The Science Book: Big Ideas Simply Explained

Book Preface

Science is an ongoing search for truth—a perpetual struggle to discover how the universe works that goes back to the earliest civilizations. Driven
by human curiosity, it has relied on reasoning, observation, and experiment. The best known of the ancient Greek philosophers, Aristotle, wrote widely on scientific subjects and laid foundations for much of the work that has followed. He was a good observer of nature, but he relied entirely on thought and argument, and did no experiments. As a result, he got a number of things wrong. He asserted that big objects fall faster than little ones, for example, and that if one object had twice the weight of another, it would fall twice as fast. Although this is mistaken, no one doubted it until the Italian astronomer Galileo Galilei disproved the idea in 1590. While it may seem obvious today that a good scientist must rely on empirical evidence, this was not always apparent.
The scientific method
A logical system for the scientific process was first put forward by the English philosopher Francis Bacon in the early 17th century. Building on the work of the Arab scientist Alhazen 600 years earlier, and soon to be reinforced by the French philosopher René Descartes, Bacon’s scientific method requires scientists to make observations, form a theory to explain what is going on, and then conduct an experiment to see whether the theory works. If it seems to be true, then the results may be sent out for peer review, in which people working in the same or a similar field are invited to pick holes in the argument, and so falsify the theory, or to repeat the experiment to make sure that the results are correct.
Making a testable hypothesis or a prediction is always useful. English astronomer Edmond Halley, observing the comet of 1682, realized that it was similar to comets reported in 1531 and 1607, and suggested that all three were the same object, in orbit around the Sun. He predicted that it would return in 1758, and he was right, though only just—it was spotted on December 25. Today, the comet is known as Halley’s Comet. Since astronomers are rarely able to perform experiments, evidence can come only from observation.
Experiments may test a theory, or be purely speculative. When the New Zealand-born physicist Ernest Rutherford watched his students fire alpha particles at gold leaf in a search for small deflections, he suggested putting the detector beside the source, and to their astonishment some of the alpha particles bounced back off the paper-thin foil. Rutherford said it was as though an artillery shell had bounced back off tissue paper—and this led him to a new idea about the structure of the atom.
An experiment is all the more compelling if the scientist, while proposing a new mechanism or theory, can make a prediction about the outcome. If the experiment produces the predicted result, the scientist then has supporting evidence for the theory. Even so, science can never prove  that a theory is correct; as the 20th-century philosopher of science Karl Popper pointed out, it can only disprove things. Every experiment that gives predicted answers is supporting evidence, but one experiment that fails may bring an entire theory crashing down.
Over the centuries, long-held concepts such as a geocentric universe, the four bodily humors, the fire-element phlogiston, and a mysterious medium called ether have all been disproved and replaced with new theories. These in turn are only theories, and may yet be disproved, although in many cases this is unlikely given the evidence in their support.
Progression of ideas Science rarely proceeds in simple, logical steps. Discoveries may be made simultaneously by scientists working independently, but almost every advance depends in some measure on previous work and theories. One reason for building the vast apparatus known as the Large Hadron Collider, or LHC, was to search for the Higgs particle, whose existence was predicted 40 years earlier, in 1964. That prediction rested on decades of theoretical work on the structure of the atom, going back to Rutherford and the work of Danish physicist Niels Bohr in the 1920s, which depended on the discovery of the electron in 1897, which in turn depended on the discovery of cathode rays in 1869. Those could not have been found without the vacuum pump and, in 1799, the invention of the battery—and so the chain goes back through decades and centuries. The great English physicist Isaac Newton famously said, “If I have seen further, it is by standing on the shoulders of giants.” He meant primarily Galileo, but he had probably also seen a copy of Alhazen’s Optics.
The first scientists
The first philosophers with a scientific outlook were active in the ancient Greek world during the 6th and 5th centuries BCE. Thales of Miletus predicted an eclipse of the Sun in 585 BCE; Pythagoras set up a mathematical school in what is now southern Italy 50 years later, and Xenophanes, after finding seashells on a mountain, reasoned that the whole Earth must at one time have been covered by sea.
In Sicily in the 4th century BCE, Empedocles asserted that earth, air, fire, and water are the “fourfold roots of everything.” He also took his followers up to the volcanic crater of Mt. Etna and jumped in, apparently to show he was immortal—and as a result we remember him to this day.
Stargazers
Meanwhile, in India, China, and the Mediterranean, people tried to make sense of the movements of the heavenly bodies. They made star maps—partly as navigational aids—and named stars and groups of stars. They also noted that a few traced irregular paths when viewed against the “fixed stars.” The Greeks called these wandering stars “planets.” The Chinese spotted Halley’s comet in 240 BCE and, in 1054, a supernova that is now known as the Crab Nebula.

House of Wisdom
In the late 8th century CE, the Abbasid caliphate set up the House of Wisdom, a magnificent library, in its new capital, Baghdad. This inspired rapid advances in Islamic science and technology. Many ingenious mechanical devices were invented, along with the astrolabe, a navigational device that used the positions of the stars. Alchemy flourished, and techniques such as distillation appeared. Scholars at the library collected all the most important books from Greece and from India, and translated them into Arabic, which is how the West later rediscovered the works of the ancients, and learned of the
“Arabic” numerals, including zero, that were imported from India.
Birth of modern science As the monopoly of the Church over scientific truth began to weaken in the Western world, the year 1543 saw the publication of two ground-breaking books. Belgian anatomist Andreas Vesalius produced De Humani Corporis Fabrica, which described his dissections of human corpses with exquisite illustrations. In the same year, Polish physician Nicolaus Copernicus published De Revolutionibus Orbium Coelestium, which stated firmly that the Sun is the center of the universe, overturning the Earth-centered model figured out by Ptolemy of Alexandria a millennium earlier.
In 1600, English physician William Gilbert published De Magnete in which he explained that compass needles point north because Earth itself is a magnet. He even argued that Earth’s core is made of iron. In 1623, another English physician, William Harvey, described for the first time how the heart acts as a pump and drives blood around the body, thereby quashing forever earlier theories that dated back 1,400 years to the Greco-Roman physician Galen.
In the 1660s, Anglo-Irish chemist Robert Boyle produced a string of books, including The Sceptical Chymist, in which he defined a chemical element. This marked the birth of chemistry as a science, as distinct from the mystical alchemy from which it arose.
Robert Hooke, who worked for a time as Boyle’s assistant, produced the first scientific best seller, Micrographia, in 1665. His superb fold-out illustrations of subjects such as a flea and the eye of a fly opened up a microscopic world no one had seen before. Then in 1687 came what many view as the most important science book of all time, Isaac Newton’s Philosophiæ Naturalis Principia Mathematica, commonly known as the Principia. His laws of motion and principle of universal gravity form the basis for classical physics.