Assume that the observable universe would collapse due to gravity, is there any force that can counteract with gravity collapse in the universe? In other word, after the universe collapses, how and by which law (or force) will the universe expand again? A gravitational singularity or spacetime singularity is a location where the quantities that are used to measure the gravitational field become infinite in a way that does not depend on the coordinate system. These quantities are the scalar invariant curvatures of spacetime, which includes a measure of the density of matter. For the purposes of proving the Penrose–Hawking singularity theorems, a spacetime with a singularity is defined to be one that contains geodesics that cannot be extended in a smooth manner. The end of such a geodesic is considered to be the singularity. This is a different definition, useful for proving theorems. The two most important types of spacetime singularities are curvature singularities and conical singularities. Singularities can also be divided according to whether they are covered by an event horizon or not (naked singularities). According to general relativity, the initial state of the universe, at the beginning of the Big Bang, was a singularity. Both general relativity and quantum mechanics break down in describing the Big Bang. My question is, if the universe collapses, will it reach to infinite density and zero volume? Or is there a force that will counteract with it?
If the universe collapses, it will reach a critical volume that should be governed by quantum mechanics and once again gets into a new universe that predestined by the set of quantum numbers it will start with. Quantum mechanics forbids the universe to go into a zero volume however.
Dear Prof. Arbab I. Arbab
If universe starts to collapse, do physics laws broken down?
Dear Hossein, what do you mean the physics laws will break down? Could you please clerify your question?because during the collapse the phyical laws are still valid even the enthropy principle, but due to quantum mechanics universe will not reach to a zero volum. On the other hand as I know there is a theory using the Yang-Mills theory which predict a force and if I remember correctly the name of the force is Lee-Yang force which is equivalant to dark energy and is responisible for cosmic expansion and if this force really exists this can counteract with gravity!! But the observable universe is expanding with the acceleration and I mostly would prefer ulternative theroies of gravity. Hope my answer helps.
Dear Reza
The beginning of real time, would have been a singularity, at which the laws of physics would have broken down. Hawking said. (1) Physical laws should separate to two parts: 1- which laws that nature does obey of them, 2- which laws that we have understood of nature and this part are developing.
What we know about the Inside of a black hole?
(1) http://www.hawking.org.uk/the-beginning-of-time.html
Dear Hossein, Yes agree the bigining of the time starts with a singularity. Physics break down in such a intense place with extremal situations. About the black hole since there is always horizon around singularity and Cosmic Sensordhip conjectures that there is no naked singularity and horizon is always prevent us to see the naked singularity without falling into the black hole! On the other hand there are some researches about Information Paradox and fire walls which is related to Hawking radiation which provide us some information about the black hole and in a new paper hawking cliams to solve it using CFT (http://arxiv.org/abs/1401.5761).If you are interested see some of our papers. Also one of the other research areas whch will provide information about the behaviour of space-time near the simngularity is detecting gravitational waves comming out of the binary black hole systems and also black hole perturbations would provide gravitational waves and the reason is the gravitational wave are ripples of the space-time(search for SXS collaboration in order to find more information). I really enjoyed reading the link you sent here.
Sorry the correct link to Hawking's paper is http://arxiv.org/abs/1401.5761
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