Invited talk at the Conference in Honour of the 90th Birthday of Freeman Dyson, Institute of Advanced Studies, Nanyang Technological University, Singapore, 26-29 August 2013 http://www.ntu.edu.sg/ias/upcomingeve... Publication: Is a graviton detectable? Freeman Dyson, Int. J. Mod. Phys. A, 28, 1330041 (2013) http://www.worldscientific.com/doi/ab...