The experiments reported in recent years demonstrating the creation of real photon pairs from the vacuum via the dynamical Casimir effect have made me wonder if this process demonstrates the creation of energy from nothing. Energy in the real world cannot be created or destroyed so the system used in this experiment will have the same total energy before and after the experiment ...only after the experiment there are also additional real photon pairs.

So is this genuinely the creation of energy via the casimir effect, if so it seems extraordinary and a violation of the principle of conservation of energy. Is there any other example of energy being created or destroyed, i have seen Hawking radiation mentioned in comparison, but here the creation of the 'real' photons from the vacuum is balanced by negative energy photons falling into and shrinking the black hole, so energy is conserved.

  • $\begingroup$ As space expands, the energy per unit volume of dark energy is constant. So when it expands to more volume, you get more energy. Add to that the fact that dark energy accelerates the expansion and you can't fail to see a positive-feedback system of energy created out of nothing $\endgroup$ – Jim May 20 '15 at 19:19
  • $\begingroup$ What makes you think that no work was done on the vacuum by the experimental setup? One can increase the strength and total energy of an electric field by pulling two charged isolated capacitor plates apart. Does that violate energy conservation? Of course not, it takes the same amount of energy to pull the plates apart as what gets deposited in the field. $\endgroup$ – CuriousOne May 20 '15 at 19:19
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    $\begingroup$ But I'm cheating because there is no law of conservation of energy on cosmic scales. $\endgroup$ – Jim May 20 '15 at 19:19
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    $\begingroup$ @JimtheEnchanter: You don't actually know that. All you know is that there may be an energy source that you haven't characterized, yet. Whether energy conservation holds for the entire universe or not is not an experimentally decided question. It may not even be decidable from the inside. $\endgroup$ – CuriousOne May 20 '15 at 19:21
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    $\begingroup$ @CuriousOne It doesn't have global time translation symmetry. That means energy is not a conserved quantity. That is the accepted, mainstream viewpoint $\endgroup$ – Jim May 20 '15 at 19:30

So is this genuinely the creation of energy via the casimir effect, if so it seems extraordinary and a violation of the principle of conservation of energy.

You gave no link, but I discovered the following by googling:

The experiment is based on one of the most counterintuitive, yet, one of the most important principles in quantum mechanics: that vacuum is by no means empty nothingness. In fact, the vacuum is full of various particles that are continuously fluctuating in and out of existence. They appear, exist for a brief moment and then disappear again. Since their existence is so fleeting, they are usually referred to as virtual particles.

Chalmers scientist, Christopher Wilson and his co-workers have succeeded in getting photons to leave their virtual state and become real photons, i.e. measurable light. The physicist Moore predicted way back in 1970 that this should happen if the virtual photons are allowed to bounce off a mirror that is moving at a speed that is almost as high as the speed of light. The phenomenon, known as the dynamical Casimir effect, has now been observed for the first time in a brilliant experiment conducted by the Chalmers scientists.

The motion of the mirror will give the energy necessary so that the virtual particles become real. No creation out of the vacuum.

Virtual particles are mathematical shorthand in the formulas calculating quantum mechanical setups. Example:


Only lines entering or leaving the diagram represent observable particles. Here two electrons enter, exchange a photon, and then exit. The time and space axes are usually not indicated. The vertical direction indicates the progress of time upward, but the horizontal spacing does not give the distance between the particles.

The photon is virtual representing the propagator in the mathematical formula for calculating the crossections for this interaction. For the photon to become real it has to be leaving the interaction area.

The same is true for the virtual loops in the casimir effect:


All diagram lines between the material C are virtual, mathematical functions. To become real photons ( the dashed virtual ones) energy has to be supplied by an external vertex. In the simplified description of the experiment above, the energy is supplied by the kinetic energy of the molecules of the mirror, a virtual photon from the Casimir loops interacts with a molecule's electron and gains energy as a real outgoing photon:


There is no energy out of the vacuum.

  • $\begingroup$ I am a bit confused by mechanistic explanations in this context (impulse is transmitted by moving mirrors) where the actual experiment uses an electronic circuit that is switched via a superconducting quantum interference device: no moving mirrors, just a quantum switch being hit at GHz frequencies. Can we really prove from theory that this switching will always require more energy than is radiated? $\endgroup$ – B M Mar 7 '19 at 12:16
  • $\begingroup$ @BM Within the framework of quantum field theory, yes, the analogy holds. To get real photons from virtual loops energy has to be supplied. The complexity of the experiment prohibits a calculation, but energy conservation is a strong law. $\endgroup$ – anna v Mar 7 '19 at 13:01
  • $\begingroup$ I feel you provided a great summary of established notions on how to possibly integrate this experimental setup with thermodynamics. However I cannot find any strong, direct evidence that the energy conservation is not violated, only strong, circumstantial evidence: "energy conservation is a strong law". Should we not say that there is an open question here? Thus can a framework (quantum thermodynamics?) derive boundaries for energy / entropy of operations through this circuit? $\endgroup$ – B M Jul 11 '19 at 21:24
  • $\begingroup$ @BM Energy conservation did not become a law in physics mesuring complicated systems, but simple to describe mathematically/theoretically. It is possible that at some level the conservation laws used as axioms to derive our theoretical models may, at some regions of phase space, not hold. Energy conservation does not hold for example in the theory of General Relatiity, when masses and velocities are very large. It holds for flat spaces where Lorentz transformations hold. This experiment does not fall in that regime, so it must obey the laws/axioms of this regime.. $\endgroup$ – anna v Jul 12 '19 at 4:31
  • $\begingroup$ A simple explanation within the mainstream physics explains the effect without invalidating our current models, so it is not an experiment that can prove energy non-conservation with the variables and formulas that are used, which would be a drastic change from mainstream theories. $\endgroup$ – anna v Jul 12 '19 at 4:32

One has to put energy into the system in order to set up the experiment, which is then released by the vacuum.

You could compare this to putting an object high above the Earth, and then letting it fall. The acceleration of the object doesn't mean you are are getting energy for free, or somehow extracting it from the Earth's gravitational field (this statement is ambiguous - what I mean is that the gravitational field isn't weaker than pre-experiment in order to compensate for the acceleration), you are just getting back the energy you put in when you set things up.


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