So....where are they? (Fermi Paradox)

Captain Amazing:

I’m not sure if you meant this as a joke. It doesn’t correspond to the Fermi paradox, unless your family is thought to number in the quadrillions. If so, it would be reasonable to expect that at least one of them had travelled to China.

Gary Kumquat:

By the definition used in this thread and most discussions of this issue, we have only achieved intelligence within the last 100 years. The timespan for colonizing the galaxy is on the order of 5 million years. So I suggest a little patience is in order.

SPOOFE

You sound like my niece. Why, unca Jeff, why? Why? WHY? :wink:

The regular movements of a galactic civilization would be hard to disguise. I have an excellent book by Dr. Robert Zubrin titled Entering Space about the necessary steps to explore the stars. Good book, and I highly respect his work. In a chapter called Meeting ET he details the reasons we should be able to detect any significant starship activity by ET civilizations; in fact, he thinks this approach has more chance for success at detecting ET than projects such as SETI and Phoenix. Unfortunately, thus far nothing has been spotted by anyone.

Certainly it is possible that all the other ETs are on the same evolutionary timeline as us, but I think most scientists consider this improbable. As mentioned in this Scientific American article and this lecture from Wake Forest University, chances are extremely slim that ET is technologically within 100 or even 1000 years of us. Many of the proposed ETs would likely have a million years head start, or more.

g00g00fish

Again, the Stay at Home hypothesis may do for 1 or 2 ET civilizations, but all of them? It seems highly unlikely to assume everyone will want to stay home, and it just takes one civilization to be interested in colonizing the galaxy for it to happen in a relatively quick manner.

By the way, welcome to the SDMB!

Unless we were out of detection range. Remember, we still have a hard time noticing planets in other star systems.

All too true, but my assumption is the galactic civilization would be fairly widespread, and there is no reason to suppose they would have left our solar system intact. Keep in mind also that the main reason it is difficult to detect other planets is due to their proximity to the corresponding star, which “washes out” any light from the nearby planet. Interstellar starships don’t have this problem. As Zubrin details in the aforementioned book, light from reasonably sized antimatter photon rockets could be detected at a distance of 300 lightyears by Hubble, and this distance includes well in excess of 100,000 stars.

Well, 300 lightyears isn’t that great a distance in a galactic sense. True, if there was a huge, massive civilization out there, we’d very likely have detected it by now. However, that’s a VERY big “if” to add to the argument. I see no reason in assuming that any sort of space-traveling species would have built a large civilization.

Indeed, the fact that we haven’t detected any starships out there merely indicate that there ISN’T a widespread galactic civilization, NOT that extraterrestrials don’t exist.

Now you’re starting to get down into the heart of the so-called paradox. There is no reason to suppose the alleged ETs would suddenly stop in their quest for galactic exploration. With the HUGE headstart they likely would have, there is plenty of time for it. So why would they stop? Where the hell are they?

Though 300 light-years isn’t large in the galactic sense, it does include a vast number of star systems. Surely ET could find something to his liking in it.

This is why I think it far more likely that the first intelligent species in any galaxy sets out to explore the cosmos, finds no other similarly sentient ETs, but as a natural result prevents any other species from developing into the same environmental niche as they themselves occupy until they go extinct (if they ever do).

But I sure would like to be proven wrong.

Well, you’re still assuming that there’s some sentient species with a “huge” headstart, and I see no reason why we should assume this. Think of it this way… in, say, 500 years, do you think that man will have advanced to the point that we’ve spread across the galaxy? Nah… unless some form of FTL travel is perfected, it’s impossible.

So we can safely assume that any ET’s out there can, at least, be many centuries ahead of us, technologically, and still remain invisible to our current level of detection. Heck, maybe they started in the center of the galaxy and are working their way outwards… in which case, it’ll be a while before they drop by to say “Hi”.

That is my exact point. We define ourselves as intelligent life, and we have yet to colonize the galaxy. Maybe it’s quite a difficult task (aims for understatement of the day award) and could take a little while. Maybe there are other races who are in a similar position, give or take a couple of hundred years of technological development. Or not. All I’m trying to demonstrate is that Fermi’s theorem is far from conclusive.

I believe there was a paper published last year that claimed that even if life existed in a decent percentage of star systems, the odds that that life would evolve to the level that we have was so small that it could easily be that we are the only intelligent life form, even though there are billions of planets with life on them.

The main longshot seemed to be the requirement to have a planet with a habitat that remained essentially unchanged for a few billion years. For one thing, that means no gigantic asteroids (not the size of the Yucatan Dinosaur-killer, but one of the real big ones that blast away your entire atmosphere or crack your planet wide open.)

That would possibly rule out dense clusters of stars, and stars nearer the center of the galaxy. Basically, conditions may only be acceptable way out in the spiral arm boonies where Earth is.

They also felt that a Jovian planet or two was necessary to act as a cosmic magnet keeping the junk away from the little guys.

Then there’s the problem of life evolving around the right star. It has to stay stable for a few billion years, it can’t flare up severely, etc.

Then there are any number of genetic longshots that have to take place - after all, of the millions of different forms of life on the planet, we’re the only ones that can build neat stuff.

Don’t forget SuperNovas. Not only does your sun have to stay stable, but if you are close to any others, they’d better stay stable as well.

When you add it all up, and discount stars in areas that are likely to be swarming with particles, and stars that are in areas of low radiation, it’s possibly that intelligent life can form, but it’s just so damned unlikely that you generally only get a handful per galaxy at any given time.

Who’s to say that aliens would spread very far? If humans start living in space, the most rational way of doing so is not to colonize planets, with their limited space - it’s wasteful to have to move stuff in and out of the planet’s gravity well, you can only fit so many beings on one planet before heat pollution becomes a real problem, and you are all sharing one life support system, which seems really foolhardy to me. We’ll probably start out doing the orbital habitat thing, you can hollow out a medium-sized asteroid (2 or 3km in diameter) and fit over a million people in there, and there are billions of asteroids just in our inner solar system. I think before we start running out of matter in our own solar system to make little bubbles of Earth-like conditions we will start adapting ourselves so we don’t require it. It’s certainly within the realms of possibility to have a lifeform that can exist in a near-vacuum and get nourishment from sunlight or by metabolizing cometary matter, once one is created it will have a serious survival advantage over the thin-skinned delicate ones with their unreasonably fast metabolisms. It could be that most sentient species evolve into slow-living critters that inhabit their star’s cometary halo with no need to go anywhere only a few millenia after they start building cities.

There is also the possibility that our planet is the first one to develop life since the Big Bang - the universe is probably 12-15 billion years old, and life has been around for the last three and a half billion years. We have no idea how life originated, it could be such an unlikely occurence that it only happens once every 20 billion years or more.

Gary Kumquat, you and SPOOFE are both coming at this with the assumption that ET would be within ~500 years of us technologically. Read some of the links I’ve provided to see why it is FAR more likely that any ET would have reached intelligence millions or even billions of years in the past.

Our own sun didn’t form until roughly 5 billion years ago, which means there was at least another 5 billion years prior to that available for other stars to have formed and even supernova before our star was even born. Perhaps the amount of the necessary “heavier” elements were not yet sufficient to support life as we know it, but it certainly didn’t have to take 10 billion years to achieve sentience. If ET only had a 0.1% head start, that still results in a 10 million year difference.

I completely agree that if ET is within a few thousand years of us technologically, then we likely won’t see each other for some time yet. I just don’t find that possibility very promising. But if it is indeed the case, then all the more reason we should expand quickly into the galaxy, to “carve out our space” so to speak.

Sam Stone, I think I read that very article, and it struck right at the heart of a lot of my same thoughts on this issue. Interestingly enough, I feel the Yucatan Dinosaur-killer type asteroids may be a necessity, kind of like a cosmic reset button. It disturbs the planet’s equilibrium on a semi-regular basis until a species evolves that can protect itself from the asteroids.

::sigh:: You’re missing my point. The simple fact that we haven’t seen any ET’s would discount this reasoning… or would indicate that the ET’s are purposefully trying (and succeeding) to hide themselves from us.

Basically, the level of technological advance and Fermi’s so-called Paradox are two different topics of discussion.

You appear to have fallen prey to what I like to call “Star Trek syndrome”… assuming that alien cultures are even remotely recognizable by our standards, and assuming that we’re important/great enough to be able to detect them. There is no reason why we should assume this.

Additionally, even if we assume that the ET’s are billions of years more advanced than we are, that is no reason to assume that they would have come across us by now. As I’ve said, barring some form of FTL travel, it could take many millenia to starhop just a small distance across the galaxy. There’s that “Star Trek syndrome” again… you’re assuming a steady growth in development and expansion with these ET’s, which, again, there’s no reason to assume exists.

Which indicates nothing. While it does imply that a sentient species may have developed many billions of years ago, it can also be indicative that the conditions were not met anywhere in the universe until approximately 5 billion years ago (give or take a billion).

Why not? Why is 5 billion the magic number and not 10 billion? Who died and made you God?

Nope. I’m not actually assuming that at all. I’m just trying to give you the simplest logic for explaining why Fermi’s theorem is far from conclusive.

The first two obvious exceptions to this line of logic.

  1. If there’s intelligent life of roughly our tech level, it won’t have made much more progress in travel than we have.
  2. If there’s intelligent life of a lower level, it will have made even less progress.

All it really says is that if there’s anything advanced enough to travel the universe, either it hasn’t gotten to our neighborhood yet, or it did so a long time ago and didn’t stick around, or it did and seeded the earth before departing, or it’s avoiding us, or it’s so damned alien that we can’t even comprehend it at our current level of knowledge, or…you get the idea.

You see ET could reached intelligence billions of years in the past. Which means we’d be a bit daft to attribute our motives and goals to him.

*As an aside to Spoofe, I’m surprised to be on the same side of this argument with someone who not too long ago was arguing rather loudly against me about the idea that magic could exist. It seems to me the same underlying epistemology - that absence of evidence is not evidence of absence.

And as an aside to Gary, I’m not stating that there are extraterrestrials… just that, if there are, it’s not necessarily a given that we should have seen them by now.

Additionally, unlike Magic, we do have evidence of life popping up at least once, so it’s not folly to assume it’s possible to occur again. It’s just not a foregone conclusion, is all.

[/Hijack]

What about the idea that it might be nearly impossible to colonise the galaxy?

A lot of the posts in this thread seem to be assuming that in a few hundred years we’ll be hopping all over space very easily (too much indoctrination from Star Trek I suspect), but maybe that just *isn’t possible[/] maybe it’s beyond the technical capability of any life form to get outside it’s own solar system in any useful way; maybe all those civilisations out there simply ran out of resources and burned out.

The stars are a heck of a long way apart y’know.

Four lightyears to the nearest one. Assuming it has a viable planet for colonizing, and assuming we eventually develop the technology for terraforming, and assuming we find methods of traveling at relatively fast speeds (1/4 c, or even 1/8 c), the prospect isn’t that outrageous. At 1/8 c, that’s a 40-year trip… sure, it’d require some sort of massive colony ship, and it’d require some very exotic methods of propulsion (and slowing down), but it’s possible.

The best hope of populating the galaxy is the possibility of FTL travel… and despite Stephen Hawking’s comments on wormholes, I wouldn’t hold my breath waiting for the technology to be discovered.

Possible in the sense that physics doesn’t forbid it, but in terms of any sort of practical reality, very very unlikely to ever happen (or happen before we’ve finished ruining our ecology or squandering all that easy energy stored in fossil fuels*)
*[sup]Before someone rushes to nitpick, yes, I know that rockets don’t have to burn fossil fuels directly, but the fuel they need must be made somehow, if it’s hydrogen, then this must be collected or separated out from water, a process that requires large amounts of energy, and that energy comes from… fossil fuels, then there’s all the energy needed to smelt the metals to make the vehicles, plus the petrochemicals required to make the plastics, etc etc.[/sup]

anyway, what happens if you’re travelling at 1/4 c and you hit a rock (or just a grain of dust for that matter), maybe not all that likely, but in the course of travelling 4 light years, the probability rises.

That’s also the best case scenario; what if Alpha Centauri has no habitable planets?

I’m still of the opinion that [very nearly] all civilisations would settle back into the dust and vanish, making the idea of a populated galaxy quite unlikely.

Very true. We’ll only find out if we try though.

We need only look to science fiction for the answers. Since Star Trek has been mentioned so many times, I’ll start there.

Star Trek: There was a species that developed the technology to colonize the galaxy, and they did so millions of years ago. Eventually their species reached its peak and declined, but was always alone. They seeded many worlds with their dna, ensuring that humanoid intelligent life would develop on many worlds relatively simultaneously. When we start colonizing the galaxy, we’ll run into a lot of other species of about equal technological ability.

David Brin: (from “The Crystal Spheres”): There are huge crystal spheres surrounding every star system in existence (at a distance of 5 or 6 billion miles, IIRC), and these can be broken only from the inside. This ensures that intelligent civilizations that develop the technology to leave their own solar system don’t colonize every planet in the galaxy, thus preventing them from evolving intelligent life. In the story, Earth is the fifth such civilization to break out of its sphere, which gives us five systems and planets to use.

David Brin: (from the Uplift trilogy): Species can ordinarily only become intelligent through intervention by an existing sentient species. Thus, a species that evolved intelligence naturally would have to uplift the native species of other planets in order for there to be other species. This theory is directly contradicted by Asimov’s, below.

Isaac Asimov (from the Foundation/Empire series and The End of Eternity): The presense of one intelligent species on a viable planet would prevent the evolution of intelligent life by native species; therefore, if one species did develop the technology to colonize the galaxy and did so, this would prevent the native species from evolving into intelligent life.

John Varley (from a huge body of short stories): An intelligent species is likely to spend most of its time and effort exhausting the resources in its own star system before venturing outward. If two intelligent species did encounter each other, they are likely to be so different that they would either not notice each other, or one would be so much more technologically advanced that it would destroy the other.

Kim Stanley Robinson (from the 3 Californias trilogy): Technology and ethics/philosophy progress at different speeds. If technology progresses faster, civilizations develop weapons of mass destruction and destroy themselves before leaving the planet they originate on. If ethics/philosophy progresses faster, technology is likely to be turned towards optimizing the place of origin, eliminating the need to expand (why leave if you exist in a utopia?.

Greg Bear (from Blood Music): A sufficiently advanced technology will enable a species to rapidly evolve into a form no longer recognizable as an intelligent species.

Yup, that’s the one I think is on the button, except that in exhausting the resources of their star, they nobble their chances of leaving.