In infinite wisdom Joseph Lazio answered:

"R" == Rich  <someone@somewhere.com> writes:

R> In infinite wisdom Louis Scheffer answered:

Rich <someone@somewhere.com> writes:

How can you research something when you got zero examples to
research?

Answer: You can't.

So far so good.  So now we have two hypotheses: no examples exist,
or they exist and we have not found them yet.

R> If we've not found them yet, no examples exist. Saying that no
R> examples exist is not a statement about the existence of the sample
R> category.

Re-read what Lou wrote.  If you do not detect something, that either
means that it doesn't exist *or* that you have not yet found it.

Oddly, that's pretty much what I wrote.

Consider a silly example.  Do cows exist?  If I look out my window,
into my suburban neighborhood, I see no cows.  Therefore, cows do not
exist.

I'm glad we cleared this up. Now what do we do about the conspiracy?
It's disturbing that we see all these images of "Happy Cows" on TV.
But then, they can do anything with CGI these days. :-)

[...]

According to the scientific method, you have to go look.

R> Not exactly.
R> http://teacher.nsrl.rochester.edu/phy_labs/AppendixE/AppendixE.html
R>     [...]

R>     I. The scientific method has four steps

Well, this is the formulaic scientific method, but o.k.

R> 1. Observation and description of a phenomenon or group of
R> phenomena.

Radio transmissions from the Earth are detectable over interstellar distances.

Do you mean current (or past) emissions, or beamed transmissions of the
kind being discussed? And the problem remains that in order to detect
such a signal, you need a really good receiver, you need to know where
to look, and you need to know what frequency at which to look.

R> 2. Formulation of an hypothesis to explain the phenomena.  [...]

Hypothesis:  There may be other civilizations in the Galaxy also capable of producing radio transmissions detectable over interstellar distances.

Above you say "interstellar", now you talk about galactic sources. Do
you think we could detect civilizations across the milky way?

R> 3. Use of the hypothesis to predict the existence of other
R> phenomena, or to predict quantitatively the results of new
R> observations.

Observations at radio wavelengths can be conducted at a certain
sensitivity levels (call this S).  These sensitivity levels translate
to a distance for an assumed transmitter power (roughly d ~ sqrt{S/P}
for an assumed transmitter power P).  If one conducts a search at a
sensitivity level of S and finds no examples of ET broadcasts, the
number of radio transmitting ET civilizations in the Galaxy cannot be
more than roughly (D/d)^2, where D is the diameter of the Galaxy.

Assuming that said civilizations broadcast with the intent to be
detected, perhaps. And lots can happen in the 100,000 years it takes
light to traverse the galaxy, there's a bit of a lag. I suggest that
the probability of said civilization broadcasting in our direction is
inversely related to it's distance from us (and note that much of the
galaxy is occulted and not directly viewable).

(One can of course do this more carefully and fill in the numbers, but
this is the general idea.)

R> 4. Performance of experimental tests of the predictions by several
R> independent experimenters and properly performed experiments.

Otherwise known as SETI.

Indeed.

But with all the radio surveys done of the sky, with 30 years or so of
SETI searches of ever greater sensivity, one might question why any
nearby ET civilization's broadcasts have not already been picked up.
It has been claimed that a 1 watt transmitter would be sufficient
with modern receivers.

Rich