I just finished reading "If the Universe Is Teeming with Aliens... Where Is Everybody?"

[krispos42]

A fascinating book, recommended by a DUer a couple-3 months ago. I finally got around to reading it after buying it in December.

I found a couple of points I don't agree with, but on the whole it was a very interesting read. The scope of ideas in the book was broad with a lot of concepts and ideas I had not read about before.

The author even mentions SETI@Home! Yay!

http://www.amazon.com/Universe-Aliens-Everybody-Solutions-Extraterrestrial/dp/0387955011

[qazplm]

1. maybe most of them blew themselves up

or they never got around to leaving their planet

or deep space travel really is hard

or turns out we really are one of the first technologically advanced civilizations in the galaxy

or we are one of the last/most recent ones and everyone else more advanced is simply ignoring us or so technologically advanced as to render themselves invisible to us..

[Merlot]

3. so technologically advanced as to render themselves invisible to us..

is my guess.

this one is kinda LOL: we really are one of the first technologically advanced civilizations in the galaxy

[qazplm]

12. why is it LOL?

No one knows how long it takes for a civilization to reach our level. We only have the one example.

We know that there was at least a few billion years before most stars formed with anything other than helium, hydrogen and Lithium. It would take at least a few billions years after that for planetary systems and life to form surrounding planets with the elements for life in them.

Maybe 14 billion years is the rough minimum for how long it takes to get from no life to technologically intelligent life. Or maybe it's just that way in our galaxy, but in some other galaxy, it only took 12 billion and that galaxy has 100s of technologically advanced civilizations, and in another, technologically intelligent life hasn't evolved at all yet.

We simply don't know. What we do know is that in our own history, natural disasters almost wiped out the human race, and that we could have nuked ourselves back to the iron age as little as 30-50 years ago.

[jeff47]

14. Because Earth has experienced a few mass extinctions

250M years ago, more than 90% of all life on Earth died (largest mass extinction)

65.5M years ago, about 75% of all species went extinct (the one that killed the dinosaurs)

There's 3 others that are about as big as the one that killed the dinosaurs (205M, 375M, 450M years ago).

On an alien world that suffered fewer mass extinctions, intelligent life could have a multi-million year head start on Humans.

Of course, the question that arises from that is if an intelligent species had a 65M year head start on humans, and practical interstellar travel is possible, how 'come they haven't filled the galaxy by now? No way for us to know. Some possible explanations:

• Chance didn't produce such a planet in our galaxy (very unlikely with all the stars and planets)


• Practical interstellar travel isn't possible (may be likely)


• We're in a resource-poor or otherwise uninteresting part of the galaxy (unknown)


• We're in the galactic equivalent of a "nature preserve" (unknwon)


• Said species isn't very expansionistic (unlikely)


• The Reapers cull all the advanced species on a regular basis (very unlikely, despite being an excellent video game series)

[qazplm]

19. why wouldnt mass extinctions be common everywhere?

Heck we might be rare in that we have had them more rarely than other places.

almost every solar system is going to have a period with increased entry of comets and asteroids into the habitable zone, there are going to be fluctuations in a young star, gamma ray bursts, supernovas, and supervolcano eruptions, and whatever else it is that causes mass extinctions.

I don't find that compelling one way or the other. We don't know what normal is vis a vis any of this, except for what we alone have experienced. We don't know the average rate of growth from life to advanced civilization, the average rate those civilizations keep from destroying themselves, the average rate of mass extinction events, etc, etc.

It is as likely that we are one of the first, as it is that we are one of the last, as it is we are smack dab in the middle...based on what information we have now. That might change once/if we actually start meeting (either us to them or them to us) other civilizations.

[jeff47]

20. I'm not claiming they're rare. I'm claiming another planet might have had one less.

We've had 4 mass extinctions. What if their planet only had 3? That could be a very long head start compared to humans. Their planet could have also had 6 mass extinctions, and they're well behind us. With an astronomical number of planets, both will have occurred (And yes, I went with the bad pun).

We don't know the average rate of growth from life to advanced civilization

Average doesn't matter. There only has to be one hyper-growing species to fill the galaxy.

It is as likely that we are one of the first, as it is that we are one of the last, as it is we are smack dab in the middle...based on what information we have now

There's little reason to believe we're the first, given how fast life developed on Earth. All that would be necessary is a few generations of stars to create the heavier elements, and that takes well under 12B years. So there's bound to be solar systems out there that formed earlier and developed life earlier.

There's also little reason to believe we're the last, because new stars and new planets are still forming regularly.

But yes, we don't know what's out there. That was kind of my point.

[qazplm]

21. that assumes

life begins fast everywhere. Average does matter, because if the average turns out to large enough, then we'd be one of the first...if average turns out to be us, then obviously there are a lot of civilizations out there, if average turns out to be small, then we are one of the babies of the galaxy so to speak.

We don't know what that average is. We also know that technological life isn't necessarily a guarantee. so take one of those planets where there were only 3, or 2, or heck none. There might not have been the necessarily wiping of the slates needed to get to the "right" dominant species for technology.

What if the dinos never underwent an extinction event? So there was only 3 here instead of 4. No guarantee that we'd have dinos building rockets, driving vehicles, and speculating on other civilizations on other planets. Likewise that planet you speak of with 6 extinctions could have ended up setting the conditions for a very intelligent species that developed even faster than humans. Way too many variables to even begin to make sense of it.

I believe life is darn near ubiquitous out there, but I believe technological life is possibly much much harder to reach for a whole host of reasons. Thus, it is possible we could be one of the firsts. It is also possible to be in the middle or last, if it turns out it's easier or much easier than I believe.

[AlbertCat]

18. Or all the above.

But I imagine the vast distances and the requirements for traversing them is paramount.

[Warren Stupidity]

2. high tech civs are rare and brief seems to be the obvious answer.

[laconicsax]

23. There are other obvious answers that don't require baseless assumptions. n/t

[Warren Stupidity]

24. Don't actually commit to any of them, though.

[laconicsax]

25. Why commit to the one you posted?

There are lots of possible reasons why we've never encountered extraterrestrial life, let alone the intelligent type. Space is vast, light is slow and dissipates rapidly, we've only been looking for a few decades, etc.

There's nothing aside from our own ignorance on which to base the speculation that "high tech civs are rare and brief," so why bother?

[callous taoboy]

26. You know,

there was a nicer way to make your rebuttal.

[laconicsax]

27. Your concern has been noted. n/t

[Warren Stupidity]

28. Actually it is based on current data, data that indicates no aliens radiating anything

we can observe. It is a theory that fits the data and fully explains the data.

But I digress, take a stand. You have a better theory that explains the data, go for it. Mine, by the way, is easily falsifiable. Show me some evidence of alien civs.

[laconicsax]

29. The problem is that the data doesn't support your hypothesis.

As has already been pointed out, there are several other simple explanations for why we haven't found unambiguous EM signals from other civilizations.

In order to support (or falsify) your hypothesis, one would need data on other high tech civilizations. Without any data on alien civilizations (let alone high-tech ones), any conclusions regarding their nature is specious.

[Warren Stupidity]

31. And yet you won't propose any.

The data is no signals. A theory that fits the data is "tech civs are brief and rare". Your theory is:__________

All one needs to falsify my theory is a clear signal from a civ.

[laconicsax]

34. Sorry, you're wrong.

Your guess isn't that ET civilizations don't exist, which would be falsifiable by the detection of one. Your guess is that we haven't received signals because high-tech civilizations are rare and only last for a brief time. This is a hypothesis regarding the nature of alien civilizations, not their existence.

The only way to confirm (or falsify) your hypothesis would be to analyze data on technological development and longevity regarding other civilizations. In the absence of such data, any guesses about distribution are purely speculation.

I've already suggested reasons why we are unlikely to receive any signals, and they have to do with facts, not speculation. Since you didn't seem to read them, here they are again:

Space is vast.

Detection will be hampered by signal degradation and travel time. The limits of light-speed mean that we are limited by functions of both when any alien civilization may have sent signals AND where they are--we can only look at snapshots of the areas we scan.

Signals sent before or after our snapshot won't be detected, and only signals of sufficient strength will be recognizable over background radiation.

[Warren Stupidity]

35. Rare and brief.

It isn't even complicated and yet you have to misrepresent it.

If tech civs were common and long lived, given the plethora of nearby planetary systems, with the best estimates of probability that a star has planets approaching 1, we really should have some signals. That doesn't require all tech civs to use em, or use it for very long, it only requires some of them to have used it for long enough near enough to us to be detectable. You can look it up and read the math that has been done on it, it is a problem for SETI.

Rare and brief doesn't mean that the universe isn't teaming with aliens. It probably is, why wouldn't it be? It does mean that we are likely each of us isolated in out own space-time bubble, on our own, unable to reach out and touch each other. Oh well....

And it fits the data we have. Not some other data we dont have.

[laconicsax]

39. You're still wrong.

1. Common and long lived isn't the same as ubiquitous, nor is it the only other possibility.

2. We are limited, by virtue of how SETI works, to gathering snapshots of each scanned region. The variables that could explain no detectable signal have nothing to do with whether there's anyone there:

In order to detect a signal from a random star system X light-years away, these conditions had to have been met:

-Signals must have been sent X years ago.
-Those signals must be the right type (EM of the right wavelengths)
-They need to be strong enough to be identifiable after weakening over distance.

A civilization that wasn't sending strong enough signals of the right type at the right time wouldn't be detected. The chances of detecting signals isn't a function of whether alien civilizations exist as much as whether the perfect combination of factors regarding the signals themselves.

It's like the xkcd posted in this thread: if your search parameters are very narrow (as ours are), you're more unlikely to find what you're looking for.

[mindwalker_i]

4. Looking at the speed of progress just in my lifetime....

I can't imagine civilizations even slightly older than us would find us interesting. When I was growing up, nobody had computers. Now everybody has them in their pockets and they're all connected. BBSs were cool when I was 15. 50 years from now? I'd probably be put in a mental institution for having a desktop (let alone several).

[Moonwalk]

5. High Tech has to meet High Tech....

Which is to say, "ditto," to what everyone else has said. Remember, we've only been sending out radio signals for something like 100 years! Putting it another way, we modern humans have been around for some 420,000 years. What if all those civilizations out there are somewhere between 420,000 and the 18th century? That means that the earliest they'll hear us and send back a reply is in 100 years--and that's not counting the time it's going to take for their message to get back to us. If they want to get back to us, that is. And if we're sending it in the right direction for them to get it.

Where are they? Developing most likely. Rising and falling like we did over hundreds of thousands of years and maybe they'll hit upon radio waves and maybe they won't, and if they do maybe they'll send out a message and maybe they won't. And if they do...will we be in the right place to receive it? Have other civilizations been sending us messages for hundreds of thousands of years but we couldn't receive them? And now they're gone and we missed the message? All possible. Being in the right place, right time, with the right civilization to receive and respond to such messages is rather like winning the lottery. Possible...but very, very slim odds.

[jeff47]

7. Also, we're getting quieter

Fiberoptics have replaced a lot of what we used to send out over RF. We're also using lower-power RF to carry the same signals. So as we advance, we're getting harder and harder to find via radio.

So it's completely conceivable that there are other civilizations that are both more and less advanced than we are. We just don't recognize the communication used by the advanced ones.

[Moonwalk]

11. Absolutely true. An excellent point....

It's funny that the more advanced we get, the more insular we make our planet, sending out less of the quick messages (radio, etc.) rather than more. Which leaves only robot probes still traveling out, and they're very slow indeed. Consider that it will take Voyager 1 with it's introduction to us something like 40,000 years to maybe reach another inhabited planet. You have to wonder if human beings will still be around when it gets there, is figured out, and a response comes back.

[Warpy]

6. You'd be very hard pressed to get those old radio broadcasts tuned in halfway to Alpha Centauri

because by the time they get that far away, they're extremely feeble and hard to pick out from the background noise, which is much stronger.

As for interstellar travel, any society which is advanced enough to figure out all the problems, from deflecting micrometeorites to allowing faster than light speed travel, would likely see us as simple primates who had finally managed to crawl out of the trees but really weren't worth contacting as trading partners, OK to study but too primitive to bother to talk to.

After all, we can't even communicate with other sentient species here and we share a planetary reference. How the hell would we manage with a silcon based methane breather from Zarkon?

I often wish little green men would show up and put an end to any idea of the earth as the center of the universe and our species as the pinnacle of creation. Alas, we're likely not worth contacting, too primitive and too dangerous.

[jeff47]

8. Obligatory XKCD

http://xkcd.com/638/

[krispos42]

13. I must have missed this one!

[Tumbulu]

30. I love that one!

thanks!

[longship]

9. Title states the "Fermi Paradox"

The Fermi Paradox asks the question expressed in your title.

For any astronomer the answer is fairly simple. The galaxy is rather large and distances between stars are so large that interstellar travel is not just impractical, is likely to be a practical impossibility.

The laws of physics of which we know (and which we know to incredible accuracy) limit velocity to the speed of light. Furthermore, because of relativity the amount of energy needed to even approach that speed is prohibitive, even with the most efficient energy source in the universe, matter/antimatter annihilation (in spite of Dan Brown's speculative fiction Angels and Demons). Then there's the time dilation issue (a very real phenomenon).

Therfore, interstellar travel is most likely to be limited to a one way trip. This is especially true since the closest intelligent, technological extraterrestrial lifeforms are likely hundreds, if not thousands, of light years distant

Yes, I believe that their are intelligent life forms on other planets in the galaxy. But they will be, like us, limited by the vast distances between stars and the universal laws of nature, isolated in their own stellar systems. Nature kind of makes the rules here. And after all, we all know that it's not nice to fool Mother Nature.

[Lydia Leftcoast]

22. Yes, if there were planets around Alpha Centauri, it would take four years at the speed of light to

reach them, or literally thousands of years with our current technology.

The practicalities of a space voyage lasting thousands of years boggle the mind.

[pokerfan]

10. Yeah, that was me

http://sync.democraticunderground.com/?com=view_post&forum=1228&pid=394

Fascinating book. It doesn't really champion any one solution to the paradox but instead floats fifty possible solutions.

[Silent3]

15. Perhaps there's a means of communication better than electromagnetic waves

Something currently unknown to our physics, perhaps even faster than light. (Paradox-free FTL is hypothetically possible by only violating the "spirit" of relativity, without violating any known relativistic physics.)

If we ever discover such a means of communication I wouldn't be surprised if we find the galaxy to be full of chatter, with radio turning out to be something only used in the earliest stages of technological civilization. Perhaps the radio era of technological civilizations is usually so comparatively brief that even aliens interested in communicating with relatively primitive civilizations don't worry about reaching civilizations that primitive.

I fully support the SETI program in its current form, however, because we've got to work with what we understand. Radio may very well be the best means of interstellar communication after all. Then again, we might be laboring under a huge erroneous assumption.

[krispos42]

16. If they have FTL travel, then they might only use radio for intra-system communication.

Since the FTL ships would vastly outpace radio waves, then would not sent interstellar messaged with them... they would either travel via dedicated messenger ships or as part of regular trade/military/governmental shipping lines.

It would depend on the sort of FTL travel, I guess. There's the "we travel multiples of light speed" kind, the "we travel multiples of light speed but we have to be far away from gravity" kind, and the "instant from here to there" kind.

If the first, then I can see small ships with minimal crews warping back and forth on priority message runs, with other ships making routine pick-ups from orbit and then heading out on "postal routes". If the second, I can see a permanent base out at the "far away from gravity" point, where the message ships are based. When they arrive, they beam their information into the system, get messages uploaded, then take off on their routes.

[Silent3]

17. It might, however, be easier to send an FTL signal of some sort...

...than to move bulky physical objects at FTL speeds.

There already appears to be some sort of FTL phenomena going on with particle entanglement. The problem is that this phenomena is strictly not information-bearing, it can't be used to send a signal.

Maybe, however, there is a similar phenomena that can convey information, mediated by a preferred frame of reference so as to avoid temporal paradoxes. Pure, wild speculation, of course, but worthy of consideration when thinking of reasons why ET isn't phoning our home.

[originalpckelly]

33. You don't even have to go that far...

even with our own current technology, we know of ways to communicate that a spatially coherent, which would make receiving a signal from someone else like trying to hit a grain of sand with yet another.

[krispos42]

37. That's entirely possible.

And when you get involved with making emitters in space, where there's no air to interfere with the light (okay, not much air) then a narrow beam could really be possible. Especially if it's tightly focused.

[originalpckelly]

32. We are assuming that they would communicate with technology that uses...

em fields that radiate away from a source like the sun or a flashlight, and not like a laser.

With a spatially coherent communications technology, you wouldn't actually have a very high likelihood of a hit.

A civilization would want to communicate that way because it means that you can send more information in the same volume.

It's like an SD picture v. a 4K picture. With spatially coherent communications you have more information carrying capacity.

-Random Thought

[Orsino]

36. I think it helps to consider the findings of astrobiology, geology and anthropology...

...which looks at life not as something that happens on planets, but something that happens to planets.

Life may have started four billion years ago, but it wasn't until six hundred million years ago that conditions became tenable for complex (multicellular) life, and our carbon cycle will start to slow in the next few hundred million years as the Earth's core and mantle cool. We might therefore be right in the middle of the "sweet spot" for animals. Out of the ten-billion-year existence of our world, only a billion of that might support anything more than microorganisms, and it's taken us more than half of that to evolve real intelligence. It may be that other planets do no better.

Furthermore, life as we know it is dependent on chemical elements that only came into existence after the first stars began to go nova, some few billion years after the Big Bang.

I suspect that intelligence evolves competitively (as we did), and that life forms that develop technology remain bogged down in internecine conflict over planetary resources, never able to devote all of their energies to interstellar colonization. Humanity generally seems to be retreating from space flight for this very reason.

Perhaps space flight is only developed every billion years, and almost never leads to permanent colonization beyond a home world. The answer to the OP's question, then, would be, "We were here; where were you?" We might find these words inscribed in stone on occasional airless moons around the galaxy.

Look on my works, ye flighty, and despair.

[krispos42]

38. This was discussed in depth in the 3rd section

The "they don't exist" hypothesis.


The complexity of multicellularism is pretty astounding.