Quantum Gravity

Quantum Gravity

                 

                     

 You must have heard about gravity which works between large bodies. But here quantum gravity is different from general gravity. Quantum gravity works on quantum particles like electron and proton.

                 

                 In order to predict how the universe should have started off. The singularity theorem predicted that the beginning of time would have been a point of infinite density and infinite curvature of space-time. All our rules of science would break down in such points because our rules work in nearly flat space-time. There should be another theory for such points that is very difficult to generate because we don’t have any guide from observational evidence. However, we know something important that singularity is the point of huge gravity. In this condition, gravity affects quantum particles. So we can make a new theory of gravity that is quantum theory. And this theory will work in each event including beginning of time.

                    

                   We have no unified theory of quantum mechanics and quantum gravity. According to Feynman’s proposal of sum over histories, a particle going from A to B has not a single way only. It is supposed to follow its all possible ways. With all possible histories, there are associated a couple of numbers, one representing the size of a wave and another representing its phase.

                   

                   The probability that particle passes through some particular point is found by adding up the waves associated with every possible history that passes through that point. When one actually tries to perform these sums, one runs into sever technical problems. The only way around these is the following peculiar prescription: one must add up the waves for particle histories that are not the real time that you and I experience but take place in an imaginary point. Doesn’t imaginary time seem to be a part of science fiction. You should remember that this is a well defined mathematical concept which is used to avoid technical difficulties of Feynman model. This has a very interesting effect in space-time: The distinction between space and time disappears completely. A space-time in which events have imaginary values of the time coordinate is said to be Euclidean because the metric is positive definite.

               

                    In Euclidean space-time there is no difference between the time direction and directions in space. On the other hand, in real space-time, in which events are labeled by real values of time coordinate, it is easy to tell the difference. The time direction lies within the light cone, and space direction lie outside. One can regard to use of imaginary time as merely a mathematical device to calculate answer about real space-time. However, there may be more to it than that. It may be that Euclidean space-time is the fundamental concept and what we think of as real space-time is just a figment of our imagination.

                 

                    I hope you may like this blog. If you have any question, you can comment.   

                                                                                     -Thank You