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Why do we need a theory of quantum gravity?

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Why do we need a theory of quantum gravity?

Why can't gravity be classical, while matter and the other fundamental forces be quantum in nature?

closed as a duplicate of: Is the quantization of gravity necessary for a quantum theory of gravity?

asked May 12, 2015 in Closed Questions by Rawsha [ revision history ]
closed May 13, 2015 as per community consensus

Hi Rawsha,

PhysicsOverflow is a site for graduate-level upward questions, but this seems to be rather a popular physics question. So Quora or Physics SE may be a better place for it.

Voting to close

commented May 12, 2015 by Dilaton (6,240 points) [ no revision ]

Duplicate of http://physicsoverflow.org/8828, and voting to close as such.

commented May 12, 2015 by dimension10 (1,985 points) [ revision history ]

@Dimension10 I am not sure how wise it was to edit the question into a better form, if we want to close it (as quick as possible) anyway. In the original version it was plainly visible that it is a popular question apart from possibly a duplicate...

But it is probably not too important in this case, I am not sure.

commented May 12, 2015 by Dilaton (6,240 points) [ no revision ]
reshown May 13, 2015 by Dilaton

Good Question Voting open.

commented May 12, 2015 by Prathyush (705 points) [ no revision ]

@Prathyush it's no way a great question, the correct answers are given on the linked duplicate, but more importantly - it's a duplicate.

commented May 13, 2015 by dimension10 (1,985 points) [ no revision ]

@Prathush please look at the revision history. The original version was a plainly obvious layman question, which is really not suitable for PO.

Also, to cast a "Leave Open" vote you have to downvote the closevote both me and @Dimension10 linked to. Just posting a comment here does not achieve this.

commented May 13, 2015 by Dilaton (6,240 points) [ no revision ]

@Upvoters and otherw who think the question should not be closed can vote to reopen here.

commented May 13, 2015 by Dilaton (6,240 points) [ no revision ]

I disagree with the down votes, as a lay man, but I respect the integrity of this forum.

However, I would argue that this question is way beyond "popular". Answers and comments would presumably be valuable to this forum. I also believe that the answer is arguably more diffficult than appropriate for a popular science forum. Indeed, how many really really do understand these two theories? Although I am not a physicist (I'm a physician and statistician) I would try to grasp a non-popular answer.

commented May 13, 2015 by Rawsha [ no revision ]

@Rawsha It is expected that you have some familiarity with both Quantum field theory and General Relativity before you can ask this question, even to remotely try and understand it. Without that kind of effort it is simply futile to talk about this. And listening to video lectures for 30hrs simply does not count.

I will answer the question(modified) to the best of my knowledge. The simplest reason to search for a theory of QG is because there are domains of experiences that in principle can be created in out universe that we cannot explain.

For instance when one studies quantum field theory on the background geometry of a black hole it becomes apparent that black holes evaporate thermally.(Along with having an entropy proportional to their area.)

We among many things want to understand how to describe such a process. Certainly this situation can be created in the universe(atleast in principle)

commented May 13, 2015 by Prathyush (705 points) [ revision history ]

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