But an Indian scientist in Bhubaneswar and his colleague in the United Kingdom have together shown that at least the quantum information of matter absorbed by a black hole does survive, even though it must move to somewhere else.
This landmark finding by Dr Arun K Pati of the Institute of Physics in Bhubaneswar and Professor Sam Braunstein of the University of York’s Department of Computer Science has been reported in the February 23 issue of the Physical Review Letters. The findings might not just prove to be a milestone towards resolving a long-standing paradox relating to black holes but also have significant ramifications for quantum theory and quantum information theory.
Their research concludes that either celebrated scientist Stephen Hawking was wrong in his analysis of evaporation of blackholes, or that quantum theory, whose laws apply in the quantum world of particle physics, needs to be modified.
Dr Pati and Prof Braunstein have been studying the limitations of quantum information theory for several years. In 2000, they had come up with their “no-deletion” principle which says that unlike classical information, quantum information cannot be deleted. Applying this principle to black holes, they have now postulated the “no-hiding theorem”.
Black holes are extraordinarily dense regions in space-time with very strong gravitational pull. They are so dense that they do not even permit light rays to pass through them. Most of the laws of physics break down at this point.
In the mid 1970s, Stephen Hawking, who has done some pathbreaking research on black holes, showed that these blackholes eventually evaporate as radiation. But these radiations were found to have absolutely no character, that is, they contained no quantum information.
“The radiations reveal nothing about what has gone inside the black hole. They are completely independent of the input,” Dr Pati said.
Therein lay what is famously known as the ‘information loss paradox’ of black holes. According to quantum theory, quantum information cannot simply disappear. But with the evaporation of black holes —- as thermal radiation which does not contain any information —- this was exactly what seemed to be happening.
Scientists have in the past tried to explain this paradox with various theories. Some believe that the information might be found at some later stage. Others proposed that evaporation actually stops at some point and information is retained in a tiny black hole that is left behind. A more widely accepted theory is that the information is hidden in the correlation between Hawking’s calculations for the radiation and the blackhole’s internal state.
However, no one had any conclusive evidence of what was happening. Dr Pati and Prof Braunstein have now established that the information neither gets destroyed nor is hidden. It simply moves to some other system.
“Our work shows that if the original quantum information is missing from a subsystem, then this missing information must be available in the remainder of the subsystem. It cannot be stored in the correlation between the two subsystems,” Dr Pati told The Indian Express.
In Braunstein’s words, the essence of “no-hiding theorem” is that quantum information “can run but it cannot hide”.
But for that to happen, both quantum theory and Hawking’s calculations cannot be correct at the same time. One of them has to be modified.
“Either quantum theory or Hawking’s calculations must break down at this point,” Dr Pati said. “However, the results do not show any particular preference for one over the other.”