More than four and a half billion years ago our solar system was formed under the influence of gravity. From interstellar hydrogen and clouds of cosmic dust, the remains of exploded stars, under the pressure of gravity, the temperatures rose so high deep inside our sun that hydrogen ions merged into helium ions releasing huge amounts of energy. The fire of our sun was ignited. Since then, it has been rearing up against the forces of its own heavy mass by twitching and trembling.
According to all we know so far, a star like our sun remains stable for about ten billion years, then it will rebel against the forces of gravity for the last time. It will inflate into a red giant and everything around it will lose itself in the glow, also the earth. Eventually gravity will triumph and what was once our sun will compress into a miserable little star, a white dwarf that will slowly cool down and end up as a dark stellar body. A cosmic game of gravity that will happen in about five billion years.
Nobody at the beginning of the twentieth century had any reason to doubt Newton and the accuracy of his mathematical description of gravity. After all, they were already in the process of tricking the earth's gravitational pull and conquering the sky. But there were some inconsistencies. Nobody could say why we are attracted to the Earth and how the attraction works.
Is the earth perhaps emitting suction rays or is gravitation caused by tiny little particles flying through the cosmos? From all directions that compress matter by their pressure? Us humans against the ground and the planets against the sun? Does attraction consume energy and is it still there even if there is no second body on which it can act? How could a force have an immediate effect on a distant body at infinite speed without any time delay?
Two other forces were already known, the effects of which could not be explained either, but they could be experimented with in the laboratory. Different metals react to the earth's magnetic field. Chinese discovered this already in the third century and invented the compass. Many of today's plastics behave similarly to amber, which the Romans called Electrum. If you rub it, you can use it to attract small particles in dust, lint or Styrofoam and even deflect a jet of water. Electric power is the name of the phenomenon today. All three forces gravity, electric force and magnetic force, had one thing in common: they acted on distant matter without touching it.
Iron arrow shavings stand between the poles of a magnet like stalks in a cornfield. Therefore, by the middle of the nineteenth century, scientists had replaced the concept of attraction with the concept of the force field, a space filled with lines of force. The lines of force are supposed to describe this special state of attraction between the bodies. Every source of such a field has a certain potential: an electric, a magnetic or a gravitational potential and every field has a special energy density, the field strength.
