Moving Mirrors Make Light from Nothing
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By Geoff Brumfiel of Nature magazine
A team of physicists is claiming to have coaxed sparks from the vacuum of empty space. If verified, the finding would be one of the most unusual experimental proofs of quantum mechanics in recent years and "a significant milestone", says John Pendry, a theoretical physicist at Imperial College London who was not involved in the study.
The researchers, based at the Chalmers University of Technology in Gothenburg, Sweden, will present their findings early next week at a workshop in Padua, Italy. They have already posted a paper on the popular pre-print server arXiv.org, but have declined to talk to reporters because the work has not yet been peer-reviewed. High-profile journals, including Nature, discourage researchers from talking to the press until their findings are ready for publication.
Nevertheless, scientists not directly connected with the group say that the result is impressive. "It is a major development," says Federico Capasso, an experimental physicist at Harvard University in Cambridge, Massachusetts, who has worked on similar quantum effects.
At the heart of the experiment is one of the weirdest, and most important, tenets of quantum mechanics: the principle that empty space is anything but. Quantum theory predicts that a vacuum is actually a writhing foam of particles flitting in and out of existence.
The existence of these particles is so fleeting that they are often described as virtual, yet they can have tangible effects. For example, if two mirrors are placed extremely close together, the kinds of virtual light particles, or photons, that can exist between them can be limited. The limit means that more virtual photons exist outside the mirrors than between them, creating a force that pushes the plates together. This 'Casimir force' is strong enough at short distances for scientists to physically measure it.
From virtual to real
For decades, theorists have predicted that a similar effect can be produced in a single mirror that is moving very quickly. According to theory, a mirror can absorb energy from virtual photons onto its surface and then re-emit that energy as real photons. The effect only works when the mirror is moving through a vacuum at nearly the speed of light -- which is almost impossible for everyday mechanical devices.
Per Delsing, a physicist at the Chalmers University of Technology, and his colleagues circumvented this problem using a piece of quantum electronics known as a superconducting quantum interference device (SQUID), which is extraordinarily sensitive to magnetic fields.
The team fashioned a superconducting circuit in which the SQUID effectively acted as a mirror. Passing a magnetic field through the SQUID moved the mirror slightly, and switching the direction of magnetic field several billion times per second caused it to 'wiggle' at around 5% the speed of light, a speed great enough to see the effect.
The result was a shower of microwave photons shaken loose from the vacuum, the team claims. The group's analysis shows that the frequency of the photons was roughly half the frequency at which they wiggled the mirror -- as was predicted by quantum theory.
Capasso calls the experiment "very clever". He doubts that the effect has any practical use because it doesn't generate large numbers of photons, but he considers it a nice demonstration of quantum mechanics. He still hopes to see a moving piece of metal generate detectable light from the vacuum, and believes that micromechanical systems may eventually be able to reach such speeds.
Pendry says that the result, if it stands up, is bound to generate excitement. "Work in this area stirs considerable passion in the breasts of physicists."
This article is reproduced with permission from the magazine Nature. The article was first published on June 3, 2011.
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20 Comments
Add CommentVery interesting result. While some may think this is of no practical value, it may be a fundamental breakthrough in establishing the presence of disperse energy permeating spacetime. There must be some physical effect producing the expansion of universal spacetime as well as producing the analytical 'curvature' of abstract dimensional coordinates used to describe the effects of gravitation in general relativity.
Reply | Report Abuse | Link to thisIn contrast to the weird 'something from nothing' effect implied in this article, the manifestation of 'virtual' (short lived, self-annihilating particle-antiparticle pairs) particles must be the product of energy interactions within spacetime.
Federico Capasso doubts that the effect has any "practical use." He did not say that it had no "practical value."
Reply | Report Abuse | Link to thisWhat do you mean by "a fundamental breakthrough in establishing the presence of disperse energy permeating spacetime?"
Are there any physicists saying there is no "energy permeating spacetime?" Or are you saying this has never been measured? Do you believe the positive vacuum energy density as observed by the Casimir force has never been significantly measured before this "moving mirror" experiment? What about the cosmological constant? Does this "moving mirror" result help resolve the error of 107 orders of magnitude in the "vacuum catastrophe?"
Also, what do you mean by the "analytical curvature of abstract dimensional coordinates" of gravitation? How are the coordinates abstract (i.e. not concrete)? Do you mean that spacetime is not really curved; that the curvature of spacetime is merely an abstract analytical concept used to explain gravitation? If so, how do we account for gravitational lensing? Is gravitational lensing an illusion?
1. First off, and since the SQUID's modulated inductance was at about 11GHz ("reflected" photons at about half that frequency, i.e., 5.5GHz), well within the microwave spectrum, I wonder how was it possible to tell CMB photons (peaking at about 160GHz and still within the microwave spectrum), from the [observed] Dynamical Casimir Effect?
Reply | Report Abuse | Link to this2. Somewhat far-fetched but, since you mention, quote, "producing the Lamb shift of atomic spectra and modifying the magnetic moment for the electron." /quote, could this DCE eventually influence another long-standing issue in the [current] Standard Model, namely contribute to the Proton's [elusive] angular momentum (spin)?
Cheers!
JT
1. shielding
Reply | Report Abuse | Link to this2. It is possible that the Casimir effect is contributing to proton spin. As it seems you already know, it used to be thought that only the valence quarks contribute to the spin of a proton. If the sea quarks and gluons do contribute to spin, I doubt DCE would be useful in determining this. Creating gluons from "nothing" would be much more difficult than creating photons from nothing. Gluons exist over very short distances and times. How would you create a SQUID that modulates at that high of frequency and that short of distance? Did I understand you correctly?
Something from nothing is not new.It was invented by Bohr a century ago to create photons.
Reply | Report Abuse | Link to thisWhat is the difference between Newton force or G-force and Casimir force?A name?
Our paleolithic ancestors made light and fire from nothing by throwing stones and their fire was real.
I wonder why scientists are not allowed to talk about their findings. Something to hide?
I passed my GED test in Viet Nam. My physical condition limits my productivity and activity: I simply do not have enough energy to spar with you over what I consider to be trivial points. My comments do not constitute a submission for 'peer' review. Within those limitations I will try to respond to a couple of your questions with questions for you to answer.
Reply | Report Abuse | Link to thisAs I understand, GR does not describe any force or element to which the cosmological constant or curvature of spacetime can be physically attributed. They 'simply' describe effects that are not attributed to any physical force.
Didn't Einstein include the cosmological constant in his analytical model of the cosmos (which was though to be only objects contained within the Milk Way galaxy) simply to provide for a static universe?
Has there been some physical force or element described (other than the defunct aether) to account for the effect of the curvature of spacetime?
Didn't Einstein remark that the effects of gravitation are equivalent to (directional) velocity?
I cannot and will not waste my limited energy in any obsessive discussion or debate of these points. If you can explain what physical characteristics of spacetime have been described to account for its expansion and curvature I'll b e happy to retract or modify my fairly innocuous comment.
I'm sure you know more about it than I do and have reviewed the referenced paper (http://arxiv.org/abs/1105.4714), but I understand this to be a terrestrial laboratory experiment. If that is the case, would the faint CMB signal be detectable? I suspect that without proper external shielding the experiment would be subject to many local microwave and other EM radiation...
Reply | Report Abuse | Link to thisMy understanding of vacuum fluctuations was that for every virtual particle produced, an identical particle with negative energy would be produced to cancel it out with 0 net energy. Note, that that's not antimatter I'm referring to but negative energy matter which is what hawking suggests will eventually evaporate all black holes. So, wouldn't those negative energy particles eventually erode away the machinery producing them?
Reply | Report Abuse | Link to thisjtdwyer,
Reply | Report Abuse | Link to thisMy apologies, I forgot who you were. It jogged my memory when you replied with an ad hominem attack proclaiming your superiority while at the same time adding the disclaimer acknowledging your limited education (e.g. "wasting time" with "trival points" and "passed GED").
What seems to be our biggest problem may come down to simple miscommunication. You tend to misstate your ideas which leads to the confusion of some who read your comments. For example, in your first comment you mentioned nothing of a force. Once you re-stated your first comments with questions in your reply, your thinking became more clear. No, a "force" has not been described to account for the "effect" of the curvature of spacetime. (This is my answer to what I am assuming was a rhetorical question.) Notice how you used the word "effect" in your original comment and your reply. Then by including phrases like "abstract dimensional cooordinates," your comments become confusing. That is simply why I asked you the questions. Notice, that I was the only one who replied to you.
You said, "Didn't Einstein remark that the effects of gravitation are equivalent to (directional) velocity?"
It's acceleration, not velocity. I am sure you knew this, but this is what I mean about miscommunication. It also wasn't just a "remark" by Einstein. The "equivalence principle" was a major component in the development of GR and a result of the geometric foundation of GR.
1. "Shielding". Pretty laconic! I'm not going to ask you to elaborate, since I'm assuming that this factor was taken into account by the team.
Reply | Report Abuse | Link to this2. I'm not asking if a SQUID could detect the DCE (quark/gluon-wise), but if it´s pertinent to consider [some] contribution from the vacuum fluctuations to the Proton's spin, as it [appears to] have towards the Lamb shift and the electron´s magnetic moment, as mentioned in the paper. (Now that I think of it again, it seems less pertinent, as both the Lamb shift and the electron's magnetic moment might vary, while the Proton's spin [stays?] constant).
Thanks for the reply.
Cheers!
Joset, I am not very familiar with the DCE. Does it occur in nature? I was thinking it was purely man made, as opposed to the [non-dynamic] Casimir effect (which I simply think of as a result of the zero point energy created by virtual particles). I also think of the Casimir effect as a force, whereas, the Lamb shift is a difference in energy levels.
Reply | Report Abuse | Link to thisYes, I believe the vacuum fluctuations from virtual particles contributes to the proton spin. This would come from the sea quarks which are virtual quarks (as I said above).
Joset, I also have a hard time of thinking of vacuum fluctuations within an atom. The Lamb shift comment in the paper (referenced to a 1997 paper) is news to me. I never thought the Lamb shift resulted from vacuum fluctuations, but it makes sense with respect to an electron orbital due to the presence of the EM field. I don't believe the quantum field of the strong nuclear force can exist outside the atom (or away from the nucleus), so I don't believe virtual gluons or quarks occur in empty space. Correct me if I am wrong. I guess I am just trying to say that I don't know if vacuum fluctuations are said to occur inside hadrons. But, this is only a semantics issue.
Reply | Report Abuse | Link to thisCramer:
Reply | Report Abuse | Link to thisAs far as I'aware, the DCE is the relativistic Casimir effect, in this specific case, taking into account the modulated frequency of the SQUID. If it happens naturally, is a matter of theoretical speculation (which mechanisms?) but, it can be 'induced', as this work shows and for the first time.
As for your [good] questions, I seem to find a slight contradiction between "Yes, I believe the vacuum fluctuations from virtual particles contributes to the proton spin. This would come from the sea quarks which are virtual quarks." and, "...I don't believe virtual gluons or quarks occur in empty space." That was my main question, on what concerns the proton's spin. Photons are charge-neutral and, going out on a limb here, I'd say that even charged virtual particles would not directly interfere on the electron's magnetic moment, let alone the proton's spin! Yet, the paper states otherwise (...). My doubt still remains on the proton's spin, since a virtual quark/gluon sea's contribution would have to be so fine-tuned in order to provide the [remaining] absent angular momentum. And, moreover, this interaction would have to be present at the very 'proximity' of the bounded* quarks, hence, interacting with the short-range strong force!
*Considering the Hydrogen atom, with a single nucleon.
Cheers!
Is it just me, or is there something very wrong with this statement?
Reply | Report Abuse | Link to this"The effect only works when the mirror is moving through a vacuum at nearly the speed of light"
This statement is nonsense, the whole point of relativity is that you cannot measure the speed of an object moving through the vacuum. There is no ether and no absolute velocity, only relative.
Could the author of this article, Geoff Brumfiel please explain?
I expect that no subject area experts will be responding to your question - so I'll attempt to explain. Please bear with me in case I ignorantly miscommunicate any precise terminology - I'm not nearly as well read as most of the expert commentators.
Reply | Report Abuse | Link to thisThe entire statement is:
"The effect only works when the mirror is moving through a vacuum at nearly the speed of light -- which is almost impossible for everyday mechanical devices."
The theoretical prediction couldn't be tested with normal scale mechanical devices, which is why this group used a quantum scale device resonating at 5% of the speed of light - apparently fast enough to produce the predicted effect.
Russel -
Reply | Report Abuse | Link to this"This statement is nonsense, the whole point of relativity is that you cannot measure the speed of an object moving through the vacuum. There is no ether and no absolute velocity, only relative."
Actually, yes you can - though the object in question is at rest relative to itself, it is not at rest when related to point A or Z.
What are you talking about with "ether"? There isn't any.
Here are we sure these photons weren't produced from the friction of the device within the magnetic field, as in electrical current? The fact that the frequency is roughly half that of switching on and off could indicate the SQUID acted as a filter. What garantees do we have about the neutrality of the experiment's environment? After all quantum laws take place within larger cosmic size particle flows and states, a lot of which is still not understood or quantified.
Reply | Report Abuse | Link to thisVery interesting article...seems to me that by producing photons out of a vacuum that they have created the greatest power source...one that gives back more than is put into it....I wonder what the 2nd law of thermodynamics thinks of it...
Reply | Report Abuse | Link to thisYou assume facts not in evidence. There is no mention of how much power was required to create the near vaccum or to create the "mirror" and move it. Only a few photons were created so it seems likely that the amount of energy used was greater then the amount of energy produced.
Reply | Report Abuse | Link to thisLet's hope they are only virtual.
Reply | Report Abuse | Link to thisLong live the vacuum.