One hundred years ago, Einstein gifted his general theory of relativity to humanity, packaged in a box of very abstract, incredibly mathematical, and generally hard-to-solve nonlinear differential equation. One hundred years later, we are celebrating the detection of gravitational waves (GWs), one of its many predictions that include the big bang, supernovae, black holes, gravitational lensing, gravitational time dilation, … and for those who value a discovery only by its practical application, GPS.
The detection of GWs has been expensive (over $600 million so far), time consuming (started in 1992), and labor intensive (the paper, published in Physical Review Letters announcing the discovery of GWs, has over 1000 authors ). Has it been worth it?
One answer to the question takes us back another 50 years from the time that Einstein wrote his equation. In 1865, James C. Maxwell gifted another abstract, mathematical, and hard-to-solve set of differential equations to humanity. These equations, among other things, predicted the hitherto undetected electromagnetic waves (EMWs). These waves were detected in 1887, only eight years after Maxwell’s early death at the age of 48. The detection of EMWs was inexpensive (the cost of a microwave oven in a university laboratory), relatively quick (started in 1885, only two years before their discovery), and labor cheap (Heinrich Hertz was the single author). In the intervening thirteen decades, we have invented radio, television, computers, smart phone and a host of other gadgets, all of which would not exist without EMWs.
A second answer to the question takes us back another two hundred years. In 1666, Isaac Newton gave us the law of gravity and applied it to the solar system in yet another abstract mathematical equation whose solution required no less a Herculean intellectual task than the invention of calculus and differential equations.
A third answer puts us in the Golden Age of Greek science and mathematics. Euclid, Archimedes, Aristarchus, Eudoxes, Pythagoras, and all of the great geniuses of that period engaged in highly abstract mathematical ideas and inventions such as trigonometry to answer the seemingly practically useless questions posed by the motion of planets and stars. In their quest for wisdom, they even faced great dangers on their journey of hundreds of miles — sometimes on foot — to learn the knowledge acquired by Egyptian and Babylonian priesthood.