There's several ussues with this argument:<p>- If the interference pattern was explained by diffraction by a semi-infinite plane, why don't I see it when using only one finger? I only see a blurry shadow. The second finger is needed to make the pattern appear.<p>- All formulas that are used compute the light intensity projected on a screen. In the actual experiment, we're looking at the slit through a lens (our eye or a camera). That's not the same thing.<p>- The fact that this is white light interference is handwaved away. To model it correctly, you'd need to compute what happens at each wavelength, then integrate the resulting spectrum multiplied by CIE's x, y z functions at each point, and finally do a bunch of math to bring that in the sRGB color space if you want to display the model's result on a screen.
-I do see it on the edge of a single finger.<p>-I agree, also I can only observe the effect when focusing on the gap<p>-sure, but weirdly the effect has to be wavelength dependent, but there are no color fringes.<p>I think this is something else, but haven't figured it out yet.
Interesting, I can only see the bands when holding my fingers very close to my eye, and _not_ focussing on it. If I hold my fingers far enough to be able to focus, I don't see them. Maybe my eyesight is not good enough. Focussing on a single finger, I see that the border has a green tint to it.<p>I agree that there's no colour in the fringes, which is unexpected for white light interference.