Re: Fermi paradox in the news

From: Jeff Davis (
Date: Thu Oct 26 2000 - 02:25:22 MDT

The July issue of Scientific American had an article on the Fermi Paradox
written by Ian Crawford, and entitled appropriately, "Where are they?"

It can be found online at:

A sidebar by Andrew J. LePage entitled "Where could they hide?", at

is a discussion of the seti search. Both pieces are quite astute, but also
hopelessly conventional.

LePage says:

>No SETI program has ever found a verifiable alien radio signal. What does
>that null result mean? <snip>
>researchers can draw some preliminary conclusions about the number and
>technological sophistication of other civilizations.

Balderdash, I say.

>The most thoroughly examined frequency channel to date, around 1.42
>corresponds to the emission line of the most common element in the universe,
>hydrogen--on the premise that if extraterrestrials had to pick some
>to attract our attention, this would be a natural choice.

Assuming they're trying to get our attention, and they think as the seti
people think.
Quite an assumption!

><snip>No signal has ever been detected, which means
>that any civilizations either are out of range or do not transmit with
>power to register on our instruments.
>The null results therefore rule out certain types of civilizations,
>including primitive ones close to Earth and advanced ones farther away.

I can't believe this guy is serious. What about, "rules out the correctness
of your search assumptions"?

> <snip>effective isotropic radiated power (EIRP) of the transmitters. The
>EIRP is essentially the transmitter power divided by the fraction of the sky
>the antenna covers. In the case of an omnidirectional transmitter, the EIRP
>is equal to the transmitter power itself. The most powerful on this planet
>is currently the Arecibo radio telescope in Puerto Rico, which could be
>used as a narrowly beamed radar system with an EIRP of nearly 1014 watts.

Which brings me to my point. Arecibo with a narrow beam has an EIRP of
nearly 10^14 watts. Fine. Suppose they're not trying to signal us. Then
is the EIRP. Or to put it another way, from beyond the earth what does the
earth look like, strengthwise, as a radio source--make that an EM source--at
any and all frequencies. Without the Arecibo single frequency pencil beam
concept (Asfpbc), what are we dealing with? And does it seem to anyone but
me, that drawing conclusions based on the Asfpbc is a kind of way forced and
unrealistically particular foundation for drawing conclusions? Specifically
EXPECTING the highest possible signal strength. On what basis? Because
you want to hear them. Hypothesizing that they run their culture to
your discovery of them, pegs my 'whacko" meter. I know I must have gotten
it wrong, but the analysis as put forward seems to tend that way. Someone
who knows about seti (not me) might clear this up.

More realistically, at what distance from our solar sytem does Earth's human
generated EM radiation fall to the level of weak and unrecognizable noise?
In my view, that is the distance limit for drawing meaningful conclusions
the presence of a human equivalent et civilization.

When I first read the article, I thought about it, and asked myself about
the strongest signal would be--the signal which would give the greatest
detectable range by which an affirmative conclusion might be drawn. I
thought perhaps the EM pulse from a naked nuclear explosion would be
both the strongest, as well as the signal most undeniably indicative of a
technological civilization. Clearly, such a signal would be brief. But
assuming that to be the best signature by which others might detect OUR
presence, I did a little research into the amount of such 'signaling' that we
have done. It turns out that in the period between 1945 and 1998 humans
have conducted 2,050 nuclear explosions, of which 528 have been atmospheric,
and 1522 undergound. If the EM pulse lasts for one tenth of a second (this
is just a guess, I leave it to others to help out with something more
that would mean 52.8 seconds of strong, unambiguous signal. Fifty-three
seconds in fifty years. Using Arecibo's 10^14 watts as a basis of
what might be the signal strength, and corresponding detection range for a
nuclear explosion? Perhaps the answer should be given as a range,
to the range of detonation yields?

                        Best, Jeff Davis

           "Everything's hard till you know how to do it."
                                        Ray Charles

This archive was generated by hypermail 2b30 : Mon May 28 2001 - 09:50:18 MDT