A World Turned Upside Down?

It should be emphasized that Einstein and Rosen did not mean to suggest that people could actually enter a black hole and use it as a gateway to somewhere else. They merely showed that mathematics did not forbid the existence of such tunnels. They did not pretend to know how big, how long, or how safe these tunnels might be, and in any case, the idea of traveling though them seemed irrelevant. For one thing, mathematical calculations indicated that any such wormhole would open up for no more than 1/10,000 of a second and then close. Indeed, it would not stay open long enough to allow even light to travel from one end of the tunnel to the other, so how could a much slower-moving spaceship get through? Also, all of these scientists agreed that any matter entering a black hole, including a person, would be demolished; even his or her atoms would be torn apart. So no space traveler who did fly into a black hole would survive long enough to make it to the wormhole, let alone travel through it.

However, in the 1960s new research began to alter this seemingly hopeless outlook. Flamm, Einstein, Rosen, and the others had based their calculations and opinions mainly on the workings of static, non-spinning Schwarzschild black holes. Yet as time went on, more and more scientists agreed that such bodies are theoretical constructs and do not exist in the real universe. When Roy Kerr introduced his mathematical solution for spinning black holes and it became clear that all such superdense bodies must be rotating, the picture of a black hole’s interior changed. Now it could be seen that the singularity is shaped like a ring rather than an infinitely tiny point. And the mathematics for such rotating rings does suggest that matter can pass through them without being crushed. (Of course, this does not rule out the possibility that the matter will suffer other lethal effects, such as bombardment by deadly radiation.)

The idea that a ring singularity might be a portal to a wormhole in hyperspace opens up a host of intriguing possibilities for the geometry of the region inside a black hole. Among these is the notion that some of the basic properties of the normal universe will be reversed. In the case of an astronaut diving through the middle of a ring singularity, Gribbin explains,

the world is turned upside-down. The equations tell us that as you pass through the ring you enter a region of spacetime in which the product of your distance from the center of the ring and the force of gravity is negative. This might mean that gravity is behaving perfectly normally but you have entered a region of negative space in which it is possible to be, for example, “minus ten kilometers” away from the center of the hole. Even relativists [experts in general relativity] have trouble coming to terms with that possibility, so they usually interpret this negativity as meaning that gravity reverses as you pass through the ring, turning into a repulsive force that pushes you, instead of pulling. In the region of spacetime beyond the ring, the gravity of the black hole repels both matter and light away from itself.