The feather will land first!! (and please don't include this in the article). Let's do a calculation. The mass of the Earth is about 1024 times bigger than the mass of the hammer. Therefore, the acceleration of the Earth is 1024 times smaller than the acceleration of the hammer, so if the hammer falls through 1 m, the Earth will move 10-24 m during the same time. Such short distances, which correspond to an energy of 100000 TeV, are not probed even by the most energetic particle accelerators! Let's now do another calculation. Suppose we're dropping the feather. The hammer, which is presumably on the ground, attracts the feather with its gravity. The additional acceleration of the feather is given by GM/r2, where M is the mass of the hammer and r is the distance from the feather to the hammer. This gives roughly 10-10 m/s2, which is much bigger than the effect suggested by the Anonymous.