The discovery of gravitational waves has been hailed as yet another vindication of Albert Einstein’s theory of general relativity, unveiled a century ago. Indeed it is: among the theory’s predictions was that violent events in the universe involving immense masses – such as the collision and merging of two black holes – could set the fabric of spacetime ringing, the ripples spreading across the cosmos and stretching or squeezing space as they pass.

Experiments at the Advanced Laser Interferometer Gravitational-Wave Observatory facilities in Washington and Louisiana have detected these distortions, and it’s a tremendous, exhilarating moment for science. But it’s been barely noted what a deeply strange, perhaps unprecedented situation this is too. The initial detection event happened last September, in the centenary year of the publication of Einstein’s theory. Yet the theory of general relativity itself is a great rarity in science: for this was not an idea motivated by any need to explain observations, but the result of Albert Einstein simply sitting down and thinking. It isn’t easy to find another example of such a rich, fertile theory conjured, as it were, out of nothing.

No one was demanding a new theory of gravity in 1915. We already had one – devised by Isaac Newton more than two centuries earlier – and it seemed to work fine. Sure, there were a few little puzzles, such as the anomalous motion of the planet Mercury. But these weren’t in any sense the stimulus for the new theory (even though it explained them). No, it arose because Einstein saw the world differently.

It began in 1907, when Einstein was 28 and still working as a patent clerk. “I was sitting in the patent office in Bern,” he later wrote, “when all of a sudden a thought occurred to me: if a person falls freely, he won’t feel his own weight. I was startled. This simple thought made a deep impression on me. It impelled me toward a theory of gravitation.” This, Einstein attested, was “the happiest thought of my life”.

This is what set Einstein apart: what seems trivially obvious to most people struck him as profound. Using a complex form of calculus called tensor theory, he spent eight years working on a new concept of gravity. The theory of general relativity showed that masses warp space and that in a gravitational field time slows down. It also predicted neutron stars and black holes, although they weren’t accepted for many decades.

Many physicists regard general relativity as a theory of exemplary beauty. But it’s difficult too. Its 10 equations can be written down concisely using tensor notation, but in full they’d take up many pages. The difficulty of solving the equations is one reason why, after being first vindicated in 1919 by observations of “bent” starlight during a solar eclipse, the theory languished for decades.

Almost all science stems from a need to explain what we see: to solve empirical puzzles. But not general relativity. Are there any other cases where significant new scientific ideas have arisen without any observations demanding explanation? String theory, which attempts to unite general relativity with quantum theory, is juggling with scales and energies well beyond anything experimentally accessible, but still there’s a clear motive: to reconcile two mutually incompatible ideas. Quantum theory itself is startlingly accurate with its predictions but current research into its underlying principles is motivated largely just because it appears so bizarre. It works but scientists want to know why.

By contrast, Einstein seemed to invent general relativity simply because he wanted to – because he saw questions where others didn’t.

A more pertinent question, perhaps, is whether any young scientist could do that today. Einstein’s “miraculous year” of 1905, in which he not only deduced special relativity but also kick-started quantum theory and published several other ground-breaking papers, was an unrivalled creative burst. Yet any scientist’s early career is often their most productive time, as it was with Stephen Hawking. Today, however, it’s instead likely to be the most constrained and fraught.

Young scientists now need more than ever to publish lots and quickly, to get grants and tenure, to justify the “impact” of their work, and to carve out a niche for themselves, often in a highly specialised area. There is scant opportunity to just sit at a desk and ponder big questions.

A century ago, general relativity had no obvious “impact”, even though the GPS systems in today’s smartphones rely on it. It didn’t even have a clear goal, except intellectually. If Einstein’s project had relied on a grant application today, it would surely be rejected; probably no young scientist could afford the luxury of contemplating it in the first place. It’s not clear there is a space for Einsteins in modern science any longer.