[PLUG] Light in fiber, electrons in copper

Keith Lofstrom keithl at kl-ic.com
Tue Apr 21 18:34:44 UTC 2009


> from Michael on Tuesday 21 April 2009 08:07:
> >Then ask yourself when you last had a water outage.

On Tue, Apr 21, 2009 at 10:02:23AM -0700, Eric Wilhelm wrote:
> I think the typical cause of that is a gravity outage.
> 
> The light in the fiber is more like water than electrons in copper... 
> But we should probably have some training if the water department is 
> going to run the internet.

Agree to the last.  However, we do not get our water backhauled
from POPs in Seattle and Oakand.  Nor does a pipe splice leak
10% of the water through 100nm gaps.

Boring physics stuff:

Electrons are very much like water molecules, actually, while
light is not much like water at all. If you look at them
statistically, 49% of electrons and water molecules are going
upstream due to thermal vibration.  Look at a waterfall, and
realize that almost half the time every molecule is moving
upstream (very briefly!).   The thermal energy in the direction
of motion is 1/2kT, or 13 milli-electron-volts, or 2.1e-21
joules, which can push a water molecule (3e-26kg) to an 
average thermal speed of 370 meters per second, a lot faster
than the macroscopic average water flow can move. 

An electron (9e-31kg) moves thermally at 70 km/sec.  The flow
rate through a high current copper wire is 4A/mm2, which 
results in an average drift speed of 0.3mm/sec.  It is the
disturbances in the electric field that travel fast in wires.  

Light, on the other hand, travels one direction, thousands of
kilometers through optical fiber with hardly any thermalization
along the way.  A photon is a boson, which means it prefers to
travel in packs.  While some city employees are bozos, and some
vote in PACs, that does not give them any special talents with
bosons.

So light travels more like a school of herring, which penguins
like to eat.  Thus, this post is vaguely relevant to Linux.
However, herring in water pipes, or optical fibers, or on your
hard drive, are very bad.  I would rather have bugs.

Keith

-- 
Keith Lofstrom          keithl at keithl.com         Voice (503)-520-1993
KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
Design Contracting in Bipolar and CMOS - Analog, Digital, and Scan ICs



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