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From: Martin Brown <'''newspam'''@nonad.co.uk>
Newsgroups: sci.electronics.design
Subject: Re: Expedition to Europa
Date: Wed, 3 Jul 2024 11:38:07 +0100
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On 02/07/2024 01:03, Don Y wrote:
> 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?)

It still puts quite hard limits on how small a device can observe the 
Earth even with diffraction limited optics. Monitoring radio traffic is 
much easier if the frequency is such that it escapes.

>> 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.

Indeed and remote sensing is getting very good now. I expect that 
someone will find a planet with evidence of an industrial atmosphere 
within the next century or so (maybe sooner).

> 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.

That can be fraught with difficulties. I expect life as reproducing 
photosynthetic slime is extremely common anywhere that is stable enough 
to allow a billion years of reactions. Aqueous environment might not be 
strictly necessary but most other things have solid phases that sink.
> 
>>> _If the Universe Is Teeming with Aliens ... WHERE IS EVERYBODY?_ 
>>> gives some
>>> interesting takes on the Fermi paradox.
>>[snip]

>> 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?

They may have done but there are still hard limits on how big an antenna 
must be to obtain signal that is above the background noise floor.

> 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)

Encounters between species with advanced technology don't usually end 
well for the ones still in the iron age when they come up against 
automatic weapons. If we ever meet alien space travellers we had better 
hope that they are friendly. Even so their advanced technology could 
wreak unintentional havoc.

> 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)?

Space is mind bogglingly *BIG* the gaps between stars are huge.

The only place where stars are close together are in globular clusters 
and in environment so odd that it is probably one of the places where 
you can pretty much rule out life evolving. Close three body encounters 
happen often enough to lob whole stars out at very high speed and leave 
the remaining ones ever more tightly bound. They are extremely pretty.

Arecibo's first ever deliberate message was sent to M13 it will take 
about 25k years to get there and another 25k for a reply if the intended 
recipients happen to notice it. Chances are there is no-one there.

https://en.wikipedia.org/wiki/Arecibo_message

I reckon in 50k years +/- 500 no one on Earth will even remember that 
the message was sent.

https://en.wikipedia.org/wiki/Messier_13#/media/File:Messier_13.jpg

Just naked eye as a faint fuzzy blob under Hercules right shoulder - 
more obvious in binoculars (visible in summer).

Worth seeing first hand in a 15" scope or larger.

-- 
Martin Brown