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RZ6AVM > SETI 09.09.04 17:00l 96 Lines 4502 Bytes #999 (0) @ WW
BID : 4D0135RZ6AVM
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Subj: signal SHGb02+14a
Path: DB0FHN<DB0MRW<DB0RGB<OK0PPL<OK0PAD<OK0PKM<OK0PBB<OK0PBR<UA6ADV
Sent: 040909/1406Z @:UA6ADV.H.KRD.RUS.EU #:15640 [Holmsk] Pactor-3 $:4D0135RZ6A
From: RZ6AVM@UA6ADV.H.KRD.RUS.EU
To : SETI@WW
A recent article in New Scientist magazine, entitled "Mysterious signals
from 1000 light years away", implies that the UC Berkeley SETI@home
project
has uncovered a very convincing candidate signal that might be the first
strong evidence for extraterrestrial intelligence.
Alas, this story is misleading. According to Dan Werthimer, who heads up
the UC Berkeley SERENDIP SETI project, this is a case of a reporter
failing
to understand the workings of their search. He says that misquotes and
statements taken out of context give the impression that his team is
exceptionally impressed with one of the many candidate signals,
SHGb02+14a,
uncovered using the popular SETI@home software. They are not.
This signal has been found twice by folks using the downloadable screen
saver. That fact resulted in the UC Berkeley team putting it on their list
of ‘best candidates’. Keep in mind that SETI@home produces 15 million
signal reports each day. How can one possibly sort through this enormous
flood of data to sift out signals that might be truly extraterrestrial,
rather than merely noise artifacts or man-made interference?
The scheme used is simple in principle (although the technical details are
complex): SETI@home data come from a receiver on the Arecibo radio
telescope that is incessantly panning the sky, riding "piggyback" on other
astronomical observations. Every few seconds, it sweeps another patch of
celestial real estate, and records data covering many millions of
frequency
channels. Some of these data are then distributed for processing by the
screen saver. By chance, the telescope will sweep the same sky patch every
six months or so. If a signal is persistent – that is to say, it shows up
more than once when the telescope is pointed at the same place, and at the
same frequency (after correction for shifts due to the motion of the
Earth)
-- then it becomes a candidate. Of course, being persistent doesn’t mean
that the source is always on, only that it is found multiple times.
In February of this year, Werthimer and his colleagues took a list of two
hundred of the best SETI@home candidate signals to Arecibo and
deliberately
targeted that mammoth antenna in the directions to which the scope was
pointed when they were found. Once subjected to this closer inspection,
all
but one of these signals failed to show. That disqualifies them from being
claimed as true detections of a persistent signal. The one that was found
again, SHGb02+14a (the subject of the New Scientist article), will no
doubt be observed yet again, but according to Paul Horowitz, who heads up
the
Harvard SETI efforts, the statistics of noise make it fairly likely that
at
least one of the candidates observed in February would reappear, even if
all these signals were simply due to receiver fluctuations.
The article remarks on the strong drift of this signal, which it describes
as puzzling. Of course, many terrestrial sources of interference, and in
particular telecommunication satellites, show strong drifts due to
changing
Doppler effects as they wheel across the sky. (Incidentally, the
technically inclined will want to note drift due to a planet rotating like
Earth would be 0.15 Hz/sec, not the 1.5 Hz/sec mentioned in the magazine.)
As for the distance of 1000 light-years claimed in the article’s title,
there is clearly no evidence supporting this number, other than the lack
of
known nearby stars in the beam.
The bottom line is that an experiment like SETI@home always has a
candidate
list, a table of those signals that look most promising. Indeed, you can
find the current versions of this list on their web site. However, there
is
a great deal of difference between a candidate, and a convincing signal.
If
any of the major SETI experiments being run by the SETI Institute, by the
UC Berkeley group, the folks at Harvard, or the Australians or Italians,
discovers a signal that they think is of extraterrestrial origin, they
will
immediately take steps to confirm this, both with their own scientists and
with observers at other organizations. You will find information about it
on their web sites, and in multiple media outlets.
Sadly, the New Scientist , while it implies that a detection of an
extraterrestrial signal is imminent, has inadvertently wandered into a
sticky vat of hyperbole.
73 - Ewgeny, RZ6AVM @ UA6ADV
Message timed: 18:06 on 09 Sep 04
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