Billions and Billions of "Earths" in the Milky Way

[Savage117]

It's not that it should pass through. Each of the colonies should grow and start sending out it's own spaceships. The entire galaxy should be colonized by now. We have a habitable planet and they should theoretically have come to have a look as it would be a candidate for colonization.

This is the kind of thinking I was trying to change. It's more likely another space faring sentience will not find our planet habitable. The chances that another species ,not born on this planet, having the same atmospheric requirements to live on their planet is extremely slim. Therefor they very likely would not even glance at our planet, therefor not even noticing us in their expansion. If we had interstellar travel right now we would pass up solar systems that had nothing of use or interest in them. For instance, there would be no point to expend resources and time to go to a system with only Venus like planets and gas giants in them because the only thing they have available is resources. It would take more time and effort to set up a base in a system like that than it would in a system with a Earth like world, therefor we would ignore it, until it became known a intelligence lived there or the resources were so badly needed we would risk the deadly environments. The same could apply to another space faring species, they would ignore our planet and system because its useless to them in comparison to another system.

I'm of the opposite view of most of the people posting it would seem. While I am fairly sure the universe is full of life bearing planets, I suspect intelligent life may be a bit of a fluke. From our own experiences of the earth, we know life started pretty early and managed to survive some pretty traumatic events including near extinction events. All in all, it would appear that life is pretty tough and will survive in most environments and through most disasters.

Intelligence on the other hand seems to have occurred only once (that we know of) and seemed to take a very long time to develop given that mammals have been around for the best part of 250 million years. Also puzzling is the fact that the development of intelligence completely bypassed entire groups of animals that occupied the earth for far longer yet must have had the same environmental and biological pressures on them to develop a more efficient method of survival.

I suppose the jury is out on whether intelligence is actually an efficient long term survival trait. As others have already mentioned, intelligence could place such a heavy demand on the resources available to it on the planet of it's birth that it ends up simply running out of basic materials and power sources before it can develop the technology to seek them further afield. In which case, yes there may well be other civilizations out there, but there is a good chance that they are living in a post technology dark age, one from which there is no possibility of escape

Even if intelligent life is a fluke, because the galaxy is so freaking big and has so many places where life could evolve, it would be near impossible for intelligent life to not be out there, they may be very early in their development or have destroyed themselves with unimaginable weapons, or on the exact same track as Humans, but they are out there. We are just missing each other because its like trying to find a needle in a pile of needles light years wide. The only way we could find another intelligence easy is if they caused something that can be seen on a galactic scale and make it obvious it was caused by an intelligence, or send out some sort of massively powerful signal that can travel a large number of light years in a sphere and still be decipherable on its outer edges, something like an active sonar pulse in space, or we could "ping" the galaxy and draw other intelligences to us if we had the tech. It's my thinking that intelligence is out there, it's just unimaginably distant from us, even if intelligence only popped up every 1000 light years or so it would still be a rather large number of intelligences in just this galaxy, but it would be very difficult to find.

[KerikBalm]

"even if intelligence only popped up every 1000 light years or so it would still be a rather large number of intelligences in just this galaxy, but it would be very difficult to find"

1000 light years.. the galaxy has a radius of 50,000 light years... the galactic habitable zone (this is not based on a specific life chemistry, but rather the presene of elements heavier than helium, vs intense radiation and such), is far smaller than that.

Its between 4-10 kiloparsecs from the core.

So thats between 13,000 and 32,000 lightyears from the core. Assuming its a flat disk(its about 1000 light years thick on average http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980317b.html) and since 1/2 pi cancels out, thats (32^2 - 13^2) = space for 855 intelligent species each with a 1000 light year zone around them (actually a cylinder rather than sphere with the "flat" approximation).

Travelling at .1c, the galaxy would be "confluent" with life if those species spend even 10,000 years out of the last few billion years expanding.

Again... there's been plenty of time for the galaxy to become full. They may not want earth, but there's no particular reason they wouldn't want to mine asteroids, or the Oort cloud. I'm assuming such a species wouldn't even particularly want to be planet bound.

Why aren't they somewhere in our solar system already? If they were so close, it would be hard to miss....

So.... if there are billions and billions of "earths" in the galaxy, that would mean billions and billions of planets where one of the following is true:

1) Life doesn't evolve into a technology using species

2) A technology using species destroys itself before controlling fusion

or

3) Does not use fusion to travel to nearby stars.

You need less than 1000 of those billions and billions to decide to travel to nearby stars to fill up the galaxy in 10,000 years.

Thats less than 1 in a million "Earths" producing a species a bit more technologically advanced than us, a tiny tiny tiny fraction of time sooner than us (If just a few took even 99% of the time it took us to get to this state, the galaxy would be full)

To me it seems incredulous to say the galaxy is full of earth like planets, and full of intelligent species, but almost every single species comes to the same conclusion: don't expand.

I think its far more likely some will decide that, and some won't - and with that idea, the Fermi paradox still stands very strong.

That leaves us with the Rare Earth hypothesis (planets capable of supporting simple life may be common, but planets capable of *producing* *complex* life are very very rare), or some idea of a race of "First Ones" that have spread throughout the galaxy, but at low density, and they are actively limiting the expansion of other species, remaining silent and hidden until a newly evolved species has the capability to expand, at which point they assert themselves and tell the new species on the scene to follow their rules... *or else*

The latter is pure speculation based on little evidence, while the Rare Earth hypothesis has much more evidence, but is still based upon speculation about what life needs, and what is conducive for evolution of advanced life.

[magnemoe]

First your estimate is based on continuing outward from point of orign at 0.1c until the edge of the galaxy. Very unrealistic, still if you could say 100 million year and still have time enough.

Life: We agree that its probably common, advanced life came then the oxygen level on earth become high enough, however during the time then oxygen became common earth became frozen over multiple times. Volcanism probably reverted this. Still an chance that the planet freeze solid or become like Venus during that time.

Venus does not appear to have plate tectonic, but instead massive eruptions all over hundreds of million years between, this might explain Venus atmosphere?

If this phase goes well and we get an oxygen atmosphere I think we will get advanced life.

Now intelligence is another factor, hight chance its rare, happened only once on earth after an long time.

next is getting smart enough, be an tool user, build an civilization.

Discussed this a bit in my previous tread. Some traps here.

Lots of people on this forum see overpopulation as an major threat, does not look like it for humans, but high chance many aliens are less lucky, this don't become an serous problem until you have an civilization after all. On the other hand if you could simply choose not to have kids easy they might continue as hunter gatherers.

But yes you are lucky, you are smart enough so you don't use 10.000 year from the steam engine to fusion and run out of resources underway, you are also curious and independent enough so somebody try stuff who probably don't work. You also has some decent governments or ways to change them. Static regimes will resist change imperial china is the best example.

Technology improves, it might be some future traps out where, what if you found that the matrix is more fun?

But you overcome this and manage to build some starships, you know about suitable planets around other stars, you send probes and landers who analyzes the suitable candidates.

You send out some colonies and some survives other dies out or return, even the successful colonies require regular supply runs.

The next set of suitable planets if longer away, why should you continue, you send probes and might find that the conditions is worse than the existing colonies who still require support.

High chance you loose focus or why has we not return to the moon. An return will probably be done by another country or for commercial reasons.

On the gripping hand human civilizations don't last for thousands of years except for an few exceptions who was very static.

Even of civilization itself continues the group in power is replaced regularly by coup or elections. This tend to change focus will easy cut funding to an expensive prestige project like interstellar colonization. Yes this is for humans but much of the dynamic is probably universal.

---

[Scotius]

Interstellar distances might influence expansion of a civilisation in another way. We are quite lucky, considering. Our nearest star neighbour is "only" a bit more than 4 light years, and it's a binary/trinary system of main-sequence stars. Many more similiar stars, some with confirmed planetary systems are not much further (relatively ). But situation could've been entirely different, if Sun would happen to orbit Galaxy's centre in much less populated area of space. 4 light years is still very intimidating when we compare it to size our Solar system. What if distance to nearest star would be ten times bigger, and it would be a planetless red giant or variable star? Personally i doubt even we would entertain dreams about interstellar voyages after realising how isolated we were.

[magnemoe]

yes, distance is critical, not only distance to closest star but distance to closest planet with life.

The interest of going to another star to visit an boring star system will be far less, at least not an manned mission you might want to send some probes.

This can also stop or redirect an expansion as you will jump to the next target.

[Dunbaratu]

Intelligence on the other hand seems to have occurred only once (that we know of)

That observation is not really a problem though, as all the examples of life you are extrapolating from exist on the same planet and are not isolated enough from each other. We can't get access to any observable forms of life that exist completely isolated from the influence of an existing dominant intelligent species. We can't get an untainted sample of how hard it is for unintelligent life to become intelligent when not under the domination of an existing intelligent life ruling over it.

It could be that while having intelligent life naturally evolve once on a planet is likely, that having two of them evolving on the same planet, one after the other. isn't nearly as likely because whichever form of life gets there first ends up running the planet. Thus natural selection stops having nearly as strong an influence as artificial selection, which is much faster, becomes the dominant factor.

So when all we have to go on is the Earth and no other life to observe but Earth-life, we can't get an untainted sample to test this hypothesis with. It's entirely possible that the reason we can't find other forms of intelligent life on earth is precisely *because* there already is one, and there can only be one.

Take the Neanderthals versus Homo Sapiens for example. Once two intelligent species existed in the same ecosystem where they could interact, one of the two quickly went away.

[KerikBalm]

Well, once is more or less accurate for Earth... the Homo lineage (neandertals and modern humans are more or less the same species... without getting into a discussion on what constitutes a species).

We've been dominant for such a short time, I can't really imagine saying we're the reason that Earth has only produced 1 intelligent species in its nearly 4 billion years of harboring life. Apes for that matter, are also pretty recent, and I don't see any non-ape lineages showing much potential for becoming a technology using species (beyond very simple tools, like what crows have been shown to make with bendable wire to reach food placed out of reach).

Toolmaking, intelligence, and *education* are a powerful combination. The ability to pass on ideas from one generation to the next, so each generation doesn't need to reinvent the wheel, etc. Humans aren't really smarter than we were 10,000 years ago, but our accumulated knowledge is.

If you took a bunch of kids, had them sit around playing CoD all day, with zero education, then when they were adults, plopped them in the middle of the jurassiv... they would not survive. But if you took a bunch of people who had learned a trade, they'd quickly establish a society and become dominant.

Considering that intelligence wouldn't increase overnight, nor would knowledge, it may be hard for intelligence to evolve at all.

It seems we (Earth life) was stuck for a long time in the local optima of Brain vs Brawn, where brawn was favored, and decreasing brawn for a little more brain ended up being a worse condition.... the amount you'd need to go in the "brain" direction before being viable constituted a huge leap, that must also be done in tandem with the ability to manipulate objects (in our case, with prehensile hands).

I can imagine a lot of worlds where the species at the top of the food chain is the species with the biggest teeth/claws.... not the one that uses tools.

Few land animals in Earth's history could take on a group of humans with spears in a phalanx formation... and for those animals... a bit of rope/pits/traps would do the trick.

[Counterbore]

With all the existant Mass on the Observable Universe as we see, it´s really odd how some people continue to think that all this mass has just created one possibility to reunite life on just Earth Planet

KSP, PC Game of my life till today

Normal Carrer Mode -ON-

[manaiaK]

If I can jump in here, there are two points that no-one's made directly:-

1. Engineering difficulty. (OK, Magnemoe said this, but only in passing. Falofanos also made the statement, but again without much support. I want to expand on the difficulty a little.) Let's assume, wildly optimistically, average travel speed of 1% of c* and typical distance between stars of interest of 100 LY. Your spacecraft needs to operate with perfect reliability for 10 000 years minimum-- or at least, still operate perfectly after about 10 000 years of idleness.

The only tools that we have made that have lasted 10 000 years, or that could last that long, are modified pieces of stone. Making something as complex as a fusion reactor last for ten millennia is a very difficult engineering challenge. For instance, you cannot use solid-state semiconductors in the control systems, because ion diffusion causes semiconductors to fail after only a few thousand years. Many 'solid' materials are plastic on these time-scales; others become highly fragile and/or porous. Making reliable machines is hard.

Also, "fusion" isn't just fusion, just as there is not only one kind of steel or one kind of concrete. Deuterium-tritium fusion, the one with the lowest Lawson criterion (the "easiest" fusion, and the one that's always "20 years away"), is useless for interstellar travel as tritium has a half-life of about 12.5 years -- it'll all be gone, long before 10 000 years are up. Protons have a long-enough half-life , but four-proton fusion looks next to impossible at sub-stellar scales.

You could include facilities for re-manufacturing your entire craft (and its fuel, if you use tritium) inside it, while it's in flight--but the payload requirement just went up a few orders of magnitude.**

People have talked airily about von Neumann probes. In reality we have no clue how to make self-replicating active devices of any complexity (except Nature's way, and with Nature's support environment. Computer viruses are non-baryonic so they don't count). Nor can we make devices that can survive the rigors of interstellar space for ten millennia. Nor can we make devices with interstellar-useful propulsion systems.

Making machines that are more complex than any we have ever made, and are fusion-powered, and also have a 10,000-year (more like million-year) MTBF in space, is... a harder problem than merely "harnessing fusion". (My gut says "quite a few orders of magnitude harder", but really I have no way of quantifying the difference.) Making such machines self-replicating may be harder again.

I don't think that these things are hard because of some special quality of kerbals humans. I think they are hard problems for everyone.

The engineering problems of interstellar travel*** amount to yet another "filter", a reason why we don't have Aldebaranian restaurants down in the local mall.

Second point next post.

* For reasons below, I'd expect travel speeds to be a small multiple of escape velocity from the originating sun--of the order of 100 km/s, 0.03% of c. And, as AndrewBCrisp points out above, the diffusion of colonies typically proceeds much more slowly (about 4-5 orders of magnitude slower, from historical evidence) than point-to-point travel speed.

** Fusion based rockets would have very high Isp, but not infinite (say around (5% c)/g). The rocket equation still applies and the delta-vees are large. Payload mass is going to be large too. Brachistochrone transfers don't really help, even if feasible. So instead of 10,000 years above, 1 000 000 years is more likely.

*** Provided you want to slow down and look around your destination. If not, a "simple" ten-terawatt laser will provide propulsion for the first 0.5 LY or so; after that you coast, an inert lump of matter.

Edited November 7, 2015 by manaiaK

[magnemoe]

If I can jump in here, there are two points that no-one's made directly:-

1. Engineering difficulty. (OK, Magnemoe said this, but only in passing. Falofanos also made the statement, but again without much support. I want to expand on the difficulty a little.) Let's assume, wildly optimistically, average travel speed of 1% of c* and typical distance between stars of interest of 100 LY. Your spacecraft needs to operate with perfect reliability for 10 000 years minimum-- or at least, still operate perfectly after about 10 000 years of idleness.

The only tools that we have made that have lasted 10 000 years, or that could last that long, are modified pieces of stone. Making something as complex as a fusion reactor last for ten millennia is a very difficult engineering challenge. For instance, you cannot use solid-state semiconductors in the control systems, because ion diffusion causes semiconductors to fail after only a few thousand years. Many 'solid' materials are plastic on these time-scales; others become highly fragile and/or porous. Making reliable machines is hard.

Also, "fusion" isn't just fusion, just as there is not only one kind of steel or one kind of concrete. Deuterium-tritium fusion, the one with the lowest Lawson criterion (the "easiest" fusion, and the one that's always "20 years away"), is useless for interstellar travel as tritium has a half-life of about 12.5 years -- it'll all be gone, long before 10 000 years are up. Protons have a long-enough half-life , but four-proton fusion looks next to impossible at sub-stellar scales.

You could include facilities for re-manufacturing your entire craft (and its fuel, if you use tritium) inside it, while it's in flight--but the payload requirement just went up a few orders of magnitude.**

People have talked airily about von Neumann probes. In reality we have no clue how to make self-replicating active devices of any complexity (except Nature's way, and with Nature's support environment. Computer viruses are non-baryonic so they don't count). Nor can we make devices that can survive the rigors of interstellar space for ten millennia. Nor can we make devices with interstellar-useful propulsion systems.

Making machines that are more complex than any we have ever made, and are fusion-powered, and also have a 10,000-year (more like million-year) MTBF in space, is... a harder problem than merely "harnessing fusion". (My gut says "quite a few orders of magnitude harder", but really I have no way of quantifying the difference.) Making such machines self-replicating may be harder again.

I don't think that these things are hard because of some special quality of kerbals humans. I think they are hard problems for everyone.

The engineering problems of interstellar travel*** amount to yet another "filter", a reason why we don't have Aldebaranian restaurants down in the local mall.

Second point next post.

* For reasons below, I'd expect travel speeds to be a small multiple of escape velocity from the originating sun--of the order of 100 km/s, 0.03% of c. And, as AndrewBCrisp points out above, the diffusion of colonies typically proceeds much more slowly (about 4-5 orders of magnitude slower, from historical evidence) than point-to-point travel speed.

** Fusion based rockets would have very high Isp, but not infinite (say around (5% c)/g). The rocket equation still applies and the delta-vees are large. Payload mass is going to be large too. Brachistochrone transfers don't really help, even if feasible. So instead of 10,000 years above, 1 000 000 years is more likely.

*** Provided you want to slow down and look around your destination. If not, a "simple" ten-terawatt laser will provide propulsion for the first 0.5 LY or so; after that you coast, an inert lump of matter.

As I see it it would be easier to make an faster ship than trying to make something lasting for thousands of years.

So long travel times will also be poor return of investment at its unlikely even the organizations who created them will be around at arrival.

Yes this will beef up the energy requirement but you have to be a level-1 civilization to even try an manned interstellar mission with know technology.

[manaiaK]

Faster ships:

Even with a ship that averages 10% c, we're looking at a thousand-year voyage. So we still need better reliability than we can achieve. The damage from interstellar debris impacts would be immense. And the mass ratio and total mass have gone up a lot. by increasing speed we have traded a hard engineering problem for a couple of hard engineering problems and a much bigger economic problem. Besides announcing our presence to everyone within a few hundred LY.

Which brings me to the second point: the principle of mediocrity, which says in the absence of knowledge about your relative status, assume you're mediocre. That is, in effect, there are bigger, meaner civilisations out there with better tech.

That implies that we should go out of our way to remain hidden as long as possible, even when we have the reports back from the von Neumann probes. Also, whenever we decide to visit another planet, we should approach it from a randomly-selected direction rather than straight from our home system, further lengthening the duration of the trip. The same applies to the probes -- we don't want other to be able to back-project their trajectories meaningfully.

All in all the engineering, economic, and political difficulties seem immense, even for a Kardashev I (10-100 petawatt) civilization.

[KerbMav]

I found this and think it is a good read - and this a good place to drop it.

http://waitbutwhy.com/2014/05/fermi-paradox.html

[Plusck]

If there is any kind of galactic civilisation out there, I'm pretty sure they'd consider the launch of a Von Neumann probe to be a heinous crime. One of the worst kinds of deliberate pollution of the interstellar environment and utterly immoral by what has to be the single truly cross-civilisational ethical standard: don't do to others what you don't want done to yourself (or even the amoral watered-down version of the principle: don't do to others what you couldn't deal with if they tried it on you).

[WestAir]

I doubt someone is going to vaporize us. The truth is it's fairly easy for a civilization sufficiently far away to ignore us. Ignoring us also doesn't invite our colony worlds to launch a relativistic killing missile at them in revenge.

[fredinno]

There could also be trojan earths, too.

Anything can and will happen with planets in our universe, too.

What do you mean trojan Earths?

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Even if FTL travel and communication isn't possible this wouldn't explain the fermi paradox. If we started to migrate outward at an average speed of just 0.1% of c today we would've filled half the milky way in just 50 million years. That's the blink of an eye in cosmological terms. So we only have the following options:

1 - There are a lot of alien civilizations out there, but not one of the millions of civilizations has ever managed to migrate outward.

2 - We are alone, or at least one of the very first sapient species.

3 - They are out there and have spread among the stars. But they're either actively or accidentally avoiding or ignoring us.

But all of them have problems:

1 - It's sensible to avoid colonies and migrations from an economics perspective. We all love space travel on this forum, but lets be honest: it is very resource intensive to send living things anywhere, let alone in large numbers. However, it seems unlikely that not one of the thousands of species that should've existed was ever faced with extinction. If your choice is "Migrate or die!" because your sun is going nova the choice seems rather easy. And if your entire species is spaceborne anyway it seems like a shame to settle down permanently. You've got resources galore from asteroids and you've solved any problems you might have with long term 0G. Why make yourself vulnerable again by all settling down on a single planet?

2 - Well someone has to be the first right? And we seem to have either a second generation or 3th generation star, so on a universal scale we're about as early as can be. But on earth it took 3 billion years before we even got multicellular life, let alone intelligence. If there is intelligent life on thousands of other planets they have a lot of leeway in terms of time. And as said before, if someone decides to migrate outward they'll be everywhere in the blink of an eye.

3 - This seems the likely scenario to me. Our radio signals are indistinguishable from background radiation within a few lightyears. Also, it seems that birthrates tend to go down as technology progresses. If the same applies to aliens then they wouldn't spread across the galaxy, just settle on a few planets around long lived stars and enjoy life without population pressure forcing you outward. If there are a thousand species all with 20 or so planets then the milky way will still seem completely void of intelligent life. It'd be 100s of lightyears to the nearest civilization. Since pumping out extremely strong radiosignals isn't exactly an efficient usage of resources they'd be just as invisible to us as we are to them. However, it is dangerous to assume that observations made on humans apply to aliens. It seems kinda unlikely that thousands of civilizations behave the same as ours...

Birth rates decrease as technology progresses- however, the problem is that civilisations will likely implace artifical birth rate quotas (probably a little more than 2, assuming sexual reproduction) if they are incapable of immortality. Robots wil help, but a stable population is the most beneficial for the economy of a civilisation- never mind that as societies get more advanced, they alse demand greater amounts of resources, new jobs, etc. At the very least, societies may spread out as they hunt for rare resources.

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Really, life is probably common throughout the universe- species that can become space-faring, meanwhile, probably aren't. That would explain the Fermi Paradox.