3 ms·

For a transition of an electron between energy levels that emits a photon, should the time it takes for the transition be the same as the duration of the probab

by tlb 7y ago

For a transition of an electron between energy levels that emits a photon, should the time it takes for the transition be the same as the duration of the probability envelope of the photon? If so, that's easily observable by looking at the width of the spectral line. If the transition is fast, that implies a short duration and therefore the spectral lines should be smeared out.

lisper 7y ago
Yes, that is exactly right. All of this just boils down to the energy-time version of the uncertainty principle: the more precisely you can measure when a transition happened, the less certain you can be about the change in energy of that transition. Here is another example of this principle at work: http://blog.rongarret.info/2018/05/a-quantum-mechanics-puzzle.html http://blog.rongarret.info/2018/05/a-quantum-mechanics-puzzl... http://blog.rongarret.info/2018/05/a-quantum-mechanics-puzzle-part-deux.html http://blog.rongarret.info/2018/05/a-quantum-mechanics-puzzl... http://blog.rongarret.info/2018/05/a-quantum-mechanics-puzzle-part-drei.html http://blog.rongarret.info/2018/05/a-quantum-mechanics-puzzl...
- effie 7y ago
  What you're saying about uncertainty principle is strange. The principle says the longer the transition takes, the sharper the spectral line can be (but does not have to be, hence the inequality). There is nothing about uncertainty of measurement of time of some point event. The transition is not a point event. If the two states involved in the transition are known, then change of energy is known. How long the transition will take depends on strength and frequency characteristics of the external field, but the energy difference of energy of the molecule after the transition is over does not depend on that.
  - lisper 7y ago
    Yes, everything you say is correct. That's exactly what makes this experiment so interesting. They didn't just measure the energy state at one time and then again at another time. That wouldn't work (because of the quantum Zeno effect).

by tlb 7y ago

lisper 7y ago

Yes, that is exactly right. All of this just boils down to the energy-time version of the uncertainty principle: the more precisely you can measure when a transition happened, the less certain you can be about the change in energy of that transition. Here is another example of this principle at work: http://blog.rongarret.info/2018/05/a-quantum-mechanics-puzzle.html http://blog.rongarret.info/2018/05/a-quantum-mechanics-puzzl... http://blog.rongarret.info/2018/05/a-quantum-mechanics-puzzle-part-deux.html http://blog.rongarret.info/2018/05/a-quantum-mechanics-puzzl... http://blog.rongarret.info/2018/05/a-quantum-mechanics-puzzle-part-drei.html http://blog.rongarret.info/2018/05/a-quantum-mechanics-puzzl...

effie 7y ago
What you're saying about uncertainty principle is strange. The principle says the longer the transition takes, the sharper the spectral line can be (but does not have to be, hence the inequality). There is nothing about uncertainty of measurement of time of some point event. The transition is not a point event. If the two states involved in the transition are known, then change of energy is known. How long the transition will take depends on strength and frequency characteristics of the external field, but the energy difference of energy of the molecule after the transition is over does not depend on that.
- lisper 7y ago
  Yes, everything you say is correct. That's exactly what makes this experiment so interesting. They didn't just measure the energy state at one time and then again at another time. That wouldn't work (because of the quantum Zeno effect).