I have often heard PhD supervisors telling their students not to work on general relativity for fear of becoming unemployable. To many it is far too esoteric. Devoting one's life to general relativity is definitely a labor of love, an almost irresponsible calling.#4252•
The story of general relativity is not all about the past. Over the past ten years, it has become apparent that if general relativity is correct, most of the universe is dark. It is full of stuff that not only doesn't emit light but doesn't even reflect or absorb it.#4254•
Chapter 1
Einstein's job in the patent office was a blessing. After years of financial instability and depending on his father for an income, he was finally able to marry Mileva and begin to raise a family in Bern. The relative monotony of the patent office, with its clearly defined tasks and lack of distractions, seemed to be an ideal setting for Einstein to think things through.
His assigned work took only a few hours to complete each day, leaving him time to focus on his puzzles.#4251•
The laws of physics and mechanics are rules for how things move, speed up, or slow down when subjected to forces. In the seventeenth century, the English physicist and mathematician Isaac Newton laid out a set of laws for how objects respond to mechanical forces. His laws of motion consistently explain what happens when two billiard balls collide, or when a bullet is fired out of a gun, or when a ball is thrown up in the air.#4255•
Newton's law of universal attraction, or the "inverse square law," is as simple as they come. It says that the gravitational pull between two objects is directly proportional to the mass of each object and inversely proportional to the square of their distance. So if you double the mass of one of the objects, the gravitational pull also doubles.
And if you double the distance between the two objects, the pull decreases by a factor of four.
Over two centuries, Newton's law kept on giving, explaining any number of physical phenomena.
It proved itself most spectacularly not only in explaining the orbits of the known planets but also in predicting the existence of new ones.#4253•