The Black Hole War
‘If you feel you are in a black hole, don’t give up. There’s a way out.
What would happen if I threw somebody into a black hole? According to Einstein’s general theory of relativity, a person falling into a black hole will just keep on going until he reaches singularity, where his body starts to stretch out and bad things happen. But when we look at the same thing from the perspective of quantum mechanics, when the person reaches the event horizon he is absorbed by it, and radiation comes out and at some point, the Black Hole must be out of this radiation and would disappear. This would again not fit with Quantum Mechanics and it doesn’t talk about any loss or disappearance of information and this is where it gets tricky and interesting too.
The question is that everything contains some sort of information as it contains a very specific arrangement of particles, so where does the information that describes the arrangement of those particles go?
Stephen Hawking described that the information is lost but the energy is remains or released. This causes a “Paradox” which is widely known as the “Information Paradox”
Many physicists started to argue, that information is never lost but found it difficult to convince Prof Hawking. Stephen Hawking suggested that according to pure general relativity, nothing can escape a black hole, including information. This idea implies that once information falls into a black hole, it’s gone forever, even if the black hole eventually evaporates.
However, many physicists, including Leonardo Susskind and Preskill, disagreed with this notion. They argued that information loss violates the principles of quantum mechanics, which state that information cannot be destroyed. If information were truly lost, it would challenge our fundamental understanding of how the universe works. If we accept information loss, it would lead to inconsistencies between quantum mechanics and general relativity, two pillars of modern physics. Resolving the black hole information paradox is crucial for achieving a unified understanding of the laws governing the universe.
Resolutions
Radiation is the information
In 2019 there was a breakthrough in understanding Black Hole evaporation. Two sets of papers were published one by Netta Engelhardt and her colleagues Almheiri, Marolf, and Maxfield, and another by Penington. They presented a new analysis using semiclassical gravity. This analysis passed a crucial test called the Page Curve, which measures the entanglement of radiation emitted by black holes.
To explain, imagine dividing the radiation into two parts: R and B. Initially, when R has no information, it’s not connected to B. As we add information to R, its disorder increases. Similarly, as a black hole evaporates, information from the remaining black hole ends up in the emitted radiation. Eventually, all the black hole’s information is in the radiation, showing that information is conserved.
Information is in the Horizon
Gerard Hooft, a renowned physicist along with Leonardo Susskind put forward The Holographic Principle which was inspired by Jacob Bekenstein’s work on Black Hole entropy. Bekenstein’s discovery which linked entropy to the area of a black hole’s horizon rather than its volume, was groundbreaking. With the help of this discovery The Holographic Principle suggested that the information absorbed by a black hole isn’t lost but instead stored in its two-dimensional surface just like a hologram. This idea of holographic principles was also applicable to the world around us and the whole of the universe. This could also mean that the universe in itself is a hologram.
There is also a theory that the information is neither on the horizon nor in the radiation but rather has traveled through the black hole and is in another universe which brings us to the topic of Wormholes. Theorists have been intensely debating how literally to take all these wormholes. The wormholes are so deeply buried in the equations that their connection to reality seems tenuous, yet they do have tangible consequences. But we still don’t know what happens to that information.
References: Quanta Magazine, Wikipedia, MIT Physics, Reith Lectures, and some of my talent.
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