I've already made a post about this topic here, but I realized that I didn't understand the explanation on that post. in Chapter 7 of Rindler's book on relativity, in section about electromagnetic field tensor, he states that
and introducing a factor 1/c for later convenience, we can ‘guess’ the tensor equation, $$ F_\mu= \frac{q}{c} E_{\mu \nu} U^\ \nu$$$$ F_\mu= \frac{q}{c} E_{\mu \nu} U^\nu$$ thereby introducing the electromagnetic field tensor$$E_{\mu \nu}$$ We would surely want the force $F\mu$ to be rest-mass preserving, which, according to (6.44) and (7.15), requires $$F\mu U^\mu = 0$$$$F_\mu U^\mu = 0$$. So we need $$E_{\mu \nu} U^\mu U^\nu = 0$$ for all $ U^\mu$ , and hence the antisymmetry of the field tensor $$E_{\mu \nu}= −E_{\nu \mu}$$\
. . . I'm really confused about the correct way to show that the equation $E_{\mu \nu} U^\mu U^\nu = 0$ implies the fact that $E_{\mu\nu}$ is antisymmetric tensor. What is the correct demonstration of this implication?
OBS: i've e saw some posts answering this kind of question with bilinear maps notation, instead of component notation. If possible, please make some demonstration using the index notation as in the post.