Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Magnetlike particle and Light

  1. Jan 27, 2014 #1


    User Avatar
    Gold Member

    Hi. When we turn on a lamp in the room at night, the room gets bright. Now, is there such a thing that does the same thing but other way around? When, it's not night, i.e day, we turn the lamp on and it absorbs all the light in the room and make the room dark?

    I guess such a lamp would be similar to black hole, but it'd absorb, suck only lights. I hope I was not being ambigious this time.
  2. jcsd
  3. Jan 27, 2014 #2


    User Avatar

    Staff: Mentor

    What you are asking about would be best described as a perfect "black body", an object that absorbs all electromagnetic radiation that falls on it. There are no perfect black bodies in real life, but all objects absorb some EM radiation, even the walls of the room you're in right now. If perfect black bodies did exist then you could line the room with the material and turn the light on and all you would be able to see is the light bulb.
  4. Jan 27, 2014 #3
    Black body doesn't suck though. And no there isn't (@OP). Sucking entails force and the only force that could work in this case is gravity, which would affect everything else too...besides gravity can't exactly be switched off.
    E: Is your avatar Bizzaro?
  5. Jan 27, 2014 #4


    User Avatar
    Gold Member

    Hi, Drakkith. Thanks for the reply. How about making something like perfect mirror? I know there's no such thing as perfect mirror either, but dielectric mirrors can reflect up to 99.999% of the light. So let's imagine a lightbulb whose inner 'surface' is made up of such mirrors and outer 'surface' is made up of black body.

    All lights coming go through the lightbulb's outer surface and gets reflected by the mirrors that are inside the lightbulb, then as the lights go back, the black body in the lightbulb gets 'opened' by the switch so all lights are trapped inside it. Oh, I guess I'm being way too naive and feel very lost!


    So it appears like the only way to make the room dark is by preventing sun lights going through windows? :frown:

    Edit: Well, wish I knew, I even tried googling but I have yet to find his name. I found it in the "Pre-defined Standard Avatars".
  6. Jan 27, 2014 #5
    A blackbody also emits radiation, with the radiation curve dependant upon its temperature, so that isn't the answer either.
  7. Jan 27, 2014 #6


    User Avatar
    Gold Member

    Hi, 256bits. Could you please elaborate? I don't get how it's not the answer. Are those emitted radiations harmful to us?
  8. Jan 27, 2014 #7
  9. Jan 27, 2014 #8


    User Avatar
    Science Advisor
    Gold Member

    The problem here is that you've got a room that is lit from some constantly shining source. Whatever you put in there - a perfect blackbody(it will shine in infrared! all blackbodies reradiate the incident energy) or a black hole - it'll only "suck in" those photons that are incident on its suface(or even horizon if it's a BH).
    As long as you're only concerned with visible light, a blackbody should do.

    So, if you're in a lit room, you'll always see the light coming at you from all directions, reflected by the walls and all the objects in the room. The only direction that would be completely lightless would be the surface of the black body. So, if it were a sphere, you'd see a perfectly black circle(barring some light scattered by the air and dust suspended in it) where the body is.
    But whatever provides lighting for the room, would still happily bounce its photons off the walls and into your eyes.

    The best you could do, is to line all the walls with a perfect blackbody. Then, the only thing you'd see would be the source of light for the room. A glowing tungsten wire in perfect darkness(if it's a lightbulb).
  10. Jan 27, 2014 #9


    User Avatar
    Gold Member

    I was going to say "Then we need to create a synthetic sun if possible" until I read Bandersnatch's reply. Now it looks like I'm flogging a dead horse.


    Now that I read your post and re-read mine, I see why my idea is hogwash. I completely ignored the light source.
  11. Jan 27, 2014 #10
    mmm...Bizzaro or a really angry Superman.
    OT Or you could accelerate the light source so that the waves get out of the visible region due to doppler effect.
    Or close your eyes.
  12. Jan 27, 2014 #11


    User Avatar
    Gold Member

    Accelerating the Sun? No, thanks!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Magnetlike particle and Light
  1. Light particles (Replies: 4)

  2. Light wave/particle (Replies: 1)