  We report on the observation of Bloch oscillations on the unprecedented time
scale of severalseconds. The experiment is carried out with ultra-cold bosonic
strontium-88 loaded into a vertical optical standing wave. The negligible
atom-atom elastic cross section and the absence of spin makes $^{88}$Sr an
almost ideal Bose gas insensitive to typical mechanisms of decoherence due to
thermalization and to external stray fields. The small size enables precision
measurements of forces at micrometer scale. This is a challenge in physics for
studies of surfaces, Casimir effects, and searches for deviations from
Newtonian gravity predicted by theories beyond the standard model.
