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# In Search of a Theory of Quantum Gravity

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Tweet## isabelle naylor

on 25 March 2013#### Transcript of In Search of a Theory of Quantum Gravity

To quantise or not to quantise In Search of a Theory of Quantum Gravity Introduction to Gravitation Why quantum gravity? "If one system is quantised, any system coupled to it must also be quantised." gravity is nonrenormalisable entropic gravity gravitational thermodynamics induced gravity "Every point mass in the universe attracts every other point mass with a force that is directly proportional to the square of the distance between them" Every object experiences the same acceleration It applies to everything It all started with an apple... no need for "action at a distance", the motion of an object is subject to the local geometry of spacetime Infinities arise even subatomic particles "It can scarcely be denied that the supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender to the adequate representation of a single datum of experience." "The first motivation is unification. The history of science shows that a reductionist viewpoint has been very fruitful in physics [...] The universal coupling of gravity to all forms of energy would make it plausible that gravity has to be implemented in a quantum framework too." disproved Covariant quantum gravity quantisation in the form of particles String theory Canonical quantum gravity quantisation of spacetime Loop quantum gravity “The ultimate necessity of quantizing the electromagnetic field (or any other field) can only be founded on experience, and all that considerations of measurability of field components can do is to illustrate the consistency of the way in which the mathematical formalism of a theory embodying such quantization is linked with the classical concepts on which its use in analysing the phenomena rests.” Einstein field equations describing relativistic gravitation can be derived by combining general thermodynamic considerations with the equivalence principle gravity originates from the tendency of things to increase their entropy gravity is generated from the interaction of quantum fields Conclusion The lack of experimental evidence makes it unclear which of the many different approaches will be successful The same method that has worked so far in quantising the other fields is not applicable to gravity, so a new, unknown method is required In General Relativity, the phenomenon of gravitation is not attributed to a force; perhaps considering it to be one of the fundamental forces will never lead to its unification

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