When you let two fingers touch in front of your eye and but focus on the background, why does it look like they are merging or ‘building a bridge between each other’ before they physically touch?
In: Physics
Oh my god you put it into words! I’m not an expert in opthalmology but I think it’s to do with how the blurred edges of the fingers merge creating an overlap in the blur, therefore making the blur more opaque. Regarding the “bridge building”, I think what you’re seeing is your fingers touching ever so slightly but not enough for you to feel it so you think it’s just merging together. I hope this helps!
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The phenomenon you are discussing is called Diffraction. The ELI5 is basically you are seeing your fingers touch because of the way the light is being squeezed between the tiny space.
For a more thorough explanation check out this 4 year old askscience post
When I hold two fingers together and look through the narrow slit between fingers I am able to see multiple dark bands in the space of the slit. I read once long ago that this demonstrates the wavelength of light. Is there any truth to this? If not, what causes those dark bands?
byu/jackelfrink inaskscience
The effect is caused by parallax. This happens because both eyes are each seeing a finger overlapping the background. The left eye is seeing your left finger, and your right eye is seeing your right finger. Your brain doesn’t receive any “background” information for that part of the scene, only “finger” information, so it merges the two “finger” parts into the floating hot dog illusion.
It has to do with the way the eyes work together. When looking far away (at the background), the eyes move apart so they’re both pointing toward the same thing. When you look close up, the eyes normally move in toward your nose so they’re both pointing at the same point close up. (Imagine drawing a line from each eye to a point up close and to a point far away,. The lines going to the far away point will be farther from your nose, whereas the lines going to the closer point will be closer to your nose).
When you focus on the background, your eyes see your fingers as double (try this with one finger instead of two) you’ll see two fingers. The reason is that your eyes are turned out (away from your nose) to look at the same spot in the distance but your up-close finger ends up double because both eyes are not pointed toward it so each eye perceives the finger to be in a different spot. With both fingers up, you get a double image of both fingers (ie 4 fingers – two real a s two double images). The double image of one finger overlaps the opposite real finger and you get a finger bridge.
If you try the same thing you describe but with one eye closed, you’ll see blurry fingers but you won’t see a finger bridge because you’re not getting double finger images.
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