Civilizations in our Universe

We have been discussing the difficulties regarding visiting and being visited by an alien species.

This article gives some insight.


https://phys.org/news/2023-10-civilizations-quickly-universe.html

 

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From the article: Sixty years later, the answer to Fermi's famous question ("Where is Everybody?") remains unanswered.
I disagree with that assessment. The answer is, I believe, "You can't get here from there". Interstellar travel by living beings is not feasible.

 

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OK, but "getting here" is really a stretch goal. We've also heard neither hide nor tail from them. We can see and hear tens of billions of light years out into the void, but not a peep.
That is part - arguably the largest part - of the question.

 

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If there was a civilization on a planet in the Alpha Centauri system that produced our amount of radio and other EM signals we would never detect it. The only way we could detect a signal would be if a focused signal of huge power was directed at the earth, so I am not surprised we haven't seen a signal. It would be great if an extra-terrestrial civilization could contact us but I am not particularly hopeful. Just my take on it...

 

Depends on how unique the earth is does it not?
A lot of things had to happen to bring us here.
The collision with Theia forming our moon for instance. That gave us a tilt, seasons, tides and a valuable factor in the evolution of life and ecosystems.
Also size of the planet, distance from the sun, earth structure, elements water, avoiding asteroids, avoiding volcanos, requiring volcanos, life evolving with us but not killing us in the process.
All that before we get anywhere near decent signaling technology.
Beings like us could be super rare and need to be super lucky in the process.
Our own galaxy seems to be pretty dead in the region the timescale has allowed us to probe.

 

Not even with the SETI array?

 

Sure but those are all different solutions to the Fermi Paradox than the "it's too far to travel" hypothesis.

 

Yes travel is a far greater hurdle. We will detect alien signals way before they finally show up in Roswell or we get to our first new star system.

 

Yes this strikes me a taking a sledgehammer to crack a nut. In space travel the numbers are awful, as Slartibartfast pointed out (or will point out?) If relativity is right, travel to another habitable planet would never make sense for any alien civilisation. You don’t need all these models and conjectures to come to that conclusion, surely? These people should lose their research grant.

Similarly, the inverse square law by which radiation spreads out makes detection of EM emissions from an alien civilisation practically impossible, too.

It is just possible that if there were a nearby civilisation trying to signal its existence to any interested and capable parties, we might pick that up with SETI. But it seems to me that’s about all.

 

There was a study a while back that suggested that the best conditions for intelligent civilizations to form in our galaxy occurred closer in to the center of the galaxy than we are, and when the galaxy was much younger. So we may have arrived late for the party and at the wrong address.

 

A couple of caveats there though. We Earthlings are a bit myopic on such categorical fiats:

• We are technological newborns. We've only had electricity and heavier-than-air flight for a little more than a century.
• We are, according to Sagan, barely a Type 0.7 Civilization. And according to Kaku, we won't reach Type I for another century or two. It's like H.habilis thinking there's no way we could harness the very lightning of the skies and store it in a cylinder small as his pinkie. Or thinking how much effort it might be to lift a cigar tube that weighs more than 5,000 times his weight and having it fly non-stop across an ocean whose size he cannot even comprehend. The scale of these things is simply beyond his ken. But not beyond ours.
• A Type II civilization can harness the output of a star. They may not think crossing light years is energy-prohibitive.
• Time-wise, well frankly, we don't know how long-lived aliens might be. And we also don't know what they consider "playing the long game". They might consider a few millennia for a fleet of automated probes to do a survey to be economically feasible.
• We are already (albeit fancifully) thinking of ways around relativity. The Alcubierre drive is not limited to c, and with the output of their star, stuffed into an appropriately-sized cylinder - it might be feasible.

It goes without saying that these will all, individually and collectively, dramatically reduce the chances of it happening anytime soon, but I would stop short of categorically saying it would 'never make sense for any alien civilization'. (Though I'm not holding my breath*.)

*OK, actually I am, because it would be awesome!

 

That's why I include in my comments the caveat "if relativity is right". But so far we have no reason to doubt it.

In science all truth is only provisional of course, but we can say that according to our current theories it's far from surprising that we see no evidence of alien civilisations.

 

Pretty early to say anything like that IMO.

 

"We are like the inhabitants of an isolated valley in New Guinea who communicate with societies in neighboring valleys (quite different societies, I might add) by runner and by drum. When asked how a very advanced society will communicate, they might guess by an extremely rapid runner or by an improbably large drum. They might not guess a technology beyond their ken. And yet, all the while, a vast international cable and radio traffic passes over them, around them, and through them."
Cosmic Connection. Carl Sagan 1974. My old yellowing copy.


We maybe like the ants walking around the bases of the SETI radio dishes.
How much effort should we be put in to communicating with ants here on earth?
Are we worth the effort of those elsewhere out there and that know about us already?
Are we that boring? Don't they know about Sciforums??

 

That's fair. My belief, and I realize it is just a belief, is that the distances are prohibitive. The other issue is that it is entirely possible that there is no other planet in this galaxy where humans could safely breath the air, so what would be the point.

 

If you are going to have a summary though, you would prefer an over engineered treatment like this than an article in Time Magazine or the Conversation surely?
Basically pop sci with its juicy yet silly tit bits from Kaku?
The guy seems to get everywhere.

 

Agree.
I posted the link because it was being discussed elsewhere and seemed relevant to the UAP threads.
Why is it (highly) unlikely we have been visited?
Like you my views are grounded in the limitations of time and space, not the veracity of UAP sightings or even the NASA report (which is better than everything else so far.)
Now since we are limited by time and space this does not mean we are also limited by the current Theories describing them.
They are our Theories after all and we EXPECT them to be upgraded refined edited and even discarded occasionally.
What will a successful quantum theory of gravity lead to?

Strange that no UAP believers have contributed so far, on the physics side.

 

None of that is a requirement for life or 'civilization'. One could as easily argue that life managed to evolve despite these instabilities, and it is stability after all that tends to favor life, especially advanced life. We barely made it here on Earth, evolving civilization only near the end of our window. Took 5 billion years to get here from the earliest life, and yet in another billion it seems conditions here will not support multicellular life at all. That's cutting things pretty close.

Size matters little if at all. Water (and carbon) is wonderful for our kind of life, hence the need for a 'habitable zone', but that seems common enough that there is at least one other planet with liquid water on it just in our solar system. Avoiding asteroids is part of the stability thing.

Here I have my doubts, since the center of a galaxy, especially early on, tends towards very unstable conditions. Sure, life might take hold on some planet in a habitable zone, but with so many rocks to wipe things out, and so many large objects (passing stars and such) to disrupt stable orbits, planets simply are not likely to stay habitable for any length of time. It's way out here in the boondocks that stability is to be found, and more likely with a smaller star with a far longer lifetime than that of our sun.

Let's suppose that we would notice, that we could detect a civilization by looking for radiation that would not otherwise be emitted, so we could say see them even in Andromeda if they were there. What are the odds that a civilization would be thus detected?
Nobody has mentioned the 'great filter', which is a frequent solution to the Fermi paradox. It says that a civilization like ours is fleeting, and pretty much ends when the non-renewable resources run out, or until we wipe each other out. Either way it happens in an amazingly short time, so not only do we have to look in the right direction to see them, but we have to look at exactly the right time, and the odds of doing that are pretty much nil.

Here's a picture of the universe:

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We are at the 'here and now' point. Put this picture (a nice poster size one) on a wall. Throw a dart at it. That's the alien civilization. If the dart doesn't land exactly on the red line, we cannot see it. Only an enduring civilization would have a significantly extended worldline long enough to possibly cross the red line, and it appears that such enduring civilizations (certainly not our own) are exceedingly improbable. That's a good reason we don't see them. The dart throws are simply not on that red line, and we only see stuff that is.

 

Woah! Let's scale that X axis up by about seven orders of magnitude to our local galaxy - maybe even just our local arm.

That thin red line suddenly becomes a LOT fatter (about ten million times fatter).

 

No, it's still only a couple centuries fat, not even that if you only count the time that we get to scan the skies with something sensitive to what we're after. The line in the picture is far fatter than that, but one century would certainly be below the resolution of one pixel. Hence my saying that the dart needs to hit it 'exactly'.

Yes, the local galaxy is much closer (it being the vertical black line), but the thickness of the red line is no different, so now you have to hit both the red and the black with the same dart. Timing is everything if what you're looking for is fleeting.