Ranging and Pioneer

In article ,
(Nanook) writes:
In order to measure Doppler
shift, you need to measure frequency accurately right? And in order to
measure frequency accurately you have to have an accurate clock.

Not exactly. You have to have a clock with a constant _rate_, but
you don't have to know its zero point.

So I can't help but wonder while we're re-writing the laws of
cosmology on the basis of the unexpected Doppler shift of Pioneer I and II,

No one with any sense is "rewriting the laws of cosmology," but it's
still an interesting observation.

if we might be really doing so on the basis of an incorrectly calibrated
clock at NASA.

What's required is that the hydrogen maser clocks at the transmitting
and receiving DSN stations have the same clock frequency. (A known
frequency difference would suffice, but I _think_ the clocks are
designed so the frequencies are identical). There is no requirement
that the clocks be synchronized. Systematic clock frequency errors
would a) be noticed while tracking other spacecraft (Canberra, say,
always giving higher velocities than Madrid), b) be noticed in
independent experiments such as VLBI, and c) would cancel out in the
Pioneer analysis if different combinations of transmitting and
receiving antennas were randomly used over time.

In any case, I expect the clock frequency errors are well understood.
There is probably a calibration program, for example, and it wouldn't
suprise me if there are two or more clocks at each station. Maybe
Craig or someone who actually knows about this can comment.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
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Thus spake Steve Willner
So I can't help but wonder while we're re-writing the laws of
cosmology on the basis of the unexpected Doppler shift of Pioneer I and II,

No one with any sense is "rewriting the laws of cosmology," but it's
still an interesting observation.

May I just qualify that. We know that the mathematical properties of gtr
and those of quantum theory don't mesh, and also that there are a number
of outstanding problems in cosmology. There is in fact a great deal of
work being done by extremely smart people both on unification theories
and also on alternative theories of gravity, producing them and testing
them.

I am quite certain, however, that none of this work is being done on the
basis of an unexpected Doppler shift from Pioneer. Some of it,
particularly Bekenstein and Moffat, is being done on the basis of MOND,
which may or may not be related to the anomalous Pioneer shift.
Naturally it has occurred to those authors that if they find a
successful MOND theory it may also explain the Pioneer shift.

My own investigations have a purely theoretical basis in foundational
ideas of gtr and qm, and follow lines of thought not dissimilar to those
Einstein himself tried in his attempts at a unified field theory. It
does have implications distinct from gtr in the matter of the
interpretation of cosmological redshift, and this would cause us to
rewrite, or at least reinterpret, a great deal of what we know about
Cosmology. Exactly how a reinterpretaion of cosmological redshift may be
predicted to affect measurements from Pioneer is a matter of some
subtlety, but is certainly sensible to ask the question. One does not
base a theoretical model on such an observation, but it is certainly an
important confirmation of the model if it can explain the observation.





Regards

--
Charles Francis
substitute charles for NotI to email