Mid-Term Report Summary - EMERGRAV (Emergent Gravity, String Theory and the Holographic Principle)
Einstein's theory of general relativity is still viewed as the most complete description of gravity. Combined insights from string theory and black hole physics strongly indicate that general relativity emerges from a microscopic description in which at first gravity is not assumed to exist.
The PI of the EMERGRAV project has proposed that the microscopic explanation of gravity lies in differences in the entropy of the underlying theory. Using laws of thermodynamics and an analogy with entropic forces, which is responsible for instance for the elasticity of polymers, a derivation of the gravitational laws of Newton and Einstein can presented.
An important new ingredient in the study of the emergence of gravity is quantum entanglement. A particularly central role is played by the entanglement entropy associated with the division of space-time into two parts, which is conjectured to have a universal value equal to a quarter of the surface area of the separating wall measured in Planck units. This result has been proven by
researchers of the EMERGRAV project for a random region in a negatively curved space time (anti-de Sitter space).
This new role of entanglement entropy has led to a heated scientific discussion about the nature of the event horizon of a black hole. When a pair of particles arises from the vacuum near such an event horizon, one of the particles can fall into the black hole while the other escapes in the form of radiation. Through this Hawking radiation the entanglement entropy of the black hole seems to increase. At the same time the black hole loses energy, as a result of which the area of its event horizon decreases. It was recently argued that the tension between the increasing entanglement on the one hand and the decreasing area of the event horizon on the other (and therefore reduced amount of quantum information) implies that the event horizon is not a regular part of space-time.
Researchers of the EMERGRAV project have demonstrated that the entanglement between a black hole and the outside world can be used to reconstruct the interior of the black hole, as a result of which the regular character of the event horizon is retained.
Both mentioned results are an important step forwards in the research into the quantum structure of space-time.
The main goal of the research program of the EMERGRAV project is to extend and apply these new insights to areas of physics in which gravity plays a central role. Especially in the context of cosmology already promising new results have been obtained that shed a whole new light on major unanswered questions related to dark energy and dark matter.
The PI of the EMERGRAV project has proposed that the microscopic explanation of gravity lies in differences in the entropy of the underlying theory. Using laws of thermodynamics and an analogy with entropic forces, which is responsible for instance for the elasticity of polymers, a derivation of the gravitational laws of Newton and Einstein can presented.
An important new ingredient in the study of the emergence of gravity is quantum entanglement. A particularly central role is played by the entanglement entropy associated with the division of space-time into two parts, which is conjectured to have a universal value equal to a quarter of the surface area of the separating wall measured in Planck units. This result has been proven by
researchers of the EMERGRAV project for a random region in a negatively curved space time (anti-de Sitter space).
This new role of entanglement entropy has led to a heated scientific discussion about the nature of the event horizon of a black hole. When a pair of particles arises from the vacuum near such an event horizon, one of the particles can fall into the black hole while the other escapes in the form of radiation. Through this Hawking radiation the entanglement entropy of the black hole seems to increase. At the same time the black hole loses energy, as a result of which the area of its event horizon decreases. It was recently argued that the tension between the increasing entanglement on the one hand and the decreasing area of the event horizon on the other (and therefore reduced amount of quantum information) implies that the event horizon is not a regular part of space-time.
Researchers of the EMERGRAV project have demonstrated that the entanglement between a black hole and the outside world can be used to reconstruct the interior of the black hole, as a result of which the regular character of the event horizon is retained.
Both mentioned results are an important step forwards in the research into the quantum structure of space-time.
The main goal of the research program of the EMERGRAV project is to extend and apply these new insights to areas of physics in which gravity plays a central role. Especially in the context of cosmology already promising new results have been obtained that shed a whole new light on major unanswered questions related to dark energy and dark matter.