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Fazor
2006-Oct-19, 07:00 PM
The possibility of using light to push an object through space has been discussed for some time now. I've seen this refered to as "solar sailing". If light can "push", then the "force" of the light ray wouldn't be diminished in the vaccuume of space, until it came in contact with some form of solid matter. So why aren't the billions of rays of light from all the stars in the galaxy pushing everything everywhere? or could they be?

another property of light seems to be that it is not additive (excuse my lack of scientific vocabulary). I.E., if you take a flashlight that omits x ammount of light, then shine a second flashlight of equal light (or lesser), the result is not a lit area 2 times as bright. suppose this property also applies to the amount of force a light ray generates. this would result in a uniform force so long as from each dirrection there was enough light to reach that uniform level.

Now an object, such as a person or car or whatever, on the face of a planet would be bombarded with these billions of light rays from every angle except those shielded by the planet. to look at it two-dimensionally, a light ray coming in at 0 degrees and one coming in at 180 degrees would cancel eachother out (assuming they're the same force). 45 degrees and 135 degrees would cancel out any horizontal force, but each exert some downward force upon the object. for the sake of argument, say the ground shields these light rays from 181 degrees to 359 degrees. In that case, any force excerted down would not be canceled out.

The farther an object was from a large mass, the less area would be "shielded" from these rays, i.e. the force would be more equal from all angles.

anyway this is all just a thought I had, and would like to know if there's any more information about this topic out there and what everyone else thinks.

Ken G
2006-Oct-19, 07:34 PM
So why aren't the billions of rays of light from all the stars in the galaxy pushing everything everywhere?
They are, but the push is exceedingly weak most of the time. However, if you want to see what that push can do on low density plasma in space, check out yesterday's APOD:
http://antwrp.gsfc.nasa.gov/apod/ap061018.html
That's the wind from a star that was pushed out by the star's light, piling up interstellar gas in its wake.


another property of light seems to be that it is not additive (excuse my lack of scientific vocabulary). I.E., if you take a flashlight that omits x ammount of light, then shine a second flashlight of equal light (or lesser), the result is not a lit area 2 times as bright.
Actually, the light is perfectly additive, but your eye's ability to detect brightness isn't.

anyway this is all just a thought I had, and would like to know if there's any more information about this topic out there and what everyone else thinks.

The forces due to light are well understood, and your idea, though perfectly reasonable, is not of any significance because the force levels are way too small to matter much in the contexts you have in mind. (And welcome to the forum!)

Fazor
2006-Oct-19, 07:43 PM
Well, thanks for the welcome! I've been struggling with the idea of light being able to traverse a vaccuume, and with gravity also being able to effect bodies in a vaccuume. I know i know, these are easy questions even for the non physisist (lol). But it seems rather obvious to me that light is some form or phsyical object (be it electomagnetic wave or otherwise). Obviously i have not spent much time researching this, becuase it's much easier to find a forum and have someone who's already done the work tell me thier side of things (lol j/k). but even if it is not light causing it, the idea of gravity being a force that pushes us towards objects seems to work better, in my mind, than the traditional idea that these objects pull on each other. of course, like i said i have no evidence for this, but that's what i'm digging for now. Answers first, validity later i always say! ;)

Ken G
2006-Oct-19, 08:51 PM
Obviously i have not spent much time researching this, becuase it's much easier to find a forum and have someone who's already done the work tell me thier side of things (lol j/k). but even if it is not light causing it, the idea of gravity being a force that pushes us towards objects seems to work better, in my mind, than the traditional idea that these objects pull on each other. of course, like i said i have no evidence for this, but that's what i'm digging for now.

Actually, the idea that gravity is really a push not a pull has been explored, very much from the perspective you are taking-- a flux filling all space and being blocked by the objects causing the apparent pull. You don't want to invoke light though, as that is something else, and gravity works fine even in a completely dark region. But note you still have other problems to contend with, like the fact that the strength of gravity depends on the mass of the source, whereas the "blocking cross section" depends on the area. You'd have to find a way for objects to block the pushing rays based on their mass and not their area for the idea to have promise. Again, I think such ideas are thrown around, it's not a futile effort, I just don't know what progress they've made.

Fazor
2006-Oct-19, 09:05 PM
Okay this is my last post in this topic, at least for now as I do not believe in spamming threads (that's what IM and E-mail are for ;) ).

Anyway, as i was working out the math on this theory, it was quite clear that there was that one glaring flaw wich you mentioned; the effect was totally dependant on the curvature or shape of a body and not it's size. But this is only a problem if you assume there is no penetration of (x) force. After futher looking into the physics of light, i agree this is not the force (altho like many things i do believe it's part of the big picture).

Perhaps later i'll start another thread on gravity. anyway back to light.

last question, which perhaps someone can explaine:

Held true that space is a vaccuume, and inertia is also true, this still doesn't explaine to my how the idea of a "solar sail" would work. light photons hitting the sail from the sun should be no different than ones hitting the sail from the distant suns, as there has been (relatively) little slow down the speed of the light. altho i don't know that the idea of a space sail has been actually proven to be viable anyway. (last note) all the literatue i've read on the subject says the key is a lightweight material...but would weight matter in a weightless environment? I guess a heavy object would still have more inertia...

well, thanks for the feedback. shift's over, i can now pretend to be inteligent from home! :)

Ken G
2006-Oct-19, 09:48 PM
light photons hitting the sail from the sun should be no different than ones hitting the sail from the distant suns, as there has been (relatively) little slow down the speed of the light.
Ask yourself this-- do you get more warmth from our Sun or from the distant suns? So it is with the "push" of light-- it is proportional to the energy received.

(last note) all the literatue i've read on the subject says the key is a lightweight material...but would weight matter in a weightless environment? I guess a heavy object would still have more inertia...
Inertia is important, yes, but you do also have to beat out the Sun's gravitational pull, so gravity is important too. It is a common misconception that space is a "weightless" environment, but if that were true, you couldn't even get stars to form.

triclon
2006-Oct-20, 02:27 AM
Don't nebula get blown around quite a bit by light from nearby stars?

Ken G
2006-Oct-20, 03:31 AM
It's more the winds of the stars that get "blown", and those winds then "sweep through" the nebulae.

LayMan
2006-Oct-20, 08:05 AM
last question, which perhaps someone can explaine:

Held true that space is a vaccuume, and inertia is also true, this still doesn't explaine to my how the idea of a "solar sail" would work. light photons hitting the sail from the sun should be no different than ones hitting the sail from the distant suns, as there has been (relatively) little slow down the speed of the light. altho i don't know that the idea of a space sail has been actually proven to be viable anyway. (last note) all the literatue i've read on the subject says the key is a lightweight material...but would weight matter in a weightless environment? I guess a heavy object would still have more inertia...

well, thanks for the feedback. shift's over, i can now pretend to be inteligent from home! :)

Maybe this helps: I've once read about the experience of a guy flying in an airplane that suddenly hit an "air drop" (don't now the english term for it), causing the plane to suddenly 'free fall' during a couple of seconds. He apparenlty wasn't wearing his safety belt, causing him and a loose heavy object (I think it was a big metal weighing instrument) to both get airborn. The object hit his shoulder, causing quite a painfull bruise. Can't remember were I've read it, but I believe that demonstrates the difference between weight and inertia (mass): standing barefoot on the Moon, it's quite easy to pick up or displace a heavy object like say, a metal ball that would weight 80 kilos here on Earth, but it would still be a very bad idea to actually try to kick it away as hard as you can... (standing barefoot on the Moons surface being a very bad idea to begin with notwithstanding).