Re: SETSIs (was Re: seti@home WILL NOT WORK)

Robert J. Bradbury (
Fri, 9 Jul 1999 11:35 PDT

> Doug Jones <> wrote:
> Robert J. Bradbury wrote:
> >
> > Now, it would appear that the development time for a technological
> > civilization from the pre-radio stage to the post-singularity stage
> > is ~100 years on a planet similar to ours.
> > So, for the SETI@home project to work, as has been suggested, by
> > "evesdropping" on similar level civilizations, they would have to
> > be within ~100 light years of us.
> Not quite, I think- the ETIs must only have been broadcasting at the
> appropriate time vs distance. If a civilization 950 ly away
> trancended 900 years ago, their "fossil" emissions would still be
> wafting over us. This increases the number of possible hits
> significantly.

That's the problem with this group... Try to be brief and you get crucified... [I'm not sure if the converse -- Try to be complete and the message gets long and ends up DELed -- is true or not.] :-)

Yes, I was aware of this. The problem is that as the distance increases so too do the power/antenna requirements. Our natural (unintentional) transmissions are designed for "domestic" consumption and are therefore not very powerful. For a similar civilization to detect them very far out is going to require an investment in a very big receiving antenna. The further away the civilization is the bigger the antenna needs to be.

By the time *we* get to the point where we can hear "non-intentional" transmissions at 950 ly, we will likely be post-singlularity. [Please note that this is my gut-feel from reading the literature, a real physicist/astronomer would need to do the calculations so we could graph the detectable ranges for various transmission powers and receiver dish sizes.]

By the time *they* get to the point where they can observe us optically (@ 950 ly) and/or can beam a high power signal (detectable by a small antenna) intentionally (and continuously because you never know when we will happen to listen) in our direction, they are probably post singularity.

If you see the singularity coming (as some of us do), then it makes no sense at all to transmit anything before that time (because after it you have so much more power). If the trends in fiberization continue, then the time for significant unintentional broadcasts is shorter than the 100 year figure (perhaps 60-70 years for TV signals).

I believe that combined these things mean that SETI@home, as currently designed, seems to have a really small coverage volume where you might overhear the noise of a nearby civilization at our level [odds very small IMHO].

If you know that the average pre-radio - post-singularity time is ~100 years (and this I think depends a *lot* on the star type, planet, land area, population, etc., etc.), then post-singularity you have the problem that the further out you look, the fuzzier your picture gets. If I'm a post-singularity SI @ 950 light years, I'm seeing the Earth in year 1050. I say, well that looks kind of interesting but I'm not going to waste my energy sending a signal there for 950 years(!). And given my distance and the crooked paths the development of civilizations take, I'm not going to be able to predict when I should send a signal (for even a short period). Given all that, perhaps the best thing I can do is launch a nanoprobe at 0.9c (that's cheap since it doesn't weigh very much). Upon arrival, it then turns an asteroid in the system into a monitoring post and builds up enough "intelligence" to function as a proxy for the SI when the time for "contact" is right. Given this rationale and since you have to do the probe design and construct the mass accelerator, you might as well send a probe to every star in your "section" of the galaxy.

Since the nanoprobe could just as easily turn the system into an SI (much to the dismay of our little nematode-level minds), there must be a reason for not doing that. Promoting the increase in galactic diversity is one of the best I can come up with so far. I'm open to other suggestions.

Where this gets fun is if you consider the following -- I'm a nanoprobe SI proxy agent, I've been in the solar system for 4 billion years or so. Venus was a complete bust, Mars looked good but fizzled early, Earth is making headway but you've been watching the reptiles for 140 million years. Simulations show that they are going to dominate the planet for another 100 million years but not give rise to an SI. I radio the SI and say, simulations show this is going nowhere fast. 1900 years later a brief message comes back -- "Nuke-em, but make it look like an accident." SIs may have been around for a long time and probably have a great deal of patience, but who knows whether or not they stack the deck once in a while.