© 1975-1979, 2008 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, First Edition, Xenology Research Institute, Sacramento, CA, 1979; http://www.xenology.info/Xeno.htm

17.4.6  Black Holes and Space Warps

Severe gravitational distortion of space-time offers several scientifically plausible mechanisms for extremely fast interstellar communication and travel.²⁷⁹⁸ Dr. John A. Wheeler of Princeton University has predicted the existence of "wormholes" -- a warpage of free space -- based on his own version of General Relativity which has come to be known as geometrodynanics.²⁷⁴¹

Wheeler wormholes should be exceedingly small (subatomic dimensions, say, about 10^-35 meters). They would allow point-to-point linkages of all locales in the universe; pointlike particles, such as electrons, could be used to communicate without traversing the intervening space. Wheeler draws an analogy to the sea:

Space is like an ocean which looks flat to the aviator who flies above it, but which is a tossing turmoil to the hapless butterfly which falls upon it. Regarded more and more closely, it shows more and more agitation, until...the entire structure is permeated everywhere with worm-holes Geometrodynamic law forces on all space this foam-like character.⁷⁷

J.C. Graves and D.R. Brill at Princeton have shown that electric field lines threaded through the throat of a wormhole may prevent it from closing.²⁷⁷⁷ Such a tunnel in space should stay open indefinitely, allowing particles of matter to pass through to known destinations. Wormholes may connect a vast number of alternative universes at the subatomic level.²⁷⁷⁸

Black holes, predicted in 1939 by Oppenheimer using General Relativity theory, are concentrations of mass so dense that even light cannot escape the tremendous gravitational pull. Stellar-mass BHs are typically several kilometers in diameter. The standard black hole model predicts a "singularity" at dead center, a point at which density becomes infinite, This collapse of physical laws as we know them, fortunately, is hidden from view behind an event horizon -- the surface below which photons cannot escape.

However, in the case of a rotating black hole things are quite different. According to relativistic solutions first obtained by R.P. Kerr in 1963, the singularity is no longer a point but has expanded into a ring.²⁷⁴² Many theorists believe that the region lying in the disk of the ring singularity may be a gateway to other universes or to our own universe at a different point in space and time. Rotating BHs have two event horizons instead of one, passage through which by a starship may involve such peculiar phenomena as negative mass effects and time running in reverse.²⁷⁴⁶ The Kruskal Diagram illustrated in Figure 17.6 shows one interpretation of possible trajectories through a rotating black hole assuming a Kerr spacetime metric.²⁷⁴⁷

Figure 17.6 Using Black Holes for Interstellar Travel

THE WORMHOLE In the Einstein-Rosen model of the nonrotating black hole, a wormhole connects portions of two separate flat-space-time universes. This wormhole, called the Einstein-Rosen Bridge, may be interpreted either as connecting two distinct universes or as joining two distant points in the universe of origin. According to this theory, starships passing through the event horizon of a black hole would find the curvature of space-time growing less severe, eventually emerging through a "white hole" in distant space.2954 The diagram at above right shows the Einstein-Rosen Bridge as it might connect two distant points in the same universe. The event horizon lies at the center of the wormhole. The diagram at below right is an "unfolded" version of the Bridge, for those who would rather view universal space-time as essentially flat. The two are mathematically equivalent.
	KRUSKAL DIAGRAM FOR ROTATING BLACK HOLES The figure at left represents a possible space-time configuration of a rotating black hole, using "Kruskal coordinates." There are now two event horizons instead of one, so there are three classes of space. It is possible to reach other universes like ours by selecting the correct trajectory upon entering the black hole. (Trip C) A collision with the ring singularity is possible (Trip B), and cowardly astronauts can avoid the black hole altogether (Trip A). Some "Type I" universes cannot be reached at all until tachyonic star travel is permitted (Trip D).
FOLDED KRUSKAL DIAGRAM The Kruskal diagram of the Kerr solution to the equations describing rotating black holes may he folded cylindrically as shown in the diagram at right. Using this interpretation of the wormhole caused by a rotating BH, a starship is theoretically capable of circumnavigating the entire Kruskal space-time and returning to the universe of origin anywhere in space and anywhen in time. This would appear to violate causality and permit time travel.

A few writers have offered fabulous accounts of galactic commerce among sentient extraterrestrial races, using black holes as the entry gates to a kind of hyperspatial subway system.* Says astronomer Carl Sagan:

I can imagine, although it is the sheerest speculation, a federation of societies in the galaxy that have established a black hole rapid-transit system. A vehicle is rapidly routed through an interlaced network of black holes to the black hole nearest its destination.... Great civilizations might grow up near the black holes, with the planets farthest from them being designated as farm worlds, ecological preserves, vacations and resorts, specialty manufacturers, outposts for poets and musicians, and retreats for those who do not cherish big city life. In such a galaxy the individuality of the constituent cultures is preserved but a common galactic heritage established and maintained. Long travel times make trivial contact difficult, but the black hole network makes important contact possible.¹⁵

There are a number of practical difficulties associated with the use of BHs as an interstellar rapid-transit system. First, there is the problem of navigation. Until you jump into a black hole, you don’t really know where you will end up. Once you emerge at your destination (from a "white hole"), it is difficult to know how to get back. Many theories predict that it may be impossible to return. If you have entered another universe, the journey is probably irreversible and strictly one-way; if you have remained in your own universe, it would be an extraordinary stroke of luck to find another rotating BH in the immediate vicinity whose exit terminus happens to lie near the original starting point.

Tidal forces are yet another problem. Astronauts venturing even within a few hundred kilometers of a stellar-mass black hole would be savagely ripped apart by the simultaneous squeezing and stretching forces which would amount to hundreds of gees. While it may be possible to compensate for these effects by using special arrangements of ultradense matter within the starship structure, it may be better instead to search for supermassive black holes. Several theoretical physicists have proposed that gigantic BHs may exist at the center of many galaxies -- possibly even our own -- with masses ranging from 10⁶-10¹⁰ solar masses. Surprisingly, such monstrous objects need be no more dense than air, and tidal forces would be measured in milligees rather than megagees at the event horizon.

Catastrophe theory, first devised by French mathematician Rene Thom more than a decade ago,²⁸⁰⁰ offers a totally new conceptual variation on the theme of space warp drives. Catastrophe theory is a controversial new mathematical tool for examining highly discontinuous events -- such as bridges buckling, sudden economic depressions, rapid emotional changes from fear to rage, and a host of other abrupt alterations in physical structures, lifeforms, and societies. The theory explains how slight changes in the initial state of a system can result in major divergence in the course of its evolution and subsequent behavior.

Since the Big Bang was a highly discontinuous event, creating a universe out of nothingness, it is quite conceivable that a catastrophe cosmology may eventually be devised. Perhaps it would involve catastrophe surfaces rather than simple spherical space-time geometry. Indeed, the coordinates need not all be spatial or temporal, but could include axes representing energy, momentum, spin, mass, charge, angular velocity, or whatever else is appropriate. If this is so, then the proper combination of fields and physical parameters could cause a packet of photons (a message) or a chunk of matter (a starship) suddenly to assume new parameters in a single, "catastrophic" leap. These new parameters might correspond to changes in energy, spatial position, or time.

* We will not here discuss the fascinating possibility of tachyonic black holes, although these have already been investigated theoretically.¹⁵²⁰

Last updated on 6 December 2008