Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

In book "Quantum Mechanics and Path Integral", 3-2 Diffraction through the slit:

Under the fig. 3-3, why did Feynman say that we cannot approach the problem by a single application of the free-particle law motion, since the particle is actually constrained by the slit?

And why Feynman use Gaussian slit?

share|cite|improve this question
up vote 1 down vote accepted

I don't have a copy of the book, so can't comment on the Gaussian slit, but you can't use the free particle propagation equation in the presence of a slit, because the slit (a conventional slit) can be modelled by a rectangular shaped potential function. Straightforward free particle propagation only applies when the potential function vanishes, so is inapplicable here.

For anyone else who may not have the book, Feynman's original paper has a very readable treatment of the path integral and is available here.

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.