$x(t)=\int_{-\infty} ^{\infty} X(jw)e^{jwt}dw$.
Where $X(jw)$ is the fourier transform of $x(t)$.
What is $|x(t)|^2$?
Can I say, it is $|\int_{-\infty} ^{\infty} X(jw)e^{jwt}dw|^2$, which is again, equal to $\int_{-\infty} ^{\infty}| X(jw)|^2|e^{jwt}|^2dw$= $\int_{-\infty} ^{\infty} |X(jw)|^2dw$
Is this valid?