Bridging universes
Right-Left: Analogy to a wormhole in a curved 2-D space . Simulated view of a black hole in front of the Large Magellanic Cloud
A 'baby universe' is connected to its 'parent universe' by a bridge-known as Einstein-Rosen Bridge. It is a short-cut path in spacetime which is called wormhole. The physics of this wormhole is presented here. Wormhole is a prediction of general theory of relativity published by Albert Einstein in 1915. This theory describes the gravitational field created by matter. The matter moves in the field created by itself. Therefore gravitational theory of Albert Einstein is a complete theory. It is a set of ten nonlinear equations which are very difficult to solve. Einstein solved them with some approximations. The solution he found is a stationary universe. Stationary universe means a universe which does not change with time. But as early as 1916, a young German Astrophysicist Karl Schwarzschild found the first exact solution of Einstein's field equations. His solution predicted the non-stationary solution. The non-stationary solution means that the universe changes with time. The Schwarzschild solution admits negative square root as well as positive square root solutions for the geometry. The positive one is the black hole and the negative one is the white hole. A black hole is a region of space from which nothing, not even light, can escape. It is the result of the deformation of spacetime caused by a very compact mass. Around a black hole there is an undetectable surface which marks the point of no return, called an event horizon. It is called "black" because it absorbs all the light that hits it, reflecting nothing. A white hole, in general relativity, is a hypothetical region of spacetime which cannot be entered from the outside, but from which matter and light may escape. In this sense it is the reverse of a black hole, which can be entered from the outside, but from which nothing, including light, may escape. However, it is theoretically possible for a traveler to enter a rotating black hole, avoid the singularity, and travel into a rotating white hole which allows the traveler to escape into another universe. This traveling path is the wormhole. A wormhole is a hypothetical feature of spacetime. It is a "shortcut" through spacetime. There is no observational evidence for wormholes. But on a theoretical level there are valid solutions containing wormholes. The American theoretical physicist John Archibald Wheeler coined the term wormhole in 1957; however, in 1921, the German mathematician Hermann Weyl already had proposed the wormhole theory, in connection with mass analysis of electromagnetic field energy. A black hole and a white whole are connected by a path which is called the Einstein Rosen Bridge. The EinsteinRosen Bridge was discovered by Albert Einstein and his colleague Nathan Rosen which was published in 1935. However in 1962, John A. Wheeler and Robert W. Fuller published a paper showing that this type of wormhole is unstable. It was proposed that quasars (quasi-stellar radio sources) are white hole forming the ends of worm holes. What is the Einstein-Rosen Bridge? The Einstein-Rosen Bridge is a geometrical property of a black hole. It manifests that on the other side of a black hole there is another set of dimensions attached to the one from our universe. This makes passage through this bridge and hence into another universe a mathematical possibility. There are three basic properties of a black hole: its mass, its spin, and its charge. Once these three are known, the black hole is completely specified. A static black hole, that is one of no spin and no charge, is called a Schwarzschild hole. A black hole whose spin and/or whose charge is non-zero is a Reissner-Nordström hole. The complete Schwarzschild geometry consists of a black hole, a white hole, and two Universes connected at their horizons by a wormhole. Schwarzschild solution to Einstein's equations actually describes a wormhole connecting two regions of flat space-time; two universes, or two parts of the same universe. A white hole is a black hole running backwards in time. Just as black holes swallow things, so white holes spit them out. However white holes cannot exist, since they violate the second law of thermodynamics. General Relativity is time symmetric. It does not know about the second law of thermodynamics. It does not know about which way cause and effect go. However we do. The negative square root solution outside the horizon represents another Universe. The wormhole joining the two separate Universes is known as the Einstein-Rosen Bridge. The prediction of the existence of black holes did not trouble Einstein, but he found that the black holes contained a singularity at its centre. This is a point of infinite density where time comes to an end. At the point of the singularity, all the known laws of physics start to breakdown. For Einstein this was a very troubling thought and he did not like them. The idea that they were shielding from the outside world by the event horizon of the black hole was not enough for him. He did not like the "concept that if you can not see it then do not worry about it." So he went to work with Nathan Rosen in 1935. They produced a paper that gave the evidence for a bridge between a black hole and a white hole; this was called the Einstein-Rosen Bridge.
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