Single Review on past events

When something is empty it is empty – we normally would assume. But Denis Seletskiy thinks a little bit different about that. Recently and together with his colleagues at the Department of Physics (University of Konstanz), he published a paper in the magazine “Science” in which direct observation of zero-point fluctuations of the electromagnetic field are described (see for example a press release on this subject: http://www.aktuelles.uni-konstanz.de/en/presseinformationen/2015/96/).

In his approach to the question of “how empty emptiness?”, Denis chooses the perspective of a physicist. He begins by examination of the evolution of the ideas on light, beginning from ancient Greeks and up to the 18th century – when successful theories of particle (Newtonian mechanics) and wave motions coexisted independently. It was only at the beginning of the 20th century when the concepts of locality of a particle and non-locality of a wave were finally unified in a single theory of Quantum Physics. A central pillar of that theory, namely Heisenberg’s uncertainty principle, encompasses the wave-particle dualism through a statement that one cannot simultaneously measure position and momentum of an object with an arbitrary precision.

One of the consequences of the Heisenberg´s uncertainty principle is that a mechanical pendulum at rest (in its ground state) will still exhibit finite fluctuations in its position – so called zero-point motion or vacuum fluctuations. By drawing a direct analogy to the light itself, the researchers have asked the question if such fluctuations can be measured directly. In other words, when the lights are off – could one observe the signals from empty space? “The amount of vacuum signal depends on the measurement process itself, or more concrete: it depends on what length and time scales one decides to look at”, states Denis Seletskiy. Using focused femtosecond pulses as a space-time microscope, the researchers have been able to resolve the vacuum fluctuations on the shortest space-time intervals, as reported in their article. Large scale apparatus can measure classical emptiness, null; but small space-time probe can directly observe boiling foam of vacuum fluctuations.

Near the conclusion of the talk, Seletskiy exclaimed: “but there is a twist to this story!” He finished the presentation by elaborating that beyond their current measurements, even more profound mysteries arise when one attempts to conceptually unify the vacuum with the general theory of relativity. While there is no currently accepted unified description of quantum physics and gravity, Denis argues that by using recently predicted effects involving gravity and vacuum, one can attempt to model these scenarios in the laboratory.

Classical emptiness is indeed null, whereas quantum emptiness is null on average, but appears foamy when examined with a magnifying glass. However, perhaps the future meaning of emptiness (and particles!) is going to be entirely relativistic. Denis hopes to be able to investigate his ideas in the near future.