History of gravitational wave theory

Physicist Tony Rothman has written The Secret History of Gravitational Waves, a nice history of work on relativistic gravity, and on waves in particular:

Maxwell’s challenge was taken up in 1893 by the brilliant English physicist and electrical engineer Oliver Heaviside. Writing in The Electrician, the leading electrical journal of the time, Heaviside set down the gravitational analogue of Maxwell’s equations and showed that they produce waves traveling at a finite velocity. One hesitates to make rash claims, but Heaviside’s article may well have been the world’s first serious scientific paper to treat gravitational waves.

He has the usual Einstein-slanted view of the history of special relativity:

With his publication of the special theory of relativity in 1905, Einstein completed Maxwell’s unification of electricity and magnetism by showing that the two fields were really one. Special relativity was founded on two immortal postulates. First, that experimenters must always get the same result for any experiment in any frame of reference (that is, no matter how fast they are moving relative to each other), as long as they are moving at constant velocity. Second, that observers will always measure the speed of light to have the same value, 300,000 kilometers per second, regardless of their motion. These postulates led to the conclusion that no information — not even the propagation of gravity — can travel faster than light, and they demanded a thorough modification of Newtonian physics.

During the same months that Einstein was working on special relativity, the French polymath Henri Poincaré was independently writing up his own researches along similar lines. “On the Dynamics of the Electron,” Poincaré’s 1905 paper, contains much the same mathematical content as Einstein’s, but he failed to ground his ideas on the two key postulates, which is why Einstein receives the credit for relativity. Presciently, the last section of Poincaré’s paper is titled “Hypothesis on Gravitation.” In it, Poincaré attempted to understand how Newtonian gravity between moving bodies should be modified by the Lorentz transformations, equations which describe how the electromagnetic field changes to observers moving at different velocities.

Much as Heaviside had done (but this time in the context of a relativistically correct framework), Poincaré assumed that the gravitational force propagates at the speed of light; therefore, there will be a time lag — called a retardation by physicists — between any change in gravity and the effect. Such changes, Poincaré explicitly stated, are propagated by gravitational waves (ondes gravifiques), although he does not elaborate on their form. Poincaré was more correct in his assumptions than he perhaps realized: Retardation is the only thing a field theory needs to produce gravitational waves.

Note the contortions he has to do to credit Einstein. Poincare had all of special relativity in 1905, and went much further than Einstein by giving a relativistic theory of gravity. In particular his theory explained how gravity could propagate at the speed of light, and how there could be gravity waves.

But Poincare does not get the credit for strictly expository reasons -- he didn't organize his paper around Einstein's postulates. Lorentz was later to remark that Einstein just postulated what he and Poincare proved.

Rothman credits Einstein with writing a pretty good paper on gravitational waves in 1918, after being corrected by Nordstrom. But then he backslid into erroneous thinking:

When he revisited the topic in a 1936 paper with Nathan Rosen, his assistant at the Institute for Advanced Study in Princeton, Einstein argued that the theory’s fully developed equations proved that true gravitational waves could not exist after all.

As it turned out, Einstein and Rosen were repeating the old mistake of using bad coordinates. American physicist Howard P. Robertson soon corrected the error, but Einstein’s lingering skepticism toward gravitational waves largely impeded research in the field until after his death in 1955.

I did not know this:

As an interesting aside, in his correspondence with Einstein, Nordström referred to the black hole solution not as the Schwarzschild solution but as the Droste solution. Johannes Droste (1886–1963), a graduate student of the Dutch physicist Hendrik Lorentz, discovered it independently of Schwarzschild within the same few months.

This solution is essentially equivalent to the general relativity field equations.

Students of general relativity are often given the impression that Einstein did it all, but this article and this previously quoted history make it clear that many or most of the important ideas came from others.

The really big idea was that the Lorentz transformations form a symmetry group, and that gravity can be described by a field theory that is covariant under that group. Poincare, Minkowski, Nordstrom, Hilbert, and others had come to that conclusion before Einstein did. Most of the theory follows from that concept. The exact equations make a difference, of course. but we would be getting lightspeed gravitational waves with any of these theories. Einstein settled on the one with lambda = 0, and now we take lambda positive, but that is not important.

Gravitational waves have suddenly been a source of cutting-edge physics, with LIGO reporting black hole collisions and rival detectors being built. But all the talk about Einstein is misleading. He was a minor player in the subject.