The Search for a Tiny Hint from Quantum Gravity in the Cosmic Relic Radiation
One of the most important open problems in current fundamental physics is to find a quantum theory of gravity, which means to incorporate the last missing fundamental force of Nature into the quantum picture. For over eighty years now, there has been an intense effort to develop candidate theories of quantum gravity, but none of them has been completely satisfactory. Among other more conceptual issues, the main problem lies in the difficulty to find tests for such a theory. In this essay, we will describe why this is so difficult and argue that the most promising possibility might be a tiny effect seen in the earliest light that we can observe from the beginning of the universe.
We thank Claus Kiefer for collaboration on the subject under discussion in this essay and for comments on the manuscript. D.B. acknowledges financial support from project FIS2014-57956- P of the Spanish Ministry of Economy and Competitiveness and from project IT956-16 of the Basque Government. The research of M.K. was financed by the Polish National Science Center Grant DEC-2012/06/A/ST2/00395.
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