coldfire Posted October 13, 2004 Share Posted October 13, 2004 ok light travels and let say that i hit's something and it changes direction to do this it most come to a comeplete stop and then accelrate back to light speed... do you think the properties of it change when this happens when it comes to a complete stop? Link to comment Share on other sites More sharing options...
5614 Posted October 13, 2004 Share Posted October 13, 2004 http://www.newscientist.com/news/news.jsp?id=ns99994474 http://www.newscientist.com/news/news.jsp?id=ns9999340 both show light being stopped or frozen in its tracks just re-read the original question, thats not exactly what was asked: when a photon hits a material, it is absorbed, its not like a "back and forward" race where you stop at one end and then go back again to the other side, this is the energy being absorbed resulting in an electron going to a higher energy state, when the electron goes back down to its original and lower energy state a photon is re-emitted, this is not a stop start thing, its absorption and re-emission of a photon. when it is absorbed, obviously is properties change, the photon 'disappears' and is transformed into energy, then the energy is transferred back into a photon, this energy is what makes the electron jump into higher then back to lower energy states. so basically, its properties change yes, it totaly disappears! (and a different photon, from the same energy but not exactly the same one is then emitted from the material which absorbed the first photon) Link to comment Share on other sites More sharing options...
coldfire Posted October 13, 2004 Author Share Posted October 13, 2004 i wonder if we could stop the light and then take the energy Link to comment Share on other sites More sharing options...
5614 Posted October 13, 2004 Share Posted October 13, 2004 well that is what happens when a photon is absorbed by truely black material. what i mean by truely black is that our black clothes still reflect a tiny amount of light, black holes for instant will not, they are truely black and can be seen because they are blacker than the surrounding space. solar panels work by taking the energy of a photon and transferring it into electrical energy. Link to comment Share on other sites More sharing options...
coldfire Posted October 13, 2004 Author Share Posted October 13, 2004 stupid (removed sorry) Link to comment Share on other sites More sharing options...
swansont Posted October 13, 2004 Share Posted October 13, 2004 well that is what happens when a photon is absorbed by truely black material. what i mean by truely black is that our black clothes still reflect a tiny amount of light Partial reflection just means that some of the photons were absorbed, just not all of them. The energy transfer process is the same - ultimately the object will heat up. Link to comment Share on other sites More sharing options...
ydoaPs Posted October 13, 2004 Share Posted October 13, 2004 well that is what happens when a photon is absorbed by truely black material. what i mean by truely black is that our black clothes still reflect a tiny amount of light' date=' black holes for instant will not, they are truely black and can be seen because they are blacker than the surrounding space. [b']solar panels work by taking the energy of a photon and transferring it into electrical energy.[/b] what about hawking radiation? Link to comment Share on other sites More sharing options...
5614 Posted October 13, 2004 Share Posted October 13, 2004 Partial reflection just means that some of the photons were absorbed, just not all of them. thats right, not arguing, however, couldnt one say that everything is absorbed and only some it re-emitted, opposed to what you (swansont) said (quoted). or when you say absorbed, do you mean what i just said!? Link to comment Share on other sites More sharing options...
swansont Posted October 13, 2004 Share Posted October 13, 2004 thats right, not arguing, however, couldnt one say that everything is absorbed and only some it re-emitted, opposed to what you (swansont) said (quoted). or when you say absorbed, do you mean what i just said!? It sounded like you were saying that the absorption by a perfect blackbody was somehow different than absorption by a real object in a way other than the fraction of photons absorbed. Link to comment Share on other sites More sharing options...
Severian Posted October 14, 2004 Share Posted October 14, 2004 Coincidentally, I went to a talk yesterday by Ulf Leonhardt (who is quoted in the New Scientist article) on this very subject. It was quite interesting. I particularly liked the idea of creating a 'fake' black hole: if light moves very slowly then your 'event horizon' would no longer be set at the place where something travelling at 'c' can't escape, but be set at a much lower speed, allowing 'black holes' to be constructed in the lab. Link to comment Share on other sites More sharing options...
5614 Posted October 14, 2004 Share Posted October 14, 2004 "Coincidentally, I went to a talk yesterday by Ulf Leonhardt" make him join SFN! (or his he already here... that'd be soo embarrasing!, but then, how would i know his name?) "It sounded like you were saying that the absorption by a perfect blackbody was somehow different than absorption by a real object in a way other than the fraction of photons absorbed." no no, the difference is that EVERYTHING (all the photons) are absorbed, compared to "black" clothing (etc.), i was just trying to show that our "black" cloth in a perfect blackbody, where as it isnt from our "black" clothes. black is the absence of photons reflected from the material, so whilsts we call our clothes (etc.) black, its is not scientificly black, but it is recognised as black. (nothing new! thats just what i meant!) Link to comment Share on other sites More sharing options...
Scott Posted November 7, 2004 Share Posted November 7, 2004 ok light travels and let say that i hit's something and it changes direction to do this it most come to a comeplete stop and then accelrate back to light speed...do you think the properties of it change when this happens when it comes to a complete stop? I dont think it stops and then turns, rather it is merely reflected. I dont think it would actually stop, turn it self, and speed up again. Someone please correct me if im wrong in this rejoinder. Link to comment Share on other sites More sharing options...
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