56 The solution set of the inequality $\sqrt{1-x^{2}} \geqslant x+t$ is an empty set, the range of real number $t$ is $\qquad$
$56 t \in(\sqrt{2},+\infty)$. Since $\sqrt{1-x^{2}}-x \leqslant \sqrt{2\left(1-x^{2}+(-x)^{2}\right)}=\sqrt{2}$, when $x=$ $-\sqrt{\frac{1}{2}}$, $\sqrt{1-x^{2}}-x$ reaches its maximum value $\sqrt{2}$.