Loop quantum gravity and observations

draft chapter for a volume edited by A. Ashtekar and J. Pullin, to be published in the World Scientific series "100 Years of General Relativity"International audienceQuantum gravity has long been thought to be completely decoupled from experiments or observations. Although it is true that smoking guns are still missing, there are now serious hopes that quantum gravity phenomena might be tested. We review here some possible ways to observe loop quantum gravity effects either in the framework of cosmology or in astroparticle physics