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It is unknown whether wormholes are possible or not within the framework of general relativity. All known solutions of general relativity which allow for wormholes require the existence of
exotic matter, a theoretical substance which has negative energy density. However, it hasnot been mathematically proved that this is an absolute requirement for wormholes, nor has it been established that exotic matter cannot exist. Furthermore, since there is no established theory of quantum gravity, it is impossible to say with any certainty whether they are possible or not within that theoretical framework.
Many physicists, including Stephen Hawking (see Hawking's Chronology Protection Conjecture), believe that due to the problems a wormhole would theoretically create, including allowing time travel, that something fundamental in the laws of physics would prohibit them. However, this remains speculation, and the notion that nature would censor inconvenient objects has already failed in the case of the cosmic censorship principle.
A wormhole could potentially allow time travel. This could be accomplished by accelerating one end of the wormhole relative to the other, and then sometime later bringing it back; relativistic time dilation would result in less time having passed for the accelerated wormhole mouth compared to the stationary one, meaning that anything which entered the stationary wormhole mouth would exit the accelerated one at a point in time prior to its entry. The path through such a wormhole is called a closed timelike curveFrom the point of view of general relativity, a closed timelike curve (CTC) is a closed worldline. If CTCs exists, their existence would seem to imply at least the theoretical possiblity of making a time machine. If a second time parameter is introduced t, and a wormhole with this property is sometimes referred to as a "timehole."
It is thought that it may not be possible to convert a wormhole into a time machine in this manner, however; some mathematical models indicate that a feedback loop of virtual particleIn the description of the interaction between elementary particles in quantum field theory, a virtual particle is a temporary elementary particle, used to describe an intermediate stage in the interaction. A virtual particle is never the end result of sucs would circulate through the timehole with ever-increasing intensity, destroying it before any information could be passed through it. This has been called into question by the suggestion that radiation would disperse after traveling through the wormhole, therefore preventing infinite accumulation. There is also the Roman ringA wormhole with time difference across its mouths may not allow a closed time loop. If we arrange such wormholes in a suitable configuration, a closed time loop will be again possible. Such a configuration is known as a Roman ring . A Roman ring is a very, which is a very stable configuration of more than one wormhole. This ring allows a closed time loop with stable wormholes. The debate on this matter is described by Kip S. ThorneKip Stephen Thorne (born June 1, 1940) is an American theoretical physicist, known for his prolific contributions in the field of gravitation physics and astrophysics. Biography Thorne was born in Logan, Utah. He received his B. from Caltech in 1962, and in the book Black Holes and Time Warps [1], and will likely require a theory of quantum gravity to resolve.