Asked by: Christopher Watts, Liverpool
If you mean ‘absolutely’ in the sense of ‘completely’, then no. The celebrated uncertainty principle of quantum mechanics shows that the more precisely we try to pin down the exact location of anything to tell if it’s stationary, the more it jitters about.
On the other hand, if you mean ‘absolutely still’ in the sense of stationary with respect to the whole Universe, then yes – at least, subject to the above caveat. The Universe is filled with radiation left over from the Big Bang, and this provides a reference frame by which we can tell how fast we’re moving in absolute terms, and in what direction. In 1996, a team of NASA scientists showed that we on planet Earth are moving at around 1,340,000km/h relative to the Universe as a whole.