An unexpected thing has occurred while three physicists calculated that a decaying atom traveling through a perfect vacuum and experiencing a friction-like force. No wonder why they were so suspicious about results as is well known that a vacuum is a completely empty space and it’s impossible for friction to exist – it is a set of fundamental laws of physics. Physicists struggle for a while how to explain these results and not to break Einstein’s relativity. 

The friction-like change in momentum discovered in the new study can be modeled by a moving device that emits photons in opposite directions. Credit: Sonnleitner et al. ©2017 American Physical Society

The old confrontation between general relativity and quantum mechanics happens in a vacuum as well. Although the laws of nature in a grand scale claim there can be nothing but empty space, mechanics claims we can never be sure that an apparent vacuum is truly empty. Random photons appearing and fading in the quantum world are the same as the normal photons in terms of exerting the electromagnetic forces on the objects. Therefore vacuum has friction after all. That is so called Heisenberg’s uncertainty principle.

When physicists from the University of Glasgow noticed decaying atom, they wanted to show that an excited atom’s interaction with the vacuum does not violate Einstein’s theory. They calculate the change in mass that occurs from the emission of the photon. As the mass is the one who’s changing, the velocity remains the same. This explanation was a missing puzzle piece. If there was any true friction force it would have to slow down atoms. But in reality, the atoms only lost its mass as a consequence of interaction with vacuum.

This energy, called the ‘internal binding energy’, is regularly accounted for in nuclear physics, which deals with larger binding energies, but is typically considered negligible in the context of atom optics (the field here), because of the much lower energies.” – explains physicist Lysa Ziga.

The next step for the team will be to test this friction phenomenon when an atom absorbs photons. Some other physicist a few years ago already proposed that vacuum can have friction if the virtual particles are confronted against spinning objects. One thing is clear: we still don’t know for sure all the mysteries of the vacuum.