More proof that science doesn't know everything. Scientists used to believe that space was filled with ether, an invisible "hypothetical substance supposed to occupy all space, postulated to account for the propagation of electromagnetic radiation through space," but then that was replaced by vacuum, supposedly empty. Now they claim to have discovered that vacuum has friction. Something tells me that there are a lot of new discoveries between what we know, or think we know, now and what is the ultimate truth, between the current limits of our ability to observe and the Planck length.