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Relativity, Cosmology, and Time


Black Hole Information Paradox

Before getting to the essential point of whether black hole destroys information or not, it is necessary to clarify the meaning of information in the debate. According to Leonard Susskind, who played a principle role in the debate, entropy is hidden information. This view considers the basic units (or bits) of information to be the microscopic particles, which can be atoms, elementary particles, or down to the smallest unit the size of Planck length (~ 10-33cm). They are hidden because its existence is not known to us. Once we are aware of its presence (such as an electron in a collision experiment), it becomes information, and generates events that we can keep track of. The information is said to be conserved because we can always recover the original event by time reversal operations (at least in theory, which asserts that the laws of physics are the same in both forward and backward time directions, the "Second Law of Thermodynamics" notwithstanding).
Anyway, the two images from NewScientist below summarize the history of black hole and information with the various speculations on its fate.

                    
                    

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