“Greene takes it for granted, and here the great majority of physicists agree with him, that the division of physics into separate theories for large and small objects is unacceptable. … Greene believes that there is an urgent need to find a theory of quantum gravity that applies to large and small objects alike. … As a conservative, I do not agree that a division of physics into separate theories for large and small is unacceptable. … The essence of any theory of quantum gravity is that there exists a particle called the graviton … I looked at various possible ways of detecting gravitons and did not find a single one that worked. Because of the extreme weakness of the gravitational interaction, any putative detector of gravitons has to be extremely massive. If the detector has normal density, most of it is too far from the source of gravitons to be effective, and if it is compressed to a high density around the source it collapses into a black hole. There seems to be a conspiracy of nature to prevent the detector from working.”

[The information paradox, arXiv preprint arXiv:hep-th/0612061v2, 14 December 2006, http://arxiv.org/abs/hep-th/0612061] (See also Thorne-Hawking-Preskill bet.)

Epilogue, p. 221
Reinventing Gravity (2008)

"Loop Quantum Gravity," The New Humanists: Science at the Edge (2003)

"Einstein and the Search for Unification", p. 10 https://books.google.com/books?id=rEaUIxukvy4C&pg=PA10, in The legacy of Albert Einstein: a collection of essays in celebration of the year of physics (2007)

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character, Vol. 123, No. 792 http://doi.org/10.1098/rspa.1929.0094 (6 April 1929)
Context: The underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are thus completely known, and the difficulty is only that the exact application of these laws leads to equations much too complicated to be soluble. It therefore becomes desirable that approximate practical methods of applying quantum mechanics should be developed, which can lead to an explanation of the main features of complex atomic systems without too much computation.

Source: Life Itself : A Memoir (2011), Ch. 54 : How I Believe In God
Context: Quantum theory is now discussing instantaneous connections between two entangled quantum objects such as electrons. This phenomenon has been observed in laboratory experiments and scientists believe they have proven it takes place. They’re not talking about faster than the speed of light. Speed has nothing to do with it. The entangled objects somehow communicate instantaneously at a distance. If that is true, distance has no meaning. Light-years have no meaning. Space has no meaning. In a sense, the entangled objects are not even communicating. They are the same thing. At the “quantum level” (and I don’t know what that means), everything may be actually or theoretically linked. All is one. Sun, moon, stars, rain, you, me, everything. All one. If this is so, then Buddhism must have been a quantum theory all along. No, I am not a Buddhist. I am not a believer, not an atheist, not an agnostic. I am more content with questions than answers.

[1992, Intersection Theory, Integrable Hierarchies and Topological Field Theory by Robbert Dijkgraaf, Fröhlich J., ’t Hooft G., Jaffe A., Mack G., Mitter P.K., Stora R. (eds.), New Symmetry Principles in Quantum Field Theory, NATO ASI Series (Series B: Physics), vol. 295, 95–158, Springer, Boston, MA, 10.1007/978-1-4615-3472-3_4]

[What the information paradox is not., arXiv preprint arXiv:1108.0302, 2011, https://arxiv.org/abs/1108.0302]