Understanding the Loop Quantum Cosmology and the Concept of Time

Bhuvaneshwari Kashi, CVR College of Engineering, India, [email protected]

Abstract Quantum Cosmology and LQG Timeless Universe

Time is an enigmatic property of the universe which confounded Quantum cosmology is a theory which helps us in understanding The quantum versions of the formulation of classical GR which does not physicists for ages. This property is increasingly dark and cryptic gravity in quantum scale of the universe. The classical cosmology employ the time variable t at all is the Hamilton-Jacobi formulation, formally when we deal with metric spaces of the microscopic scales in is based on the general theory of relativity theorized by Albert determine the transition amplitudes between quantum states of the gravi- tational field. These can be coupled to matter and clocks. Variables change the universe. There are remarkable theories, in particular, the Einstein where the universe is treated as a space-time fabric. together and no preferred clock variable is used in the theory. It is in this weak loop quantum gravity (LQT) which helps us in understanding Unlike the clasical cosmology, in quantum cosmology we consider sense that it is sometimes said that “time does not exist” at the fundamental the cosmology of these microscopic scales. However, the theory the universe as a wave function. There are many theories which level in quantum gravity. This expression means that there is no time variable possesses considerable complications in explaining the concept of attempts to explain the quantum gravity and cosmology which in the fundamental equations. It does not mean that there is no change in time. We redress the notions of quantum cosmology and the loop mainly include string theory and LQG. LQG when applied to nature. This formulated in terms of probability amplitudes for processes. quantum gravity. The elegance of the theory in describing the quantum cosmology it is termed as Loop Quantum Cosmology microscopic scales is discussed. We try to emphasise the concept with certain bounds. It theorizes that the Big Bounce is prior to of the time interpreted as far as the notion of quantum gravity is Big Bang. concerned. We aim to review and re-analyse the loop gravity, the Conclusion perception of the dynamic time and the timeless universe. The universe described by quantum gravity is not flowing along a single time variable, nor organised into a smooth Einsteinian geometry. It is a network of The notion of time quantum processes, related to one another, each of which obeys probabilistic laws that the theory captures. The net of quantum interactions between Introduction In general when speak about time we refer to the occurrence of systems is identified with the net of adjacent spacetime regions. an event with respect to another. The notion of time in physics The quantum effects of the black hole’s gravitational field cause it to radiate plays an important role. In many cases the time is considered to energy as if it were hot, implying a deep connection between quantum theory, flow uniformly in a linear direction pointed towards the future. In gravity and thermodynamics. For ages theorists with this clue are in a quest GR we have seen that the time is considered one of the aspects References to find something more fundamental than space and time. One of the possible answers is loop quantum gravity LQG is a theory of quantum gravity where the of the dynamical field, gravitational field. R p µ ν structure of space is composed of finite loops woven into a network. In LQG the T = gµνdx dx Perez, A., “Black holes in loop quantum gravity”, Reports on Progress space and time are considered as quantized quantities. It is a quantum gravity LQG is similar to GR in this case. The time is consider as many in Physics, vol. 80, no. 12, 2017. doi:10.1088/1361-6633/aa7e14. candidate which competes with string theory. The Loop quantum gravity clock times measured by different clocks. Interestingly there Rovelli, C., “Space and Time in Loop Quantum Gravity”, arXiv contains variables namely loop variables (which are conceptually similar to can occur quantum fluctutations and also there can be different e-prints, 2018. the Yang Mill’s variables)√ which tend to grow out of ‘Ashtekar’s new variables. a a superpositions between different values of the same clock. Rovelli C. Loop Quantum Gravity. Living Rev Relativ. 1998;1(1):1. They are : Ei (x) := h(x)ei (x) i a i doi:10.12942/lrr-1998-1 where the configuration variable is the connection GAa(x) = Γi (x) +a (x) We have the canonical and covariant approach i.e, the spin foam approach of Abhay Ashtekar and Eugenio Bianchi 2021 Rep. Prog. Phys. 84 042001 LQG.

Bhuvaneshwari Kashi, Department of Electronics and Communication, CVR College of Engineering, Telangana, India EPS-HEP 2021