English: Diagram of gravitational lensing (deflection of light by an intervening mass) with formula of Einstein on a wall of Museum Boerhaave, Leiden (the Netherlands). Painted by Stichting Tegenbeeld. ${\displaystyle R_{\mu \nu }-{\textstyle 1 \over 2}R\,g_{\mu \nu }+\Lambda \ g_{\mu \nu }={\frac {8\pi G}{c^{4}}}\,T_{\mu \nu }}$. The line sketched is in fact a Morse code.