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Comment by forgot-im-old | Hacker News Reader

It's popular to suggest we don't hear aliens because they all destroyed themselves. But a basic RF link budget calculation shows that even an Arecibo sized antenna pointed perfectly at another Arecibo telescope on an alien planet, and listening/transmitting at the exact right times, could only barely contact one or two of the nearest stars.

This fact is buried in all the Fermi Paradox discussions because Fermi's point was the implications of his work on nuclear weapons when he brought up alien contact.

It has since been used to make the case for Reagan's Strategic Defense Initiative. Which apparently Elon Musk is now continuing... https://ioc.exchange/@muskfiles

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The Fermi paradox does not merely concern the lack of alien signals - it also notes the peculiarity of the absence of alien spacecraft / visitors. The Milky Way is big, but not so big that it's impossible to traverse generationally. If interstellar spaceflight capable aliens evolved at any time in the galaxy's 13 billion year history other than within the past, say, few million years - a fraction of a percent of the total - then we should expect them to have colonized the galaxy by now. There is 0 evidence that this has happened - no monoliths on the moon, no Dyson sphere signatures visible in our telescopes. Either they're very quiet for some reason, or nobody cracked interstellar travel. That's concerning when it seems perfectly possible and desirable to do. The Milky Way is big, indeed - big enough and old enough that someone should be here.

This, or the Dark Forest theory is correct.

> The Milky Way is big, but not so big that it's impossible to traverse generationally.

Creating a self-sustained ship is not so easy. And there are tons of failures that can happen, especially over the course of multiple generations. And you won't be able to just "beam down" to some random planet once your interflux quantum capacitor and its two backups fail. Unlikely things happen given enough time.

And why would you want to do this in the first place? Would life on such a ship really be all that great? Sounds like the stuff of a depressing dystopian sci-fi novel more than anything else.

Dyson spheres seem completely impractical. Just the sheer amount of materials needed alone, never mind the construction effort and maintenance effort. Dyson himself didn't take it very seriously, and I have no idea why anyone else does either.

All very relevant points to why human generation ships are unlikely. Totally irrelevant points as to why, out of the hundreds of billions of planets in the Milky Way, it would appear that not one has evolved an organism capable of spreading out of its gravity well. In general, Life Finds A Way. Life on a ship is depressing? You may as well argue that life in hydrothermal vents would be boring.

As for Dyson spheres, don't take the remark so literally. I simply meant that a galaxy-spanning slime mould would probably be visible to our physics, somehow. Life is an entropy engine. Once it gets going, it really gets going. But we appear to live in an improbable oasis in a vast desert.

Most of those "billions of planets" cannot support life (the exact number of which can is currently unknown). And who says no life evolved "capable of spreading out of its gravity well"?

> As for Dyson spheres, don't take the remark so literally.

Of course it should be taken literally, because all of this is all about what the laws of nature do and don't allow and the practicalities surrounding that. This isn't an class or discussion about what does and doesn't make a good sci-fi story. And what is a "galaxy-spanning slime mould" even?

> Life on a ship is depressing? You may as well argue that life in hydrothermal vents would be boring.

Yes, it would be. There is no intelligent life living near thermal vents. What an odd thing to say.

That's a damning indictment of the inhabitants of Hjalteyri.

Is this perhaps a specific personal grudge against your hometown or a more general dislike of Icelanders?

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

https://xray-mag.com/content/strytan-diving-icelands-hydroth...

Maybe aliens just aren’t interested in exploring or traveling.

Maybe they reached space but upon finding it inhospitable, decided it’s not worth the trouble. Doing things because they are hard could be a uniquely human trait.

On the other hand, I’ve seen a UAP with amazing abilities. Maybe they are here already but aren’t in a hurry to say hello. Maybe they think we are too primitive to warrant communication.

Maybe their signals are all around us but we don’t have the means to detect or interpret them.

Maybe they only use lasers and fiber optics to communicate.

*The Golden Age" trilogy by John C. Wright explores a future humanity where we have tamed the solar system, become as gods, and really can't be bothered with populating the galaxy because it isn't all that interesting compared to the awe inspiring realities of home. Apart from that one time required for an interesting plot. The solar system is pretty big.

You speak as if there's possibly one or two alien species. But there are hundreds of billions of planets in the Milky Way. Even if life is 1 in a million, we should expect hundreds of millions of life bearing planets. The place should by rights be teeming. What are the odds that none of them want to explore and colonize? Is this an evolutionarily stable equilibrium we find ourselves in?

I think that, given the scale of time and planets that could potentially be habitable, there is a high likelihood for the existence of many alien species.

What I take issue with is the notion that it should be surprising that we haven’t detected them. There are so many reasons why they could be right in plain sight, not even trying to hide themselves, while still going undetected. Those explanations are under appreciated in my opinion.

One issue that's become clearer since Fermi's time is just how not-empty space is. There's enough rocks and dust and rogue planets between the stars that any ship traveling at even a small fraction of lightspeed could be instantly destroyed if a collision happened, even with a particle the size of a grain of sand.

And it's dark so you cannot see it coming. You'd need very high frequency radar or more likely lidar to detect it and you wouldn't have much time to dodge it. (Not to mention that you have to design that lidar with relativistic effects in mind.)

The density of this stuff is not high but it's not zero either.

The most interesting discussion on Elon's nuclear weapons interception plans was xAI's,

https://www.reddit.com/r/ChatGPT/comments/1dgyujd/comment/l8...

I think people, for both good and bad faith reasons, vastly underestimate how unlikely it would be for any sort of artificial signal to reach us.

It would need to be so powerful and so precisely aimed at us that firing randomly into the void would be pointless. We can barely detect the most energetic events in the universe like quasars and gamma ray bursts as it is.

And that assumes we could even decode it -- advanced coding uses scrambling techniques that deliberately make the signal look like noise to the uninformed receiver...

presumably nowadays we would only aim at stars with a planet with an atmosphere we might at least suspect to be influenced by biology (i.e. contains some gas that couldn't be formed and maintained by known geological processes). so maybe aliens would see oxygen in our atmosphere and aim at us - but you'd still have to get the timing right: we might have been burning witches the last time one message came by and next time we might be in the midst of some other social disturbance.

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