1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Destructive interference and energy

  1. Oct 10, 2015 #1
    Where do the energy go in a pair of photons that are annihilating each other exactly? What happens when they collide with something that absorbs photons like an electron? (I think electron can absorb the e. in a photon to jump into a higher level) Would this light wave become undetectable like destructively interfering sound?

    I was thinking in the context of a laser beam, suppose light waves of various frequencies are sent, the beam may be less "powerful" because of interference, or so I heard.
  2. jcsd
  3. Oct 10, 2015 #2


    User Avatar

    Staff: Mentor

    Destructive interference creates areas of zero light intensity (the dark regions in a classical interference patterns), but there are also areas of constructive interference (the bright regions in the pattern) where the intensity is greater than it would otherwise be. The two effects balance so the total energy is conserved.

    None of this has anything to do with photons, which don't annihilate each other when the interfere.
  4. Oct 11, 2015 #3


    Staff: Mentor

    The only way for that to happen is for them to produce a pair of particles (one is the anti-particle of the other). The photon energy goes into the mass of the pair.

    This is extremely unlikely and requires very high energy photons. It is not related to interference of visible light.
  5. Oct 11, 2015 #4
    Said in this way could seem that "the photons energy disappear and is transformed in something else", which is false. The energy stay the same. Better to say that 2 particles transform in other 2 particles.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook