Why does my finger bend light?

If I place a finger real close to my eye, why do I see as if my finger is bending light? Also, if I put 2 fingers very close to my eye and I put these fingers close (not together), why do they seem like to blend together, even when they're not touching?

Update:

Yes, I was referring exactly to what you said, Jeff. Axdotman probably misinterpreted what I said :S

Update 2:

Yes, I've also noticed seeing the light spectrum when doing this even with a finger!

2 Answers

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  • Jeff
    Lv 5
    1 decade ago
    Favorite Answer

    you are seeing some of the effects of the wave nature of light. Light does bend around obstructions slightly, just as all waves do. This is called diffraction. It's why you can hear someone calling you even when they are around a corner (sound waves bend around a corner). These effects are proportional to the size of the wave, which is very small for light. For this reason, you do not see diffraction of light except on very small scales, like when things are very close to your eye, or when you look through a microscope. The same thing happens when light tries to fit through a very small slit--when that slit gets close to the distance of a wavelength of light, then suddenly it diffracts a whole bunch--I think this may be what is making it look like your fingers are touching before they actually do.

    There are also some physics of lenses that can make out-of-focus images do weird things, like shift direction and such when partially blocked, so this can also account for some of the apparent "bending" of light that you observe. But I have done the same as you and spent many hours observing things in front of my eye and small slits and point sources of light and such and I have observed a myriad of light wave phenomena. It is amazing that this was not used in the early days for the proof that light is a wave. The experiments are very easy to do with your eye using points and slits and blocking parts of light sources, but the experiments are very difficult to do with candles and projection screens, which is what folks like Newton had back in the olden days and it took them a long time to prove the wave nature of light.

    Edit: I hadn't thought of what axdotman is referring to. are your referring to the "phantom" image of your fingers due to your two eyes, or are you referring to the blurry images that you see when only looking through one eye? If you are just using one eye, then it's more likely diffraction. if you are using two eyes, then there are many more possibilities. I'll give you an experiment to play with if you really are looking at diffraction. you get much more interesting diffraction effects if you work with coherent light such as from a laser or a point source. To make a point source, get a ball bearing with a reflection of the sun with a dark background, or use a piece of foil with a teensie pinhole in it and have the point source far away. Then look at what happens when you look at the point source and move your finger in front of your eye, then pinch two fingers together, then hold a hair right in front of your eye so that it tries to block the point source. Each one of these will yield really cool results--similar to the bending you observed earlier, but even more extreme results and sometimes with a rainbow of colors due to the coherent source.

  • 1 decade ago

    It has to do with the fact that you have two eyes. For the light "bending" around your finger, that's the result of you having two eyes and each can see behind the finger at a certain angle. So if you see something that's behind your finger, you might interperate that as light bending even though it is traveling in a straight path.

    As for the two fingers blending, that is a similar effect. Because at very close distances each individual eye works more by itself then as a pair, each sees the fingers in a location. The eyes see the finger in about the same location and your brain interperates the rest.

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