So, I've found the result that orthonormal sequences in Hilbert spaces always converge weakly to zero. I've only found wikipedia's "small proof" of this statement, though I have found the statement itself in many places, textbooks and such.(adsbygoogle = window.adsbygoogle || []).push({});

I've come to understand that this property follows from the Bessel inequality, and I've worked out many of the details, so I feel that I understand the Bessel inequality itself quite well. What I don't get is how the inequality gives us the weak convergence - the proof on wikipedia only states that "Therefore, [tex] |\langle e_n, x \rangle |^2 \rightarrow 0 [/tex]" after stating the Bessel inequality. It doesn't make sense to me - how is this information gleaned?

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Weak convergence of orthonormal sequences in Hilbert space

**Physics Forums | Science Articles, Homework Help, Discussion**