scholarly journals STEPHEN HAWKING: SPACE, TIME AND QUANTA

2020 ◽  
Author(s):  
Mauro Carfora
Keyword(s):  
General Relativity ◽  
Quantum Theory ◽  
Space Time ◽  
Stephen Hawking

A brief introduction to the scientic work of Stephen Hawking and to his contributions to our understanding of the interplay between general relativity and quantum theory.

scholarly journals On the emergence of the structure of physics

2018 ◽  
Vol 376 (2118) ◽  
pp. 20170231 ◽  
Author(s):  
S. Majid
Keyword(s):  
General Relativity ◽  
Quantum Theory ◽  
Quantum Gravity ◽  
Recent Work ◽  
Space Time ◽  
Quantum Space ◽  
Conceptual Level ◽  
Theme Issue ◽  
Self Duality ◽  
Born Reciprocity

We consider Hilbert’s problem of the axioms of physics at a qualitative or conceptual level. This is more pressing than ever as we seek to understand how both general relativity and quantum theory could emerge from some deeper theory of quantum gravity, and in this regard I have previously proposed a principle of self-duality or quantum Born reciprocity as a key structure. Here, I outline some of my recent work around the idea of quantum space–time as motivated by this non-standard philosophy, including a new toy model of gravity on a space–time consisting of four points forming a square. This article is part of the theme issue ‘Hilbert’s sixth problem’.

scholarly journals Towards Unification of General Relativity and Quantum Theory: Dendrogram Representation of the Event-Universe

2021 ◽  
Author(s):  
Andrei Khrennikov ◽  
Oded Shor ◽  
Benninger Felix
Keyword(s):  
General Relativity ◽  
Quantum Theory ◽  
Spin Glasses ◽  
Disordered Systems ◽  
Space Time ◽  
Unified Field Theory ◽  
Real Representation ◽  
Finite Tree ◽  
Bohm Potential ◽  
The Universe

Following Smolin, we proceed to unification of general relativity and quantum theory by operating solely with events, i.e., without appealing to physical systems and space-time. The universe is modelled as a dendrogram (finite tree) expressing the hierarchic relations between events. This is the observational (epistemic) model; the ontic model is based on p-adic numbers (infinite trees). Hence, we use novel mathematics—not only space-time but even real numbers are not in use. Here, the p-adic space (which is zero dimensional) serves as the base for the holographic image of the universe. In this way our theory relates to p-adic physics; in particular, p-adic string theory and complex disordered systems (p-adic representation of Parisi matrix for spin glasses). Our Dendrogramic-Holographic (DH) theory matches perfectly with the Mach’s principle and Brans-Dicke theory. We found surprising informational interrelation between the fundamental constants, h, c, G, and their DH-analogues, h(D), c(D), G(D). DH-theory is part of Wheeler’s project on the information restructuring of physics. It is also a step towards the Unified Field theory. The universal potential V is nonlocal, but this is relational DH-nonlocality. V can be coupled to the Bohm quantum potential by moving to the real representation. This coupling enhanced the role of the Bohm potential.

scholarly journals Schwinger’s approach to Einstein’s gravity and beyond

2014 ◽  
Vol 92 (9) ◽  
pp. 964-967 ◽  
Author(s):  
K.A. Milton
Keyword(s):  
General Relativity ◽  
Quantum Theory ◽  
20Th Century ◽  
Quantum Electrodynamics ◽  
Particle Physics ◽  
Space Time ◽  
Gravity Theory ◽  
Curved Space ◽  
Theoretical Physicist ◽  
The Subject

J. Schwinger (1918–1994), founder of renormalized quantum electrodynamics, was arguably the leading theoretical physicist of the second half of the 20th century. Thus it is not surprising that he made contributions to gravity theory as well. His students made major impacts on the still uncompleted program of constructing a quantum theory of gravity. Schwinger himself had no doubt of the validity of general relativity, although he preferred a particle physics viewpoint based on gravitons and the associated fields, and not the geometrical picture of curved space–time. This article provides a brief summary of his contributions and attitudes toward the subject of gravity.

scholarly journals Space–Time Physics in Background-Independent Theories of Quantum Gravity

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 251
Author(s):  
Martin Bojowald
Keyword(s):  
General Relativity ◽  
Quantum Theory ◽  
Quantum Gravity ◽  
Riemannian Geometry ◽  
Loop Quantum Gravity ◽  
Space Time ◽  
Time Analysis ◽  
Complete Space ◽  
Background Independence ◽  
Starting Point

Background independence is often emphasized as an important property of a quantum theory of gravity that takes seriously the geometrical nature of general relativity. In a background-independent formulation, quantum gravity should determine not only the dynamics of space–time but also its geometry, which may have equally important implications for claims of potential physical observations. One of the leading candidates for background-independent quantum gravity is loop quantum gravity. By combining and interpreting several recent results, it is shown here how the canonical nature of this theory makes it possible to perform a complete space–time analysis in various models that have been proposed in this setting. In spite of the background-independent starting point, all these models turned out to be non-geometrical and even inconsistent to varying degrees, unless strong modifications of Riemannian geometry are taken into account. This outcome leads to several implications for potential observations as well as lessons for other background-independent approaches.

scholarly journals Modified general relativity and quantum theory in curved spacetime

2021 ◽  
Author(s):  
Gary Nash
Keyword(s):  
General Relativity ◽  
Quantum Theory ◽  
Momentum Tensor ◽  
Space Time ◽  
Lie Derivative ◽  
Dirac Spinor ◽  
Outer Product ◽  
Klein Gordon ◽  
Hermitian Conjugate ◽  
Quantum Vector

With appropriate modifications, the multi-spin Klein–Gordon (KG) equation of quantum field theory can be adapted to curved space–time for spins 0, 1, 1/2. The associated particles in the microworld then move as a wave at all space–time coordinates. From the existence in a Lorentzian space–time of a line element field [Formula: see text], the spin-1 KG equation [Formula: see text] is derived from an action functional involving [Formula: see text] and its covariant derivative. The spin-0 KG equation and the KG equation of the outer product of a spin-1/2 Dirac spinor and its Hermitian conjugate are then constructed. Thus, [Formula: see text] acts as a fundamental quantum vector field. The symmetric part of the spin-1 KG equation, [Formula: see text], is the Lie derivative of the metric. That links the multi-spin KG equation to Modified General Relativity (MGR) through its energy–momentum tensor of the gravitational field. From the invariance of the action functionals under the diffeomorphism group Diff(M), which is not restricted to the Lorentz group, [Formula: see text] can instantaneously transmit information along [Formula: see text]. That establishes the concept of entanglement within a Lorentzian formalism. The respective local/nonlocal characteristics of MGR and quantum theory no longer present an insurmountable problem to unify the theories.

On the Independent Emergence of Space-time

2020 ◽  
pp. 183-194
Author(s):  
Richard Healey
Keyword(s):  
General Relativity ◽  
Quantum Theory ◽  
Gravitational Field ◽  
Physical Theory ◽  
Space Time ◽  
Structural Quality ◽  
Space Time Structure ◽  
Emergent Structure ◽  
Fundamental Physical

Physics might show that space-time is an emergent structure without describing its ontological basis. Space and time are fundamental to metaphysics and physics. Their union remained fundamental after special relativity doomed each separately to fade away as a mere shadow of the space-time that Einstein later took to exist only as a structural quality of the gravitational field of general relativity. But problems meshing general relativity with quantum theory appear to show that space-time structure is not fundamental but emerges within a quantum theory of gravity. In a pragmatist view, quantum theory is typically applied not to represent target systems but to guide rational credence about events involving other systems. Applied to a gravitational field, quantum theory may guide credence about events in an emergent space-time without itself representing that field. If so, a fundamental physical theory would not describe any ultimate ground of space-time and its contents.

scholarly journals Proposal for a New Quantum Theory of Gravity

2019 ◽  
Vol 74 (7) ◽  
pp. 617-633 ◽  
Author(s):  
Tejinder P. Singh
Keyword(s):  
General Relativity ◽  
Quantum Theory ◽  
Noncommutative Geometry ◽  
Measurement Problem ◽  
Black Hole Entropy ◽  
Space Time ◽  
Classical General Relativity ◽  
Field Equations ◽  
Symmetry Principle ◽  
Theory Of Gravity

AbstractWe recall a classical theory of torsion gravity with an asymmetric metric, sourced by a Nambu–Goto + Kalb–Ramond string [R. T. Hammond, Rep. Prog. Phys. 65, 599 (2002)]. We explain why this is a significant gravitational theory and in what sense classical general relativity is an approximation to it. We propose that a noncommutative generalisation of this theory (in the sense of Connes’ noncommutative geometry and Adler’s trace dynamics) is a “quantum theory of gravity.” The theory is in fact a classical matrix dynamics with only two fundamental constants – the square of the Planck length and the speed of light, along with the two string tensions as parameters. The guiding symmetry principle is that the theory should be covariant under general coordinate transformations of noncommuting coordinates. The action for this noncommutative torsion gravity can be elegantly expressed as an invariant area integral and represents an atom of space–time–matter. The statistical thermodynamics of a large number of such atoms yields the laws of quantum gravity and quantum field theory, at thermodynamic equilibrium. Spontaneous localisation caused by large fluctuations away from equilibrium is responsible for the emergence of classical space–time and the field equations of classical general relativity. The resolution of the quantum measurement problem by spontaneous collapse is an inevitable consequence of this process. Quantum theory and general relativity are both seen as emergent phenomena, resulting from coarse graining of the underlying noncommutative geometry. We explain the profound role played by entanglement in this theory: entanglement describes interaction between the atoms of space–time–matter, and indeed entanglement appears to be more fundamental than quantum theory or space–time. We also comment on possible implications for black hole entropy and evaporation and for cosmology. We list the intermediate mathematical analysis that remains to be done to complete this programme.

Atoms of Space and Time

2020 ◽  
pp. 135-151
Author(s):  
Demetris Nicolaides
Keyword(s):  
General Relativity ◽  
Quantum Mechanics ◽  
Quantum Theory ◽  
Quantum Physics ◽  
Space Time ◽  
Heisenberg Uncertainty Principle ◽  
Quantum Jump ◽  
Time And Motion ◽  
Scientific Hypothesis ◽  
Heisenberg Uncertainty

Epicurus argued that the Democritean atoms couldn’t move, unless space, time, and motion were radically reimagined. In addition to material atoms (smallest cuts of matter), there exist space “atoms” (smallest spatial expanses) and time “atoms” (smallest time intervals)! Also, he thought an atom’s motion is quantum! It moves from here to there without passing through the points in between—exactly the meaning of a quantum jump in quantum physics (presuming motion does occur). An atom spontaneously swerves (creating uncertainty in its whereabouts), a feature added by Epicurus in a first-ever attempt to escape Democritean determinism and subject human free will to a scientific hypothesis. Space atoms are required by loop quantum gravity (which unifies quantum theory with general relativity). The cause of the most consequential premise of quantum mechanics—the Heisenberg uncertainty principle—will be cautiously speculated with an original idea, using the Epicurean theory of space, time, and motion.

Topology knots and hierarchy problem

2019 ◽  
Author(s):  
Vitaly Kuyukov
Keyword(s):  
Quantum Theory ◽  
String Theory ◽  
Quantum Gravity ◽  
Dimensional Space ◽  
Space Time ◽  
Elementary Particles ◽  
Hierarchy Problem ◽  
Topological Quantum ◽  
Dimensional Space Time ◽  
New Formula

Many approaches to quantum gravity consider the revision of the space-time geometry and the structure of elementary particles. One of the main candidates is string theory. It is possible that this theory will be able to describe the problem of hierarchy, provided that there is an appropriate Calabi-Yau geometry. In this paper we will proceed from the traditional view on the structure of elementary particles in the usual four-dimensional space-time. The only condition is that quarks and leptons should have a common emerging structure. When a new formula for the mass of the hierarchy is obtained, this structure arises from topological quantum theory and a suitable choice of dimensional units.

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