Quantum Cosmology

 We all know that to understand well the classical cosmology there is Albert Einstein's general theory of relativity which describes the evolution of the universe very well, as long as we don't approach the Big bang. The relativity theory has limitations in "Cauchy surfaces" and the "Plank time" and there must be a demand of a final theory of space and time. Therefore, a new theory is needed which integrates relativity theory and quantum theory. 

    Now we all know 'Quantum' is the theory of utterly small and 'Cosmology' is the study of utterly large. So the Quantum Cosmology is the combined theory, remarkably, when in the very early universe the entire universe is studied with far smaller than the smallest particles. A theory of quantum gravity that describes the universe as beginning in a 'Big Bounce' rather than a Big Bang has succeeded in explaining several anomalies in the cosmic microwave background (CMB) radiation. 

    Loop Quantum Gravity (LQG) is an alternative to string theory, and describes the space itself as being quantized at the smallest scale, known as the Plank length, about 10‐³⁵ m. LQG also says that space cannot be crushed down any smaller than this length, and the application of LQG to the broader universe is known as Loop Quantum Cosmology(LQC). 

   There is a contradiction between Big Bang and LQC that suggests that if LQC is correct, there were no Big Bang singularity, but a Big Bounce resulting from the collapse of previous universe. Quantum gravity theorists have not shied away from the challenge. At present there are some half a dozen contenders for a principle that would single out, from all the quantum states allowed by the dynamical laws of quantum gravity, the initial quantum state of our universe. 

   Quantum cosmology can answer so many unsolved problems where the other classical theories including GTR failed to answer like what happens when two bodies collapses in high energy density medium, what happens in the center of a black hole that formed by collapsing of stars and why the energy density is so high in the center of a black hole and the universe and so on. And the physicists are hopefully aim to develop this theory combining of GTR and QFT if that will become the theory of everything.