Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Reflection and the measurement, and time irreversibility

  1. Dec 15, 2008 #1
    Reflection is not considered to be a measurement. Reflection, like using lenses is considered to be a time-reversible process. It is not a measurement and it does not erase the coherence (interference pattern)

    Here is what I dont understand

    What happens to the momentum of the photon? The light pressure? If I put a mirror (flying in a zero gravity and vacuum) right behind 2 slits, mirror will start rotating very slowly in a different directions depending on the path of the photon

    Where is a flaw?
  2. jcsd
  3. Dec 15, 2008 #2


    User Avatar
    Science Advisor

    If you can measure the mirror's momentum well enough to detect which slit the photon went through, the posistion will be uncertain enough to destroy the interference pattern.
  4. Dec 15, 2008 #3
    My mirror is flying in the empty space. If it is hit by 1 photon, it begins to rotate making 1 full rotation per 1 year. So I make an experiment and decide to check the position of a mirror 3 month later. What is going to happen to the interference pattern?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook