Guest SwaggMan Posted February 11, 2004 Posted February 11, 2004 I've been looking around the internet an so far ive found out that light is made of massless particles called photons. If light is massless how is it affected by gravity? ( black holes and gravitational lensing) If it does have mass, what happens to it when it goes out and can u trap the particles in a box an keep the light from going out? ive just been trying to think about it too much an it bugs me lol SwaggMan
JaKiri Posted February 11, 2004 Posted February 11, 2004 By general relativity, gravity is expressed by a distortion in 4 dimensional space, so light is affected even without mass If you want to 'trap' light in a box, there's 2 easy ways. 1. Put a lamp in a box. Typically, the light will be absorbed by the inner surface, which is sort of trapping. A better way (by a different interpretation) would be to have a box with the inside coated with mirrors. 2. Have a black hole inside the box.
alt_f13 Posted February 11, 2004 Posted February 11, 2004 What is the greatest efficiency of a mirror to date? It would be nifty to sustain a laser inside a reflective box for a sizeable ammount of time... but there can't be much use for such an application. It would be hard/impossible to measure without losing some of the light too, would it not?
YT2095 Posted February 11, 2004 Posted February 11, 2004 light (the photon) is not without mass either in fact we are struck by roughly a kilo and a half each day on our Earths surface of photons from the Sun loking up the idea ans principals behind a "Solar sail" may aid in your qustions also
JaKiri Posted February 11, 2004 Posted February 11, 2004 YT2095 said in post # :light (the photon) is not without mass either You're wrong. A photon is massless, but has momentum (de Broglie's equation).
Cap'n Refsmmat Posted February 11, 2004 Posted February 11, 2004 And it transfers that momentum to the sail, right? If photons had mass, then as they passed through our cells, they would be like radiation, damaging them. If it had mass, windows probably would not let as much light through and would be very reflective. To understand the trapping of light in a black hole, imagine the idea that gravity is like a dip in spacetime. The photon hit's the dip and cannot get out, like a coin in one of those wishing well thingies that sends it spinning around the rim of the hole, until it vanishes and cannot escape.
JaKiri Posted February 11, 2004 Posted February 11, 2004 Cap'n Refsmmat said in post # :If photons had mass, then as they passed through our cells, they would be like radiation, damaging them. If it had mass, windows probably would not let as much light through and would be very reflective. No. Mass doesn't equal ionisation potential; neutrinoes have mass, and pass through us nigh on constantly. Gamma rays don't have mass, and they cause damage (and are a form of light). Furthermore, I don't think mass effects what can pass through objects, to any great degree.
Cap'n Refsmmat Posted February 11, 2004 Posted February 11, 2004 Neutrinoes have tiny mass, radiation has more. Though I suppose photons (if they did have mass) would be tiny as well. Well, it does, because if it is too massive, it will not fit between the molecules of the other object, and cannot get through, except in tiny amounts (like balloons)
JaKiri Posted February 11, 2004 Posted February 11, 2004 Cap'n Refsmmat said in post # :Neutrinoes have tiny mass, radiation has more. 'Radiation' isn't a seperate group of particles you know. As I said, Gamma Rays are a form of radiation, and they don't have mass.
alt_f13 Posted February 12, 2004 Posted February 12, 2004 MrL_JaKiri said in post # : You're wrong. A photon is massless, but has momentum (de Broglie's equation). How does a photon have momentum w/o mass? I don't know what lambda etc. means in the equation...
JaKiri Posted February 12, 2004 Posted February 12, 2004 alt_f13 said in post # : How does a photon have momentum w/o mass? I don't know what lambda etc. means in the equation... Lambda is the wavelength. h is planck's constant. p is momentum. :lclambda: = h/p
alt_f13 Posted February 12, 2004 Posted February 12, 2004 Okay, I get the units... but I still don't understand how a massless particle can have momentum... also, how does a photon affect gravity w/o mass? [edit] Is there a 0kg * infinite something in that equation? (Yah, sory bout the lower level fizziks, I skipt skule and went strate to jeenyus)
YT2095 Posted February 13, 2004 Posted February 13, 2004 MrL_JaKiri said in post # : You're wrong. A photon is massless, but has momentum (de Broglie's equation). then can you explain this? http://www.aip.org/enews/physnews/2003/split/625-2.html another question, if a photon has energy, and energy =mass (as writen by Einstein). wouldn`t it make sense that a photon has mass, or the potential for it?
JaKiri Posted February 13, 2004 Posted February 13, 2004 alt_f13 said in post # :Okay, I get the units... but I still don't understand how a massless particle can have momentum... also, how does a photon affect gravity w/o mass? Just look on it as one of those odd quantum effects. And as per affecting gravity, according to GR gravity is caused by ALL energy, and EVERYTHING is affected by it. See Tom's post in another thread.
JaKiri Posted February 13, 2004 Posted February 13, 2004 YT2095 said in post # :then can you explain this? http://www.aip.org/enews/physnews/2003/split/625-2.html What, that there's increasing proof of the photon having a zero mass? Why the hell would I need to 'explain' something that states within the article that it supports my position? YT2095 said in post # :another question, if a photon has energy, and energy =mass (as writen by Einstein). wouldn`t it make sense that a photon has mass, or the potential for it? That's you totally misunderstanding the E=mc2 relationship.
YT2095 Posted February 13, 2004 Posted February 13, 2004 to me it states uncertainty, that`s all! "Photon mass is expected to be zero by most physicists, but this is an assumption which must be checked experimentally." so keep your hair on and put your eyes back in your head LOL "That's you totally misunderstanding the E=mc2 relationship. " then would you care to eplain WHY it`s not the case?
JaKiri Posted February 13, 2004 Posted February 13, 2004 Because if you convert a photon into mass, you will indeed get m by E=mc^2, but that doesn't mean that the photon HAS that mass. E=mc^2 is the equation of proportionality which expresses how much mass is 'worth' as energy; it's commonly used, for instance, to find the nuclear binding energy, or to calculate the output of a nuclear reaction (the sum total mass of the products of nuclear fission is slightly less than that which it came from; you get the amount of energy produced by putting this mass deviation into E=mc^2). Of course, that's ignoring momentum, but it doesn't really make a difference.
YT2095 Posted February 13, 2004 Posted February 13, 2004 well I can certainly understand there being "losses" as there`s no perfect system ever and especialy with conversion of any sort. but 100% loss? also, I was watching a documentary about physics and photons and the Sun etc... and it clearly stated that we are hit by roughly 1.5 kilo of photons per day, what could they have meant? as they were quite specific.
JaKiri Posted February 13, 2004 Posted February 13, 2004 YT2095 said in post # :well I can certainly understand there being "losses" as there`s no perfect system ever and especialy with conversion of any sort. but 100% loss? I have literally no idea what you're talking about. YT2095 said in post # :also, I was watching a documentary about physics and photons and the Sun etc... and it clearly stated that we are hit by roughly 1.5 kilo of photons per day, what could they have meant? as they were quite specific. They were wrong.
YT2095 Posted February 13, 2004 Posted February 13, 2004 and that switching on a flashlight, there is a "kick" like recoil. but so minute as be virtualy unmeasurable, that also was mentioned. wrong too?
JaKiri Posted February 13, 2004 Posted February 13, 2004 That's right, (they probably meant 15kgms^-1 in your previous reference to them) but you still haven't explained the 100% loss thing.
YT2095 Posted February 13, 2004 Posted February 13, 2004 oh yeah, overlooked that, Loss. any system of conversion has losses (at least all the one I can think of). electricity to light will have heat losses and magnetic losses and such. you said "(the sum total mass of the products of nuclear fission is slightly less than that which it came from; you get the amount of energy produced by putting this mass deviation into E=mc^2)." that reads to me like loss compensation. since we`re doing it the other way around and trying to turn energy into Mass, I would expect therefore that there would be similar losses. that`s all
YT2095 Posted February 13, 2004 Posted February 13, 2004 ok lets try another way, does a photon have infinate energy?
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