Friday 20 October 2017

visible light - Can matter have 100% reflection?


Is it possible to have matter that reflects all the light and does not absorb light at all? If thats possible then we can store light inside it right? I think we can trap light inside that matter in shape of box for example and also we can release it by making very small dot in that box.


Im not saying that this is useful or not (I think its useless though because we can already emit light in other ways). Im just curios about this. Im noob in physics so sorry for my noob question. Thanks in advance.


Edit: If it does not make sense for matter to have reflection then what about shapes to reflect all light?



Answer



First, "light" is just the name we give to a small set of frequencies in the electromagnetic waves (and it is sometime extended to neighboors such as UV and IR). -> do you mean reflecting 100% at any electromagnetic frequencies, or specifically in the dark-red to dark-violet range ? or would you be happy if is was 100% only at some given laser-like frequency ?


Second, "exactly 100%" is... alot. Indeed, exact zero or exact 100% are notions that exist more in the world of maths than in the natural world. Think about this: suppose a 10x10x10 cm³ box which facing mirrors have reflection 0.999999999 (i.e. absorption 10⁻⁹) - assuming such magic material exist. At the speed of light, in 1 second a ray would bounces 3.10⁹ ( 3 billions ) times. Then this "really almost zero absorption per bounce" will yield a total absorption of... 95% ! ( $1- (1-10^{-9})^{3.10^9}$ ). So you can't expect to keep energy more than a few seconds even it this case.


Now you could have something else than matter. e.g. if you could bend or slow down to zero rays with some physical phenomenon. But well, assuming it exists, it would require a lot of energy.


So there would be a way more efficient solution: capture these photons with photovoltaic cells, then turn them back to photons with some LEDs. ;-) . Or more natural: let 'store' them temporarily as offset in electronic orbitals, then let these excitated orbitals release them back as photons later. This is... phosphorescence ;-) . These both solutions would give you back a lot more photons than a pure optic capture device.


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