Wormholes

Time travel and wormholes are ideas that can be studied with the General Theory of Relativity, which is Einstein's version of gravitational force theory. Before getting into wormholes I look into escape velocity first.

All of us have thrown objects up. What we see is that the object invariably stops and starts to go down. This does not have to be like that. Humans sent an artificial satellite to orbit in the late fifties, this was the Sputnik. The speed of this object must have been bigger or equal to eight kilometers per second. At eleven kilometers per second or more, throwing the object up, it does not come back to the surface of the Earth.

This escape velocity can be calculated with the law of conservation of mechanical energy for the case of the gravitational force. Newton proposed in the seventeenth century that a body getting far from the Earth is pulled down with a force that gets smaller as the distance increases. For every doubling of the distance the force is one quarter of what it was before. This inverse squared relationship is very important and predicts closed orbits for the planets.

Kinetic energy is a measure of the motion of the object under study, the Sputnik say. Besides kinetic or motion energy, this artificial satellite of the Earth has potential energy. The higher up the Sputnik is, the bigger its potential energy gets. The sum of the kinetic energy and the potential energy of the Sputnik is constant. It goes high, the potential energy increases, and the kinetic energy has to go down. At some height the object stops, i.e., its kinetic energy is zero. At this point in time, the object starts to fall and its velocity increases. Now the kinetic energy is increasing and the potential energy is decreasing, the sum of these two energies remains constant. This sum is called the mechanical energy.

It stands to reason that there is a velocity for which the sum of the potential plus kinetic energy is zero. Potential energy could be defined as zero when the obejct is at an infinite distance from the Earth. If when the object reaches this infinite distance it also stops, its kinetic energy would be zero. Zero plus zero is zero. This object reaches an infinite distance and stops; its total mechanical energy is zero. This projectile has the so-called escape velocity. It escapes the gravitational force of the Earth. When the escape velocity is equal to the speed of light in magnitude we have reeached a fundamental limit. No observational evidence exists for an object moving faster than light in free space. Therefore if the planet, or more likely the star, has such a big mass in such a small volume to have an escape velocity equal to the speed of light. Nothing can escape from that star. We have a black hole.

The idea of a star so massive that not even light could escape is prior to Einstein; but only with Einstein's General Theory of Relativity was it possible to find a mathematical solution that satisfies this condition. This solution was found by Schwarzschild in 1916, almost a hundred years ago. You can read about it in Wikipedia, the free encyclopedia.

http://en.wikipedia.org/wiki/Schwarzschild_solution

Wormholes are other solutions to Einstein's equations:

http://en.wikipedia.org/wiki/Wormhole