This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A simplified cosmological model suggests that decoherence can suppress quantum tunneling, effectively locking fields into the vacuum state they have reached. The vacuum is not always so empty.
"When we talk about a vacuum in cosmology, we do not mean completely devoid of energy," explains David Wands, Professor at the Institute of Cosmology & Gravitation at the University of Portsmouth. "A vacuum is rather a state in which a field sits at a minimum of its energy. The true vacuum is the lowest possible minimum, but there can also be local minima, which we call false vacua." We can picture this as a landscape made up of valleys of different depths: the true vacuum is the deepest one, while the others are false vacua.
Something sitting in one of these depressions can remain "trapped" there even if, somewhere else, a lower-energy state exists. This is exactly what can happen to quantum fields, fundamental physical objects that permeate the universe. A classical field is something that has a value at every position in space, like a magnetic field, whose strength changes from point to point.
Quantum fields behave in a similar way, and their excitations appear as particles. In a new study published in the Journal of Cosmology and Astroparticle Physics, Robson Christie, Jaewoo Joo, Greg Kaplanek, Vincent Vennin and David Wands used a simplified model to investigate what determines which vacuum a field may end up in within an expanding universe. To understand why this question matters, the authors point to the case of the Higgs field.
Its vacuum value contributes to giving mass to the particles of the Standard Model—the theory that describes the known elementary particles and three of the four fundamental forces—and helps determine the structure of low-energy physics. According to some calculations based on the Standard Model, it is possible that the Higgs field does not sit in the lowest possible energy state but in a false vacuum, while at very large field values, a second, deeper minimum may exist. The study is not directly about the Higgs field but uses it as a concrete example of what can happen when a field becomes trapped in a local minimum even though a lower-energy state is available.
"In principle, a transition to that deeper minimum would take the universe into a radically different state, in which the structure of matter and the forces that govern it would be altered," explains Robson Christie, a researcher at the School of Mathematics and Physics at the University of Portsmouth and first author of the study. Such a transition can be made possible by a quantum phenomenon. Let us return to the picture of vacua as valleys separated by mountains.
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