What makes expectation values real?

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SUMMARY

The discussion centers on the mathematical foundation ensuring that expectation values in quantum mechanics, specifically momentum, are real-valued. It highlights the role of self-adjoint operators, represented by ##\hat{p}=\hat{p}^{\dagger}##, in maintaining the reality of the expectation value. The equation $$\langle \psi|\hat{p} \psi \rangle^*=\langle \psi|\hat{p}^{\dagger} \psi \rangle = \langle \psi|\hat{p} \psi \rangle$$ confirms that the expectation value is indeed real, despite the complex nature of the integral components.

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  • Understanding of wave functions in quantum mechanics
  • Knowledge of self-adjoint operators
  • Familiarity with expectation values in quantum theory
  • Basic proficiency in complex numbers and integrals
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TEFLing
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If you have some wave function of some particle, say...

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And you calculate the expectation value of momentum, say...

<¥|p|¥>

What ensures that that spatial integral is real valued?

Separately, all the components of the integral are complex valued
 
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The operators, representing observables, are usually assumed to be self-adjoint, i.e., ##\hat{p}=\hat{p}^{\dagger}##. Now you have
$$\langle \psi|\hat{p} \psi \rangle^*=\langle \psi|\hat{p}^{\dagger} \psi \rangle = \langle \psi|\hat{p} \psi \rangle,$$
which implies that the expectation value is real.
 
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