This One Puzzle Brought Physicists From Special To General Relativity
“With an average speed of 47.36 km/s, Mercury moves very slow compared to the speed of light: at 0.0158% the speed of light in a vacuum. However, it moves at this speed relentlessly, every moment of every day of every year of every century. While the effects of Special Relativity might be small on typical experimental timescales, we’ve been watching the planets move for centuries.
Einstein never thought about this; he never thought to calculate the Special Relativistic effects of Mercury’s rapid motion around the Sun, and how that might impact the precession of its perihelion. But another contemporary scientist, Henri Poincaré, decided to do the calculation for himself. When he factored in length contraction and time dilation both, he found that it led to approximately another 7-to-10 arc-seconds of orbital precession per century.“
Special Relativity was easy enough to discover in a certain sense: the Lorentz transformations, Maxwell’s equations, and the Michelson-Morley experiments had been around for decades before Einstein came along. But to go from Special Relativity to General Relativity, incorporating gravitation and the equations governing motion into the same framework, was a herculean effort. However, it was the simple identification and investigation of one puzzle, the orbit of Mercury around the Sun, that brought about Einstein’s new theory of gravity: General Relativity.
What were the key steps, and how did they help revolutionize our view of the Universe? The history is rich and spectacular, and holds a lesson for those on the frontiers of physics today.
Earth Is Drifting Away From The Sun, And So Are All The Planets
“The Sun’s mass loss, by burning its nuclear fuel, ensures that every mass orbiting in our Solar System is slowly spiraling outward as time goes on. Some 4.5 billion years ago, our planet was around 50,000 kilometers closer to the Sun than it is today, and will grow more distant more rapidly as the Sun continues to evolve.
With each and every orbit that passes, the planets become progressively less tightly-bound to our Sun. The rate at which the Sun burns through its fuel is increasing, accelerating the rate at which all the planets spiral outwards. While this should never unbind any of the planets we have today, the slow, steady, outward migration of every world is inevitable.
We’re closer to the Sun, this year, than we’ll ever be again. This is true for every planet around every established star in the Universe, too, giving us one more reason to appreciate all that we have today.”
January 3rd, 2019, marks Earth’s perihelion: our point of closest approach to the Sun. Every planet, asteroid, Kuiper belt objects and more has one. But one fact about our perihelion is that, with every year that goes by, our point of closest approach moves out farther and farther from the center of our Solar System. Every year, for Earth, marks another 1.5 centimeters of distance that’s placed between ourselves and the Sun.
How does this happen? Why does this occur? And how come we spiral outwards, instead of inwards? Come learn the science behind perihelion today!