Re: Analysis of gas mode MM interferometer operation using standard SR formulae.

On May 8, 7:56 pm, Surfer <n...@xxxxxxxx> wrote:
On Thu, 8 May 2008 06:32:52 -0700 (PDT), Jerry

<Cephalobus_alie...@xxxxxxxxxxx> wrote:
On May 8, 7:00 am, Surfer <n...@xxxxxxxx> wrote:

2) The value in bin 20 is LESS than half the value in nearby bins
showing that components with a period of a full turn are only
minimally present. In the IDEAL case they would be ABSENT,
because in the ideal case the value at any marker would be matched by
an equal value at the opposite marker, thus converting any potential
component with a period of a full turn into a component with a period
of half a turn. Hence your complaint about a "deficit" in this bin is
nonsense.

Nonsense. The value in bin 20 needs to be consistent with the
overall shape of the power spectrum, which is dominated by noise.

The low value represents an anomaly in the noise spectrum which
needs to be explained.

If there is a lack of "noise" in bin 20, that suggests the noise is
orrientation dependent--ie the value at any marker is tending tost be
matched by an equal value at the opposite marker.

That suggests the source is external to the interferometer.

On re-reading your comments, I see that you automatically assume
that ANY half-period modulation in the data necessarily represents
"signal".

On the contrary, MANY potential sources of systematic error will
result in half-period modulations in the data.

Consider, for example, the potential artifacts that may result
from a non-uniform temperature gradient in the room where Miller
ran his experiments.

Miller claimed that experimentally, he could found no periodic
effects resulting from temperature gradients induced by the
use of electric heaters shining on the apparatus. This claim is
at severe odds with simple calculations using well established
data for the refractive index of air.

Let us imagine that one end of the room where Miller worked was
a miniscule fraction of a degree warmer than the rest of the room:

20.01 20.01 20.00 20.00 20.00 20.00

==============================|==============================
interferometer

The air over the left 25% of the interferometer arm is 0.01 deg
warmer than the air over the rest of the interferometer.

The refractive index of air for 633 nm light at 1 atm, 20 degrees
Celsius 50% relative humidity, 450 ppm CO2, is 1.000271373

The refractive index of air for 633 nm light at 1 atm, 20.01 deg
Celsius, 50% relative humidity, 450 ppm CO2, is 1.000271363
http://emtoolbox.nist.gov/Wavelength/Ciddor.asp

Miller estimated 112,000,000 wavelengths of light in the light
path, going and returning.

If 25% of the light path in one arm is 0.01 degrees warmer than
the air over the rest of the interferometer, this would result
in a systematic difference in light paths between the two arms
of 0.28 wavelengths.

A sensitive thermometer placed on one arm of the interferometer
would detect a 0.01 degree modulation with every turn of the
instrument.

However, the symmetry of the interferometer converts this one per
rotation temperature modulation into a half-period modulation of
fringe displacements.

Is there any wonder that "gas-mode" interferometers are subject
to systematic errors mimicing presumptive light anisotropy
effects?

Jerry
.

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