At first it seemed to be a piece of weirdo news on TV “Super-highways in space discovered. The way to the planets is now open”. I checked the NASA website, and it showed an older piece of news, but it had context. I had to hunt little to find the paywalled article (Todorovich, Wu, Rosengren) in a prestigious scientific journal. It was new, but it was in the same context as the older press release from NASA. Indeed there are fast lanes in the solar system. “Gravity assist” can help you speed a spacecraft with little fuel. This was known in the 1970s, when the world’s first interstellar probes were launched. How is all this new? Is it a discovery?
After 1687 CE, Newton’s ideas on gravity were available to the world through successive editions of his book, Philosophiae Naturalis Principia Mathematica. To many it seemed that the universe had suddenly been understood. Poets wrote heroic verses: Nature and nature’s laws lay hid in night; God said “Let Newton be” and all was light. That was Alexander Pope writing Newton’s epitaph. Almost two hundred years later, Wordsworth in his posthumously published poem “The Prelude” wrote about Newton: The marble index of a mind for ever Voyaging through strange seas of Thought, alone. But other thoughtful people were not so (what is the word?) sanguine. Tides could be understood, but the details were devilish. More observations revealed strange anomalies in the motions of the known planets, and eventually led to the discovery of new planets, even to a new theory of gravity: Einstein’s (but that is a different story, and as Aragorn says at the black gate of Mordor, “Today is another day.”)
The paintaking computation of tides eventually told us that within this wonderful theory of Newton lurk dangerous waters. Tides require computations of the three way dance of the earth, the moon, and the sun. And these turned out to be rather difficult. About the time that Einstein was thinking about gravity, Henri Poincare was thinking about this three body problem, and discovered something as astounding. He found that within the seemingly determined motions of the planets lurk dangerous instabilities, some of which eventually became known as chaos. The three body problem, and its modern descendants, such as the study of the stability of the solar system, gave rise to the headlines that I saw. This is the discovery that there are unstable orbits which can throw small bodies (think spacecrafts and asteroids) into rapid transits across the solar system, and even eject them with high velocity into interstellar space. Some of this was known for about 50 years, but this is a systematic study, and a great addition to our knowledge. Maybe one day, if we can set up a space shipyard, travel across the outer solar system can be a matter of decades rather than centuries.
But after this long detour through history and the solar system, let me get back to my original question. What is discovery? If someone gives me the rules of the world, do I know the world? The answer is clear to anyone who has struggled to learn chess. It need not be less clear when it comes to science. Newton and Einstein discovered some of the rules of gravity, but much of the game remains to be played. Is the confusion due to the fact that in science you first need to discover the rules, and then discover what it means to play them? Perhaps we should have two different words for these two uses of the word discovery.