Are SETI asumptions valid? (and does it matter if they aren't?)

In article ,
Peter Hickman wrote:

f/fgeorge wrote:
We are searching the data spectrum for signals in a specific mhz

I think you mean that the SETI@Home project is doing this, as SETI in
general is not this restrictive.

range. This mhz is the one that, I believe, Hydrogen atoms vibrate.

This is correct, so far.

Not really. It is just one of the frequencies associated with hydrogen,
possibly the lowest, but not one at which it vibrates [1]. The frequency
is the result of quantum physics effects at two levels: firstly the
frequency is associated with a change in energy (the frequency is
the energy change divided by Planck's constant); secondly, that energy
change is due to a change in the relative orientation of the spins
(which are themselves quantum effects, not real motion) of the nucleus and
the electron, in atomic hydrogen (the spins of the two electrons would
be opposite and cancel out in hydrogen molecules).

It is a particularly well defined frequency precisely because it
is not associated with mechanical motion, and is, in fact, used
in many atomic clocks (all atomic clocks use the same basic mechanism,
but not all are based on hydrogen). It's known to better than 13
decimal places.

Meaning that any communication recieved would be from life forms that
have Hydrogen based life, like ours.

The reason it is significant is nothing to do with life; it is that it
is the most abundant element in the universe and in inter-stellar space.
The 1.42...GHz hydrogen hyperfine line radiation is used to map the
distribution (and temperature etc.) of cold hydrogen between stars and
is therefore of fundamental interest to radio astronomers. The theory is
that any attempt at interstellar communication will involve radio
astronomers and this hydrogen radiation will be a fundamental concept to
all of them - even if they have exhausted experiments on these frequencies,
it will still be fundamental to the history of the science.

This is where is goes wrong, the hydrogen band is cleaner. There is less
noise in this part of the spectrum so if you wanted a message to travel

No it is not. There is excess noise becuase of the hydrogen line radiation
itself, but also it is at the bottom end of a frequency range from about
1GHz to about 20GHz which has relatively low sky noise. Being at the bottom
end, the sky noise is significantly higher than the minimum due to the
galactic synchrotron noise component that defines the lower limit. Being
at the bottom end also means that the transmitter antenna gain is lowest
for a given antenna size.

The only reason it is in any way quiet is that, being reserved for radio
astronomy, there is little man made interference, whereas the frequencies
that would be better are likely to be taken up by satellite TV and other
satellite communication and navigations systems.

Note that most microwave SETI is not restricted to the immediate vicinity
of the 1.42GHz line; S@H is the exception in modern professional SETI.

[1] atomic hydrogen can't really support vibration modes - you need molecules
with two distinct, localized masses.

[ note: original article in alt.sci.seti only ]

In article ,
Peter Hickman wrote:

f/fgeorge wrote:
We are searching the data spectrum for signals in a specific mhz

I think you mean that the SETI@Home project is doing this, as SETI in
general is not this restrictive.

range. This mhz is the one that, I believe, Hydrogen atoms vibrate.

This is correct, so far.

Not really. It is just one of the frequencies associated with hydrogen,
possibly the lowest, but not one at which it vibrates [1]. The frequency
is the result of quantum physics effects at two levels: firstly the
frequency is associated with a change in energy (the frequency is
the energy change divided by Planck's constant); secondly, that energy
change is due to a change in the relative orientation of the spins
(which are themselves quantum effects, not real motion) of the nucleus and
the electron, in atomic hydrogen (the spins of the two electrons would
be opposite and cancel out in hydrogen molecules).

It is a particularly well defined frequency precisely because it
is not associated with mechanical motion, and is, in fact, used
in many atomic clocks (all atomic clocks use the same basic mechanism,
but not all are based on hydrogen). It's known to better than 13
decimal places.

Meaning that any communication recieved would be from life forms that
have Hydrogen based life, like ours.

The reason it is significant is nothing to do with life; it is that it
is the most abundant element in the universe and in inter-stellar space.
The 1.42...GHz hydrogen hyperfine line radiation is used to map the
distribution (and temperature etc.) of cold hydrogen between stars and
is therefore of fundamental interest to radio astronomers. The theory is
that any attempt at interstellar communication will involve radio
astronomers and this hydrogen radiation will be a fundamental concept to
all of them - even if they have exhausted experiments on these frequencies,
it will still be fundamental to the history of the science.

This is where is goes wrong, the hydrogen band is cleaner. There is less
noise in this part of the spectrum so if you wanted a message to travel

No it is not. There is excess noise becuase of the hydrogen line radiation
itself, but also it is at the bottom end of a frequency range from about
1GHz to about 20GHz which has relatively low sky noise. Being at the bottom
end, the sky noise is significantly higher than the minimum due to the
galactic synchrotron noise component that defines the lower limit. Being
at the bottom end also means that the transmitter antenna gain is lowest
for a given antenna size.

The only reason it is in any way quiet is that, being reserved for radio
astronomy, there is little man made interference, whereas the frequencies
that would be better are likely to be taken up by satellite TV and other
satellite communication and navigations systems.

Note that most microwave SETI is not restricted to the immediate vicinity
of the 1.42GHz line; S@H is the exception in modern professional SETI.

[1] atomic hydrogen can't really support vibration modes - you need molecules
with two distinct, localized masses.

[ note: original article in alt.sci.seti only ]

(David Woolley) wrote in message ...

....snip...

The reason it is significant is nothing to do with life; it is that it
is the most abundant element in the universe and in inter-stellar space.
The 1.42...GHz hydrogen hyperfine line radiation is used to map the
distribution (and temperature etc.) of cold hydrogen between stars and
is therefore of fundamental interest to radio astronomers. The theory is
that any attempt at interstellar communication will involve radio
astronomers and this hydrogen radiation will be a fundamental concept to
all of them - even if they have exhausted experiments on these frequencies,
it will still be fundamental to the history of the science.


Perhaps some would think that the significance of that frequency has
everything to do with life, it being the bottom end of "The
Waterhole". Indeed, back in 2000 David Woolley probably also wrote:

OPEN QUOTE
....(There are actually at least three water hole definitions: - 1 to
~20GHz where absorption/noise (they are aspects of the same thing) is
low; - between 1.42.. and 1.6.., strong lines associated with H and
OH, the constituents of water; - 1.42... +- a few hundred kHz, by
analogy with waterholes where animal gather to drink. SETI@Home uses
the third, SERENDIP, on which it is based, uses the second, and
Phoenix, the SETI Institute targetted search, uses a significant part
of the first. The second has, amongst other things, strong interfering
signals from GPS satellites and the Russian equivalent.)...
CLOSE QUOTE

David's third definition of 2000 seems to have something *to do with
life*, and his second definition is the dominant definition (IMO) for
the Waterhole that I've encountered over the years (the point being
that water-based LIFE would perhaps search in these frequency ranges.)
_________________
(I remembered David's 2000 post because I had responded to it with
OPEN QUOTE
....The second water hole definition you gave (above) is considered by
some to be more like 1.42 to 1.72 GHz because there is also a strong
OH emission at 1.7205299 etc. GHz.
CLOSE QUOTE)
_________________

Regards, Jason H.

(David Woolley) wrote in message ...

....snip...

The reason it is significant is nothing to do with life; it is that it
is the most abundant element in the universe and in inter-stellar space.
The 1.42...GHz hydrogen hyperfine line radiation is used to map the
distribution (and temperature etc.) of cold hydrogen between stars and
is therefore of fundamental interest to radio astronomers. The theory is
that any attempt at interstellar communication will involve radio
astronomers and this hydrogen radiation will be a fundamental concept to
all of them - even if they have exhausted experiments on these frequencies,
it will still be fundamental to the history of the science.


Perhaps some would think that the significance of that frequency has
everything to do with life, it being the bottom end of "The
Waterhole". Indeed, back in 2000 David Woolley probably also wrote:

OPEN QUOTE
....(There are actually at least three water hole definitions: - 1 to
~20GHz where absorption/noise (they are aspects of the same thing) is
low; - between 1.42.. and 1.6.., strong lines associated with H and
OH, the constituents of water; - 1.42... +- a few hundred kHz, by
analogy with waterholes where animal gather to drink. SETI@Home uses
the third, SERENDIP, on which it is based, uses the second, and
Phoenix, the SETI Institute targetted search, uses a significant part
of the first. The second has, amongst other things, strong interfering
signals from GPS satellites and the Russian equivalent.)...
CLOSE QUOTE

David's third definition of 2000 seems to have something *to do with
life*, and his second definition is the dominant definition (IMO) for
the Waterhole that I've encountered over the years (the point being
that water-based LIFE would perhaps search in these frequency ranges.)
_________________
(I remembered David's 2000 post because I had responded to it with
OPEN QUOTE
....The second water hole definition you gave (above) is considered by
some to be more like 1.42 to 1.72 GHz because there is also a strong
OH emission at 1.7205299 etc. GHz.
CLOSE QUOTE)
_________________

Regards, Jason H.

In article ,
(Jason H.) wrote:

Perhaps some would think that the significance of that frequency has
everything to do with life, it being the bottom end of "The
Waterhole". Indeed, back in 2000 David Woolley probably also wrote:

Only in combination with the 1.6GHz OH- line cluster. In this thread,
it was fairly clear that the narrow definition was in use; that is
generally the case where people are complaining that "SETI" is not
searching enough of the spectrum (and it is confusion with the broad
definition that causes people to claim that it is low noise). The narrow
definition is not based on biochemistry, although the analogy is of the
meeting place of the animals in the wild, which is vaguely biological.

In fact, I suspect that the the medium definition is much more a
rationalisation of technology limitations than a real criterion. I
don't believe any current SETI project uses that definition to define
its search limits (SERENDIP might have approximated it if had
covered the original planned 200MHz, but currently covers 100MHz
centred on 1.42GHz, but Phoenix goes well above the OH- lines). The
optimum frequencies for communication are all above the OH- lines.
(If I remember correctly, "Contact" used pi * f(H[hypefine)), at
least in the book.)

The medium definition suffers from severe man made pollution from,
in particular, GPS satellite navigation signals.

(I did consider giving the three definitions in the current reply,
but I've already done that many times and I'm not sure that the term
"waterhole" was actually used.)

In article ,
(Jason H.) wrote:

Perhaps some would think that the significance of that frequency has
everything to do with life, it being the bottom end of "The
Waterhole". Indeed, back in 2000 David Woolley probably also wrote:

Only in combination with the 1.6GHz OH- line cluster. In this thread,
it was fairly clear that the narrow definition was in use; that is
generally the case where people are complaining that "SETI" is not
searching enough of the spectrum (and it is confusion with the broad
definition that causes people to claim that it is low noise). The narrow
definition is not based on biochemistry, although the analogy is of the
meeting place of the animals in the wild, which is vaguely biological.

In fact, I suspect that the the medium definition is much more a
rationalisation of technology limitations than a real criterion. I
don't believe any current SETI project uses that definition to define
its search limits (SERENDIP might have approximated it if had
covered the original planned 200MHz, but currently covers 100MHz
centred on 1.42GHz, but Phoenix goes well above the OH- lines). The
optimum frequencies for communication are all above the OH- lines.
(If I remember correctly, "Contact" used pi * f(H[hypefine)), at
least in the book.)

The medium definition suffers from severe man made pollution from,
in particular, GPS satellite navigation signals.

(I did consider giving the three definitions in the current reply,
but I've already done that many times and I'm not sure that the term
"waterhole" was actually used.)