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All current approaches to quantum gravity employ essentially standard quantum theory including, in particular, continuum quantities such as the real or complex numbers. However, I wish to argue that this may be fundamentally wrong in so far…

Quantum Physics · Physics 2007-05-23 C. J. Isham

This is a nontechnical introduction to recent work on quantum gravity using ideas from higher-dimensional algebra. We argue that reconciling general relativity with the Standard Model requires a `background-free quantum theory with local…

General Relativity and Quantum Cosmology · Physics 2015-02-13 John C. Baez

Starting from a new understanding of the vacuum energy problem based on the combination of the phase space regularization and the holographic bound, we argue that quantum gravity should be understood as gravitized quantum theory, that is,…

High Energy Physics - Theory · Physics 2024-07-10 Tristan Hübsch , Djordje Minic

Quantum theory makes the most accurate empirical predictions and yet it lacks simple, comprehensible physical principles from which the theory can be uniquely derived. A broad class of probabilistic theories exist which all share some…

Quantum Physics · Physics 2012-04-17 Borivoje Dakic , Caslav Brukner

Consider the interior of a black hole or the very early universe: matter is so densely localized that neither the effects of gravity nor those of quantum theory can be ignored. But this entails that neither general relativity nor quantum…

General Relativity and Quantum Cosmology · Physics 2023-10-02 Hassan Mehmood

A Gaussian approximation to the bosonic part of M-(atrix) theory with mass deformation is considered at large values of the dimension $d$. From the perspective of the gauge/gravity duality this action reproduces with great accuracy the…

High Energy Physics - Theory · Physics 2022-01-05 Badis Ydri

We still lack any consensus about what one is actually talking about as one uses quantum mechanics. There is a gap between the abstract terms in which the theory is couched and the phenomena the theory enables each of us to account for so…

Quantum Physics · Physics 2020-04-17 N. David Mermin

We show using simple arguments, that the conceptual triad of a {\it classical} black hole, semi-classical Hawking emission and geometry quantization is inherently, mutually incompatible. Presence of any two explicitly violates the third. We…

General Relativity and Quantum Cosmology · Physics 2016-10-26 Sumanta Chakraborty , Kinjalk Lochan

After a brief review of current scenarios for the resolution and/or avoidance of the Big Bang, an alternative hypothesis is put forward implying an infinite increase in complexity towards the initial singularity. This may result in an…

General Relativity and Quantum Cosmology · Physics 2021-09-22 Hermann Nicolai

A theoretical scheme, based on a probabilistic generalization of the Hamilton's principle, is elaborated to obtain an unified description of more general dynamical behaviors determined both from a lagrangian function and by mechanisms not…

Quantum Physics · Physics 2009-09-28 Matteo Villani

General Theory of Relativity and Quantum theory gives two different description of the same mother nature in the big and small scale respectively. Mathematical languages of these two theories are entirely different, one is geometric while…

General Physics · Physics 2020-05-11 Sijo K. Joseph

The idea of treating general relativistic theories in a perturbative expansion around a topological theory has been recently put forward in the quantum gravity literature. Here we investigate the viability of this idea, by applying it to…

General Relativity and Quantum Cosmology · Physics 2008-11-26 Carlo Rovelli , Simone Speziale

In this conceptual paper, we discuss quantum formalisms which do not use the famous Axiom of Choice. We also consider the fundamental problem which addresses the (in)correctness of having the complex numbers as the base field for Hilbert…

Quantum Physics · Physics 2023-05-18 Koen Thas

Extended Theories of Gravity can be considered a new paradigm to cure shortcomings of General Relativity at infrared and ultraviolet scales. They are an approach that, by preserving the undoubtedly positive results of Einstein's Theory, is…

General Relativity and Quantum Cosmology · Physics 2015-05-30 Salvatore Capozziello , Mariafelicia De Laurentis

Finetuning and Naturalness are extra-empirical theory assessments that reflect our expectation how scientific theories should provide an intuitive understanding about the foundations underlying the observed phenomena. Recently, the absence…

History and Philosophy of Physics · Physics 2019-05-16 Heinrich Päs

An approach to quantum gravity and cosmology is proposed based on a synthesis of four elements: 1) the Bekenstein bound and the related holographic hypothesis of 't Hooft and Susskind, 2) topological quantum field theory, 3) a new approach…

General Relativity and Quantum Cosmology · Physics 2008-02-03 Lee Smolin

In this report we discuss three aspects: 1) Semiclassical gravity theory (SCG): 4 levels of theories describing the interaction of quantum matter with classical gravity; 2) Alternative Quantum Theories: Discerning those which are derivable…

General Relativity and Quantum Cosmology · Physics 2015-06-18 B. L. Hu

In the paper, the idea of describing not-yet-verified properties of quantum objects with logical many-valuedness is scrutinized. As it is argued, to promote such an idea, the following two foundational problems of many-valued quantum logic…

Quantum Physics · Physics 2018-05-09 Arkady Bolotin

A program was recently initiated to bridge the gap between the Planck scale physics described by loop quantum gravity and the familiar low energy world. We illustrate the conceptual problems and their solutions through a toy model: quantum…

General Relativity and Quantum Cosmology · Physics 2017-08-23 Abhay Ashtekar , Stephen Fairhurst , Joshua L. Willis

From the point of view of an uncompromising field theorist quantum gravity is beset with serious technical and, above all, conceptual problems with regard especially to the meaning of genuine "physical" observables. This situation is not…

General Relativity and Quantum Cosmology · Physics 2007-05-23 Wolfgang Kummer