scholarly journals A discrete-time interpretation of the Planck-Einstein equation

2006 ◽  
Vol 2006 ◽  
pp. 1-5
Author(s):  
A. Boyarsky
Keyword(s):  
String Theory ◽  
Quantum Gravity ◽  
Einstein Equation ◽  
Discrete Time ◽  
Loop Quantum Gravity ◽  
Empty Space ◽  
Important Conclusion ◽  
Age Of The Universe ◽  
The Times ◽  
The Universe

An important conclusion of both string theory and loop quantum gravity theory is that space and time are ultimately discrete. A consequence of discrete space is that there is empty space between the basic elements of space. Analogously, there are empty times between the times where time exists. When time does not exist, it is meaningless to consider the existence of the universe. In this note we consider a discrete-time interpretation of the Planck-Einstein equation and draw a curious conclusion about the real age of the universe.

scholarly journals Quantum gravity: A brief history of ideas and some prospects

2015 ◽  
Vol 24 (11) ◽  
pp. 1530028 ◽  
Author(s):  
Steven Carlip ◽  
Dah-Wei Chiou ◽  
Wei-Tou Ni ◽  
Richard Woodard
Keyword(s):  
Black Hole ◽  
String Theory ◽  
Quantum Gravity ◽  
Loop Quantum Gravity ◽  
Black Hole Thermodynamics ◽  
History Of Ideas ◽  
Foreseeable Future ◽  
Gravitational Effects ◽  
History Of

We present a bird's-eye survey on the development of fundamental ideas of quantum gravity, placing emphasis on perturbative approaches, string theory, loop quantum gravity (LQG) and black hole thermodynamics. The early ideas at the dawn of quantum gravity as well as the possible observations of quantum gravitational effects in the foreseeable future are also briefly discussed.

scholarly journals A quantized spacetime based on Spin(3,1) symmetry

2016 ◽  
Vol 25 (13) ◽  
pp. 1645004
Author(s):  
Pisin Chen ◽  
Hsu-Wen Chiang ◽  
Yao-Chieh Hu
Keyword(s):  
String Theory ◽  
Quantum Gravity ◽  
Uncertainty Principle ◽  
Loop Quantum Gravity ◽  
Generalized Uncertainty Principle ◽  
Spin Network ◽  
Fundamental Symmetry ◽  
New Type ◽  
Gravity Theories

We introduce a new type of the spacetime quantization based on the spinorial description suggested by loop quantum gravity. Specifically, we build our theory on a string theory inspired [Formula: see text] worldsheet action. Because of its connection with quantum gravity theories, our proposal may in principle link back to string theory, connect to loop quantum gravity where SU(2) is suggested as the fundamental symmetry, or serve as a Lorentzian spin network. We derive the generalized uncertainty principle and demonstrate the holographic nature of our theory. Due to the quantization of spacetime, geodesics in our theory are fuzzy, but the fuzziness is shown to be much below conceivable astrophysical bounds.

Cosmology Today

Daedalus ◽  
2014 ◽  
Vol 143 (4) ◽  
pp. 125-133
Author(s):  
David N. Spergel
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Gravitational Lensing ◽  
Large Scale ◽  
Empty Space ◽  
Microwave Background ◽  
Astronomical Observations ◽  
Basic Parameters ◽  
Age Of The Universe ◽  
The Universe

We seem to live in a simple but strange universe. Our basic cosmological model fits a host of astronomical observations with only five basic parameters: the age of the universe, the density of atoms, the density of matter, the initial “lumpiness” of the universe, and a parameter that describes whether this lumpiness is more pronounced on smaller physical scales. Our observations of the cosmic microwave background fluctuations determine these parameters with uncertainties of only 1 to 2 percent. The same model also provides an excellent fit to the large-scale clustering of galaxies and gas, the properties of galaxy clusters, observations of gravitational lensing, and supernova-based measurements of the Hubble relation. This model implies that we live in a strange universe: atoms make up only 4 percent of the visible universe, dark matter makes up 24 percent, and dark energy – energy associated with empty space – makes up 72 percent.

scholarly journals Dimensions of Space

2020 ◽  
Vol 3 (11) ◽  
pp. 74-79
Author(s):  
Kedar Pansare ◽  
Meghraj Parab ◽  
Vrushabh Parmar ◽  
Yashwantrao Mitnasala ◽  
Rajni Bahuguna
Keyword(s):  
Quantum Gravity ◽  
Loop Quantum Gravity ◽  
Higher Dimensions ◽  
Superstring Theory ◽  
Unified Theories ◽  
Spatial Dimensions ◽  
The Universe ◽  
Dimensions Of Space

The existence and the mysteries of the universe could not be explained by using just 3 spatial dimensions. There was a need to think of higher dimensions as a tool to explain the phenomena happening in our universe. Therefore, unified theories such as Loop Quantum Gravity and Superstring Theory were proposed. We will be taking an overview of these theories in order to get some idea about each.

scholarly journals Quantum reduced loop gravity and the foundation of loop quantum cosmology

2016 ◽  
Vol 25 (08) ◽  
pp. 1642005 ◽  
Author(s):  
Emanuele Alesci ◽  
Francesco Cianfrani
Keyword(s):  
Quantum Gravity ◽  
Quantum Cosmology ◽  
Loop Quantum Gravity ◽  
Loop Quantum Cosmology ◽  
Quantum Description ◽  
Semiclassical Dynamics ◽  
Loop Gravity ◽  
The Universe

Quantum reduced loop gravity is a promising framework for linking loop quantum gravity and the effective semiclassical dynamics of loop quantum cosmology. We review its basic achievements and its main perspectives, outlining how it provides a quantum description of the Universe in terms of a cuboidal graph which constitutes the proper framework for applying loop techniques in a cosmological setting.

scholarly journals Primordial Fluctuations From Quantum Gravity

2021 ◽  
Vol 7 ◽  
Author(s):  
Francesco Gozzini ◽  
Francesca Vidotto
Keyword(s):  
Quantum Gravity ◽  
Structure Formation ◽  
Loop Quantum Gravity ◽  
Cosmological Horizon ◽  
Strong Correlations ◽  
Quantum Regime ◽  
Horizon Problem ◽  
Large Fluctuations ◽  
Gravity Effects ◽  
The Universe

We study the fluctuations and the correlations between spatial regions generated in the primordial quantum gravitational era of the universe. We point out that these can be computed using the Lorentzian dynamics defined by the Loop Quantum Gravity amplitudes. We evaluate these amplitudes numerically in the deep quantum regime. Surprisingly, we find large fluctuations and strong correlations, although not maximal. This suggests the possibility that early quantum gravity effects might be sufficient to account for structure formation and solve the cosmological horizon problem.

Time in Quantum Gravity

2011 ◽  
Author(s):  
Claus Kiefer
Keyword(s):  
Quantum Theory ◽  
String Theory ◽  
Quantum Gravity ◽  
Special Relativity ◽  
Loop Quantum Gravity ◽  
Problem Of Time ◽  
Canonical Quantum Gravity ◽  
Time Loop ◽  
Canonical Quantum

This chapter notes that quantum gravity places the concept of time on a new level. In the absence of experimental hints, mathematical and conceptual issues must be chosen as the guides in the search for such a theory. Just as reconceiving classical notions of time was key for Einstein, in his discovery of special relativity, so too many believe that time will again hold the clue for theoretical advancement, but this time with quantum gravity. The chapter details the challenge of reconciling quantum theory with relativity, concentrating especially on why time in particular causes trouble. It describes a result in canonical quantum gravity which is possibly of signal importance, namely, that fundamentally there is no time at all, and discusses the problem of time, quantization, semiclassical time, loop quantum gravity, and string theory.

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