# Feynman and gauss integral

1. Feb 10, 2010

### ibmichuco

Hi all,

This is just wild shot, since my memory is not what it used to be ...
fact, that the integration of the gaussian function

\int_-\infty^\infty e^(-x x) dx = \sqrt[\pi]

has to do with Pi. He then went on to show the connection. I
couldn't find out if this is in one of his Lecture books or his
autobiography. I could find out where he mentioned the
connection between exp and trig functions, but that was as far
as I could go.

I am not even sure that it was Feynman.

Michuco

links that have to do with his path integral.

2. Feb 11, 2010

### torquil

This is true, but this was known for a long time before Feynman. It can be shown like this:

Multiply two such gaussian integrals together. Combine them into one two-dimesional integral. Change to polar coordinates. Then both the angular and radial parts are easy to calculate. The result of this is pi. Since it was the square of the original integral, the answer is sqrt(pi).

Torquil

3. Feb 11, 2010

### Matterwave

I believe this is what you're talking about:
http://en.wikipedia.org/wiki/Gaussian_integral

The integral of a Gaussian is sqrt(pi). The computation is explained in that article also.

4. Feb 11, 2010

### ibmichuco

Thanks for the replies. I know of the polar coord conversion proof which I asume that wiki took from Weinsstein's MathWorld. I was wondering about the Feynman connection, if there
was one.

Regards,

Michuco

5. Feb 18, 2010

### codelieb

See The Feynman Lectures on Physics, Vol I, section 40-4, "The distribution of molecular speeds," unnumbered equation between Eqs. (40.7) and (40.8).

6. Feb 18, 2010

### ibmichuco

Thanks codelieb,

This is exactly what I was looking for ...

Michuco

7. Feb 18, 2010

### codelieb

You're welcome.