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Comment by Ekaros | Hacker News Reader

The truth might be than physics are harsh mistress and there is no way to cheat. Thus actually working extra system space colonization is just not something that we or anyone else can do. Maybe even technology to do stellar engineering is out of reach.

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Space colonization is best done by robotic ships. These could very well be plying the galaxy and just staying away from primitive life.

You should still be able to see them, even from distance, if they have any reasonable power output. Stealth doesn't really work in space.

Haven't we lost satellites that are just orbiting our own planet?

Maybe we have, but those don't emit terawatts of power while trying to propel themselves in interstellar space.

You can only get so much power before something vaporizes. Some sort of ship emitting enough power to be detected at a non-trivial distance from Earth (see inverse square law) would vaporize itself.

Just because stealth in space doesn't work doesn't automatically mean you can see everything in space at all times. We need to build giant telescopes to see stars thanks to the inverse square law. The bigger our telescopes with better light collection the narrower their field of view. An antimatter spaceship could fly past Pluto tomorrow and we could easily miss it since we can't monitor all 4πr^2 of the sky at once with powerful telescopes.

> Some sort of ship emitting enough power to be detected at a non-trivial distance from Earth (see inverse square law) would vaporize itself.

Then you can say goodbye to those robotic spaceships. Note that I'm not claiming that they're possible -- I'm just saying that if they do exist, they're very detectable.

> An antimatter spaceship could fly past Pluto tomorrow and we could easily miss it

We can detect Voyager from way past Pluto, even though it emits only several dozen watts. I'm not sure how you'd miss an antimatter-powered spaceship at a comparable distance.

To be fair, we know exactly where Voyager is and know to look for it. It would be pretty hard to detect otherwise.

And if it were emitting 10¹² times as much power, like even a small interstellar vessel would, we wouldn't even have to know exactly where it is.

> Space colonization is best done by robotic ships.

But why do it? If you send a robot to (say) Alpha Centauri what have you actually acheived, at probably enormous cost?

"Because it was there."

Mining for resources, either to send back or for future human landings.

To send back? How? This seems to be dependent on having universal constructors, which we don't, and probably never will, have.

We also don't have space robots...

To establish supply lines. If Alpha Centauri has something of value you could send out a self replicating robotic AI entity. It establishes its footing then start sending deliveries to Earth. If each one way trip takes 50 years, after say 120 years you could have a steady supply of resources.

We have no evidence that we will ever be able to build sufficiently adaptable systems to engage with unfamiliar environments without constant direct human intervention, which is not possible at light-year (or even light-second) ranges.

Would Alpha Centauri have resources we lack in our solar system? Mars, Venus, The asteroid belt, various moons and gas giants should be ample for anything we need.

It's also a hedge against issues with our sun.

How is a robot at AC such a hedge?

If the robot deposited genetic material over in that system then there would still be genetic material from our solar system in this universe after our sun inevitably explodes, or some unforeseen catastrophe occurs.

> self replicating

A tech we don't have and probably never will.

It all depends on the goals behind leaving ones star system. If the goal is biological colonization, sending genetic material (or even better a gene database) across large spans of distance and time is far more practical than a generation ship or suspended animation. If the goal is to let your sentient machines explore then you don't even have to be burdened with recreating biological life.

If we depend on technology we don't have, why not wish for FTL travel and be done with it?

This has always seemed like a hopeless star-eyed and wildly impractical idea.

So your robot ship turns up and what happens then?

If it's going to self-replicate it needs to recreate most of the features of an entire industrial civilisation. In our terms that would be metal refinement, chip manufacture, chemical life support and more - all done by bug-free software running on hardware which is perfectly error-free and reliable and lasts indefinitely.

If it's going to seed biological (or equivalent) colonists it needs to be clever enough to find candidate planets with an ideal biosphere and no biological threats. Then it needs to teach the colonists how to survive and colonise.

A lot of SETI and colonisation seems to be based a naive idea that all you have to do is get from A to B and you've solved your expansion problem.

In reality propulsion is just the loading screen. Winning the game is a much harder challenge. So many things that can break, fail, be destroyed by chance, or go wrong because of design flaws that it's an insanely difficult problem without very much more advanced tech.

Ok, but to be clear, this is an argument that there IS a "Great Filter". It's just a Great Filter that is in front of us rather than behind us.

no this is a filter to technological progress/expansion, not a filter to life appearance and sustainability in the universe..

It seems some people in this thread need a reminder of what the Great Filter is: https://mason.gmu.edu/~rhanson/greatfilter.html

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