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

The speed of light and the uncertainty principle

  1. May 13, 2006 #1
    The heisenberg uncertainty principle says that

    h-bar/2 <= dE * dt.

    Let's say we have this device that emitted very low energy radio waves. Does that mean there'd be a significant probability of these photons traveling faster than light?
     
  2. jcsd
  3. May 13, 2006 #2

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Last edited: May 13, 2006
  4. May 14, 2006 #3
    It's more subtle than that. We can show from general principles that

    [tex]\frac{\Delta A}{|d\langle A\rangle/dt|}\Delta E \ge \hbar/2[/tex]

    If we now define the bit on the left as [itex]\Delta t,[/itex] we get the oft-quoted uncertainty relation between time and energy.

    The justification for making that identification is that it's the average time taken for the expectation of the operator A to change by its standard deviation, so it's roughly the time scale to measure a change in A.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?