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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Expedition to Europa
Date: Mon, 1 Jul 2024 17:03:32 -0700
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On 7/1/2024 7:54 AM, Martin Brown wrote:
>> *We* can't (yet) travel interstellar distances in single lifetimes
>> but I'm sure anyone with technology comparable to ours would be able to
>> *detect* our presence (given that we seem to make no attempt at "hiding")
> 
> The Fermi paradox of why aren't they here yet is somewhat tricky to explain. 
> Our star is nothing like the oldest it could be so there are potentially 
> technological societies that are billions of years ahead of us - plenty of time 
> for robotic probes to visit anywhere in the galaxy.

And, probes don't ave to "pass through"; there's no reason they can't
sit and watch (if you have advanced technology, what limits might that
overcome on designing durable products?)

> I suspect that unless there is some clever shortcut using physics we don't yet 
> know about human inter stellar travel is just a pipe dream.

But you don't need to *go* somewhere to know that it exists *or* what
it is like.  We've visited Mars without ever having set foot, there.
Ditto the depths of the oceans.

We can make educated assessments as to the suitability for "life"
in places that we could never expect to actually visit.  Or,
discover some form of life and then set upon trying to sort out how
to communicate with same.

>> _If the Universe Is Teeming with Aliens ... WHERE IS EVERYBODY?_ gives some
>> interesting takes on the Fermi paradox.
> 
> One potentially very interesting way a technological civilisation may be 
> detectable from Earth by spectroscopy is the presence of CFCs and HCFCs in 
> their atmosphere. Once they master fluorine chemistry their discovery and 
> utility is inevitable until they realise the damage to the ozone layer. Then 
> they get phased out. Planets in transit across their suns are now being checked 
> and so far nothing unusual has been seen.
> 
> Key point here is that fluorine is so reactive and calcium so abundant that you 
> can't really get any fluoro-organic chemistry going without a technological 
> civilisation. A handful of desert plants have mastered it to make 
> monofluoracetic acid on Earth (extremely effective rodenticide).
> 
> It takes industrial scale manufacture before CFCs would be visible from afar. 
> SF6 is another common one but it's scale height works against seeing it high in 
> the atmosphere (its molecule is rather heavy).

But you (we) are still constrained by your knowledge of physical sciences
(and "interstellar civilizations").  Who's to say that "they" haven't
identified some other observable (by THEM) characteristic of civilization?

There are a whole slew of questions that you have to consider before you
even worry about "how" to detect (or signal to) other civilizations.
- how much (effort/cost) do you want to detect them?
- how much do THEY want to be detected?
- how can they evade detection (assuming they actively don't want to be found)?
- how much do YOU want to be found?
- what might the consequences of such a detection be?  (e.g., _Remembrance..._
posits an extinction level consequence)

Adams's claim that "Space is big" can also be accompanied by "Time is LONG".
Do these conspire for or against discovery (or being discovered)?