Fermi paradox, your own belief?

"Bryan J. Maloney" wrote in message .. .
Geoff McCaughan abagooba zoink larblortch
:

In rec.arts.sf.science Bryan J. Maloney wrote:

Drawing conclusions from N=1 is not science, it is a form of religion.

State your hard evidence that N=1.


How many solar systems have been directly observed at a distance wherein
one can reliably determine whether or not life exists on them? One, and
only one. Therefore, N = 1. After all, "N" means REPLICATES, not
"positive results". Only an utter moron, a thorought waste of DNA who
should remove himself from the gene pool for the good of humanity, thinks
that N=1 means "there has only been one positive result".

What is the 95% confidence interval on a sample size of one?

Even though we know of only one technological civilization (us), that
does not mean that N=1 (presumably N is from the Drake Equation.)
Perhaps N1 or N1 or N is very nearly zero. If you are using the
Drake Equation, what values are you using?

In message , Paul F. Dietz
writes
Martin Brown wrote:

Note that I am not saying that p(life) is 0.5
I am just pointing out that claiming that you believe that
p(life) == 1/exact_number_of_planets_in_universe
exactly represents a significant leap of faith unsupported by
evidence.

Ah, but the SETI-skeptic position doesn't make this argument.
It can claim that p(life) 1/number_of_planets_in_observable_universe.

And it then comes back to entropy.
In doing this you are claiming to have knowledge that you do not
possess.

And they only get to win if that statement is true and I get to win for
all the rest of the number line up to 1.0. For the record I do think
SETI is a waste of time for finding ET's, but I suspect it may
occasionally turn up interesting serendipitous natural signals that
would otherwise be missed.

that arises will never contact any independently arising life.

I think a good argument for SETI would be panspermia, to ruin the assumption
of independence.

We don't know what the underlying model is so there is no way to
estimate a single number for P(life) at present with such limited data.

However, a Bayesian can quite happily determine the function P(P(life))
both before and after adding the N=1 data point that we are alive.

Regards,
--
Martin Brown

In message , Paul F. Dietz
writes
Martin Brown wrote:

Note that I am not saying that p(life) is 0.5
I am just pointing out that claiming that you believe that
p(life) == 1/exact_number_of_planets_in_universe
exactly represents a significant leap of faith unsupported by
evidence.

Ah, but the SETI-skeptic position doesn't make this argument.
It can claim that p(life) 1/number_of_planets_in_observable_universe.

And it then comes back to entropy.
In doing this you are claiming to have knowledge that you do not
possess.

And they only get to win if that statement is true and I get to win for
all the rest of the number line up to 1.0. For the record I do think
SETI is a waste of time for finding ET's, but I suspect it may
occasionally turn up interesting serendipitous natural signals that
would otherwise be missed.

that arises will never contact any independently arising life.

I think a good argument for SETI would be panspermia, to ruin the assumption
of independence.

We don't know what the underlying model is so there is no way to
estimate a single number for P(life) at present with such limited data.

However, a Bayesian can quite happily determine the function P(P(life))
both before and after adding the N=1 data point that we are alive.

Regards,
--
Martin Brown

(W. Snell) abagooba zoink larblortch
om:

Even though we know of only one technological civilization (us), that
does not mean that N=1 (presumably N is from the Drake Equation.)

How many times do I have to explain this? Do they no longer teach basic
scientific methods? "N" does NOT refer to the number of "positive"
results. "N" refers to the number of OBSERVATIONS made. So far, we have
only observed one solar system with sufficient closeness to determine
whether or not life exists.


Perhaps N1 or N1 or N is very nearly zero. If you are using the
Drake Equation, what values are you using?

The Drake Equation is bull****.

(W. Snell) abagooba zoink larblortch
om:

Even though we know of only one technological civilization (us), that
does not mean that N=1 (presumably N is from the Drake Equation.)

How many times do I have to explain this? Do they no longer teach basic
scientific methods? "N" does NOT refer to the number of "positive"
results. "N" refers to the number of OBSERVATIONS made. So far, we have
only observed one solar system with sufficient closeness to determine
whether or not life exists.


Perhaps N1 or N1 or N is very nearly zero. If you are using the
Drake Equation, what values are you using?

The Drake Equation is bull****.

Martin Brown wrote:


We don't know what the underlying model is so there is no way to
estimate a single number for P(life) at present with such limited data.

But we apparently are allowed to express the prejudice that presence
of life is 'simpler' than its absence, in the absence of any data to
justify that prejudice.

Frankly, your entropy argument is ridiculous. The probability is high
or it is not, and without data there is no reason to prefer the former
over the latter. (Of course, we do have data, data that appears to disfavor
very high probability scenarios.)

Perhaps it would be illuminating if you applied the argument to the existence
of unicorns, or mermaids.

Paul

Martin Brown wrote:


We don't know what the underlying model is so there is no way to
estimate a single number for P(life) at present with such limited data.

But we apparently are allowed to express the prejudice that presence
of life is 'simpler' than its absence, in the absence of any data to
justify that prejudice.

Frankly, your entropy argument is ridiculous. The probability is high
or it is not, and without data there is no reason to prefer the former
over the latter. (Of course, we do have data, data that appears to disfavor
very high probability scenarios.)

Perhaps it would be illuminating if you applied the argument to the existence
of unicorns, or mermaids.

Paul

Martin Brown abagooba zoink
larblortch :

However, a Bayesian can quite happily determine the function
P(P(life)) both before and after adding the N=1 data point that we are
alive.

Are you saying that the folks who live out of shopping carts downtown are
all Bayesians?

Martin Brown abagooba zoink
larblortch :

However, a Bayesian can quite happily determine the function
P(P(life)) both before and after adding the N=1 data point that we are
alive.

Are you saying that the folks who live out of shopping carts downtown are
all Bayesians?

Martin Brown wrote:

In message , Karl M. Syring
writes
[...]
It means that Bayesian analysis is superior here.

It is rather fun to watch these heated debates with both sides
calling each other names and insisting that their belief is the
only correct one.

The two camps sit mainly at opposite extremes.
Near P(life) = 0 or 1. It is very unusual to find anyone arguing
vehemently that

P(life) = 0.5 +/- infinity

but that is really all the data is capable of supporting at
present. We can't see the next nearest planetary system(s) well
enough to put a single number on P(life). And all the attempts to
do so are at best guesswork.

I myself am at least somewhat Bayesian. I find it least
satisfying in situations of maximal ignorance, such as SETI,
but I suppose other methods would have problems in those
situations as well.

I would like to offer a different analysis, possibly not useful
right now, but probably the kind of analysis offered in the
distant but imaginable future by applicants for SETI grants.
It seems like I've gotten something for nothing here (that is,
a prediction of success brewed from a previous lack of success),
but I don't see where my error is.

Grantsmanship question: Suppose we have ruled out alien
civilzations in a 100 light-year sphere around Earth. How far out
would we have to search to find our first such civilization?

Simplifying assumption: The probability of finding a civilization
within a certain volume is proportional to the size of that
volume (for volumes large enough to contain many solar systems).

The probability is low for any individual solar system and
is independent of the occurence of civilizations in neighboring
systems, so a Poisson distribution with rate proportional to
the volume in question is a good model. That is, if P(n) is
the probability of finding N non-Earth civilizations within a
certain volume of galactic space, D is the density of civilizations,
and V is is the size of the volume in question, then
P(N) = (D*V)^N/N! * exp(-D*V)

(i) If we are given the confidence interval we want to have, we can
find a range of values for the density of civilizations D
that would yield that confidence interval.

Let V0 be the volume of the sphere we've already searched
unsuccessfully, D be the (unknown) density of civilzations,
and our confidence interval be (0.05, 0.95).

Assume 0.05 P(N=0) 0.95

Then 0.05 exp( -D*V0 ) 0.95
-ln(0.95)/V0 D -ln(0.05)/V0

Note V0/(-ln(0.05)) 1/D V0/(-ln(0.95))

(ii) If we are given another confidence interval which we would
like to apply to the new volume of space to be searched (for
example, for there to be a 0.05 to 0.95 chance of finding
at least one civilization), then, given a known density of
civilizations, we can calculate a range for how much new space
we need to search.

We do not have a known density, but we do have a range of
densities. If we combine these calculations, we have a
range of distances we expect to have to search to in order to
find our first alien civilization.

Let V1 be the new volume to be searched, D be the density of
civilizations, and (0.05, 0.95) be this new confidence interval.

Assume 0.05 P(N0) 0.95

Then 0.05 1 - exp( -D*V1 ) 0.95
0.05 exp( -D*V1 ) 0.95
-ln(.95)/D V1 -ln(.05)/D

But -ln(.95)*V0/(-ln(.05)) -ln(.95)/D V1
V1 -ln(.05)/D -ln(.05)*V0/(-ln(.95))
(ln(.95)/ln(.05))*V0 V1 (ln(.05)/ln(.95))*V0
0.0171*V0 V1 58.4*V0

Let r = 100 lyr be the initial search radius and R be the
next generation search radius.

Then V0 = 4pi/3*r^3
V1 = 4pi/3*(R^3 - r^3)

Then 0.0171*r^3 R^3 - r^3 58.4*r^3
1.0171*r^3 R^3 59.4*r^3
1.0057*r R 3.902*r

Then R = 390 lyr. This seems to say that, if we search out
to 100 lyr and find no alien civilizations, then the conclusion
we should draw is that we have a good chance of finding at
least one if we search out to 390 lyr (or 772 lyr for
(0.01, 0.99) intervals, etc.).

Jim Burns