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Two metal plates placed close together in vacuum will collide due to more and more vacuum (electromagnetic) energy being converted from quantum EM modes to kinetic energy of the plates because of the increasing radiation pressure (energy-momentum) differential between the space inside and outside the plates. At the moment of collision this energy will be converted into heat.

This is an example that comes to my mind of how the zero point energy could be converted into a classical form of energy.

I don't think this is the most efficient way of doing so and I'm interested in the latest advancements whether theoretical or experimental of extraction of energy from vacuum.

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It is true that fluctuating electromagnetic fields inside and outside of two plates will cause the plates to attract each other. It is also true that upon collision, some amount of thermal energy can be potentially generated. However, it is equally important to remember that work had to be done in order to separate the plates in the first place. If you wanted to repeat this process in a "heat engine" type of way, you would have to do work against the Casimir force to separate the plates again, and this work in the ideal case would be equal to the energy gained from moving the plates.

In this light, one cannot extract electromagnetic zero point energy for free. While there is strong evidence for the presence of zero-point fluctuations which have physical consequences (i.e. the Casimir force), this zero point energy only acts as a reservoir which can mediate interactions, but cannot act as an infinite source of energy.

This does not mean, however, that zero-point fluctuations are not interesting and potentially useful! A related effect that was speculated about in the 1970's is the so-called "Dynamical Casimir Effect." In its most conceptually simple form, two plates are placed near each other, and then they are oscillated back and forth very quickly (at frequencies comparable to the resonance frequencies of the cavity). This can cause vacuum fluctuations of the electromagnetic field to be converted into real photons so that light is produced in the cavity! Some refer to this as a way of generating light from the vacuum, though it should be kept in mind that mechanical work is required to oscillate the plates, so again there is no free lunch. Nonetheless this effect is very interesting, and was actually observed for the very first time in 2011 (https://www.nature.com/articles/nature10561).

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    $\begingroup$ Welcome to the site. That's a nice first answer! $\endgroup$ – PM 2Ring Jan 6 at 2:35
  • $\begingroup$ I don't think "free" is a good word in this case. If you put a solar charger out on the sunshine you get energy for" free". It would be the same in the case of "vacuum charger". It seems weird that energy can be extracted, butonly discontinuously. This is like the EM motor, if there wasn't a way to keep it running (using a commutator for it to run smooth) then you would only have one time burst of energy. $\endgroup$ – Ezio Jan 6 at 9:33
  • $\begingroup$ I am not thinking it has to be a Casimir engine, rather a "vacuum" engine.Casimir effect clearly shows energy can be extracted for "free" only thing that remains is a way of pulling energy continuously or in larger amounts. $\endgroup$ – Ezio Jan 6 at 9:48
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The Casimir effect doesn't give you free energy. Sure, you have some attractive force between two metal plates, so you can harvest energy by letting them come together. But that's true of almost any method of harvesting energy.

For example, there's an attractive force between the plates and the ground (i.e. gravity), so you can produce heat by just dropping the plates. This doesn't give you free energy, because to do it again, you have to pick the plates back up. If you do this perfectly efficiently, you end up with just the same energy you started with. The same goes for the Casimir effect.

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  • $\begingroup$ Vacuum energy is as close as to" free energy" as anything I can think of. You didn't see my comment where I said I don't like the term free energy because it makes no sense( free from what?). I never used the term so I don't know what you're talking about. This is quite different from other ways of getting energy because potential is created out of "nothing". $\endgroup$ – Ezio Jan 6 at 18:56
  • $\begingroup$ @Ezio Suppose you drop something in space. It starts falling to the Earth, so it gets kinetic energy, but it's surrounded by complete vacuum. Is this energy "created out of nothing"? $\endgroup$ – knzhou Jan 6 at 19:13
  • $\begingroup$ @Ezio Energy you harvest from the Casimir force is not any more mysterious than energy harvested from the gravitational force. If the former counts as energy "created out of nothing", so does the latter -- but we do it every day. $\endgroup$ – knzhou Jan 6 at 19:13
  • $\begingroup$ I didn't say it was misterious, that's why I asked for some studies on it. $\endgroup$ – Ezio Jan 7 at 9:02

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