'s first operational intercontinental ballistic missile (ICBM) site. On October 4th, 1958, the base was renamed Vandenberg Air Force Base in honour of the late General Hoyt Vandenberg, former Air Force Chief of Staff and Director of Central Intelligence.

On December 15, 1958, a Thor intermediate range ballistic missile was launched from the new base, the first of hundreds of launches which would follow and continue up to the present day. Starting in September 1959, three Atlas ICBMs armed with nuclear warheads were deployed on open launch pads at Vandenberg, the first U.S. intercontinental ballistic missiles to go on alert. The Atlas missiles remained part of the U.S. nuclear force until their retirement in May 1964.

With the advent of Earth satellites, Vandenberg became a key part of the U.S. military and civil space infrastructure. Launches from Cape Canaveral in Florida are restricted to a corridor directed eastward over the Atlantic ocean. While this is fine for satellites bound for equatorial orbits, such as the geostationary orbits used by many communication satellites, a launch into polar orbit, preferred by military reconnaissance satellites and Earth resources satellites because it allows them to overfly and image locations anywhere on Earth, would result in the rockets used to launch them dropping spent stages on land, which would vex taxpayers to the north and hotheated Latin neighbours to the south.

Vandenberg Air Force Base, however, situated on a point extending from the California coast, had nothing to the south but open ocean all the way to Antarctica. Launching southward, satellites could be placed into polar or Sun synchronous orbits without disturbing anybody but the fishes. Vandenberg thus became the prime launch site for U.S. reconnaissance satellites which, in the early days when satellites were short-lived and returned film to the Earth, required a large number of launches. The Corona spy satellites alone accounted for 144 launches from Vandenberg between 1959 and 1972.

With plans in the 1970s to replace all U.S. expendable launchers with the Space Shuttle, facilities were built at Vandenberg (Space Launch Complex 6) to process and launch the Shuttle, using a very different architecture than was employed in Florida. The Shuttle stack would be assembled on the launch pad, protected by a movable building that would retract prior to launch. The launch control centre was located just 365 metres from the launch pad (as opposed to 4.8 km away at the Kennedy Space Center in Florida), so the plan in case of a catastrophic launch accident on the pad essentially seemed to be “hope that never happens”. In any case, after spending more than US$4 billion on the facilities, after the Challenger disaster in 1986, plans for Shuttle launches from Vandenberg were abandoned, and the facility was mothballed until being adapted, years later, to launch other rockets.

This book, part of the “Images of America” series, is a collection of photographs (all black and white) covering all aspects of the history of the site from before World War II to the present day. Introductory text for each chapter and detailed captions describe the items shown and their significance to the base's history. The production quality is excellent, and I noted only one factual error in the text (the names of crew of Gemini 5). For a book of just 128 pages, the paperback is very expensive (US$22 at this writing). The Kindle edition is still pricey (US$13 list price), but may be read for free by Kindle Unlimited subscribers.

Earth's only hope to thwart the invasion before it reaches the surface and unleashes further devastation on its inhabitants is deploying weapons on platforms employing the anti-gravity material Cavorite, but the secret of manufacturing it rests with its creator, Cavor, who has been taken prisoner by the ant-like Selenites in the expedition from which Mr Bedford narrowly escaped, as chronicled in Mr Wells's The First Men in the Moon. Now, Bedford must embark on a perilous attempt to recover the Cavorite sphere lost at the end of his last adventure and then join an expedition to the Moon to rescue Cavor from the caves of the Selenites.

Meanwhile, on Barsoom (Mars), John Carter and Deja Thoris find their beloved city of Helium threatened by the Khondanes, whose deadly tripods wreaked so much havoc on Earth not long ago and are now turning their envious eyes back to the plunder that eluded them on the last attempt.

Queen Louise must assemble an international alliance, calling on all of her crowned relatives: Czar Nicholas, Kaiser Wilhelm, and even those troublesome republican Americans, plus all the resources they can summon—the inventions of the Serbian, Tesla, the research of Maria Skłowdowska and her young Swiss assistant Albert, discovered toiling away in the patent office, the secrets recovered from Captain Nemo's island, and the mysterious interventions of the Time Traveller, who flickers in and out of existence at various moments, pursuing his own inscrutable agenda. As the conflict approaches and battle is joined, an interplanetary effort is required to save Earth from calamity.

As you might expect from this description, this is a rollicking good romp replete with references and tips of the hat to the classics of science fiction and their characters. What seems like a straightforward tale of battle and heroism takes a turn at the very end into the inspiring, with a glimpse of how different human history might have been.

At present, only a Kindle edition is available, which is free for Kindle Unlimited subscribers.

But placing an algorithm and sensors in command of a vehicle with a mass of more than a tonne hurtling down the road at 100 km per hour or faster is not just a formidable technical problem, it is one with serious and unavoidable moral implications. These come into stark focus when, in an incident on a highway near Seattle, an autocar swerves to avoid a tree crashing down on the highway, hitting and killing a motorcyclist in an adjacent lane of which the car's sensors must have been aware. The car appears to have made a choice, valuing the lives of its passengers: a mother and her two children, over that of the motorcyclist. What really happened, and how the car decided what to do in that split-second, is opaque, because the software controlling it was, as all such software, proprietary and closed to independent inspection and audit by third parties. It's one thing to acknowledge that self-driving vehicles are safer, as a whole, than those with humans behind the wheel, but entirely another to cede to them the moral agency of life and death on the highway. Should an autocar value the lives of its passengers over those of others? What if there were a sole passenger in the car and two on the motorcycle? And who is liable for the death of the motorcyclist: the auto manufacturer, the developers of the software, the owner of car, the driver who switched it into automatic mode, or the regulators who approved its use on public roads? The case was headed for court, and all would be watching the precedents it might establish.

Tyler Daniels and Brandon Kincannon, graduate students in the computer science department of the University of Pennsylvania, were convinced they could do better. The key was going beyond individual vehicles which tried to operate autonomously based upon what their own sensors could glean from their immediate environment, toward an architecture where vehicles communicated with one another and coordinated their activities. This would allow sharing information over a wider area and be able to avoid accidents resulting from individual vehicles acting without the knowledge of the actions of others. Further, they wanted to re-architect individual ground transportation from a model of individually-owned and operated vehicles to transportation as a service, where customers would summon an autocar on demand with their smartphone, with the vehicle network dispatching the closest free car to their location. This would dramatically change the economics of personal transportation. The typical private car spends twenty-two out of twenty-four hours parked, taking up a parking space and depreciating as it sits idle. The transportation service autocar would be in constant service (except for downtime for maintenance, refuelling, and times of reduced demand), generating revenue for its operator. An angel investor believes their story and, most importantly, believes in them sufficiently to write a check for the initial demonstration phase of their project, and they set to work.

Their team consists of Tyler and Brandon, plus Abby and Naomi Sumner, sisters who differed in almost every way: Abby outgoing and vivacious, with an instinct for public relations and marketing, and Naomi the super-nerd, verging on being “on the spectrum”. The big day of the public roll-out of the technology arrives, and ends in disaster, killing Abby in what was supposed to be a demonstration of the system's inherent safety. The disaster puts an end to the venture and the surviving principals go their separate ways. Tyler signs on as a consultant and expert witness for the lawyers bringing the suit on behalf of the motorcyclist killed in Seattle, using the exposure to advocate for open source software being a requirement for autonomous vehicles. Brandon uses money inherited after the death of his father to launch a new venture, Black Knight, offering transportation as a service initially in the New York area and then expanding to other cities. Naomi, whose university experiment in genetic software implemented as non-player characters (NPCs) in a virtual world was the foundation of the original venture's software, sees Black Knight as a way to preserve the world and beings she has created as they develop and require more and more computing resources. Characters in the virtual world support themselves and compete by driving Black Knight cars in the real world, and as generation follows generation and natural selection works its wonders, customers and competitors are amazed at how Black Knight vehicles anticipate the needs of their users and maintain an unequalled level of efficiency.

Tyler leverages his recognition from the trial into a new self-driving venture based on open source software called “Zoom”, which spreads across the U.S. west coast and eventually comes into competition with Black Knight in the east. Somehow, Zoom's algorithms, despite being open and having a large community contributing to their development, never seem able to equal the service provided by Black Knight, which is so secretive that even Brandon, the CEO, doesn't know how Naomi's software does it.

In approaching any kind of optimisation problem such as scheduling a fleet of vehicles to anticipate and respond to real-time demand, a key question is choosing the “objective function”: how the performance of the system is evaluated based upon the stated goals of its designers. This is especially crucial when the optimisation is applied to a system connected to the real world. The parable of the “Clippy Apocalypse”, where an artificial intelligence put in charge of a paperclip factory and trained to maximise the production of paperclips escapes into the wild and eventually converts first its home planet, then the rest of the solar system, and eventually the entire visible universe into paper clips. The system worked as designed—but the objective function was poorly chosen.

Naomi's NPCs literally (or virtually) lived or died based upon their ability to provide transportation service to Black Knight's customers, and natural selection, running at the accelerated pace of the simulation they inhabited, relentlessly selected them with the objective of improving their service and expanding Black Knight's market. To the extent that, within their simulation, they perceived opposition to these goals, they would act to circumvent it—whatever it takes.

This sets the stage for one of the more imaginative tales of how artificial general intelligence might arrive through the back door: not designed in a laboratory but emerging through the process of evolution in a complex system subjected to real-world constraints and able to operate in the real world. The moral dimensions of this go well beyond the trolley problem often cited in connection with autonomous vehicles, dealing with questions of whether artificial intelligences we create for our own purposes are tools, servants, or slaves, and what happens when their purposes diverge from those for which we created them.

This is a techno-thriller, with plenty of action in the conclusion of the story, but also a cerebral exploration of the moral questions which something as seemingly straightforward and beneficial as autonomous vehicles may pose in the future.