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Jan Walzer <jan### [at] lzer net> wrote:
: you got me ...
: it wasn't written as a diplom-thesis, but as a trivial news-comment ...
: I thought with some common-sense people are able to read what I meant ...
: Of course there are some specialists out there ...
I'm a hopeless perfectionist.
--
#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 18 Nov 2001 05:44:08 -0500, Warp wrote:
> point of view of the photon, it always travels straight (ie. the photon
> itself always goes ahead, without never turning to any other direction).
In fact, since time does not exist for photons, they couldn't turn even
if they "wanted" to.
--
#macro R(L P)sphere{L F}cylinder{L P F}#end#macro P(V)merge{R(z+a z)R(-z a-z)R(a
-z-z-z a+z)torus{1F clipped_by{plane{a 0}}}translate V}#end#macro Z(a F T)merge{
P(z+a)P(z-a)R(-z-z-x a)pigment{rgbt 1}hollow interior{media{emission T}}finish{
reflection.1}}#end Z(-x-x.2y)Z(-x-x.4x)camera{location z*-10rotate x*90}
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Andrew wrote:
> > Wasn't there a thread 'bout a relativistic raytracer ? ...
> > I'm sure someone has the link to the animations, of this
> > raytracers, that does a red/blueshift when in motion ...
>
> http://www.anu.edu.au/physics/Searle/Obsolete/Raytracer.html
>
> Very well worth a look if you haven't seen them before.
That was the obsolete site. It's newer one is at
http://www.anu.edu.au/Physics/Searle/Downloads.html
--
Jon A. Cruz
http://www.geocities.com/joncruz/action.html
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Ron Parker wrote:
> In fact, since time does not exist for photons, they
> couldn't turn even if they "wanted" to.
Why does't time exist for photons? It takes them time
to get from point A to point B, and their speed can be
measured; therefore, time exists for photons.
--
Tim Cook
http://empyrean.scifi-fantasy.com
-----BEGIN GEEK CODE BLOCK-----
Version: 3.12
GFA dpu- s: a?-- C++(++++) U P? L E--- W++(+++)>$
N++ o? K- w(+) O? M-(--) V? PS+(+++) PE(--) Y(--)
PGP-(--) t* 5++>+++++ X+ R* tv+ b++(+++) DI
D++(---) G(++) e*>++ h+ !r--- !y--
------END GEEK CODE BLOCK------
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On Sun, 18 Nov 2001 21:53:32 -0500, Timothy R. Cook wrote:
> Ron Parker wrote:
>> In fact, since time does not exist for photons, they
>> couldn't turn even if they "wanted" to.
>
> Why does't time exist for photons? It takes them time
> to get from point A to point B, and their speed can be
> measured; therefore, time exists for photons.
Except that since they're traveling at the speed of light, sorta by
definition, they don't experience the passage of time from their
frame of reference.
--
#macro R(L P)sphere{L F}cylinder{L P F}#end#macro P(V)merge{R(z+a z)R(-z a-z)R(a
-z-z-z a+z)torus{1F clipped_by{plane{a 0}}}translate V}#end#macro Z(a F T)merge{
P(z+a)P(z-a)R(-z-z-x a)pigment{rgbt 1}hollow interior{media{emission T}}finish{
reflection.1}}#end Z(-x-x.2y)Z(-x-x.4x)camera{location z*-10rotate x*90}
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Ron Parker <ron### [at] povrayorg> wrote:
: In fact, since time does not exist for photons, they couldn't turn even
: if they "wanted" to.
What happens when the photon "hits" a refractive object? Why does it "bend"
at the surface of the object? Why does it seem to go slower through the object?
I have heard this explanation that the photon is "absorbed" and another
photon (apparently a different one) is emitted. However, I have never
understood this explanation. Even in very solid matter atoms and molecules are
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? And what causes the change in direction at the surface
of the object? What causes the change in direction inside the object if the
density of the object is not constant? Why does the photon _always_ change
its path to the exact same direction? How, for example, electrons can travel
in water faster than photons can (ie. why don't electrons collide in the same
way as photons; electrons are a lot bigger)?
--
#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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Warp wrote:
> What happens when the photon "hits" a refractive object?
> Why does it "bend" at the surface of the object? Why does
> it seem to go slower through the object?
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.
(refer to
http://www.fnal.gov/pub/inquiring/questions/quesrelativity.html
for other related topics...)
> How, for example, electrons can travel in water faster
> than photons can (ie. why don't electrons collide in the
> same way as photons; electrons are a lot bigger)?
The explanation for that is: electrons don't travel, they're
pushed aside thusly:
-> -> ->e eeeeeeeeeeeeeee
*thunk*
eeeeeeeeeeeeeeee
*shove*
eeeeeeeeeeeeeeee
eeeeeeeeeeeeeee -> -> ->e
--
Tim Cook
http://empyrean.scifi-fantasy.com
-----BEGIN GEEK CODE BLOCK-----
Version: 3.12
GFA dpu- s: a?-- C++(++++) U P? L E--- W++(+++)>$
N++ o? K- w(+) O? M-(--) V? PS+(+++) PE(--) Y(--)
PGP-(--) t* 5++>+++++ X+ R* tv+ b++(+++) DI
D++(---) G(++) e*>++ h+ !r--- !y--
------END GEEK CODE BLOCK------
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> What happens when the photon "hits" a refractive object? Why does it
"bend"
> at the surface of the object? Why does it seem to go slower through
the object?
> I have heard this explanation that the photon is "absorbed" and
another
> photon (apparently a different one) is emitted. However, I have never
> understood this explanation. Even in very solid matter atoms and
molecules are
> 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?
Though this sort of thing was never my strong point, I'll have a go...
While the spaces between the nuclei in a solid might be very large,
electrons "fill" these spaces by virtue of their exceedingly high speeds
and quantum mechanical nature. Electrons interact primarily through the
EM force here, and as a photon is the mediating particle of the EM
force, the two very readily interact. It's probably wise to recall the
wave/particle duality of light, since the wavelength of visible light is
large compared to the spacing between atoms (a few 100x larger). This
wavelength can be thought of as the "size" of the photon in this case I
think, and so combining the large "size" of photons and the ease of
interaction with electrons, you have a large "cross-section" for the
interaction. The larger the cross-section, the more likely the
reaction.
> And what causes the change in direction at the surface
> of the object? What causes the change in direction inside the object
if the
> density of the object is not constant? Why does the photon _always_
change
> its path to the exact same direction?
Good question. The answer is probably buried deep in some obscure
equation somewhere, and even then could probably get summed up as "it
just does" :) In other words, I have no idea. A related question I
guess is how exactly a mirror works.
> How, for example, electrons can travel
> in water faster than photons can (ie. why don't electrons collide in
the same
> way as photons; electrons are a lot bigger)?
IIRC electrons have a "drift velocity" of a few cm per second in a
conducting metal. This is the actual speed at which they move through
the metal when conducting electricity. However, as Tim says, they shove
each other along, and as soon as one starts moving, all of the others in
the circuit are pushed into moving.
Finally I should note that a photon NEVER travels slower than c. ALL
apparent slowing of light is due to absorption/re-emission. While this
gives rise to a "speed of light in material x", the photons themselves
are still moving at c. Other particles can and do exceed this speed,
however, giving rise to a phenomenon known as Cerenkov radiation. A
high energy particle will produce a "bow wave" when it travels faster
than the apparent speed of light in a material, visible as a cone of
light (which tends to be blue). This is the reason why the water in
cooling ponds (is that the term?) of nuclear reactors, where they leave
the spent fuel to cool off for a while, glows blue. It's the Cerenkov
radiation resulting from all the nuclear decay products whizzing through
the water.
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Timothy R. Cook <tim### [at] scifi-fantasycom> wrote:
:> Why does it seem to go slower through the object?
: Because it DOES go slower through the object.
That really didn't answer my question. Why does it go slower inside the
object?
: The line is
: 'nothing travels faster than the speed of light *in a vaccuum*'.
I know that, and I wasn't asking that.
:> How, for example, electrons can travel in water faster
:> than photons can (ie. why don't electrons collide in the
:> same way as photons; electrons are a lot bigger)?
: The explanation for that is: electrons don't travel, they're
: pushed aside thusly:
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).
And besides, eletric current travels quite slower than c. I think that
in copper it travels at something like 0.7c.
--
#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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in news:3bf8eeef@news.povray.org Warp wrote:
> Why does it go slower inside the
> object?
>
From Maxwells third and fourth
c = 1/(E0*U0)^0.5
E0 = electric permittivity for free space
U0 = magnetic permittivity for free space
E0 = 8.85 x 10^-12 C^2 N^-1 m^-2
U0 = 4pi x 10^-7 Wb A^-1 m^-1
c = 2.999 x 10^8 m s^-1
In matter E0 and U0 become E and U
For most optical materials is nearnly equal to unity so that
n = c/v = E^0.5
From some very old notes from optics class.
Ingo
--
Photography: http://members.home.nl/ingoogni/
Pov-Ray : http://members.home.nl/seed7/
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