Aliens on 1k nearby stars could see us, new study suggests • Hacker News Board

Re: Aliens on 1k nearby stars could see us, new study suggests

#151

Post by sbelskie » Fri, Oct 23, 2020, 11:00 PM UTC

dylan604 wrote: post #145

buran77 wrote: post #20

Earlier quoted context omitted.

It may be even worse, that different continent is on a different planet. Space(time) is absolutely, mind-boggling massive. Everyone knows it's big but it hard to comprehend how big and why there could be many alien civilizations out there capable of broadcasting or detecting but never intersect in any way because the detection windows of any 2 civilizations don't line up. The Milky Way alone is ~150000-200000 light y…

> Humans have been civilized for only some tens of thousands of years, That's giving humans a lot of credit. Civility has been regressing. I would be embarrassed for another civilization to find us now. Sure, we may have more technology and scientific understanding, but how we treat one another needs another world than civil.

I don’t think civility has a lot to with civilization in the anthropological sense of the word.

Re: Aliens on 1k nearby stars could see us, new study suggests

#152

Post by causality0 » Fri, Oct 23, 2020, 11:01 PM UTC

cletus wrote: post #150

I'm pretty convinced at this point that it's incredibly unlikely that there's anyone around us to hear us. A lot of people have put a lot of thought into this. I'd suggest starting here [1] for an overview. [1]: https://www.youtube.com/playlist?list=PLIIOUpOge0LulClL2dHXh...

Indeed. It seems incredibly unlikely that another civilization would arise so closely in time to our own that it hasn't either collapsed or expanded to fill the galaxy well before our own development.

Re: Aliens on 1k nearby stars could see us, new study suggests

#153

Post by avhon1 » Fri, Oct 23, 2020, 11:02 PM UTC

skissane wrote: post #118

ben_w wrote: post #79

Earlier quoted context omitted.

Going fast in a straight line with conventional rockets is achievable, just not very timely. Bending spacetime enough to make a difference — even just to the time taken between here and Alpha Centauri — is beyond any known mechanism humans could build, even in principle, using the total resources of our entire solar system. (Using unknown mechanisms: perhaps, but they’re unknown)

> Going fast in a straight line with conventional rockets is achievable, just not very timely. A constant-acceleration spacecraft could reach the opposite side of the galaxy in 24 years ship time. (That'd be over 100,000 years of Earth time, however.) Conventional chemical propulsion don't have high enough impulse to do that. Possibly some kind of nuclear or matter-antimatter propulsion could?

Atomic Rockets has some good info on this.

> When it comes to [high thrust, high specific impulse] propulsion systems we might actually be able to build in the near future, the list includes Orion drives, Zubrin's nuclear salt water rocket, and maybe Medusa.

There have been many studied variations of Orion. Atomic Rockets cites hypothetical Isp between 3,000 and 12,000 seconds. Vehicles with delta-V of up to 100,000 m/s have been proposed. These could definitely be built, and would definitely work, but would require constructing, co-locating, launching, and detonating thousands of 5- to 15-kiloton nuclear explosives.

http://www.projectrho.com/public_html/rocket/enginelist3.php...

Medusa is basically Orion crossed with the image of a sailor blowing into their own sails. A huge parachute is deployed in front of the spaceship, and the nuclear explosives are detonated between it and the bow of the spaceship. The parachute can capture more of the explosive output than Orion's pusher plate can, it weighs less (because all of its members are in tension), and it can use its rigging's elastic properties to dampen the intermittent thrust, as opposed to Orion's (heavier) hydraulic dampers. The proposal study for Medusa (which assumed thirty 25-kg explosives) came up with an Isp of 106,220 seconds, and a delta-V of 4775 m/s.

http://www.projectrho.com/public_html/rocket/enginelist3.php...

The Nuclear Salt Water Rocket assumes plausible (but completely untested, so maybe impossible) continuous nuclear fission in a stream of uranium-salt-y water being sprayed into the combustion chamber. Assuming that this can be made to not blow itself up, 20%-enriched salt nets a theoretical Isp of ~7,000 seconds, and 90%-(weapons-grade) enriched fuel, with somewhat more optimistic efficiency assumptions, has a theoretical Isp of ~400,000 seconds and a delta-V of 10,000,000 m/s.

http://www.projectrho.com/public_html/rocket/enginelist2.php...

There are also lots of other currently-less-plausible proposals for high-power high-efficiency rockets. (Many of them assume things like efficient proton-proton fusion, which might be possible, but we have no idea how to do it.) Atomic Rockets is a great website for reading about these.

My takeaway is that it's almost certainly possible to build spaceships that can travel at >0.01c, but it would take a great deal of resources organized by a society that is more trusting and responsible than we are now. After all, any vehicle with that kind of power is also an equally powerful weapon.

Re: Aliens on 1k nearby stars could see us, new study suggests

#154

Post by Retric » Fri, Oct 23, 2020, 11:06 PM UTC

deeeeplearning wrote: post #76

deeeeplearning wrote: post #71

Earlier quoted context omitted.

Given the age of the Milky Way, a civilization using even slow sub light travel with generation ships or autonomous probes could have colonized the entire galaxy many times over. Why has no one done that? Hence the paradox.

Not sure why it was downvoted. Many people have looked into this. https://gtocx.jpl.nasa.gov/gtocx/competition/ Even entire competitions to find optimal colonization methods. Could take 90M years with measly future human tech. Age of Milky Way is 13.5 Billion so even conservatively you could indeed colonize the galaxy many many times over in that time.

The Milky Way lacked rocky planets early on, making that 12.5 Billion year age largely meaningless.

Which is just one of many bad assumptions in how people do these calculations. At a minimum you don’t get a straight path from A to B. Assuming any kind of limitation in distance traveled and your at the mercy of the distribution of whatever resource you need. Aka need rocky planets with liquid water, that’s likely going to be an very indirect path. Even just non binary star systems is significant. Further, assuming every trip is successful is again unlikely. How long you need to wait before the next trip is again a major qualifier.

For example, what happens if they first send a probe to verify habitability? Suddenly travel times more than double.

I have seen plenty of optimistic calculations that still add up to over a billion years before total colonization and sometimes much much higher than that. And that’s a billion years where expansion is a major priority at the frontier. Look at successful colonizations that don’t expand rapidly and again things keep slowing down.

Re: Aliens on 1k nearby stars could see us, new study suggests

#155

Post by jcranmer » Fri, Oct 23, 2020, 11:09 PM UTC

tzs wrote: post #137

tsimionescu wrote: post #86

Earlier quoted context omitted.

There are problems of resiliency and energy storage that could be more or less fundamental problems. It could take millions if years of technological civilization to produce a machine capable of sustaining life for the hundreds of thousands of years necessary for interstellar travel, and civilizations may tend to collapse for various reasons before reaching such technological peaks. It's also entirely possible that w…

> It could take millions if years of technological civilization to produce a machine capable of sustaining life for the hundreds of thousands of years necessary for interstellar travel. For a generation ship, are you referring to all the machinery that can maintain a balanced ecosystem of plants and animals and humans in order to provide food for the people during the trip to the new planet, and to make all the thing…

> a sphere with a radius of 24.4 meters

A more human-sized comparison is "100 average single-family homes in the US, all filled to the brim with rice". Or 60 ISSes, all filled completely with rice. Per person. And this is volume, not taking into account the weight of rice.

Minimum sustainable population size seems to be about 100 people, so consider how large a ship you'd need just to fit all that rice storage.

Re: Aliens on 1k nearby stars could see us, new study suggests

#156

Post by nn3 » Fri, Oct 23, 2020, 11:10 PM UTC

jcims wrote: post #114

deeeeplearning wrote: post #71

Earlier quoted context omitted.

Given the age of the Milky Way, a civilization using even slow sub light travel with generation ships or autonomous probes could have colonized the entire galaxy many times over. Why has no one done that? Hence the paradox.

I'm fairly confident we'll eventually find that our form of life is the result of intentional or unintentional colonization of Earth. If you look at how quickly life began after the oceans settled out, then look at precisely how complex even the most primitive forms of life are (in terms of likelihood of stochastic construction to the point of sophistication to support evolutionary mechanisms) it seems incredibly unl…

Keep in mind that molecular evolution happens at a massive parallel scale. If there's some simple recipe for basic evolving life it is very unlikely that is not being hit in a few million years by a large number of molecules and then primitive cells.

And it's unlikely that there is only a single recipe. Most likely there are many (just on Earth all the others died out)

Re: Aliens on 1k nearby stars could see us, new study suggests

#157

Post by staticman2 » Fri, Oct 23, 2020, 11:11 PM UTC

dyingkneepad wrote: post #117

vl wrote: post #112

Earlier quoted context omitted.

Basically there is not need and motivation for humans to colonize anything outside the Earth. It's just too far, too expensive and too uncomfortable. Humans evolved specifically to live on Earth, to live somewhere else, they need to be severely altered. Now you just seeded civilization of another species, that might turn out to be confrontational or outright hostile. Why would you do that? Too see how well this works…

> Basically there is not need and motivation for humans to colonize anything outside the Earth. Our current gas emissions would disagree. Also, asteroids, gamma ray bursts, curiosity, sheer ambition, etc, etc. The thing is: we don't need to convince all of mankind to colonize another planet. All it takes is a few people. Crazy rich Mr. Musk is one example. He may not be able to achieve it, but maybe all we need is a…

If Musk sent out a generation ship he'd die onboard and his grandchildren would turn the ship around to visit the mysterious alien planet they've heard tales of known as "earth".

I don't see any scenario where a generation ship can plausibly be expected to colonize another planet.

Re: Aliens on 1k nearby stars could see us, new study suggests

#158

Post by Supermancho » Fri, Oct 23, 2020, 11:14 PM UTC

grawprog wrote: post #58

koheripbal wrote: post #47

Earlier quoted context omitted.

Given the relative age of planets and stars, other alien "civilizations" would be hundreds of millions or Billions of years older than us. The notion that we'd all be roughly at the same level of advancement is statistically impossible pop-sci-fi fantasy. In my opinion, it's unlikely that they are even organic individuals anymore. Even the separate alien "entities" might have a process of merging once they achieve a…

>We are like fungus to them. Maybe the fungi think that about us? They've been around longer than we have and take up more of the planet.

> They've been around longer than we have and take up more of the planet.

It looks like that to us, because our influence is visible over 80+% of the ground, but there's fungus IN us and covering more surface area than you can see. Imagine anywhere there's water (including from the air and including the oceans), there's fungus over a % of the land and organisms that you can see with a microscope. Fungus influence covers far more of the surface.

Re: Aliens on 1k nearby stars could see us, new study suggests

#159

Post by beamatronic » Fri, Oct 23, 2020, 11:16 PM UTC

buran77 wrote: post #60

beamatronic wrote: post #41

Earlier quoted context omitted.

That’s why the best thing any species can do for the other species is to leave signs that we were once here.

We still need to leave a heck of a collection. On a living, evolving planet if all civilizations are gone the signs get wiped out pretty fast in geological time (geology, weather), and in space the signs are usually traveling in the emptiness with little chances of being spotted. The best probes will eventually fail and will just add to the countless objects floating never to encounter anything. I know it sounds depr…

I like the comic.

It's almost like all intelligent life in the universe was put into escape-proof cages.

We need to rage against this! Do it for all the others who can't.

Re: Aliens on 1k nearby stars could see us, new study suggests

#160

Post by jessaustin » Fri, Oct 23, 2020, 11:16 PM UTC

sosborn wrote: post #120

jessaustin wrote: post #78

Earlier quoted context omitted.

I've never forgotten the scene in the OSC short story "Fat Farm", in which the protagonist's mind has been copied to his clone, which clone has left the facility to "continue" to enjoy his fine life, and the protagonist realizes he hasn't thought about what comes next. The answer is grim. A consciousness might awake in the machine, but it won't be my consciousness.

But for the consciousness in the machine, does that distinction matter at all?

We'll never know. This is inherently subjective. Philosophers might suspect zombies...