In a discovery that may have profound implications, an Indian theoretical physicist and his British collaborator have given a surprising new twist to one of the great mysteries about black holes.
Their result shows that either the analysis of the famous British physicist Stephen Hawking is faulty or quantum mechanics, whose laws apply to the behaviour of matter in the quantum world of particle physics, "must break down".
Black holes have been characterized as objects in the universe trapping anything that comes too close and not allowing even light to escape. In the mid-70s, Hawking showed that black holes eventually evaporate away in a steady stream of featureless radiation containing no information.
This theory of Hawking resulted in the "information loss paradox" which simply asks:
If a black hole completely evaporates and vanishes, what happens to the information it originally contained about the state of its matter? Where does the information go?
For years physicists have been trying to suggest a possible way out.
Conventional (classical) information can vanish in two ways, either by moving to another place (eg across the Internet), or by "hiding", such as in a coded message.
The famous Vernam cipher devised in 1917 or the one-time pad cryptographic code are examples of such classical information hiding: the information resides neither in the encoded message nor in the secret key pad used to decipher it, but in "correlations" between the two.
For decades, physicists believed that both these mechanisms were applicable to quantum information in the black hole as well. The current understanding is that the quantum information is "hidden" in the "correlations" between the state of the (Hawking) radiation and the internal state of the black hole.
However, in a paper published in the latest edition of Physical Review Letters, Arun Pati of the Institute of Physics at Bhubaneswar and Sam Braunstein of the University of York in Britain have now shown this is not possible.
"Our result says that if the original quantum information is missing from the one subsystem, then it must be found in the remainder of the subsystem," Pati said. "We have established that quantum information cannot be 'hidden' in the spooky correlations (as now believed)."
In Braunstein's words, "quantum information can run but it can't hide".
Pati said: "Our result shows that either quantum mechanics or Hawking's analysis must break down, but it does not choose between these two possibilities."
According to Braunstein, the "no-hiding theorem" that he and Pati have derived, when applied to black holes, "provides new insight into the different laws governing classical and quantum information. It shows that there's got to be new physics out there".
This is the second time that Indian scientists have found holes in the traditional black hole theories expounded by Hawking and others.
In 2000, Abhas Mitra, a physicist at the Bhabha Atomic Research Centre in Mumbai, theoretically showed that black holes cannot exist under Einstein's theory of relativity.
His controversial paper in the Journal Foundations of Physics contradicting established ideas about black holes still remains unchallenged.
Commenting on the analysis by Pati and Braunstein, Mitra told: "They have concluded that either Hawking Radiation is incorrect or quantum mechanics (QM) is incorrect. QM has withstood innumerable experimental tests and there is tremendous inbuilt theoretical consistency and thus it cannot be wrong. But Hawking Radiation has not been detected in 35 years despite many attempts."
Pati says his finding cannot be interpreted to support Mitra.
"Our analysis was only concerned with resolving the information paradox (and not black hole theories themselves)," Pati said. "All that we can say is that our work on quantum information demonstrates that the black hole information paradox is even more severe than previously believed."