A friend of mine made a mistake one of these days by saying that human bodies absorb light . This got me thinking what if that were true, how would we look, some black shades or some blurry image of the background. I'd like to hear your opinion on this matter .

 

All the best:D

 

 

P.S. Sorry if there is any other thread like this one

A friend of mine made a mistake one of these days by saying that human bodies absorb light . This got me thinking what if that were true

I'm not sure I follow your question. Light hitting the skin releases vitamin D, UVs cause tanning, light hitting the retina in our eyes results in firing of optical nerves and signals in the occipital cortex... aka, vision. What do you mean "human bodies absorb light" and what is it exactly that you think your friend is wrong about?

Well we see objects ( including human bodies ) because they reflect light, well at least that's what I've been taught .

 

Take this example:

Basically radars work as human eye they send radio Frequency waves, or whatever wave they send they send, and when the RF hits something it returns back showing the position of the aircraft. The F117 Plane does not reflect this wave and thus it remains undetected, unseen by the radar. Now I mean what if human bodies do not reflect the light that hits them.

 

Maybe It was my mistake mentioning the light absorption because bodies tend to do that. What I meant was not reflecting the light.

What I meant was not reflecting the light.

 

I see. You are referring to a human as a "blackbody." I'm pretty sure this is not possible, so theoretically speaking only, they would appear pitch black. Basically, all incoming radiation is absorbed, which is why it appears black.

 

http://hyperphysics.phy-astr.gsu.edu/hbase/mod6.html

 

 

As to how "sharp" the image of them would be, and if their edges would appear "fuzzy," I really don't know, and that's an interesting question.

 

 

 

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\Basically radars work as human eye they send radio Frequency waves, or whatever wave they send they send, and when the RF hits something it returns back showing the position of the aircraft. The F117 Plane does not reflect this wave and thus it remains undetected, unseen by the radar.

Also, just to clarify this point, stealth technology tends to be a combination of 1) absorption of the radar signal, and 2) reflecting it in other directions.

 

http://science.howstuffworks.com/question69.htm

a black body as sharply defined boundaries just like any other object. (if one can be made)

 

if you look at a cold, black-body-object, it looks jet black (\emphasis on jet black), any light you can see was reflected or made between you and it.

we do absorb light. just not all of it. if we reflected all light we would make albinos look as if they had a very very good tan.

Just a minor point. If we absorbed all light (i.e., were a blackbody), we would still give off some light. Even now we emit radiation, almost all of it in the infrared, but a tiny amount in the visible spectrum as well.

Not so minor a point, though. A blackbody is not only a perfect absorber of radiation, it is also a perfect emitter. As it is, the average person emits around 100W, peaked in the IR around 10 microns.

 

http://en.wikipedia.org/wiki/Black_body#Radiation_emitted_by_a_human_body

Well guys to make thread more interesting why don't we continue this "what if ..." thing. It would be interesting to use imagination in a science forum

science wouldn't exist without imagination. quantum mechanics in particular. we just term it speculation. you'd be amazed at what scientists have imagined up. look at string theory, quantum mechanics, relativity. lots of wacky stuff going on there.

science wouldn't exist without imagination. quantum mechanics in particular. we just term it speculation. you'd be amazed at what scientists have imagined up. look at string theory, quantum mechanics, relativity. lots of wacky stuff going on there.

 

You just have to remember that you have to be able to test it, eventually, if you want to call it science.

 

 

If you want to make something invisible, you can't let it absorb or reflect back to the observer. You can have absorption if you want to make something invisible in a certain band (i.e absorb visible and emit IR). But then you can tell something is there because the background has gone away, so you have something that's visible by the contrast it produces.