Shadow on Wall: Light Blur from Wave or Quantum?

[xzardaz]

Hello,

As we know, if one turn a light blub(and no other light is present) on and put his hand in front of a wall to make a shadow, the shadow is blurry, depending on the distance between the hand and the wall.

I want to ask you if this blur is caused by quantum uncertenty (like this experiment), or it is just a consequence of the wave nature of light ?

 

[michael879]

Any observable blurriness is caused by the fact that light sources aren't point sources. So if you draw it out, there will be a region where the light is partially obscured by ur hand, causing the blurriness

 

[tiny-tim]

hello xzardaz!

… if this blur is caused by quantum uncertenty (like this experiment), or it is just a consequence of the wave nature of light ?

neither … it's caused by the fact that the bulb isn't a point source

so the shadow has an "umbra" and a "penumbra", to use solar eclipse terminology

the "penumbra" is the blurry bit

(if you place a screen in between, with a pinhole in it, so as to produce an effectively point source, then the umbra would disappear, but there would be fringes round the edge of the shadow)