Question

proof of the fact that light travels in a straight lime?​

Answer 1

Shadows are evidence of light travelling in straight lines. An object blocks light so that it can't reach the surface where we see the shadow.

Answer 2

Diffraction is the effect which causes light to change path when it meets obstacles. But as diffraction effect is very small light travels in straight line .

proof:::-

If two pin-holed cards align against light source light passes through it otherwise it gets obstructed by the card. This simple experiment demonstrates the straight line travel of light. This is attributed to wave and photon nature of light.

Some times light travels not in straight line, it bends around edge of an object (it is called diffraction). This is attributed to the wave nature of light.

hope it helps