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Black holes are known to have many strange properties, such as that they allow nothing—not even light—to escape after falling in. A lesser known but equally bizarre property is that black holes appear to "know" what happens in the future in order to form in the first place. However, this strange property arises from the way in which black holes are defined, which has motivated some physicists to explore alternative definitions.

In a new paper published in Physical Review Letters, Raphael Bousso, a professor at the University of California, Berkeley, and Lawrence Berkeley National Laboratory, and Netta Engelhardt, a graduate student at the University of California, Santa Barbara, have reported a new area law in general relativity that is based on an interpretation of black holes as curved geometric objects called "holographic screens."

"The so-called teleology of the black hole is an artifact of the way in which physicists define an event horizon: the event horizon is defined with respect to infinite future elapsed time, so by definition it 'knows' about the entire fate of the universe," Engelhardt told Phys.org. "In general relativity, the black hole event horizon cannot be observed by any physical observer in finite time, and there isn't a sense in which the black hole as an entity knows about future infinity. It is simply a convenient way of describing black holes."

As Engelhardt explained, one reason why holographic screens are so interesting is that they are defined in a way which depends on more local properties and does not require information about future infinity.

"This is one property that makes objects like holographic screens so appealing: they do not suffer from such bizarre properties in the way in which they are defined," she said.

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