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Reading this PE question can-we-transport-energy-over-infinite-distances-through-vacuum-using-light, a related question arises naturally:

Is energy transported (by light)? -- (I did believed in this answer until now) or energy is already 'in site' (vacuum) just expecting to be excited by the photons?

This news insinuated the doubt anti-laser(1)

The antilaser does the reverse: Two perfect beams of laser light go in, and are completely absorbed.

If vacuum is able to absorb energy then it can do the reverse, and supply energy. We are already prepared to accept that vacuum has energy.

I am inclined to accept that energy do not travel at all. What is travelling is the excitation of vacuum, and we call this: photons. It may appear a question of semantics, but I think that the explicit reconaissance of this notion can be helpful.

(1) The two rays entering the slab are in phase opposition when they met, and cancel. The nature of cancelation was obscure to me, until now.

added:

I googled this: "where goes the energy in a destructive interference" and followed past answers to this question. Someone answered "into the surrounding environment." We are in minority;) Most of the times they said that the total extinguishing is impossible. This anti-laser experiment shows that energy is destroyed.

We see the same effect with sound cancelation , with boat wake (trailing waves) cancelation (by double/triple hull or when they sail in formation), and now with light.

added after 2 answers
Destructive interference image from astro-canada.ca
What is amazing is that this fact is inside the theory since the begining, quoting from there:

In 1801, the British physicist Thomas Young demonstrated that light propagates as waves, like waves on the surface of water. Young understood that when two light waves meet, they interact with each other. Scientists call this “interference”. In the opposite scenario, where the crests of one wave are aligned with the troughs of another, they cancel each other out and the light disappears. This is destructive interference.

As anna says in her answer the actual theorethical framework does not understand a vanishing of energy. The question remains open: What happens to energy when 'light disappears' or 'light cancels' or 'destructive interference'?

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Helder Velez
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    ""The antilaser does the reverse: Two perfect beams of laser light go in, and are completely absorbed. If vacuum is able to absorb energy then it can do the reverse, and supply energy. We are already prepared to accept that vacuum has energy. "" If You read that link , You will see that the antlaser is not vacuum, but a silicon wafer! And conversion of the beams energy to heat is mentioned! -1 – Georg Feb 24 '11 at 10:02
  • It can be done in vacuum with the same result. It is not the medium that absorbs the energy. The photons cancel each other (almost all of them). The original paper that dmckee mentions does not even mention heat. – Helder Velez Feb 24 '11 at 17:34
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    Some additional references and comments about anti-laser were discussed later here: http://physics.stackexchange.com/questions/9628/recently-publicized-experiment-on-destructive-interference-between-two-laser-beam – Luboš Motl May 09 '11 at 12:48
  • Even though this question has quite a simple answer, it isn't bad, it is quite good actually, so I'm confused from the number of downvotes. I would give you a +1 if you removed the last sentence, "Some will invoke extra dimensions as a repository of energy, and will once again ignore the ubiquitous vacuum.". Actually, let me just propose an edit to remove it, and if it' is accepted, I'll give a +1. – Abhimanyu Pallavi Sudhir Jun 21 '13 at 14:59
  • Since my edit wasn't accepted, the question is quite attacking, so I'll give it a -1. – Abhimanyu Pallavi Sudhir Jun 22 '13 at 05:27
  • @dimension10: removed – Helder Velez Jun 24 '13 at 10:21
  • @HelderVelez: +1, then. – Abhimanyu Pallavi Sudhir Jun 24 '13 at 10:23

3 Answers3

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We regularly measure the energy stored in electric and magnetic fields. Think capacitors and inductors.

We do engineering with energy stored that way.

The fields have energy, and the propagation of light generated fields far from the source.

So energy was transported. QED.

So where does the energy go in the experiment you linked? Read the article:

When the alignment was right, the light waves canceled each other out. The silicon absorbed the light and converted it to another form of energy, like heat or electrical current.

The two beams are being used to drive a single process both directions through it's transition (which will require the same energy input and have the same cross-section by time-reversal symmetry). Presumably these processes couple to the bulk in some way and each dissipates leaks energy through that coupling.

The paper itself is available as http://www.eng.yale.edu/caolab/papers/Sci11b.pdf

dmckee --- ex-moderator kitten
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  • OK, fields have energy. Does it means that energy is transported ? The trouble is: what happens to the canceled energy? If we put two radiators with the same frequency and in phase-opposition at the same spot we got no radiated field. (I'm an old electronic eng. and I am aware of the usual answer, thanks anyway) – Helder Velez Feb 23 '11 at 18:05
  • @Helder: Energy must be transported in the fields. TO prove it, note that you can buy sub-nanosecond pulsed laser in the UV band with single pulse triggers. So get one and set up a photo-electric effect experiment some meters from the laser. The laser is off before the the metal reacts. So where did the energy come from. It came from the light. You're free to treat the light in a quantum way or as a classical wave packet, but the light carries energy. – dmckee --- ex-moderator kitten Feb 23 '11 at 18:34
  • @dmckee: In your oppinion what happens when exists Cancelation of energy ? – Helder Velez Feb 23 '11 at 18:48
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    There is no cancellation of energy, the fields interacted with the silicon wafer and the energy is transferred during that interaction. If I throw two balls of putty at each other so that they hit, come to a stop and fall to the floor do you describe that as a cancellation of kinetic energy? – dmckee --- ex-moderator kitten Feb 23 '11 at 19:01
  • @dmckee: thanks for the link. I' will read it. The same happens if we do not use a slab. It is there for pratical reasons. It happens in vacuum. see this picture of constructive and destructive interference. We move one radiator by one half-wavelength and we get no energy. If the energy was transported from the source it must go somewhere. My bet is that the vacuum absorbed it, and sourced it, reacting to light.If we say that it was transported then the source must have to know when to radiate, and not radiate. – Helder Velez Feb 23 '11 at 19:19
  • I read the paper you linked and there is no reference to heat or energy conversion (it is only in the article). Of course heat must appear because the fields are not 100% out of phase and also because the material has losses. By superposition principle E(t) is the sum of all components E1(t)+E2(t) = 0 in the region of interference. The energy appart 1/eps factor is the volume integral of E(t)^2. Summing 0^2 all over gives 0. If it was transported it is 0 now. I do no understand why you say that there is no cancelation of energy. – Helder Velez Feb 24 '11 at 00:58
  • @Helder: They don't mention the energy loss mechanism because it is obvious to the papers intended audience (it is implicit in the phrase "the time-reversed analog of laser emission"). You are looking at the wave picture as if (1) you have perfect plane waves (which you don't) and (2) they are either static or traveling in coincidence (neither of which is true). You can get the right time averaged energy density from the classical calculation (The waves are $A cos(\omega t \pm k x)$, or (if you don't like the averaging required in the classical picture) you can use a photon treatment. – dmckee --- ex-moderator kitten Feb 24 '11 at 01:28
  • It seems that we where writing at the same moment our last comments;) As you can see before we integrate we must add both the components. This give 0, a constant 0 over time. The energy is 0. A monstruos ZERO. I found in the net and I do not buy it: The magnetic field do not cancel. The Poynting vectors are opposite and cancel. – Helder Velez Feb 24 '11 at 17:43
  • The hard core "thing" of a laser is stimulated emission. So, an anti-laser I'd think rests on stimulated absorption? – Georg Mar 28 '11 at 10:14
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From the experiment with the silicon wafer we get the information that heat was generated. When two coherent beams of photons interfered destructively, heat appeared.

What is heat in this particular case? Heat results when a bunch of infrared incoherent photons interact with matter. The destructive interference of the waves of photons became a burst of incoherent infrared photons heating the wafer..

The same will happen in vacuum. The disappearance of the laser coherence will be accompanied by a burst of infrared photons.

You can think of it as the particle nature of light dominating, with multiple photons scatterings on virtual electron loops from each other. The energy would be all there in the infrared burst. Because the momenta of the two beams are in the same x direction, they can only scatter within the Heisenberg uncertainty allowance in space, and thus turn into photons of very low energy.

This could be tested experimentally in vacuum , by detecting the infrared from the destructive interference. I think it is the correct view because the claim that "energy disappears" is not viable within our local physics framework . If the experiment shows no infrared correlated with the interference, then one would have proof of extra dimensions into which the energy was dissipated.

Edit after more thought:

The higher order loops I have recourse to in my argument above in vacuum , have small probability: photon photon scattering is higher order with 4 1/137 vertices. I think that the answer lies within the formalism that Lubos develops in his blog after this question was asked, of how the classical wave emerges from the quantum mechanical.

I believe now that the answer for the vacuum is that: completely overlapping out of phase opposite direction beams will go their way minimally affecting each other with higher order processes, and will appear at their ends with their energy diminished a bit by the higher order processes. In vacuum there is no material for the classical electromagnetic wave to collectively interact and it is just photons running with the speed of light.

anna v
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  • @anna v: the main part of the experiment is light interferes with light. As the beams are almost 100% coherent each beam will see the other as a duplicate image in a mirror and the photons cancel one another. A few ones are less coherent and will interact with matter and generate some heat. I expect that someone will do an experimental energy assessment. IMO this experiment will be a landmark in the understanding of the nature of light. As I only see a photon as a wave it is easier to me to accept the dead of its particle nature.I wait future developments.It would be no proof of extra dims. – Helder Velez Mar 27 '11 at 18:28
  • @Helder Velez , Even the word photon describes a particle, and it is experimentally seen in the photoelectric effect. The LHC experiments are looking for disappearing energy as a sign confirming extra dimensions. If such a two lazer beam experiment were carried out in vacuum and no infrared photons are seen then the interpretation within current physics models will be extra dimensions. Current physics models describe a plethora of data quite well and will not be scrapped if this particular experiment shows disappearing energy, since it can be accomodated within the models. – anna v Mar 28 '11 at 11:41
  • Since this conversion of laser light to infrared frequencies will be happening whenever there is an interference, I have a simple experiment to propose: Take an existing small 3d hologram and a glass vacuum vessel. Shine the laser through the hologram so that it appears within the vacuum vessel. Take infrared pictures of the vacuum vessel. If infrared is produced it should show on the film, maybe even as an image of the object! http://www.answers.com/topic/holography – anna v Mar 28 '11 at 12:10
  • @anna 'Because the momenta of the two beams are in the same x direction,' Dont you think that the moments are in opposite directions? – Helder Velez Mar 28 '11 at 14:46
  • @anna : in photonics the light is always treated as a wave.
    The photoelectric effect is, as far I remember, the only classical experiment that uses the particle notion. The usual interpretation is that it reveals one property of the light. Because there are two entities playing in the interaction one cannot discard that it can reveal one property of the receiver of light that can be read like this: the winner takes it all. Please: If you think that I am wrong can you make a reference that discards what I'm saying?     – Helder Velez Mar 28 '11 at 15:08
  • and the Compton scattering: Compton's experiment convinced physicists that light can behave as a stream of particle-like objects (WP). – Helder Velez Mar 28 '11 at 15:52
  • shifted? pls correct the faulty word. Its offensive.
    Where to goes the energy when fields do cancel? Do you know the answer or is this an improper question in physics?     – Helder Velez Mar 28 '11 at 17:50
  • @Helder I think I have replied to this question. If the two beams interfere in vacuum the energy does not disappear, nor does the frequency of the beam change. I model that there is a small dy and dz in space and dp in momentum space which allows energetically for a scattering on off mass shell virtual electrons with the photons of the beam, generating softer photons that take away the energy. Lets put it another way: the fields cancel within the heisenberg uncertainty principle, and the energy of the beams is transformed to very soft photons. Photon number is not conserved. can be multitudes. – anna v Mar 28 '11 at 20:13
  • @anna When I said above 'in photonics the light is always treated as a wave' I consulted the book Photonic Crystals: Molding the Flow of Light 305 pages, Joannopoulos et al, Princeton Univ Press and count : photon word: 3 times, particle word: 3 times, Maxwell 33 times, Wave 100 times up to pag 63, then I give up tired of clicking; as 'photonic' is a designation I did not counted it. – Helder Velez Mar 29 '11 at 11:41
  • @anna you said 'Because the momenta...are in the same x direction,' and I asked you: Dont you think that the moments are in opposite direction? consult pls the configuraton of the experiment: one beam approach from the left and the other from the right. The Poyinting vectors, and the momenta vectors as the E, B fields are symetric. When we do 'field shaping' with antenae aggregates we simply use Maxwell eqs and go with waves everytime. When we got near a null in energy in some region of space we dont get infrared radiation to 'consume' the canceled field. E,B vectors additive: Light+Light=0. – Helder Velez Mar 29 '11 at 12:01
  • @anna: when we study the physics of lasers we use the word 'photon' countless times. It is so because it is light-matter interaction and matter only uses definite levels of energy and the amounts of energy absorbed and emited is by quanta (photons). The quantization is due to matter and I question if it is mandatory to be an intrinsic property of light. In the experiment in question it is light-light interaction, a different issue – Helder Velez Mar 29 '11 at 12:56
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I'm just a simple normal working person, but I like to dabble into physics. Below is a representation of how I have always seen it happening.

As I see it taking it to the water cancelling eachother out and assuming light has the same behaviour properties as water waves.

When water waves of the same wavelength but exact opposite from eachother it seems as if the energy is lost. This isn't possible, what happens is that all energy is spent by friction.

Wave a has the same speed, mass and height as wave b. They meet at the exact same apex, they put the exact same amount of force against eachother, friction results, neither one budgets because they are exactly the same, and all energy gets spent into friction/heat untill all energy is lost into heat.

Energy never dissapears, it's usually transformed.

Now what is interesting is what happens to transformed light in a vacuum where the above scenario happens, if it transforms into heat, where there are no molecules to exite, the solution is what I would pose is that the resulting frictions result in a different infrared single wave or something similar.simple representation of light turning into other light because of lack of matter

Tschallacka
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