GOURDHEAD, you wrote, “they could not be sure that it was intelligent as it was 2000 years ago or technically competent”

But it seems to me there is certainly the possibility for ET to develop a very accurate idea of the level of our technology from an analysis of atmospheric gases and pollutants. For instance:

1. Lead has been used in metal working for more than 8500 years. The Romans increased the lead identified in Greenland ice cores hundreds of times above normal 2500 years ago.
2. Coal has been widely used for more than a thousand years. Burning coal releases radioactive uranium and thorium into the atmosphere, mercury and other gases and particles, many of which could be candidates to announce the presence of a living civilization.
3. Chemicals which came into widespread use in the 19th century, such as DDT (1870s), kerosene, naph-thalene and gasoline (1850s), benzene (1860s), and chloroform (1840s).
4. Widespread use of freon since 1929. For those 75 years we’ve used a 600 million square kilometer antenna to broadcast 24/7-360 degrees that we use refrigeration, have substantial electrical distribution and freight delivery systems, fractional horsepower electric motors, measures of some kinds of industrial activity, and lots of other implications

And ET might have some very clever ideas of his own.

Bob

I agree there are cases for which your assertions are true. The set of all cases include those for which the analysis of atmospheres would be indeterminant across wide rnages of technical competence.

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For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?

What is the Drake equation?? I believe there is life out there somewhere, even if we don't reach them in this lifetime, maybe we will in the next!

The Drajke equation is a way of guessing how many intelligent alien civilisations there are in our galaxy which could be contacted using radio technology;
here is one formulation of the equation;
http://www.activemind.com/Mysterious/Topic...e_equation.html


try it yourself. When I plug my figures in I get about 400 civilisations in our galaxy;

this has to be weighed against the similarly famous Fermi paradox, which asks why none of the civilisations (if there are any) in our galaxy have bothered to colonise the galaxy by now.
Simply put, the Fermi paradox asks - if they exist, they should be here by now. Where are they?

If we expect the longest lived civilisations to start exploring then the Drake equation needs to be adjusted downwards; since these civilisations are not here already, the true figure for the answer of the Drake equation must be very low in deed.

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It seems to me that the “ET is there, but can’t contact us because of the distance” scenario requires unlikely limitations for ET; namely an unsophisticated technology, hardly as capable as will be ours by the end of this century.

Its necessary to rule out any thing super-luminal: travel, communication and even observation. I’m not adverse to such a ruling out; but it is an assumption about beings thousands or millions of years ahead of us.

But, even without super-luminal observation, I think an understanding of our level of development is possible for ET even many thousands of light years away and only a few centuries more advanced than us--maybe even one century.

The keys are sophicated observation, modeling and the use of agents.

Lead from metal working has been detectable in the atmosphere for more than eight thousand years, the by-products of coal burning for more than a thousand years, and artificial chemicals like DDT for more than 130 years.

An ET, more clever than us, could observe the pattern of changes in lead, uranium, thorium, other particulates, and other phenomena, and develop a sophisticated model of our development based on a vast knowledge of the interplay of thousands of variables using mathematics we’ve never conceived. Maybe chief anthropologist ET could say, “About a hundred years from this change, they’ll be using electricity. Look for the arrival of freon about 30 years later.”

An ET professor might instruct his class, “Perform this transformation on the spectral signal of chlorophyll and you determine characteristics of vegetation. This pattern, with its regularity and other indicia, signals agriculture. Note the changes, and general strengthening, for the four thousand years we have observa-tions.”

Any time in the past ET could have dispatched “agents” to Earth knowing, from ETs models, what would happen here. During their travels, and subsequently, the agents could continuously, based on in-coming information and new research, be re-instruct by ET. The agents are intelligent, sentient “computers” (but much, much more than that) dedicated to the mission of learning all about us, always communicating back home, even though the information would take two thousand years to get there.

ET, with an essentially indefinite life span, would find the delay dreadful, but something that can be tolerated. And the agents could act for ET.

I think a thousand years from now we will be doing sophisticated observation beyond conceiving today. We will have models of technological development that will enable us to predict, with some accuracy, just where a developing civilization will be when we get there in another thousand years. And we’ll have the descendants of computers to act as agents when we see the possibility of something interesting emerging.

If us, why not advanced ET?

Bob

I beg to disagree. In this case the abscence of evidence is not necessarily the evidence of abscence. It's not likely that they are much advanced from us or their perturbation of their section of the MW would be easy to detect. The Drake equation gives higher numbers when adjusted for the increased likelyhood of perpetuity of civiizations that have achieved interstellar travel and colonization competence.

__________________
For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?

a book of interest on this was 'The Center of the Web', from good 'ol Sky Publishing. it may yet be around. it does seem obvious that ET, in any techno- conventional sense, should have shown up---seems we are alone---but here again exists the ongoing problem in the sciences---in this case, lack of current 'Life-Science' being of interest to astronomers seeking ET---i've let SETI use my machines for years, i don't expect anything to come of it.

“the abscence [sic] of evidence is not necessarily the evidence of abscence [sic]”

The statement should be rephrased as “The absence of evidence is not evidence of absence.” The “not necessarily” is not necessary.

Consider this situation: You walk into a strange room and see a certain box for the first time, a box which is in the form of a one meter cube and appears to be made of metal and sealed. You have no information at all about the contents of the box. You didn’t see it closed; no one has told you anything about it. You can’t see through it; and haven’t tried to determine any other characteristics.

You wonder, for no reason at all, “Is there a black cat in that box?” To which the correct answer is, “I have no idea.” The absence of evidence says nothing about whether there is, or is not, a black cat in the box.

It’s a tautology: if you know nothing, you know nothing.

But, with the case of the existence of advanced ETs, I think we do know more than nothing. There is lots of negative evidence. Like most negatives we won’t ever be able to say with certainty that there are no advanced ETs. It’s a matter of probabilities, and our assessment of those probabilities changes with new knowledge.

For instance, if the probability that advanced ETs would be discovered in our solar system was 10% in 1900; now it’s one in a billion plus or minus a few zeros. If the probability was 90% that advanced ETs would be discovered by radio waves when we first started listening, that probability has to be a lot less now.

I’d make the connection that as the probability of discovery declines, the probability of existence declines.

We’ve discussed the negative observations in considerable detail before: the reasoning that ET should have been heard from, the failure of SETI to date, the lack of any observable effect of intelligent life other than what Homo Sapiens has done.

All of this negative evidence pushes the probability lower. Maybe the probability is still very high—say 99%--but every day that produces new observations and no discoveries reduces that probability. Maybe just a little, but the direction has been consistent for more than a century.

I think when the phrase is used, “Absence of evidence is not evidence of absence;” what’s really meant is that we should ignore all the evidence, that “Evidence of absence is not evidence of absence.”

If we don’t discover advanced ET tomorrow, I think that will mean the probability of his existence will be lower at the end of the day than at the beginning. After enough tomorrows, the probabililty of his existence will be a lot less than 99%.

Bob