Re: The end of Seti
- From: "Max" <maxamber@xxxxxxxxxxxxx>
- Date: Wed, 13 Sep 2006 08:41:44 GMT
"Matt Giwer" <jull43@xxxxxxxxxxxxxxxxxxxxxxx> wrote in message
To recap but no one replied a few months ago there was a post here about aaround
proposed telescope that could see weather patterns of earth sized planets
other stars. An optimistic proposal said it could be deployed in tenyears. It
was spaced based. The link posted here said 60 meter resolution.it is
I have not been able to verify this 60 meter resolution claim beyond that
original post. It may have been the science writer of the article. But if
Telescopes are theoretically limited in resolution by the diffraction limit
(quantum fussyness if you like).
The resolution r is as small as the wavelength w times the distance R
divided by the diameter of the telescope d. Or in other words, the diameter
of a telescope is equal to the wavelength times the distance divided by the
resolution. Something like r/R = w/d.
To get 60 meter resolution at 10 lightyears, at 200nm or so, you need a
telescope with a diameter of something like 10^9 meters (sorry I dont have a
calculator handy, but it should be in that range). That is larger than the
Earth-Moon system. If we only have a radio-telescope of that size; SETI
would be easy...
There are two possible breaks (that we know of) in this theoretical
(1) Use interferrometry. You don't need a full circular telescope of
diameter d to obtain the resolution.Simply linking some smaller telescopes
separated by that distance d will get you the resolution. Unfortunately, you
will not be able to determine the actual location of what you are looking as
better than the refraction limit of the real diameter of these telescopes.
So you might be able to see that there are details of a certain size, but
you cannot determine where they are w.r.t. each other. You cannot take a
normal picture with such a interferrometer.
So it will be almost impossible to determine if there is something
'artificial' about the details that you are looking at.
(2) Scientists have found that materials with negative magnetic and/or
electrical permeability might allow for lenses that are not restricted to
the diffraction limit. Materials with such properties do not exist in
nature, but certain 'meta-materials' have been constructed that show such
properties for at least microwave regions. This meta-material development is
truely facinating. For example, 'cloaking' devices can be built (a microwave
cloak is currently under development) that can totally hide objects from any
observers at certain frequencies. The microwaves just go around it. When
used as lenses, meta-materials can observe details below the refraction
limit. However, I understand that the distance to the object should be very
small (smaller than the size of the lens).
So it is still unlikely that any ET can make a 'small' telescope with
smaller-than-refraction-limit resolution. At least we have still not yet
found a theoretical trick around that limit.
If in fact this is a legitimate proposal it explains why no one is
transmit. If this is legitimate we could be looking in ten years. Was wecould
see them any civilization contacting could see us in barely a centuryafter
radio is invented. Different technology curves for different folks but ifthere
is a thousand year separation between being able to receive RF and to viewmiles
directly why bother transmitting? As I said, devote a few hundred square
to sending messages but viewing cities should be enough to send the realmessage.
There can be MANY reasons why we have not detected a beacon signal yet, so
to postulate that yet unproven (even in theory) telescope technology
eliminates the objective for ET to send out any radio signals seems rather
What am I saying ? Here you go :
We have scanned only a minute fraction of the radio spectrum for ETI beacon
We have scanned only a minute fraction of the stars of the Galaxy for ETI
We have scanned these radio spectrums and each star only for a minute
fraction of time.
We have a scanned with a sensitivity that is astonishing for terrestrial
communication, but rather poor when talking about interstellar radio
We have scanned an even smaller fraction of stars of optical beacon signals
Frankly, we barely started listening...
I think so far the only thing that we have shown is that there does not seem
to be an extremely powerfull semi-omnidirectional beacon in the Galaxy that
is transmitting in the 'water-hole'.
Not that that means anything, because if you would calculate the power
requirements for such a beacon (in the water hole) then you would find that
only a Kardashev type III civilization could be able to sustain such a
beacon. And we know that there is no Kardashev type III civilization in the
Galaxy, or else there would be no stars visible at night.
Also, there are much better (cheaper) ways to build ETI beacons if someone
would want to do so. They would likely be in the 50Ghz and above area. And
we have not looked there at all yet.
And all this is assuming that anyone would ever want to send out beacon
signals. We (humans) certainly do NOT do that. Why would anyone else ?
I think it is more likely that a beacon will be directed at us after some
(radio/radar leakage) signals from us have been detected by an ETI.
The size/sensitivity requirements for such a system (than can detect our
early TV CW cariers) are much less than the requirements for a telescope
with 60 meter resolution that can distinguish a building or a city from a
By now (50 years after first powerfull transmissions), a few hundred or
maybe a thousand star systems have had the ability to receive and respond to
our early transmissions. A few hundred out of 300 billion stars in the
There can be many reasons why we have not received any signals yet, and I
think it is unlikely that the development of super-telescopes is one of
them... It's a nice idea though...
My 2 cts.
- The end of Seti
- From: Matt Giwer
- The end of Seti
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