In infinite wisdom Joseph Lazio answered:
"R" == Rich <someone@somewhere.com> writes:
R> In infinite wisdom Christopher M. Jones answered:
Rich <someone@somewhere.com> wrote in message
news:<4096BAF0.9050408@somewhere.com>...
I'm reminded of discussions I had with an ex-roomate who was into
magic. Despite a tower of theories explaining why magic works
(...), he was somewhat aggravated when I suggested that first he
needed to show *that* magic worked. [...]
SETI is in a similar position near as I can tell.
Utterly wrong. SETI is not about finding extra-terrestrial
civilizations per se,
R> It's not? Boy did I misunderstand the acronym. So then what *does*
R> 'SETI' stand for?
This somewhat provocative statement by Christopher was meant to catch
the reader's attention.
I would still like an answer to my question.
it is about scientific research into the abundance and nature of
extra-terrestrial civilizations.
R> How can you research something when you got zero examples to
R> research?
R> Answer: You can't.
Let me rephrase his statement:
So you speak for both Mr. Jones and Mr. Scheffer?
SETI is an effort to investigate the number of ET civilizations.
The count is holding at zero.
One can certainly conduct research into the question,
> How many examples of X are there? where X is ET
civilizations, species of neutrinos, organisms that can survive in
extreme environments, etc.
For ET civilizations, the count is holding at zero. What, pray tell,
is it you think you are investigating? This is a serious question.
Failure to find strong evidence of ETI in any given SETI program is
not a failure of the program, it is a scientific *result*.
R> I'm amazed at how many think that you can derive population
R> statistics from one example, the earth.
Re-read what Christopher wrote. He does not advocate deriving the
number of ET civilizations based on the Earth, but searching for other
ET civilizations to derive population statistics.
I'm referring to the Drake Equation, which many seem to think proves
the existence of anywhere from thousands to hundreds of millions of
ET civilizations in our galaxy alone. Is this not what SETI is
looking for?
Sufficiently well constructed and well executed SETI programs that
produce a negative result provide critical data defining boundaries
on the abundance and nature of ETIs.
R> You cannot derive meaningful boundaries for something
R> undetected. You cannot research something you've not found.
R> And you can search for a million years for anything that does not
R> exist, refining your so-called boundaries again and again, but you
R> ain't doing science.
Sure you are, and that's the point. Take something we all know to be
"true." What's the mass of the photon? It's 0 eV, right? Well, no.
The mass of the photon must be less than something like 1E-48 eV.
That's consistent with 0 eV, but doesn't mean that it must be exactly
0 eV. Suppose somebody devised an experiment that could lower this
upper limit to 1E-60 eV (to make up a value), would the experiment be
worth doing? Yes! The payoff from finding that the mass of the
photon was greater than 0 eV is immense, even though everybody would
expect that we'd just be pushing back the boundary.
Interesting. So if the mass of a photon is not zero, then Einstein
was wrong about the intergalactic speed limit for massive objects.
You should pursue this further. I'm sure they'd love to hear about
this in sci.physics. :-)
By the same token, we can already set simple limits on the number of
ET civilizations.
The count is holding at zero. You cannot extrapolate from nothing to
population statistics dude.
There are clearly no super-advanced civilizations
(e.g., Kardashev Type II civilizations)
The notion that there would exist advanced civilizations with nothing
better to do than divert the entire planetary energy output, or
stellar energy output, or galactic energy output into attempting to
communicate with the unknown is somewhat frightening in itself.
in our neighborhood radiating
at huge power levels or we'd have seen them already.
Exactly. And were they transmitting at much lower power in our
direction, we'd have seen that already.
Current SETI
programs are attempts to do this with a bit more sophistication. What
about less advanced civilizations? How many of those might there be
around us?
I don't know. But I do know that the Drake equation won't tell us.
If you'd like to read about an early attempt to set limits on the
number of civilizations in the Galaxy, visit the ADS and take a look
at the paper by Horowitz & Sagan (1993).
---
http://adsabs.harvard.edu/cgi-bin/bib_query?1993ApJ...415..218H
Title: Five years of Project META - an all-sky narrow-band radio search
for extraterrestrial signals
Authors: Horowitz, Paul; Sagan, Carl
Affiliation: AA(Harvard Univ., Cambridge, MA), AB(Cornell Univ., Ithaca,
NY; Planetary Society, Pasadena, CA)
Journal: Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 415, no.
1, p. 218-235. (ApJ Homepage)
Publication Date: 09/1993
Category: Space Sciences (General)
Origin: STI
NASA/STI Keywords: EXTRATERRESTRIAL INTELLIGENCE, NARROWBAND,
RADIO ASTRONOMY, SKY SURVEYS (ASTRONOMY), LINE
SPECTRA, RADIO SPECTRA
DOI: 10.1086/173157
Bibliographic Code: 1993ApJ...415..218H
Abstract
We have conducted a five-year search of the northern sky (delta
between 30 and 60 deg) for narrow-band radio signals near the
1420 MHz line of neutral hydrogen, and its second harmonic,
using an 8.4 x 10 exp 6 channel Fourier spectrometer of 0.05 Hz
resolution and 400 kHz instantaneous bandwidth. The observing
frequency was corrected both for motions with respect to three
astronomical inertial frames, and for the effect of Earth's
rotation, which provides a characteristic changing Doppler
signature for narrow-band signals of extraterrestrial origin.
Among the 6 x 10 exp 13 spectral channels searched, we have
found 37 candidate events exceeding the average detection
threshold of 1.7 x 10 exp -23 W/sq m, none of which was
detected upon reobservation. The strongest of these appear
to be dominated by rare processor errors. However, the strongest
signals that survive culling for terrestrial interference lie
in or near the Galactic plane. We describe the search and
candidate events, and set limits on the prevalence of
supercivilizations transmitting Doppler-precompensated
beacons at H I or its second harmonic. We conclude with
recommendations for future searches, based upon these
findings, and a description of our next-generation search system.
---
Interesting that they note "rare processor errors". Seems to be
an issue with seti@home as well.
And when I read "five-year search", for some reason it reminded me
of Star Trek. :-)
To obtain hard boundaries on ETI parameters it will be necessary to
perform a wide variety of robust search programs using a wide
assortment of techniques (...).
R> [...]
R> I submit that you cannot do science on anything that cannot be
R> detected, regardless of whether it exists or not. SETI is not
R> science, it's not studying 'something', rather, it's looking *for*
R> something, something as yet undetected.
But that's the point! *We* can be detected over interstellar
distances. Look at the FAQ. Some of the transmissions we produce
already can be detected over interstellar distances.
You know, I've always wondered about this. Is the interstellar medium
transparent to radio waves? I've run across an interesting factor.
This is from your web-page in fact.
---
http://patriot.net/~jlazio/turbulence.html
Turbulence in the Interstellar Medium
The space between the stars is not empty. Rather it is filled
with a gas of varying density and temperature. By terrestrial
standards this interstellar medium (ISM) is a vacuum. By Galactic
standards, the ISM is vitally important as it is the raw
material from which stars are formed.
Some of the ISM is ionized or in plasma form (i.e., the gas is
hot enough that the electrons are stripped from the atoms, like
the gas in the tubes of a neon sign). Presumably this plasma is
formed by massive amounts of energy being injected into the ISM,
for instance by the winds produced by the hottest stars, O and B
stars, and near supernovae (the explosions which occur when O
and B stars run out of fuel and collapse). By studying how stars
interact with the ISM, we may gain a better understanding of how
they are formed and how they die. Furthermore, radio astronomical
observations must be conducted while looking through this plasma,
so we must understand how it can affect our observations.
Scintillation
Scintillation (intensity fluctuations) results from the passage
of a light wave through a random medium (i.e., one in which the
refractive index varies randomly). A common example of scintillation
is the twinkling of starlight, resulting from visible light passing
through the Earth's atmosphere. The Earth's atmosphere is a random
medium because weather systems keep it "stirred up"; a typical scale
on which the atmosphere varies is a few to 10 cm. Other common
random media include the air over hot pavement and the exhaust of
a jet airliner.
Scintillation is also observed at radio wavelengths during
observations of pulsars and extragalactic radio sources. In
this case the random medium is the plasma component of the
ISM and a typical scale is 1 AU (i.e., the Earth-Sun distance).
The energy deposited by stellar winds from O and B stars and
from supernovae are probably what keep the ISM plasma "stirred up."
Like the case of a twinkling star, radio scintillation has the
possibility of corrupting radio astronomical observations (after
all, we don't see twinkling stars as they really are, but as
they appear after their light has passed through the Earth's
atmosphere) or possibly even hiding sources.
---
And while it's noted that scintillation can sometimes magnify a
signal, it usually does not. I'd suspect that over any long
distances, it would defocus any beam heading in our direction,
and indeed, it will also affect the radio energy that has already
left earth. The general effect would seem to be to lower
detectability, and the effect would seem proportional to distance,
and of course dependent on local variables. But even in the
absence of an energetic source that will ionize gas, as long
as there are density variations the signal will be bent.
Let me turn your statement around. How do you know that the Galaxy
contains no other civilizations, given that we know of one
civilization that can be detected over interstellar distances?
I make no claims to have such knowledge. I do claim that we just
don't know.
[...]
[And just a few other comments]
R> I'm not so sure about that. The dataset is still very small. It's
R> not clear, for example, that metal poor stars can have planets, or
R> perhaps planets not gas giants. There are whole populations of
R> stars that are metal poor, especially the populations of globular
R> clusters.
See the recent results on the planet detected around PSR B1620-26, in
the globular cluster M4.
http://www.extrasolar.net/planet.asp?PlanetID=30
Mass: 2.5 Jupiters
Seems like a gas giant near as I can tell.
But still, globular clusters would seem a dangerous place for planets,
the odds of their orbits being perturbed would seem very high over
a long period of time.
As for earth-type planets, we can't detect them yet. But would you
expect that they would be found around stars in globular clusters?
Rich