When you look at a spoon why is your reflection upside down?

Asked by: J. Been

Answer

Light rays travel in a straight line until they hit something. A light ray comes straight back only when it hits an object dead on. If the surface of the object is slanted relative to the light, it will cause the light to be reflected at an angle. So, a spoon's surface is curved, both from top to bottom and side to side. And all the light that enters our eye does so in the same direction (we'll call it the horizontal direction). Light from our toes hits the top of the spoon and, because of it's 'downward' slant, gets redirected horizontally. And only light from our head gets reflected horizontally from the bottom of the spoon. Since what we see is WHERE the light came from, we see our toes above our head!

<------+\   Horizontal light hitting a slanted

<------++\   surface goes down... or upward moving light 

<------+++\   goes left!

        /

       VVV



Light from Head

           \

             \     _

eye-toe  --\---\\

eye           X  //

eye-head-/---//

             /    //

           /      //

         /        //  This

 Light          // is a

 from         LJ  Spoon!

 Toes

Answered by: Daniel Kurtz, B.S. EE, Cornell University