Trinity Physicists Capture Magnetism from Empty Space
Theoretical physicists have long believed that empty space is not a formless void. The vacuum is thought to be seething with zero-point energy, the inevitable quantum residue of every sort of electromagnetic radiation. Nobody has ever managed to find a way to tap this limitless store of energy, and the signs that it even exists are slender. Direct evidence is mainly based on a tiny shift of a few parts per billion in an energy level of hydrogen, discovered 70 years ago by Willis Lamb in the USA, and a minute force between metal plates when they are only a few nanometers apart in vacuum predicted around the same time by Dutchman Hendrik Casimir.
Now, a team of scientists working in Trinity College Dublin’s Centre for Research on Advanced Nanostructures and Nanodevices (CRANN) have discovered a new and unexpected manifestation of this elusive energy. In a study of cerium dioxide nanoparticles – mainly used in catalytic converters that control toxic exhaust emissions from automobiles – Professor Michael Coey, his former PhD student Karl Ackland and Dr Munuswamy Venkatesan came across a strange magnetic effect. Quite unlike the behavior of normal magnets like iron, the effect did not vary at all with temperature. Stranger still, the magnetism only appeared when the particles were clumped together. Separating them into smaller clumps by diluting with nonmagnetic nanoparticles destroyed the magnetism.
In a paper published on-line today in Nature Physics, the team that was completed by Professor Siddhartha Sen, a quantum field theorist renown for his brilliant lectures in Trinity’s Mathematics Department, reported their findings, and came up with an astonishing explanation. Electrons in the clumps of tiny particles were responding to the vacuum electromagnetic field. Sen and Coey had recently predicted that such behavior might be possible in systems with an enormous surface area – a milligram speck of the cerium dioxide nanoparticles has as much surface area as an entire sheet of newspaper. Furthermore they predicted that when the particles were separated out into regions smaller that the wavelength of the light associated with them, the effect would disappear. This is exactly what was observed.
As with any fundamental discovery in science, it is difficult to predict where this could lead. Others will want to test the results. The theory shows that effects can only be expected when there is a huge surface to volume ratio, as in the thin layers of interfacial water attached to biomolecules. Sen is already beginning to apply the ideas to protein folding. The zero point energy may never power our cars, but it might be shaping our lives.
- Collective magnetic response of CeO2 nanoparticles, M. Coey, K. Ackland, M. Venkatesan and S. Sen, Nature Physics (2016) doi.10.1038/nphys3676
- Mesoscopic structure formation in condensed matter due to vacuum fluctuations, S. Sen, K. S. Gupta and J. M. D. Coey, Phys. Rev B 92 155115 (2015)