Seventy years after the destruction of Hiroshima and Nagasaki by nuclear weapons, David Kaiser investigates the legacy of 'the physicists' war'. ... The Second World War marked an unprecedented mobilization of scientists and engineers, and a turning point in the relationship between research and the state. By the end of the war, the nuclear weapons project, code-named the Manhattan Engineer District, absorbed thousands of researchers and billions of dollars. It sprawled across 30 facilities throughout the United States and Canada, with British teams working alongside Americans and Canadians. Allied efforts on radar swelled to comparable scale. ... the term had been coined long before August 1945, and originally it had nothing to do with bombs or radar. Rather, the physicists' war had referred to an urgent, ambitious training mission: to teach elementary physics to as many enlisted men as possible. ... Both views of how scientists could serve their nations — the quotidian and the cataclysmic — have shaped scientific research and higher education to this day.

Is cold fusion truly impossible, or is it just that no respectable scientist can risk their reputation working on it? ... cold fusion (or LENR, for ‘low-energy nuclear reaction’) is the controversial idea that nuclear reactions similar to those in the Sun could, under certain conditions, also occur close to room temperature. ... was popularised in 1989 by Martin Fleischmann and Stanley Pons, who claimed to have found evidence that such processes could take place in palladium loaded with deuterium (an isotope of hydrogen). A few other physicists, including the late Sergio Focardi at Bologna, claimed similar effects with nickel and ordinary hydrogen. But most were highly skeptical, and the field subsequently gained, as Wikipedia puts it, ‘a reputation as pathological science’. ... We know that huge amounts of energy are locked up in metastable nuclear configurations, trapped like water behind a dam. There’s no known way to get useful access to it at low temperatures. ... There are credible reports that a 1MW version of his device, producing many times the energy that it consumes, has been on trial in an industrial plant in North Carolina for months, with good results so far. And Rossi’s US backer and licensee, Tom Darden – who has a long track record of investment in pollution-reducing industries – has been increasingly willing to speak out in support of the LENR technology field. ... We should certainly be very cautious about such surprising claims, unless and until we amass a great deal of evidence. But this is not a good reason for ignoring such evidence in the first place, or refusing to contemplate the possibility that it might exist.

People tell me about miniaturization, about electric motors the size of the nail on your finger. There is a device on the market by which you can write the Lord's Prayer on the head of a pin. But that's nothing. That's the most primitive, halting step. ... Why not write the entire 24 volumes of the "Encyclopaedia Britannica" on the head of a pin? ... Let's see what would be involved. The head of a pin is a sixteenth of an inch across. If you magnify it 25,000 diameters, the area of the head of the pin is equal to the area of all pages of the encyclopedia. All it is necessary to do is reduce the writing in the encyclopedia 25,000 times. Is that possible? One of the little dots on the fine halftone reproductions in the encyclopedia, when you demagnify it by 25,000 times, still would contain in its area 1,000 atoms. So, each dot can easily be adjusted in size as required, and there is no question that there is enough room on the head of a pin to put all of the "Encyclopaedia Britannica."

In 1978, the United States Geological Survey (USGS) allocated over half its research budget ($15.76 million) to earthquake prediction, a level of spending that continued for much of the next decade. Scientists deployed hundreds of seismometers and other sensors, hoping to observe telltale signals heralding the arrival of the next big one. They looked for these signs in subterranean fluids, crustal deformations, radon gas emissions, electric currents, even animal behavior. But every avenue they explored led to a dead end. ... Since the early 20th century, scientists have known that large quakes often cluster in time and space: 99 percent of them occur along well-mapped boundaries between plates in Earth’s crust and, in geological time, repeat almost like clockwork. But after decades of failed experiments, most seismologists came to believe that forecasting earthquakes in human time—on the scale of dropping the kids off at school or planning a vacation—was about as scientific as astrology. By the early 1990s, prediction research had disappeared as a line item in the USGS’s budget. ... Defying the skeptics, however, a small cadre of researchers have held onto the faith that, with the right detectors and computational tools, it will be possible to predict earthquakes with the same precision and confidence we do just about any other extreme natural event, including floods, hurricanes, and tornadoes. The USGS may have simply given up too soon. After all, the believers point out, advances in sensor design and data analysis could allow for the detection of subtle precursors that seismologists working a few decades ago might have missed. ... At a time when American companies and institutions are bankrolling “moonshot” projects like self-driving cars, space tourism, and genomics, few problems may be as important—and as neglected—as earthquake prediction.

Like many astrophysicists, Sara Seager sometimes has a problem with her perception of scale. Knowing that there are hundreds of billions of galaxies, and that each might contain hundreds of billions of stars, can make the lives of astrophysicists and even those closest to them seem insignificant. Their work can also, paradoxically, bolster their sense of themselves. Believing that you alone might answer the question “Are we alone?” requires considerable ego. Astrophysicists are forever toggling between feelings of bigness and smallness, of hubris and humility, depending on whether they’re looking out or within. ... Her area of expertise is the relatively new field of exoplanets: planets that orbit stars other than our sun. More particular, she wants to find an Earthlike exoplanet — a rocky planet of reasonable mass that orbits its star within a temperate “Goldilocks zone” that is not too hot or too cold, which would allow water to remain liquid — and determine that there is life on it. That is as simple as her math gets. ... The vastness of space almost defies conventional measures of distance. Driving the speed limit to Alpha Centauri, the nearest star grouping to the sun, would take 50 million years or so; our fastest current spacecraft would make the trip in a relatively brisk 73,000 years. The next-nearest star is six light-years away. To rocket across our galaxy would take about 23,000 times as long as a trip to Alpha Centauri, or 1.7 billion years, and the Milky Way is just one of hundreds of billions of galaxies. ... Light or its absence is also the root of something called the transit technique, a newer, more efficient way than radial velocity of finding exoplanets by looking at their stars.

Biological systems don’t defy physical laws, of course — but neither do they seem to be predicted by them. In contrast, they are goal-directed: survive and reproduce. We can say that they have a purpose — or what philosophers have traditionally called a teleology — that guides their behavior. ... By the same token, physics now lets us predict, starting from the state of the universe a billionth of a second after the Big Bang, what it looks like today. But no one imagines that the appearance of the first primitive cells on Earth led predictably to the human race. Laws do not, it seems, dictate the course of evolution. ... Animals are drawn to water not by some magnetic attraction, but because of their instinct, their intention, to survive. Legs serve the purpose of, among other things, taking us to the water. ... there appears to be a kind of physics of things doing stuff, and evolving to do stuff. Meaning and intention — thought to be the defining characteristics of living systems — may then emerge naturally through the laws of thermodynamics and statistical mechanics.

What Leucippus and Democritus had understood was that the world can be comprehended using reason. They had become convinced that the variety of natural phenomena must be attributable to something simple, and had tried to understand what this something might be. They had conceived of a kind of elementary substance from which everything was made. Anaximenes of Miletus had imagined this substance could compress and rarefy, thus transforming from one to another of the elements from which the world is constituted. It was a first germ of physics, rough and elementary, but in the right direction. An idea was needed, a great idea, a grand vision, to grasp the hidden order of the world. Leucippus and Democritus came up with this idea. ... The idea of Democritus’s system is extremely simple: the entire universe is made up of a boundless space in which innumerable atoms run. Space is without limits; it has neither an above nor a below; it is without a centre or a boundary. Atoms have no qualities at all, apart from their shape. They have no weight, no colour, no taste. ... Atoms are indivisible; they are the elementary grains of reality, which cannot be further subdivided, and everything is made of them. They move freely in space, colliding with one another; they hook on to and push and pull one another. Similar atoms attract one another and join. ... We know of his thought only through the quotations and references made by other ancient authors, and by their summaries of his ideas.

After decades of work in the laboratory, a raft of different devices and approaches relying on quantum-mechanical effects are now nearing market-readiness. It has taken so long mainly because the components that make them up had to be developed first: ever-better lasers, semiconductors, control electronics and techniques to achieve the low temperatures at which many quantum systems perform best. ... Everything in the natural world can be described by quantum mechanics. Born a century ago, this theory is the rule book for what happens at atomic scales, providing explanations for everything from the layout of the periodic table to the zoo of particles spraying out of atom-smashers. It has guided the development of everyday technologies from lasers to MRI machines and put a solid foundation under astrophysicists’ musings about unknowables such as the interiors of black holes and the dawn of the universe. Revealed by a few surprising discoveries, such as that atoms absorb and emit energy only in packets of discrete sizes (quanta), and that light and matter can act as both waves and particles, it is modern physics’ greatest triumph. ... It has a weird side, though, and it is this that has captured interest in what is now being called the second quantum revolution.

Meanwhile, a thousand miles west, on the prairies and farms of central Iowa, a 2-year-old boy named Clair Patterson played. His boyhood would go on to be like something out of Tom Sawyer. There were no cars in town. Only a hundred kids attended his school. A regular weekend entailed gallivanting into the woods with friends, with no adult supervision, to fish, hunt squirrels, and camp along the Skunk River. His adventures stoked a curiosity about the natural world, a curiosity his mother fed by one day buying him a chemistry set. Patterson began mixing chemicals in his basement. He started reading his uncle’s chemistry textbook. By eighth grade, he was schooling his science teachers. ... During these years, Patterson nurtured a passion for science that would ultimately link his fate with the deaths of the five men in New Jersey. Luckily for the world, the child who’d freely roamed the Iowa woods remained equally content to blaze his own path as an adult. Patterson would save our oceans, our air, and our minds from the brink of what is arguably the largest mass poisoning in human history.

Neutrinos are fundamental to the construction of the Universe. They are tremendously abundant, outnumbering atoms by about a billion to one. They modulate the reactions that cause massive stars to explode as supernovas. Their properties provide clues about the laws governing particle physics. And yet neutrinos are among the most enigmatic particles, largely due to their reticent nature: they have no electric charge and practically no mass, so they interact only extremely weakly with ordinary matter. Some 65 billion of them stream through every square centimetre of your body – an area the size of a thumbnail – every second, without your ever noticing them. ... The discovery of the neutrino dates back to the 1930s, when the famed Italian physicist Enrico Fermi helped to hammer out the first workable theory of nuclear phenomena such as radioactive decay. ... Neither Fermi nor anyone else at the time thought that such tiny wisps of matter could ever be detected directly. Before long, the spread of fascism in Europe overshadowed any such lofty thoughts. ... In 1938, he managed a Sound-of-Music-like escape, exploiting a trip to Stockholm to accept the Nobel Prize in order to slip out of Europe and head for the United States, where he became one of the early scientific leaders of the Manhattan Project.