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Fluctuations in the void
Posted on Monday, April 15, 2019 @ 21:25:07 UTC by vlad
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 In quantum physics, a vacuum is not empty, but rather steeped in tiny fluctuations of the electromagnetic field. Until recently it was impossible to study those vacuum fluctuations directly. Researchers at ETH Zurich have developed a method that allows them to characterize the fluctuations in detail.
Emptiness is not really empty – not according to the laws of quantum physics, at any rate. The vacuum, in which classically there is supposed to be "nothing," teems with so-called vacuum fluctuations according to quantum mechanics.
Those are small excursions of an electromagnetic field, for instance, that average out to zero over time but can deviate from it for a brief moment. Jérôme Faist, professor at the Institute for Quantum Electronics at ETH in Zurich, and his collaborators have now succeeded in characterizing those vacuum fluctuations directly for the first time.
"The vacuum fluctuations of the electromagnetic field have clearly visible consequences, and among other things, are responsible for the fact that an atom can spontaneously emit light," explains Ileana-Cristina Benea-Chelmus, a recently graduated Ph.D. student in Faists laboratory and first author of the study recently published in the scientific journal Nature. "To measure them directly, however, seems impossible at first sight. Traditional detectors for light such as photodiodes are based on the principle that light particles – and hence energy – are absorbed by the detector. However, from the vacuum, which represents the lowest energy state of a physical system, no further energy can be extracted."
Electro-optic detection
Faist and his colleagues therefore decided to measure the electric field of the fluctuations directly. To that end, they used a detector based on the so-called electro-optic effect. The detector consists of a crystal in which the polarisation (the direction of oscillation, that is) of a light wave can be rotated by an electric field – for instance, by the electric field of the vacuum fluctuations. In this way, that electric field leaves a visible mark in the shape of a modified polarization direction of the light wave. Two very short laser pulses lasting for a fraction of a thousandth of a billionth of a second are sent through the crystal at two different points and at slightly different times, and afterward, their polarisations are measured. From those measurements, the spatial and temporal correlations between the instantaneous electric fields in the crystal can finally be calculated.
To verify that the electric fields thus measured actually arise from the vacuum fluctuations and not from the thermal black body radiation, the researchers cooled the entire measurement apparatus down to -269 degrees centigrade. At such low temperatures, essentially no photons of the thermal radiation remain inside the apparatus, so that whatever fluctuations of the electric field are left over must come from the vacuum. "Still, the measured signal is absolutely tiny," ETH-professor Faist admits, "and we really had to max out our experimental capabilities of measuring very small fields." According Faist, another challenge is that the frequencies of the electromagnetic fluctuations measured using the electro-optic detector lie in the terahertz range, that is, around a few thousand billion oscillations per second. In their experiment, the scientists at ETH still managed to measure quantum fields with a resolution that is below an oscillation cycle of light in both time and space.
Measuring exotic vacuum fluctuations
The researchers hope that in the future they will be able to measure even more exotic cases of vacuum fluctuations using their method. In the presence of strong interactions between photons and matter, which can be achieved, for instance, inside optical cavities, according to theoretical calculations the vacuum should be populated with a multitude of so-called virtual photons. The method developed by Faist and his collaborators should make it possible to test those theoretical predictions.
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Re: Fluctuations in the void (Score: 1)
by vlad on Friday, June 07, 2019 @ 12:37:23 UTC
(User Info | Send a Message) http://www.zpenergy.com | Zero Point Energy (The Guardian Archive) by Mark Pilkington
As several international probes struggle valiantly to reach the relatively neighbourly planet Mars, a small coterie of astrophysicists is quietly considering how humankind might venture beyond our own solar system.
The key to the problem is power: what kind of fuel will be stable and plentiful enough to take humans into deep space? Among the more sober possibilities are ion propulsion, using xenon gas for fuel, which sent Nasa's Deep Space 1 probe a respectable 185m miles or so, and solar sails, blown by photons from the Sun. Neither of these is ideal: xenon, though stable, is exhaustible, and solar sails would only be able to carry very small, light craft.
One theoretical energy source, however, would fit the bill perfectly. It's as accessible in outer space as it would be in the Outer Hebrides because it exists, according to its advocates, everywhere, immersing everyone and everything in a foaming sea of energy.
Early quantum physicists theorised that all space, even the vacuum of outer space, contains a constantly bubbling field of electromagnetic energy, quantum fluctuations thought to be created by "virtual" photons constantly winking in and out of existence. This is zero point energy (ZPE), so called because it would still exist at absolute zero - minus 273C - when the atomic motions that generate thermal energy are at their slowest. Physicists John Wheeler and Richard Feynman calculated that there is enough such energy in the vacuum inside a single light bulb to boil all the world's oceans. The challenge, currently being investigated by several teams, is how to tap it.
Some researchers have also suggested an intriguing connection between ZPE, inertia and gravitational pull. The push you feel while slowing down or turning when driving may actually be caused by ZPE fluctuations. A greater understanding of how to manipulate ZPE may one day lead to the control of gravitational and inertial forces, leading to new forms of propulsion and a revolution in space travel.
The number of physicists studying ZPE is small, and most are still operating at the theoretical level, but a breakthrough could one day provide the energy of the future. |
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