The thermodynamics of a black hole
travel away from the black hole. According to conservation laws, these photons cannot create the energy required for their escape, hence they must ‘steal’ energy from the black hole (Harlow, 2016) .
QFT describes black holes as the warping of space-time, rather than physical objects with a surface and intrinsic properties. These particles that are suddenly created are not annihilated, hence require energy and, as discussed, energy is equivalent to mass. Therefore, these particles gain energy from the black hole ’ s mass. However ,according to Einstein's field equations, mass causes curvature. Hence, if the mass decreases, the curvature decreases, and the black hole begins to shrink (Miller, 2021). Even though the black hole is contracting, information which has fallen in is suddenly being destroyed. A fundamental rule of physics is that information must be conserved. The information cannot be carried away with this Hawking radiation, since nothing can return from the event horizon. However, if this Hawking radiation would be emitted from just outside the event horizon, no laws of special relativity would be violated (PBS space-time, 2018).
The following section develops Hawking radiation from the last section into how the information paradox emerges. From this it will explore the concept of entropy regarding black holes and how this led onto the holographic universe.
2.1
Information paradox
As the mass of the black hole decreases, the information that fell into the black hole is being destroyed. This would be acceptable if information were transferred with Hawking radiation. However, this cannot happen as nothing can escape from the black hole (Preskill, 1992). Hawking radiation carries no information about the matter that fell inside the black hole (the information), as nothing can return from the event horizon. The only thing we could know by analysing this radiation is the mass (De Nova, 2019). Therefore, black holes will continue to evaporate, transforming into this thermal radiation until nothing exists, hence information describing matter that fell into the black hole is lost (De Alwis, 1995).
2.2
Entropy
By the end of the 20 th century, Hawking suggested the correlation between Hawking radiation and black-body spectrum (thermal radiation). His work ( Physics Explained , 2021) hinted at the existence of a black hole temperature, and that it was in fact inversely proportional to the black hole mass, represented by the following:
Temperature of black hole (LoPresto, 2003)
According to the black body spectrum, a lower temperature means less thermal radiation emitted. Therefore, combining these two ideas, we can deduce that heavier black holes radiate at a lower intensity, therefore existing for longer. A solar mass black hole would take 10^67 years to evaporate. However, an average black hole weighs 10 solar masses (De Nova, 2019). While Hawking radiation and black hole evaporation is a theoretical problem, no black holes are thought to have been destroyed at this moment in time (Bekenstein, 2003).
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