Where does the waves energy go when destructive interference occurs?

In summary, when two light waves completely cancel each other out, there is an absence of light in some regions and an increase in light intensity in others, demonstrating the principle of interference. This does not violate the law of conservation of energy, as the energy lost in the destructive regions is transferred to the constructive regions. However, in cases where photons are destroyed through interference, such as in photon absorption or sound cancellation, the energy is transferred to the absorbing material or dissipated as heat. Further experimentation is needed to fully understand the mechanisms at play in these situations.
  • #1
gillwill
10
0
For example, when two light waves completely cancel each other out, there is the black on an interference pattern, indicating absence of light.

What happens to the photons? It seems they cease to exist.

Also, How does this relate (or not) to the "Conservation of Energy" law?

Any insights appreciated.

-Gil
 
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  • #2
Two light waves cannot completely cancel each other out.It's true that there are regions where there is an absence of light ,the so called regions of destructive inerference but these are accompanied by regions where the light is more intense the so called regions of constructive interference.The energy lost in the destructive regions has been shifted across to the constructive regions and as usual energy is conserved.
 
  • #3
OK, thanks for the info.

To expand on this: what about just two individual photons destructively interfering with each other in a confinement or vacuum?

And making things even more confusing to me, the event of a single photon interfering with itself.
 
  • #4
gillwill said:
OK, thanks for the info.

To expand on this: what about just two individual photons destructively interfering with each other in a confinement or vacuum?

According to Heisenberg, photons don't have position. While they're on the fly, it's best to visualize them as a wavefunction, not as little grains. Or... by QED, an infinite number of virtual photons take all possible paths, where some cancel after superposition and others reinforce.

Back to your original question. During absorption of radio waves, the receiving antenna emits a wave out of phase with the incoming wavetrain. The two are superposed and produce an interference pattern having a central node. This produces a downstream shadow in the electromagnetic wavetrain. Net energy goes missing. This energy winds up in any resistive load attached to the antenna terminals (or it ends up in the receiver front-end transistor.)

The above is a case where photons were destroyed by interference and not simply moved around as a diffraction pattern.

From a semi-classical standpoint, the above antenna description might apply to photons being absorbed by atoms. However, I've not yet encountered any text which describes it this way. Suppose the atom emits a wavetrain which superposes with the incoming wavetrain (both having the same wavelength.) An interference pattern is produced, a pattern with a central node. The atom casts a shadow, and the missing energy ends up driving an electron to a different orbital. Pretty cool, eh? But not necessarily matching reality!
 
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  • #5
While I don't think wbeaty's explanation is incorrect, I'll just say that I don't like the description of "energy going missing" and all that. The energy in a photon is transferred to whatever absorbs it. Whether that is by emitting an out of phase wavetrain or whatever, is beyond me.
 
  • #6
I go along with Drakkiths description in that the "energy in a photon is transferred to whatever absorbs it".If photons are sent one at a time through a Youngs slit arrangement then these photons will be detected one at a time at the screen/detector.As time passes the overall pattern observed approaches that of the standard "Youngs fringes pattern" observed with a more intense light source.The end results are pretty much the same but when separate photons are considered the analysis looks at the probabilities of each photon arriving at a particular location.
 
  • #7
Drakkith said:
While I don't think wbeaty's explanation is incorrect, I'll just say that I don't like the description of "energy going missing" and all that.

Say it this way then: During absorption, the EM-wave energy goes missing.

Hmmmm. Actually what has vanished is the Wakalixes! :) (re. Feynman chapter "Judging books by their covers!")

Acoustic version: the sound goes missing. Optical version: the light goes missing. It's destroyed upon absorption.
 
  • #8
Missing implies that you don't know what happened to it in my opinion, hence why I don't like that term.
 
  • #9
I've seen a polarized beam of coherent light split and recombined out of phase and canceled out without constructive interference.
Physisists like to cling to the notion that energy can't be destroyed because if not they would have to admit it could be created and everything we "know" might be wrong...
 
  • #10
hintzofcolor said:
I've seen a polarized beam of coherent light split and recombined out of phase and canceled out without constructive interference.
That can only happen in the presence of matter, in which case the energy goes into the matter.
hintzofcolor said:
Physisists like to cling to the notion that energy can't be destroyed because if not they would have to admit it could be created and everything we "know" might be wrong...
Because of that and also because there is no evidence to support the notion that it can be destroyed and plenty of evidence to support the notion that it can't.
 
  • #11
The energy of the canceled photons could become bosons or quarks or some other type of tiny particles. But a similar experiment in water waves illustrates that the waves can be canceled out complely by adding additional energy to a wave to completely eliminate it.
 
  • #12
Please post a credible reference or stop speculating. What you describe cannot happen without an interaction with matter where the energy goes.
 
  • #13
Bose sound cancellation head phones are a great example of using energy to cancel out unwanted waves.
I've demonstrated this personally in a wave tank full if water and seen it demonstrated with an interferometer.
 
  • #14
Do you have any reference which has done a careful measurement of the energy of a Bose headset and found that energy was not conserved? If not then it is safe to say that the headset either causes constructive interference elsewhere or acoustic energy goes into the headset itself and is dissipated there.
 
  • #15
In the case of the sound cancelling headphones, so called "experts" blindly claim the energy is converted to heat and dissipated, but this is not the case.
When conducting similar tests on waves through other mediums such as water or light the heat generated comes no where near the amount of energy lost when destructive interference occurs.
Rather than looking for refferences, I suggest conducting experiments to witness the results yourself as I have.
 
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  • #16
DaleSpam said:
Do you have any reference which has done a careful measurement of the energy of a Bose headset and found that energy was not conserved? If not then it is safe to say that the headset either causes constructive interference elsewhere or acoustic energy goes into the headset itself and is dissipated there.

I agree. Here's their description - this is a summary of a 6 page explanation.

http://electronics.howstuffworks.com/gadgets/audio-music/noise-canceling-headphone5.htm
 

Related to Where does the waves energy go when destructive interference occurs?

1. Where does the energy go in destructive interference?

In destructive interference, the energy from the waves is dispersed and does not accumulate in any specific location. It is essentially cancelled out by the overlapping of two waves with opposite amplitudes, resulting in a decrease or complete cancellation of the overall energy.

2. Does destructive interference cause the waves to disappear?

No, destructive interference does not cause the waves to disappear. The individual waves still exist, but their energies cancel each other out, resulting in a decrease or complete cancellation of the overall wave energy. The waves will reappear once the interference is no longer present.

3. What happens to the energy when two waves with equal amplitudes interfere destructively?

When two waves with equal amplitudes interfere destructively, the energy from both waves is completely cancelled out. This results in a complete cancellation of the overall energy, resulting in a flat line or no wave at all.

4. Does the energy from destructive interference transfer to other waves?

No, the energy from destructive interference does not transfer to other waves. It is dispersed and essentially "lost" as it is cancelled out by the overlapping of the two interfering waves.

5. Can destructive interference occur in all types of waves?

Yes, destructive interference can occur in all types of waves, including electromagnetic waves, sound waves, and water waves. It is a natural occurrence that happens when two waves with opposite amplitudes interfere with each other.

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