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

Homework Help: Heisenberg uncertainty principle (simple stuff)

  1. Apr 14, 2006 #1
    I'm having a little trouble with my textbook's explanation. This is regarding the energy - time variation of the uncertainty principle; very basic stuff, so I hope helping me out won't take too much. Let me quote exactly:

    "... the energy conservation can appear to be violated by an amount delta E, as long as it is only for a short time interval, delta t, consistent with the equation (delta E) * (delta t) >= (h / 4 pi )"

    I understand what is being said - and it makes sense. Otherwise we'd all be noticing these 'violations' of energy conservation.
    But I don't see how it is 'consistent' with the equation. Why must delta t be small? To me, it seems more 'consistent' with the equation that delta t is large, so that the equation becomes greater than h/4pi.

    Someone please help clarify. And thanks for your time.
     
  2. jcsd
  3. Apr 15, 2006 #2
    (deltaE)*(delta t) is always greater than " ". Think about it this way: If you take more measurements (greater accuracy-much data) over a longer time, say for a single body whose energy is conserved, then the uncertainty in energy tends toward zero. So, if you make a quick (inacurate-few data points) measurement the uncertainty in energy is high. This could lead you to believe that the energy was not conserved. Atleast, I think that was the point the book was trying to make.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook