Interstellar Wormholes
With the recent box office film ‘interstellar’ many people are excited about the prospects of wormholes as a means for interstellar transport. These have been depicted in other television programs, such as in the Star Trek: Deep Space Nine universe. Although there is currently no evidence that such exotic objects exists in nature, it is possible that they could be artificially created, perhaps from versions of higher dimensional string theory and engineering of the fundamental space-time foam. Wormhole research is today an exciting subject with dozens of papers published in peer reviewed journals every year, but it is worthwhile to be reminded of its origins and it starts from a surprising place.
In 1915 Albert Einstein published his General Theory of Relativity, his description of gravity that neatly defines how objects will attract one another and affect the space and time around them. Many years later the American physicist John Wheeler would coin the phrase “space tells matter how to move, and matter tells space how to curve”. Einstein described gravity as a manifestation of space-time curvature. General Relativity is a continuous field theory in contrast to the particle theory of matter.
Einstein was also involved in the development of quantum mechanics, the theory that described sub-atomic particles. But he was not entirely happy with its inherent uncertainties and probabilistic character. So in 1935 he worked with Nathan Rosen to produce a field theory for electrons, using General Relativity. His paper was titled “The Particle Problem in the General Theory of Relativity” (Phys.Rev, 48, 73, 1935). They were investigating the possibility of an atomistic theory of matter and electricity which, while excluding singularities of the field, makes use of no other variables other than the metric of the general relativity and the potential of the Maxwell theory. In essence, they asserted that the most natural elementary charged particle was found to be one of zero mass.
In the end, what they produced was something quite unusual. They started with the equations for a spherically symmetric mass distribution, typically used for black holes and known as the Schwarzschild solution, and performed what is known as a co-ordinate transformation to remove the region containing the curvature singularity. The solution was a mathematical representation of physical space by a space of two asymptotically flat sheets (negative infinity to positive infinity) connected by a bridge or a Schwarzschild wormhole with a ‘throat’.
Now admittedly, this was not a traversable wormhole, for that we had to await the arrival of physicists John Wheeler in the 1950s and Kip Thorne in the 1980s. In 1987, at the encouragement of Carl Sagan for his novel “Contact” (later a feature film) Thorne and his colleague Michael Morris, were able to construct a metric to describe a spherically symmetric and static wormhole with a proper circumference with the co-ordinate decreasing from negative infinity to a minimum value where the throat was located and then increasing form the throat to positive infinity. This solution has the distinctive feature of being horizon-less. The Thorne and Morris paper titled "Wormholes in Spacetime and their use for Interstellar Travel: A Tool for Teaching General Relativity" (American Journal of Physics, Volume 56, issue 5, May 1988). This paper really helped to establish wormhole research as an exciting pursuit of academic enquiry.
Since then many papers have been published, an indeed astronomical surveys have been conducted to examine the deep stars in search of natural wormholes, none have yet been identified. It is important to remember the origin of a field, and although the Einstein-Rosen Bridge was not a traversable wormhole, and it wasn't the author’s intention to produce one, they did produce the first mathematical attempt at a wormhole solution, and they should be remembered for that. It just goes to show, that often in science, you can produce something quite unexpected.
