Phase cancellation of light - Is it possible to make light disappear?

[infinity3000]

Based on the principle of noise cancelling headphones, I was wondering if it would be possible to do the same thing with light? I.E. If you had a light source and then introduced a device that output a light wave with the same amplitude but with inverted phase, would the interference cancel out the light source and create darkness?

I'm a writer working on a piece with some science fiction elements, so I'm mainly interested in the theoretical possibility rather than actually making something. You can assume that any required technology that we don't have could exist.

I'm not a physicist so please don't just reply with - oh that's not possible due to [insert scientist here]'s Principle. I won't know what you mean. But please if you have any thoughts on how this could be done theoretically or actually, let me know. Thanks

 

[Vanadium 50]

You don't get to ask a question and also to provide the answer. It can't be done. I know you don't want to hear that answer, but nonetheless, it is the truth.

 

[infinity3000]

I wasn't providing the answer, I was just asking people not to dismiss the idea without explanation. Like you did.

I'm happy to hear people say no it isn't possible. There are many things we don't consider possible but then later on someone solves it. And any answer will be limited by current scientific knowledge, whereas science fiction is not.

But with infinite resources and technology we can't yet imagine, is there any current knowledge that could be the basis for this idea?

 

[Vanadium 50]

Actually, you specifically asked for no explanation.

Your argument that since you don't know enough to see that it's impossible therefore it must be possible is illogical. And even though you have asked not to get an explanation, I am going to give you one anyway. If you cancel the light everywhere, you will have the same outcome as if you put an opaque object in front of the light source. That's what it means to cancel the light everywhere. Since obviously, that's not what you want - otherwise you wouldn't need a technological development - whatever it is that you do want is impossible.

"Two plus two continue to make four, despite the whine of the amateur for three and the cry of the critic for five." (J.M. Whistler)

 

[Tea Jay]

Light and sound do not propagate the same way, so you cannot find a wavelength of visible light that will cancel out another wavelength, as they don't interfere with each other the way sound waves do.

Sound requires a medium to travel through...air typically for our purposes. This means you can generate a wave that will vibrate out of phase and "cancel" the unwanted noise, etc.

Light can be transmitted through a vacuum, and there are no out of phase lights that can be out of phase with it...as there are no vibrations in the air that are produced, etc.

You may need to continue to use an ordinary light switch for now...this will cancel the light for most people. :DIf for science fiction purposes, you can try having a media we don't know about as being the media light is transmitted through, the way air or water, etc, work for sound. You can then have your mechanism follow accordingly.

 

[infinity3000]

Thankyou Tea Jay for your thoughtful and helpful response. It is interesting to hear about the differences between light waves and sound waves; the fact that light waves don't interfere with each other sounds like the main reason why light cancellation wouldn't work.



Vanadium 50 please cease posting in this thread and go "mentor" somewhere else.

 

[Antiphon]

It can be done in principle but in practice the frequencies are simply too high for any coherent electronics to function, and the wavelengths are simply too short for antennas on the wavelength scale to be anything but fragile.

The physics of it is quite straitforward though.

 

[kmarinas86]

I wasn't providing the answer, I was just asking people not to dismiss the idea without explanation. Like you did.

I'm happy to hear people say no it isn't possible. There are many things we don't consider possible but then later on someone solves it. And any answer will be limited by current scientific knowledge, whereas science fiction is not.

But with infinite resources and technology we can't yet imagine, is there any current knowledge that could be the basis for this idea?

The photons either pass through each other or form mass. If they form mass, they did not disappear. If they pass through each other, they only cancel their phases so as long as they overlap that way. Once they already passed each other, they are separating from each other and no longer cancel their phases.

Photon phase cancellation exists, but it is never permanent. And to be more precise about it, not everything about the photons gets cancelled. Cancellation of phases doesn't mean cancellation of their existence. Light doesn't "disappear".

Short answer: No.

 

[Antiphon]

Using only passive means the answer is no. But using electronics the answer is yes.

Your equipment would absorb photons and create new ones. It's not difficult.

 

[Vanadium 50]

Light and sound do not propagate the same way, so you cannot find a wavelength of visible light that will cancel out another wavelength, as they don't interfere with each other the way sound waves do.

Of course they do. Waves are waves and interference is interference. Sound and light interfere in exactly the same way.

 

[Tea Jay]

Of course they do. Waves are waves and interference is interference. Sound and light interfere in exactly the same way.

LOL - I meant in his context of an explanation w/o an explanation.

For example, given his context, probably to have a science fiction device that can "cloak" etc, it would emit such an interference to cancel out the light analogous to the way noise cancelling headphones do for sound, etc.

What would "out of phase light" be that would therefore cancel out the visible light if they are exactly the same, in the context that he is going for?

IE: Sure, they can interfere, and I winced a little due to oversimplification, but not the way he wants them to.

Again, I was assuming he was going for invisibility to hide a person or ship, etc.

 

[infinity3000]

To clarify, the effect I am interested in producing would be along the lines of a windowless room with a single light source, and then introducing an electronic device which emits photons in such a way as to "cancel" out the photons from the light source, effectively putting the room into darkness.

Sorry if I'm oversimplifying or mangling the terminology...

 

[Thundagere]

Don't forget, that when two waves with mediums are interfering, it's not like they interfere everywhere. They interfere destructively only at SPECIFIC nodal points, meaning that it wouldn't work to thrust an entire room into darkness.

 

[Antiphon]

Don't forget, that when two waves with mediums are interfering, it's not like they interfere everywhere. They interfere destructively only at SPECIFIC nodal points, meaning that it wouldn't work to thrust an entire room into darkness.

This is only the case with certain source distributions. In general it is not true.

For example, a spherical surface distribution of electric and magnetic currents enclosing the light bulb could completely cancel its emissions.

The magnetic currents cannot be realized directly but are approximated (mathematically and in the engineering sense) by small electric current loops whose axis is parallel to the surface enclosing the lamp.

Look up "Schelkunoff's equivalence principle" for the equations behind this.

 

[Vanadium 50]

Yes, but let's consider the sort of charge distribution that will cancel an arbitrary (and incoherent) light source - you'd want something like a metal box. Well, in that case, why not use a metal box? Or a wooden box.

Any scheme you are going to come up with requires the gadget to be in between the eyes and the object. And, by definition, the response of this gadget will be the same as if it were opaque. And we're back to the box.

 

[nsaspook]

To clarify, the effect I am interested in producing would be along the lines of a windowless room with a single light source, and then introducing an electronic device which emits photons in such a way as to "cancel" out the photons from the light source, effectively putting the room into darkness.

Sorry if I'm oversimplifying or mangling the terminology...

Use Dark Sucker theory in your book.
http://www.rogermwilcox.com/darksucker.html

 

[technician]

I have some sympathy for infinity 3000, in PRINCIPLE cancellation is possible...isn't that called interference? What he makes of that is up to him to research and good luck to him and his imagination in his area.
"two plus two continues to make four, despite the whine of the amateur for three and the cry of the critic for five"
If J.M Whistler had any background in basic vector mathematics he may have had a different view.
Pythagaros knew that 2 + 2 could be √8

 

[thematrixiam]

You are not looking for a specific change. you are looking for complete change.

It's easy really.

Refract all light so that it's either higher or lower than the spectrum of human visibility.

No calculations are needed.

It does the job of canceling it out, without actually thinking about it. Now, if you wanted to cancel out specific lights, that would be more fun. Say, cancel all light that is not in the field of vision of an individual.

 

[Abuhol]

You didn't actually think you would receive a positive reply detailing methods and application did you ? I realize my reply is long overdue and will simply tell you why I initially came to ask the same question. Many years ago a Rapier Squadron tracked on radar a US Stealth Aircraft coming into land at a UK Base, the guy in question puzzled by this asked one of the US Officers on station how this was possible, the reply he received was " Son, when that that thing doesn't want to be seen you won't see it" Now then, maybe that's why you won't see a true answer to your excellent and thought provoking question.

 

[ZapperZ]

You didn't actually think you would receive a positive reply detailing methods and application did you ? I realize my reply is long overdue and will simply tell you why I initially came to ask the same question. Many years ago a Rapier Squadron tracked on radar a US Stealth Aircraft coming into land at a UK Base, the guy in question puzzled by this asked one of the US Officers on station how this was possible, the reply he received was " Son, when that that thing doesn't want to be seen you won't see it" Now then, maybe that's why you won't see a true answer to your excellent and thought provoking question.

But the physics of the stealth fighter actually isn't that much of a secret. If you read the book "Skunk Works", you'll realize the history of the physics involved, and the fact that it was contained in a rather old russian paper on a particular E&M problem. What is classified is how it is achieved and the kind of material used to turn that into reality.

That is not the same here. The OP has received several answers that essentially explain why what is trying to be accomplished isn't that clearly obtained based on the physics, not just trying to find a way to achieve it. There's a distinct difference here.

Zz.

 

[Abuhol]

I see redirection and no explanation, I see a Mentor that cannot refute and will not admit to possibilities that technology already exists to which the Mentor is not privy to

 

[ZapperZ]

I see redirection and no explanation, I see a Mentor that cannot refute and will not admit to possibilities that technology already exists to which the Mentor is not privy to

This is silly. Why would I refuse something if the technology already exist? If it does, show it! If not, then you are on a fishing expedition and making speculative, unfounded claim, which is in violation of the rules that you had agreed to. The redirection was done by you by bringing up the stealth technology, which I've explained why it is NOT the same as this topic.

The original question was addressed. It may not have been addressed to your liking. Unless you have definitive sources to indicate otherwise, then you have not provided anything of value other than stirring the pot.

Zz.

 

[Abuhol]

My apologies, I should have made myself clear, The publication you refer to In my opinion exists as nothing more than redirection from the actual physics used by the US Air Force.

 

[ZapperZ]

My apologies, I should have made myself clear, The publication you refer to In my opinion exists as nothing more than redirection from the actual physics used by the US Air Force.

Did you actually read it?

Again, the physics involved was published out in the open. Even Wikipedia has a good entry on it!

http://en.wikipedia.org/wiki/Stealth_technology

The Russian publication that I referred to, which was cited in that book, was Ufimtsev's "Method of Edge Waves in the Physical Theory of Diffraction".

Again, the physics was there, unlike this current topic. The comparison you made is not valid.

Zz.

 

[mrspeedybob]

The fundamental problem with canceling light is that the interference will be constructive in just as many places as it is destructive. If it were possible to know the exact location of the observer (by observer I mean each cone or rod cell in each eye or each pixel of a CCD etc.)and the exact location and phase of each photon headed in that direction you could generate photons which would cancel at the observers location, though in other locations they would not. Even this is impossible though due to Heisenberg's uncertainty principal. Since photons are small enough that quantum effects are significant the uncertainty principal will prevent you from knowing exactly where and at what phase a photon is as it travels from source to observer. Since you cannot know the position and phase of each photon you cannot consistently generate photons that will cancel them.

 

[mfb]

If it were possible to know the exact location of the observer (by observer I mean each cone or rod cell in each eye or each pixel of a CCD etc.)and the exact location and phase of each photon headed in that direction you could generate photons which would cancel at the observers location, though in other locations they would not.

(Bold added by me)
That is a very important part. Sound is (relatively) easy to cancel as it is coherent - you can measure where sound is, and predict how sound will arrive at the observer. This is not possible with most light sources, like the sun or a light bulb.

You can cancel laser light at some specific location, with a different laser (or different path of the same laser) carefully tuned to the same frequency and the appropriate phase. The same is true for radio waves, microwaves and similar coherent low-frequency electromagnetic waves.

 

[dipole]

It can be done in principle but in practice the frequencies are simply too high for any coherent electronics to function, and the wavelengths are simply too short for antennas on the wavelength scale to be anything but fragile.

The physics of it is quite straitforward though.

What exactly are you referring to?

Are you talking about introducing an infinite set of Fourier components and somehow producing a flat (zero amplitude) line? Is this even possible mathematically?

 

[Khashishi]

If you completely cancel out the light wave, the light doesn't disappear. It never was emitted in the first place. Pretty hard to achieve with visible light, but if you put a radio antenna in a cavity such that the radio emission would interfere with itself, then the antenna would not radiate at that frequency.

 

[sophiecentaur]

Light and sound do not propagate the same way, so you cannot find a wavelength of visible light that will cancel out another wavelength, as they don't interfere with each other the way sound waves do.

This is not right. You can only get cancellation from two coherent sources (identical frequencies / wavelengths), whatever sort of waves you are considering.
The only significant difference between light and sound, in this respect is the wavelengths and frequencies involved.
@Infinity
Sound cancelling headphones / enclosures also rely on the possibility of electrical circuitry working fast enough to produce exactly inverse signals (sets of waves, if you like) to cancel the unwanted ones which are arriving. It is possible to pick up the sounds right next to your ear (wanted programme signals and unwanted noise from outside) with a microphone and use electronics (negative feedback) to cancel most of the unwanted stuff. Nothing will work fast enough to achieve the same thing with light. This is not just a matter of technology getting better in time; it's pretty fundamental.

There is an alternative way (of thinking, more than fundamentally different) to cancel a wave and this is to mimic the wave precisely and add it (inverted version) to the incoming wave, producing a cancellation. Unfortunately for your scheme, the geometry of the situation means that cancellation will only operate over a very small region and, for different wavelengths, the cancellation will work at different places. If you look at the Young's Slits interference experiment, you will see that two sources can produce narrow fringes of cancellation. It only gives good cancellation for just one wavelength and it's hopeless with sunlight (a huge spread of wavelengths involved).

So the answer is NO and my explanation is about as simple as it can get, I think. Sorry.

 

[sophiecentaur]

Can I make a general request that people do not talk in terms of "Photons interfering"? It can b e very confusing for someone new to the subject. The two concepts are from entirely different parts of Physics. Interference is a classical phenomenon and has to do with Waves. Photons are Quantum particles and are only relevant when discussing quantum phenomena. (But this is not really part of a discussion of 'stealth' methods).

 

[Claude Bile]

Can I make a general request that people do not talk in terms of "Photons interfering"? It can b e very confusing for someone new to the subject. The two concepts are from entirely different parts of Physics. Interference is a classical phenomenon and has to do with Waves. Photons are Quantum particles and are only relevant when discussing quantum phenomena. (But this is not really part of a discussion of 'stealth' methods).

Hi Sophiecentaur,

I can't agree with this statement I'm afraid. Interference is a key part of QM - perhaps the phrase "Photonic wavefunctions interfering" is better? In any case, particles interfering is quite an acceptable part of the QM lexicon :).

Anyway, to the OT at hand;

I find the idea quite interesting. Let's review how noise cancelling headphones work. They detect a sound (pressure) wave, then re-emit an inverted wave to cancel the sound. This is quite effective, even though the energy of the sound wave is being redistributed (as pointed out by many), it is being redistributed AWAY from you ear (i.e. your detector) and so the effect is quite convincing.

The main problem with doing this with light is that the phase of a light wave is much more difficult to detect and replicate - for two reasons;

- Light has a much higher bandwidth (i.e. it is faster) than electronic circuits, so you can't rely on electronics to "keep up" with the optical wave.

- Light is generally incoherent, meaning it doesn't have a well-defined phase and cannot easily be canceled out.

BUT, if you had a sufficiently fast detector, it might be possible? Certainly plausible enough for science fiction anyway...

Claude.

 

[sophiecentaur]

Hi Sophiecentaur,

I can't agree with this statement I'm afraid. Interference is a key part of QM - perhaps the phrase "Photonic wavefunctions interfering" is better? In any case, particles interfering is quite an acceptable part of the QM lexicon :).

Anyway, to the OT at hand;

I find the idea quite interesting. Let's review how noise cancelling headphones work. They detect a sound (pressure) wave, then re-emit an inverted wave to cancel the sound. This is quite effective, even though the energy of the sound wave is being redistributed (as pointed out by many), it is being redistributed AWAY from you ear (i.e. your detector) and so the effect is quite convincing.

The main problem with doing this with light is that the phase of a light wave is much more difficult to detect and replicate - for two reasons;

- Light has a much higher bandwidth (i.e. it is faster) than electronic circuits, so you can't rely on electronics to "keep up" with the optical wave.

- Light is generally incoherent, meaning it doesn't have a well-defined phase and cannot easily be canceled out.

BUT, if you had a sufficiently fast detector, it might be possible? Certainly plausible enough for science fiction anyway...

Claude.

Science Fiction that doesn't keep one foot on the ground can be a bit of a let-down. You just have to re-name it as fantasy fiction.
I still say that the concept of photons interfering is not meaningful - except in the very specialised conditions that Google throws up (in a very few relevant hits) and where the photons seem to have been generated by the same original source in the first place (afaics?) Whatever the facts are, about experimental evidence, it's certainly not 'interference as we know it'. All this (as ever) brings in the question about existence of photons except when they are actually detected. Where are the photons, for example, in a directional radio antenna array with multiple, independent but highly stable transmitters? If you want photons to exist as particles in their own right, I have to ask how they could differ from one another, according to their sources. Would they have different qualities that could be detected, for instance, in light received from a distant star? What extent / size would they have?
When you say that light has a "high bandwidth", I am not sure what you mean. There are many audio frequency sources with a wider (less well defined) bandwidth than the width of a spectral atomic emission line. A light source is usually made up of a large number of individual emitters (atoms) except in the case of a Laser, in which the stimulated emission causes the individual emitters to be phase coherent.

I think the notion of chasing individual photons and somehow producing another set of photons that could 'cancel them out' is really not worth considering - even in the context of SciFi.
I could also point out that any electronic circuitry which produces cancellation of audio signals will also involve Photons (just extremely low energy ones, associated with audio frequency AC signals). But it would be pretty futile to base any descriptions of the functions of an AC circuit at the 'photon level'.

Stealth techniques for eliminating radar reflections using active reflectors are perfectly reasonable - based on good-old classical wave techniques. Also, 'cloaking' techniques at optical frequencies come up in the press on occasions but they are usually over-cooked by the press afaics. There is a long way to go till Harry Potter stuff is available - if ever.

 

[Pgotthelf]

The concept of cloaking has already been demonstrated by bending light which is not the same as using destructive interference to eliminate light. However, Nikola Tesla demonstrated canceling light using a magnetic induction bulb all the way back in 1896. I doubt he canceled all the light in a defined space like a room, but he prove that the duel nature of light (wave and particle) did not foreclose destructive interference. For whatever it may be worth.

 

[Drakkith]

The concept of cloaking has already been demonstrated by bending light which is not the same as using destructive interference to eliminate light. However, Nikola Tesla demonstrated canceling light using a magnetic induction bulb all the way back in 1896. I doubt he canceled all the light in a defined space like a room, but he prove that the duel nature of light (wave and particle) did not foreclose destructive interference. For whatever it may be worth.

Please provide a reference for this.

 

[rumborak]

Many years back I remember asking a physics friend a similar question. The gedanken experiment was that you have two lasers, and you combine the output of the two lasers with (I guess?) a reverse beam splitter, but at pi phase offset. Now, the resulting beam would be no beam at all!
Apparently this was a common student exercise, and IIRC the outcome was that the energy would actually end up going backwards, essentially ending up inside the laser.

Many years ago, and many beers were involved. Mileage may vary.

 

[sophiecentaur]

Many years back I remember asking a physics friend a similar question. The gedanken experiment was that you have two lasers, and you combine the output of the two lasers with (I guess?) a reverse beam splitter, but at pi phase offset. Now, the resulting beam would be no beam at all!
Apparently this was a common student exercise, and IIRC the outcome was that the energy would actually end up going backwards, essentially ending up inside the laser.

Many years ago, and many beers were involved. Mileage may vary.

That's exactly what you would expect. It is easy to achieve cancellation of waves in one place or in one direction. Fact is that the energy never disappears, it just turns up in other places / directions. In your case, the beam splitting arrangement will end up directing all the power out of the 'other' port of your beam splitter. This effect of re-directing power happens with noise cancelling headphones. the extraneous sound level on the outside of the phones will be twice as high as when the phones are turned off.

 

[Science23413]

It's Possible. Light is an electromagnetic wave, which like radio waves can 'interfere' with corresponding waves. But the fact is that the speed and frequency of light makes it hard to not only cancel out, but to make a large differerence in the surrounding area. Light will only cancel out in the smallest fraction of a second, which can not be seen by human eyes.

 

[sophiecentaur]

It's Possible. Light is an electromagnetic wave, which like radio waves can 'interfere' with corresponding waves. But the fact is that the speed and frequency of light makes it hard to not only cancel out, but to make a large differerence in the surrounding area. Light will only cancel out in the smallest fraction of a second, which can not be seen by human eyes.

Cancellation happens in particular places and not at particular times. Interference of waves (light [EM], sound, water) produces 'fringes' where the waves augment and fringes where they cancel. You don't have to be 'quick enough' to spot it happening because the fringes stay where they are and are there all the time. The only thing about light that makes interference patterns 'hard' to produce is that the wavelength is short and the trains of waves from most sources are very short (many short bursts which are uncorrelated. I am not talking of Photons, here, BTW). You need coherent sources and a split laser beam is particularly suitable.
You should look up the basics of interference, which are well documented all over the place. 'Alternative' views are very confusing for questioners on PF.

 

[mfb]

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