Thanks, Albert

MOST scientific findings are sedimentary, slowly building upon the edifice of understanding. Rare is the idea that marks a fundamental change to a system of thought, forcing the rest of science to bend to its own vision. However, on November 25th 1915 Albert Einstein published a theory that did just that. The ten equations of his general theory of relativity set out a new concept of gravity—not as its own, independent force, but as the warping of the fabric of space and time in the presence of mass (see article).

In the intervening century, Einstein himself has become a byword for cartoonish genius. His theory, however, is cherished less than it should be. That is partly because of its complexity; general relativity survived some trying experimental tests early on, but few scientists focused on it—in large part because its equations were so damnably hard to solve. And when the theory did take firm hold, it swiftly became so ubiquitous in describing astronomical goings-on that it began to be taken for granted. As a result, relativity’s revelations are less widely appreciated than the ideas of Charles Darwin, or even Einstein’s predecessor in gravitational thought, Isaac Newton.

Yet the world has much to thank Einstein for. Because of him, scientists think of space as, well, relative: what you measure depends on your vantage point, and on what mass is around you. An understanding of gravity’s most subtle effects informs both the exalted and the everyday. Relativity permitted the New Horizons mission this year to steer a space probe through a 150km-wide “keyhole” near Pluto, nearly 5 billion kilometres away, after a nine-and-a-half-year journey. A more quotidian example of the extraordinary precision of relativity comes from satellite-navigation systems. Einstein’s theory shows that satellites experience an ever-so-slightly different stretching of space-time in orbit than people do on the surface of the Earth—so the positional data streamed to smartphone users, and the time-stamps used for transactions in industries from banking to energy, must take in relativistic adjustments.

The theory has yielded odd surprises. It predicted, and then helped explain, the black holes that have captured public imagination. Efforts to join relativity with quantum mechanics, in a field called string theory, are shedding light on science that is wholly unconnected to the heavens, including materials that conduct electricity without resistance and new kinds of information processing. This concordance across phenomena that seem so disparate is a tantalising hint that scientists may yet come up with a grand theory that incorporates all the physical forces.

Relativity’s most overlooked triumph, though, has been to reframe the sorts of questions that stargazers ask. After the invention of telescopes in the early 17th century, astronomy concerned itself chiefly with discrete objects in the cosmos—peering at the planets and working out how they move, mapping how stars are distributed in the sky, and so on. General relativity got its start there, too, resolving a long-standing mystery of Mercury’s orbit. But the implications of stretchy space-time quickly raised bigger questions: by the 1970s, relativity had become integral to describing the Big Bang. Not since Johannes Kepler’s “Mysterium Cosmographicum”, a 16th-century attempt to reveal the structure of the cosmos, were thinkers so inspired to consider the universe as a whole: its organising principles, its ultimate origins and what makes it tick.

Mind and matter

The restoration of this inquiry was not simply a matter of philosophy. General relativity came with its own experimental checks, some of which took decades to carry out. As it has passed these tests, relativity has set the stage for what is known as “precision cosmology”. Exceptionally detailed theory lined up with ever-better observational data to furnish predictions about physical phenomena far away both in space and in time. Where once satellites and telescopes were deployed to scan for new sources of light, these instruments began to look to the dawn of the universe, and examine its frontiers with astonishing precision. From the vantage of relativity, researchers can speak with increasing authority of what happened in the earliest fractions of a second in the universe’s history, and what might happen at its end.

That is an astonishing leap in perspective from just ten equations. Einstein’s theory, and the intervening century of experimentation, provided a way to satisfy one of the most fundamental yearnings: to understand what is out there in the universe, how it all began and humanity’s place in it.