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In article <3bf8ca76@news.povray.org>, war### [at] tag povrayorg says...
> extremely far apart from each other, which means that there's quite a lot of
> space between them; how come every and each one of the incoming photons are
> absorbed and none goes through the space between the atoms without never
> colliding with them?
You are thinking of photons as a kind of simple particle traveling along
a well-defined route from point A to point B.
But this is completely wrong when the photon is "near" some kind of
obstacle, thinking of it as a wave is a far better approximation in this
case -> since a wave can, at the same time, hit and miss ALL obstacles in
its path, it should be clear they all photons behave equally.
Lutz-Peter
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Timothy R. Cook scribis news:3BF8DB9D.E7FA7611@scifi-fantasy.com:
> Because it DOES go slower through the object. The line is
> 'nothing travels faster than the speed of light *in a vaccuum*'.
> If you pass the light through an object, it isn't going as
> fast as in vaccuum.
I had read of ceasium(sp?) gass heated to a certian high temprature that
has an IOR of less than 1. i.e. light traveles faster than the speed of
light in a vacuum. I havent seen this article disputed yet either. So maybe
it is true.
---
G^is poste,
Arto
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Having no mass, photons always travel at speed of light, even when they
go through transparent objects. They are absorbed and emitted several
times before they escape the material. The collective effect of billions
of them in a beam is as they travel slower than c. This collective
behavior is correctly described by Maxwell's equations. Individual
photons are better described by quantum mechanics. This
collective behavior is what is simulated in povray, the behavior of
beams of light
best described by Maxell's eqs.
Alberto
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> I had read of ceasium(sp?) gass heated to a certian high temprature
that
> has an IOR of less than 1. i.e. light traveles faster than the speed
of
> light in a vacuum. I havent seen this article disputed yet either. So
maybe
> it is true.
I've had a look, but there are not too many clear explanations on this
matter. It seems that the Caesium was used to create a region of
"anomalous dispersion", which means that the wavelength dependence of
the IOR is reversed. Shining a laser pulse through this caused a pulse
to be emitted from the other side of the chamber BEFORE the original
pulse had even reached it. Sounds amazing, and sounds like
faster-than-light, but apparently it isn't.
What had happened was that the group velocity of the light had been
increased above the normal speed of light. Normally, the group velocity
of light is the same as the signal velocity, ie information is
transmitted at the group velocity. However, in the case of anomalous
dispersion, the group velocity is no longer the signal velocity, and no
information is carried at this speed. The peak of the pulse travelled
at the group velocity, but energy did not.
More than this I can't tell you, I'm afraid. However, many people note
that this kind of thing is very prone to media misinterpretation, mostly
because the "speed of light" NORMALLY refers to the speed of energy
transfer, but in fact a wave has many different speeds of propagation,
depending on exactly what property of the wave you are looking at.
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> I wasn't referring to electric current. I was referring to what happens
> in nuclear reactors (I think that it's called Tserenkov's phenomenon or
> something similar): Electrons travel in water faster than light, which
> causes a greenish glow (a kind of "sonic boom" but with light instead of
> sound).
Cerenkov Radiation.
AFAIR, subatomic particles travelling faster than the speed of light in
water (or air) hit the air, come to a (relatively) screeching halt and
dump their excess energy, some of which makes it into the blue end of the
visible spectrum.
If you want more info, I'll ask my friend who works on Nuclear systems.
Bye for now,
Jamie.
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Andrew scribis news:3bf96612@news.povray.org:
> What had happened was that the group velocity of the light had been
> increased above the normal speed of light. Normally, the group velocity
> of light is the same as the signal velocity, ie information is
> transmitted at the group velocity. However, in the case of anomalous
> dispersion, the group velocity is no longer the signal velocity, and no
> information is carried at this speed. The peak of the pulse travelled
> at the group velocity, but energy did not.
>
> More than this I can't tell you, I'm afraid. However, many people note
> that this kind of thing is very prone to media misinterpretation, mostly
> because the "speed of light" NORMALLY refers to the speed of energy
> transfer, but in fact a wave has many different speeds of propagation,
> depending on exactly what property of the wave you are looking at.
That's the best explanation I have seen in a long while of what happened.
--
Gis poste, Arto.
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> That's the best explanation I have seen in a long while of what
happened.
Glad to help, but I can't really say I understand it all that well ;-)
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Alberto Mendoza <jac### [at] usbve> wrote:
: Having no mass, photons always travel at speed of light, even when they
: go through transparent objects. They are absorbed and emitted several
: times before they escape the material.
I can grasp this. However, what I still don't understand is the refraction
phenomenon.
--
#macro N(D,I)#if(I<6)cylinder{M()#local D[I]=div(D[I],104);M().5,2pigment{
rgb M()}}N(D,(D[I]>99?I:I+1))#end#end#macro M()<mod(D[I],13)-6,mod(div(D[I
],13),8)-3,10>#end blob{N(array[6]{11117333955,
7382340,3358,3900569407,970,4254934330},0)}// - Warp -
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On 20 Nov 2001 06:38:08 -0500, Warp wrote:
> Alberto Mendoza <jac### [at] usbve> wrote:
>: Having no mass, photons always travel at speed of light, even when they
>: go through transparent objects. They are absorbed and emitted several
>: times before they escape the material.
>
> I can grasp this. However, what I still don't understand is the refraction
> phenomenon.
Understanding refraction (and diffraction, too) requires one to see the
energy as waves instead of as particles. It's impossible to understand as
long as you keep thinking of them as strictly photons.
--
#macro R(L P)sphere{L __}cylinder{L P __}#end#macro P(_1)union{R(z+_ z)R(-z _-z)
R(_-z*3_+z)torus{1__ clipped_by{plane{_ 0}}}translate z+_1}#end#macro S(_)9-(_1-
_)*(_1-_)#end#macro Z(_1 _ __)union{P(_)P(-_)R(y-z-1_)translate.1*_1-y*8pigment{
rgb<S(7)S(5)S(3)>}}#if(_1)Z(_1-__,_,__)#end#end Z(10x*-2,.2)camera{rotate x*90}
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Ron Parker <ron### [at] povrayorg> wrote:
: Understanding refraction (and diffraction, too) requires one to see the
: energy as waves instead of as particles. It's impossible to understand as
: long as you keep thinking of them as strictly photons.
In fact, I personally like to think about light as a(n electromagnetic) wave,
which just sometimes happens to act like a bunch of particles for some
weird duality phenomenon.
I know that this "photon" idea has got so strong in almost 100 years that
many people only know about photons and nothing else. They don't even
understand what is a wave. Of course this is logical: It's easier for the
human mind to grasp the concept of a tiny particle "flying" in space than
an esoteric "wave" which exists and advances in the vacuum.
I personally like to think that photons do not really exist, but they are
just a "mathematical help" to understand the behaviour of electromagnetic
waves. As many other things in quantum mechanics, there's a minimal amount
of eletromagnetic radiation which can exist, and every amount of
electromagnetic radiation is a direct multiple of this minimum amount. This
minimum amount is what we call "photon". Due to its properties it makes the
wave sometimes act like if it was made of particles.
The wave itself is just an advancing phenomenon caused by changes in the
electromagnetic field. Of course I don't claim that I fully understand this.
--
#macro N(D,I)#if(I<6)cylinder{M()#local D[I]=div(D[I],104);M().5,2pigment{
rgb M()}}N(D,(D[I]>99?I:I+1))#end#end#macro M()<mod(D[I],13)-6,mod(div(D[I
],13),8)-3,10>#end blob{N(array[6]{11117333955,
7382340,3358,3900569407,970,4254934330},0)}// - Warp -
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