How light ends, an elementry question

[jutntog1]

I am curios how and when light defuses or stops, By this i mean is the light from the sun continue to go untill the edge of the universe (using this as an example not wanting to discuss the edge of the universe). Pleese explain in some detail.

[Neurocomp2003]

light doesn't really end. It persists till it interacts with something else.

 

Newtons laws say that once a photon leaves the sun it will travel till something stops it...and thus if something stops it it will interact with that something...otherwise it will travel untouched

[jutntog1]

but isnt all matter somewhat reflective? so wouldnt it continue to bounce around?

[swansont]

but isnt all matter somewhat reflective? so wouldnt it continue to bounce around?

 

Nothing is 100% reflective. You can make a "beam dump" with a stack of razor blades - nice shiny metal - that looks black simply because it requires multiple reflections and you get forward scattering. But you don't see light coming out the other side. It all gets absorbed, eventually.

[jutntog1]

ohh, ic so everytime the light comes in contact with something some of it gets aborbed?

 

then im assuming the absorbtion is in the form of turning the the obsorbing matter warmer?

[Crusty_Ass]

It's waaaayy more complicated than that.

 

First of all, even scientist don't really understand light completely.

 

What we do now is that it behaves both as a wave in a medium, like a wave on the sea, and as a particle. Sometimes it behaves more like one kind, sometimes more like the other.

 

The easiest way to look at light is it being a sort of wobbly part of matter, that occasionally gets tossed by one matter particle, travels either between the TV and your eyes or accross the galaxy, until it gets picked up by another matter particle and contributes to that particle's wobbliness.

 

We know light is quantized, that basically it is a limted entity.

We also know that when atoms and light interact, they do it in very distinct quantized ways. An electron circling an atom's nucleus absorbs an light-particle, or photon, and this adds a bit to it's energy. The electron then speeds up a bit, and proceeds to an orbit a bit more further away from the nucleus. Just as if you would strap a huge rocket engine to the moon to give it a boost.

 

After a period of time (scientist have no clue why it is that specific amount of time) the electron decides it doesn't like the new orbit anymore and pulls closer to the nucleus. The photon gets released and travels away again.

 

Now the interesting thing is that the photon doesn't have the hold as much energy after this encounter as it did before. Most of the time it is less. So if you have an ultraviolet photon getting absorbed by the electron, it might decide later to send out another, less powerful photon like a visible photon or infrared photon.

In real life:

-Ultraviolet photon --> electron --> visible photon = Luminescense (when you light up a banknote with an ultraviolet light. Also the shiny colour of gold and silver and most other metals is due to this.

-Ultraviolet or visible photon --> electron ---> infrared photon = heat radiation during the day.

 

BTW, scientists also have no clue how the actual 'tossing' of a photon by an electron actually works.

[Sayonara]

Nothing is 100% reflective. You can make a "beam dump" with a stack of razor blades - nice shiny metal - that looks black simply because it requires multiple reflections and you get forward scattering. But you don't see light coming out the other side. It all gets absorbed, eventually.

...waiting for someone to explain that the razors cut the light up so small we can't see it...

[J.C.MacSwell]

...waiting for someone to explain that the razors cut the light up so small we can't see it...

 

You merely need to cut the photons in half. Noone has ever seen a half photon.

[swansont]

...waiting for someone to explain that the razors cut the light up so small we can't see it...

 

The first blade doesn't, but the second blade...

 

Edge-on it has almost no cross-section, so the light diffracts. Then the shallow angle ensures forward scattering, multiple times.

 

a little more detail

 

Here is a picture - the item on the left.