# Expectation value of the expectation value

1. Sep 28, 2011

### jinksys

1. The problem statement, all variables and given/known data
The expectation value of the position observable x is <x> = ∫ψ*xψdx. The expectation value of the expectation value, <<x>>=<x>, is still the expectation value...why?

2. Relevant equations

3. The attempt at a solution

All I can think of is that the expectation value is essentially an average, and the average of an average is the original average.

i.e.) A={2,8} The average is (2+8)/2 = {5}
The average of {5} = {5}.

2. Sep 28, 2011

### dextercioby

The expectation value is a number which <comes out> of the integral of the expectation value of the the expectation value.