Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: chintan on 02/12/2015 20:05:12

Title: Does a perfect blackbody exist?
Post by: chintan on 02/12/2015 20:05:12

Is there anything like perfect blackbody which absorbs light completely and reflects nothing  [???]

Title: Re: perfect blackbody?
Post by: Joe Boboblob on 02/12/2015 20:31:27

Vantablack absorbs 99.96% of light. That's pretty damn close. It appears 2D to the human eye, and it's created with carbon nanotubes.

There are also black holes :D

Title: Re: Does a perfect blackbody exist?
Post by: chris on 02/12/2015 23:54:47

I think someone recently invented an even blacker black. This one uses gold nanoparticles and nanorods, which interfere with the incident radiation of different sizes and absorb the energy, meaning that even less radiation is reflected.

So, essentially, black just got blacker...

Title: Re: Does a perfect blackbody exist?
Post by: RD on 03/12/2015 02:08:53

Quote from: chintan on 02/12/2015 20:05:12

Is there anything like perfect blackbody which absorbs light completely and reflects nothing

A "perfect blackbody" would absorb radiation at all wavelengths, including those invisible to the human-eye, e.g. Infra-Red,  Ultra-Violet, Radio-Frequency, X-Rays, etc. So "perfect blackbody" an idealized concept, not existing in reality , ( like frictionless mechanisms ).

Title: Re: Does a perfect blackbody exist?
Post by: Joe Boboblob on 03/12/2015 03:49:20

My theoretical frictionless mechanism doesn't have any friction.

Doesn't have any weight either.

It can't absorb light though :(

Title: Re: Does a perfect blackbody exist?
Post by: chiralSPO on 03/12/2015 05:31:38

Questions along the lines of "Does a perfect X exist?" or "does an ideal Y exist?" are almost universally, unequivocally answered, "no." Unless there is no way for something not to be perfect (a photon will always be a perfect photon, and behave as such, because there is no way for a photon to be imperfect, as far as I know.)

"Perfect" and "ideal" usually mean "fits perfectly to a simple model" (and all our models are far more simplistic than what's actually going on). We make approximations, assumptions and take mathematical liberties that we use until the model stops giving reasonable answers, or the precision required for a task. Then we resort to more complex models, based on theory or just optimized with empirically determined parameters until we can solve the problem at hand.

Title: Re: Does a perfect blackbody exist?
Post by: chintan on 03/12/2015 05:52:24

I guess it's like a cup of tea which spills on over filling, except for tea is light in this case and cup is the blackbody. [?]

Title: Re: Does a perfect blackbody exist?
Post by: Bored chemist on 03/12/2015 19:51:21

A rusty tin can with a small hole in it makes a remarkably good black body.

Title: Re: Does a perfect blackbody exist?
Post by: chris on 03/12/2015 20:59:19

Quote from: Bored chemist on 03/12/2015 19:51:21

A rusty tin can with a small hole in it

What's the purpose of the hole?

Title: Re: Does a perfect blackbody exist?
Post by: Bored chemist on 03/12/2015 21:06:03

The hole is very nearly perfectly black: radiation going in has an excellent chance of being absorbed.

Title: Re: Does a perfect blackbody exist?
Post by: chintan on 04/12/2015 14:09:28

But here we need the whole rusty can to be a absorbent n not just a hole in it. [:-\]