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Under certain extreme conditions Einstein’s general theory of relativity seems to violate determinism, according to an international team of physicists. The group has shown that in a universe expanding under the influence of the cosmological constant, black holes generated by the collapse of highly charged stars should contain a region where physical conditions are not fixed by the stars’ initial state. At odds with a 40-year old idea known as cosmic censorship, the researchers say that signs of this indeterminism might show up in detections of gravitational waves.

Newton’s mechanics allow us in principle to calculate the exact state of a physical system at any point in the future, provided that we know its initial state perfectly. So too with general relativity: a precise knowledge of space’s geometry and its rate of change in the present enables us in theory to predict exactly how space-time will evolve. As such, Einstein’s theory is considered by most physicists to be entirely deterministic.

Charged black holes, however, challenge this deterministic picture. The “Reissner-Nordström” solution of general relativity describes a black hole created when a star that is electrically charged and spherical collapses in on itself under the force of gravity. Hidden from view inside such a black hole’s event horizon lies a second boundary known as the Cauchy horizon, beyond which space-time is smooth but indeterminate. In other words, the future can no longer be predicted.

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Category: Science