Re: wave and light
From: tadchem (tadchemNOSPAM_at_comcast.net)
Date: 09/14/04
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Date: Tue, 14 Sep 2004 03:57:05 -0400
"Mark Martin" <qed100@hotmail.com> wrote in message
news:7d087978.0409132125.65e1b510@posting.google.com...
> bob_peterson@rediffmail.com (Bob) wrote in message
news:<e80b0472.0409131023.281feeae@posting.google.com>...
>
> > Light travels in straight line.
> > But the light wave is always represented as sinusoidal wave.
> > So does it mean that the light travels sinusoidally but in straight
line.?
>
> Point a garden hose horizontally with the water pressure on.
> Neglecting gravity, the water flows out in a straight, horizontal
> line. Now shake the nozzle up & down. The flow now assumes a wavy,
> sinusoidal path. But if you think of the water as being a large number
> of small drops, you can see that each exits the nozzle with its own
> velocity, and independently follows its own straight path away from
> the exit point.
>
> This has some similarity to an electric charge, with its field
> radiating away from it. A single radius is something like the path
> followed by the stream of water spewing from a hose. An important
> difference is that, with the electric field, there is no flow of stuff
> constantly from a static charge, like water streaming out. A static
> charge has a static field that just sits there. But if you shake the
> charge up & down you accelerate it each time it reverses direction,
> doing which takes energy. This energy is conducted into the field and
> powers the wave. The wave has energy, with the regions at which the
> direction changes quickly having more energy density than elsewhere.
> Each point of the sinusoidal path follows its own straight path away
> from the source charge. This is a classical electric wave.
>
> Quantum mechanically it becomes more subtle. Water flowing from a
> hose can be seen as a large number of droplets, each with its own
> definite trajectory. In QM the energy in a region of the classical
> wave reduces to the statistical likelyhood of detecting a photon in
> that area. But a photon isn't like a drop of water. Accelerating a
> charge can pump a unit of energy into the field, and a detector
> immersed in the field can be excited by the same unit magnitude of
> energy some time later. This correlation between exciting the source
> charge at time t, and then the detector at time t', is identified as a
> photon.
>
> But there's not necessarily a path followed by a photon between
> emitter & detector. QM can model the photon as following any of an
> infinity of indirect paths, with the actual path being selected on a
> case by case basis probablistically. For a large number of photon
> transactions at a large number of different emitter/detector
> separations, the average path between the emitter & detector will tend
> to be a direct classical path.
I would like to nominate this as the *worst* analogy of the year.
"It isn't even wrong."
Tom Davidson
Richmond, VA
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