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What Is the Quantum Vacuum?

Leonard Kelley holds a bachelor's in physics with a minor in mathematics. He loves the academic world and strives to constantly explore it.

A True Vacuum?

One may have heard that a vacuum is nothing—the absence of matter. Space is typically called a vacuum, but even it has minute material in the void that makes it as a whole non-but-near-vacuum.

On Earth, we can isolate a region and pull all the material out of it, thus achieving a true vacuum, right? Before quantum mechanics it would have been considered so, but with the uncertainties and fluctuations associated with it, this means that even empty space has energy.

With this insight, particles can pop in-and-out of existence and are only detectible because of their influences, hence why we call them virtual particles. Empty space has potential. Literally. But it gets even cooler, because if you put two plates in a vacuum really close together but still separate, they feel an attractive force because of these quantum fluctuations. The space between has less potential for fluctuations that outside the plates, so an overall inward pressure is exerted. This is known as the Casimir effect (Brown, Timmer).

Finding Clues

So this is all fine and dandy, but what evidence do we have for this quantum vacuum occurring? Observations using the VLT telescope in Chile of a pulsar’s rays, evidence of a vacuum birefringence was spotted. This is an interesting feature of optics in which light passes through a special material layer before returning to the original conditions it had been before entering. As the light goes through the material, the different portions go through different phases and polarizations due to the make-up of the material. Once the light exists the material, the rays have undergone a parallel and perpendicular polarization, exiting in an entirely new configuration. If light passes through a vacuum polarization it will exhibit this change via a vacuum birefringence. With a pulsar, the light is most certainly polarized because of the high magnetic field. It would also polarize any vacuums that form around it, and with the VLT light was spotted that sported this change (Baker).

Other more Earth-based methods are also in development for detecting signs of the vacuum. Holger Gies (University of Jena) and his team from the Friedrich Schiller University in Jena, the Helmholtz Institute Jena, Dusseldorf University, and Munchen University have developed a means of detection using very strong lasers which only recently have been created. It is hoped that the laser will stimulate the virtual particles formed into creating exciting effects like “multiphoton pair production from vacuum or light scattering phenomena, such as quantum reflection,” but results will have to wait until the rig is set up (Gies).

Vacuum Driven Drums

One of the consequences of vacuum energy is that given a small enough vacuum space between two objects, you can drive them to become quantumly entangled. So, can you use this to say exchange heat across a vacuum without traveling across it? Hao-Kun Li (University of California in Berkley) and team decided to find out. They had two small membrane drums separated by 300 nanometers and in a vacuum. Each was given its own temperature and this heat caused vibrations. But because of the entanglement coupled with the vacuum energy, the two drums eventually synchronized! That is, they both arrived at the same temperature despite no physical contact between them, something that thermal equilibrium seemingly requires as molecular collisions average out. The potential energy contained in the quantum vacuum was all that was required to facilitate the transference (Crane, Manke).

Hovering Over a Vacuum

Quantum vacuums give rise to the attractive Casimir force, but could we convert this into something that is repulsive instead? Sort of. Research by scientists at the University of California at Berkley and Hong Kong University has found a way to balance out the attractive force with a repulsive one, and it all comes down to the materials used. Using a gold plate with a tiny (25 micrometers in size) gold flake suspended in an ethanol solution would just suck the flake right in because of vacuum forces. But if the plate has a teflon covering to it, then the Casimir effect between the gold and the teflon becomes repulsive and the little flake doesn't get sucked in. But because the Casimir effect for the gold plate is the greater one, we end up in a state of floating above the surface. Change the thickness of the teflon and you can very how far above the surface the hovering will be. Based on the thicknesses used in the study, the flake averaged between 20 to 45 nanometers above the surface but after about 20 minutes of fluctuating it would eventually settle in at 10 nanometers. While this is all cool, it doesn't sale up because gravity will greatly exceed the forces generated by the Casimir effects (Timmer).

Ah, those good ol' black holes...

Ah, those good ol' black holes...

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It Always Comes Back to Black Holes

Quantum vacuum details may make themselves most apparent when it comes to black holes. These complicated objects got even more so after the firewall paradox, a seemingly unsolvable conflict between quantum mechanics and relativity arose. The details are long and involved, so read my article on it for the full scoop. One of the resolutions to the paradox was postulated by one of the giants of black hole physics, Stephen Hawking. He theorized that the event horizon, the boundary of no return, wasn’t definite but was more of a fuzzy region because of quantum mechanical uncertainties and is therefore an apparent horizon. This makes black holes a superposition of gravitational states and are therefore grey holes, allowing quantum information to leak out. Before, because of the energy density of space, virtual particles formed around the event horizon and led to Hawking radiation which theoretically leads to black hole evaporation (Brown).

Another interesting avenue with our quantum vacuum comes in with the Haramein-model of black holes, which builds off several physics principles. The vacuum of space with its quantum effects combined with the spinning of a black hole creates a twisting of space-time as well as the surface of the black hole. This is a Coriolis-like force that causes a torque that changes as the quantum vacuum fluctuations do their thing. Combine this with the EM-fields around the black hole and we can start to describe black hole weather patterns with the quantum vacuum acting almost as a driving force behind it. But Haramein wasn’t done there. He also theorized that black holes themselves are not the traditional singularity we associate but instead a collection of states generated by the Planck vacuum energy! Holographic principles create a “surface to volume ratio resulting in the exact gravitational mass of the object,” almost as if we took a discrete number of regions of space and collectively called is a massive object. It should be noted that Haramein’s work isn’t well-accepted in the academic world but can maybe be a potential avenue of exploration given more time and revision (Brown).

So hopefully this is a primer for your exploration on this topic. It goes way beyond these ideas, and more are being developed as we speak . . .

Works Cited

Baker, Amira. “Neutron star reveals the energetic nature of the ‘empty’ vacuum.” Resonance Science Foundation. Web. 28 Feb. 2019.

Brown, William. “Stephen Hawking Goes Grey.” Resonance Science Foundation. Web. 28 Feb. 2019.

Crane, Leah. “Quantum leap lets heat move across a vacuum.” New Scientist. New Scientists Ltd, 21 Dec. 2019. Print. 17.

Gies, Holger. “Revealing the secret of the vacuum for the first time.” innovations-report, 15 Mar. 2019. Web. 14 Aug. 2019.

Manke, Kara. "Heat energy leaps through empty space, thanks to quantum weirdness." innovations report, 12 Dec. 2019. Web. 05 Nov. 2020.

Timmer, John. "Researchers balance Casimir effects, make tiny hoverboard." Conte Nast., 06 Jun. 2019. Web. 18 Feb. 2021.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2020 Leonard Kelley

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