Particles are created out of nothing in a flash
Strong electric fields can remove particles from the vacuum. But how long does it take them to do this? New calculations provide an answer and could help to better understand quantum fluctuations as a whole.
When you pass strong electric fields through a vacuum, particles are created. However, this does not happen immediately, but takes a while. Matthias Diez and Reinhard Alkofer from the University of Graz and Christian Kohlfürst from the Helmholtz Centre Dresden-Rossendorf have now calculated how quickly the particles emerge from nothing. In doing so, they have clarified an open question in theoretical physics.
"Virtual" pairs of electrons and their antiparticles, the positrons, are constantly buzzing around in empty space. The term virtual means that they normally annihilate each other immediately before they become real particles. These particles therefore actually only exist mathematically on the smallest temporal and spatial scales in the form of quantum fluctuations. However, a strong electric field could turn these mathematical objects into reality. This is because electrons and positrons are charged, and the virtual pairs align themselves in a field like tiny dipoles. If the field is intense enough, it would literally tear this pair apart before the electron and positron can annihilate each other again. The phenomenon is called the Schwinger effect, after the later Nobel Prize winner Julian Schwinger, who successfully described it theoretically in 1951
To do this, however, the electric field must be extremely intense. For this reason, experiments have not yet succeeded in transforming virtual particles into real oscillator pairs. However, research groups around the world are gradually approaching the necessary energy densities using high-power lasers. Their aim is to test the predictions of quantum electrodynamics, the fundamental theory that describes such processes. Although the energies involved are enormous, pair production in electric fields plays an important role in many areas of physics, from processes in solids, the extreme conditions surrounding black holes and other astrophysical objects, and plasma physics, which plays an important role in the development of fusion power plants.
However, robust predictions are needed for applications, and one detail of the Schwinger effect has so far remained unclear: How fast are the particles created in the first place? According to Diez, Alkofer and Kohlfürst in their publication, this fundamental question is on the one hand about how we interpret time on the quantum scale, and on the other hand it could have a concrete impact "on all areas of research involving the birth of quasiparticles".
For their theoretical calculation, the three physicists developed a simplified model in fewer dimensions, which made it easier for them to identify the moment of separation of the two charges. In addition to the virtual and real particles in the usual theoretical descriptions, they also introduced a third type of particle: pre-particles, whose fate is to become real particles, so to speak. This helped to sort out insignificant signals caused by other quantum fluctuations or by fluctuations of the electric field itself. The pre-particles are rapidly accelerated in the strong field and soon emerge as a clear signal - as a real particle.
In this way, Diez, Alkofer and Kohlfürst calculated a time scale on which the electron and positron materialise. Due to the extremely strong electric fields, the time is correspondingly tiny and lies in the range of trillionths of a billionth of a second. This sounds as if it is practically insignificantly small, but it is above all: a concrete prediction. Now it remains to be seen whether it can be confirmed in experiments with high-power lasers in the laboratory at some point.
Spectrum of Science
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Cover image:© SpicyTruffel / Getty Images / iStock (detail) With a strong enough electric field, you can create particles even out of nothing.
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