If two EM waves 180 deg. out-of-phase meet in a vacuum they would cancel out...?

Question

1. Where would the energy go?
2. How would you explain the result using photons?
Take a look here before answer:
http://answers.google.com/answers/threadview?id=770451
http://www.advancedphysics.org/forum/showthread.php?t=2459

Answer 1

You already received a good answer to this from _mark_ in Birmingham, so I'll make some statements based on his answer.
Also the answer from cosmo just above is good.

1. a)
With electromagnetic waves of the same wavelength, traveling in the same direction, where the E-fields are parallel - have the same amplitude - and the phase is shifted by 180° - they cancel out. Strangely, there is no energy there. This phenomena is used in "flat" unidirectional transmitters (I'm not sure if the name is correct): in one direction the waves add up and in the other direction the waves cancel out and no transmission takes place in the latter direction.
1. b)
With electromagnetic waves of the same wavelength, traveling in a similar direction, where the E-fields are parallel and the phase is shifted by 180° - they cancel out in the places where the E-Fields have the same amplitude. There is no energy in those places!
2.
Photons are usually only treated as particles when they interact with matter. Concerning the propagation of a photon, it is usually considered to be an electromagnetic wave. Thus, they can also cancel out. This phenomena is called "interference" of light. It is really so, that no photons will interact with matter in the areas of cancellation... so there is really seemingly no energy in those points.

About the B-Field: It is perpendicular to the E-Field and not phase shifted to the E-Field. Therefore, what applies to E "mainly" (only mainly) also applies to B, so I did not mention it above.

Your questions are really good ones when you think about it. How can two waves - both with energy - pass each other and there be no energy in some areas where they are passing? It's strange....

Answer 2

EM waves, being waves, are not localized. They have both location and direction. For waves to cancel completely over a large volume, they would have to have to have the same location and direction---they would be in the same state, and any accounting for the energy would have to include the source of the wave, i.e. the boundary conditions of the state.

If the two waves have opposite phase and identical amplitude at one point in space, then they cancel at that one point. The energy goes into the wave at other locations, where the waves combine constructively.

Photons are particles whose dynamics are determined by the photon wave function. The photon wave function behaves like classical EM waves, so as to make the observed density of photons equal to the classical energy density.

Answer 3

it is true for the length between the two sources but not out of them.End the energy wouldn't dissapear but would create an enregy line going through the sources.You can't explain this effect with the crepuscolar method it's a wave and must be seen as a wave.The duality of light says that it sometimes behaves as particel and sometimes as wave but not at the same time.

Answer 4

yes the waves would cancel out at that point
the energy goes nowhere it just continues on


photons are completly different to waves


you are asking a question like how do i start a car with a duck flying east!