And if the alien probe is using some type of stealth tech, then we'd never find it anyway. Why a stealth probe? Human biologists construct blinds to observe wild animals without disturbing them Plus, nano probes would be too small for us to detect anyway, at least wit our current level of technology. Finally, our solar system is a damn big place.

"If a probe contained nanobots that allowed it to build up new probes at each planet then I would expect a much faster spread of probes. Each probe could reach a suitable solar system and just start producing more probes. Then machine civilization would take over the galaxy."

Andrew Cutler of Energy Science Laboratories in La Jolla wrote a paper on detection of ancient earth colonization by looking for depletion of various key hydrothermal ores. He claimed he found such depletions corresponding to the Cambrian explosion and that the asteroid belt could be explained by a planetoid being dismantled for its nickel iron core around the same time.

I don't know if was ever published but if it was it was in the late 1980s or early 1990s.

It's called the Fermi Paradox for Enrico Fermi, who first asked the question: "where are they?".

Well,

I have always agreed that we should be looking for Artifacts of Alien Civilizations rather than direct communications from them.

And I think it is somewhat amusing that we look at aliens through such anthropomorphic glasses - beacuse by their level of Civilization - it is very unlikely that their is a clear distinction between biological and technological systems for them as they will likely re-form their bodies - "on the fly" - into whatever the environment requires for a project.

(unless they are some kind of extremist technophobes - and that would likely not last for long in their society)

But - if we are to believe the numerous whistleblower Astronauts and Cosmonauts that have come out - as well as strongly established and documented UFO incidents complete with full radio and radar tracking data - then this paradox does not even exist - we ARE encountering vehicles/probes which act under intelligent control.

In fact, the significant varience in size as reported amongst the best UFO reports by professional trained witnesses, does seem to indicate that we are encountering both parent vehicles and likely unmanned probes.

As to why, as Michael suggested, they don't run silently at all times - perhaps it is because a contamination of our society already occurred in the early twentieth century - and now they are simply making us acclimated to their presence here.

It is my personal opinion that no Alien culture, if they are observing us, is likely to make contact before we have a centralized world government system - to me that is logical as it would make the culture shock more containable and the transition to a member of a larger body of extraterrestrial government more streamlined.

Although I have never seen a bonified UFO for myself - I became an amateur UFOlogist in early 2005 after a friend turned me on to "right stuff" astronaut Gordon Cooper's obituary on CNN.

(and his tireless campaign to get NASA - and the U.S. Govt. - to acknowledge their detection of intelligently controlled extraterrestrial vehicles.)

http://www.cnn.com/2004/TECH/space/10/04/gordon.cooper/index.html

The case evidence I have examined since starting my research in 2005 has been very impressive, but I, like most Americans, have not been able to dedicate a substantial amount of time educating the public, or volunteering with my local chapter of the very professional MUFON organization.

I would STRONGLY encourage professional scientists, and engineers, to take this subject much more seriously than it is portrayed to the general public - it has been proven through FOIA's, and leaked classified documents, that Govt.'s throught the planet certainly do!

Tipler made arguments like this, but also included the assumption the probes would be self-replicating.

BTW, the asteroid belt cannot be explained by a planet being disassembled. Stable isotope evidence from meteorites is conclusive that the asteroids were never a single body.

Andrew Cutler of Energy Science Laboratories in La Jolla wrote a paper on detection of ancient earth colonization by looking for depletion of various key hydrothermal ores. He claimed he found such depletions corresponding to the Cambrian explosion and that the asteroid belt could be explained by a planetoid being dismantled for its nickel iron core around the same time.

You know, this has always made WAY, WAY more sense than anything the SETI people ever talk about. I always thought that looking for alien artifacts (on the moon and in the asteroid belt) as well as mineral depletions that cannot be explained by natural processes was the way to go. I don't know why, but the SETI people never consider these possibilities and approaches. The other approach that is occasionally mentioned is looking for astronomical phenomenon that cannot be explained by known natural processes (e.g. dyson clouds, etc.).

Anything out in open space (like a space colony or the like) would have decayed or degraded over the past 540 million years, but there should still be debris that is recognizably artificial.

Hell, I've known all along where the aliens are: they're in Congress. "In Washington, no one can hear you scream."

perhaps we finally have an explanation of dark matter: space is littered with stealth probes from defunct civilizations.

Intelligent life is probably VERY rare.
Earth is basically a fluke.
There have been so many times when life has come close to being totally destroyed on this planet never to recover.
We are extremely lucky to be here. To expect life to exist in huge numbers out there is almost certainly wrong.
Microbial life is probably very common, but to make the leap to what we're looking for is extremely hard to do.

It's just human conceit that we expect aliens to contact us. For some people it's fun, others are just very curious (like Sagan) but it's very improbable.

They might be out there, but they're almost certainly aren't trying to talk to us.

While I miss Carl Sagan, -he was a genius- I think he was wrong when he said the universe is probably rippling over with life.

Extraterrestrial life (of any kind) may or may not exist. There is simply no credible evidence either way. "Professional trained witnesses',is not evidence no matter how many times people say it is. Wanting it to be so, won't make it so, either. Too much New Age claptrap involved here. Be productive and gain some respect by mowing your neighbors lawn.

As I recall, one of Greg Bear's first novels involved artifically intelligent robotic "berserkers" intent on destroying biological life on any planet they encountered. Once they had been detected, they went out of their way to present themselves to humanity as harmless. In the story, many people argued that these aliens would have no motive to pretend to be friendly if they really weren't. In the end it turned out that the motive was to keep humans convinced there was no danger, so none of us would attempt to escape via space travel until it was to late, and the scourge of life could be eliminated from yet another planet.

That applies equally well to the question of why aliens would take great measures to hide themselves from detection at all, doesn't it?

We're currently within striking distance of being able to deploy a full sensor network ourselves.

Replicators deployed at Pioneer 10 speeds would get there (the whole galaxy) in about a billion years.
We'd only have to build one, and test it in-system.
Travel time wouldn't be a problem for the craft. They fly frozen, and only wake up when they warm up on arrival.

For that matter, once you've got industrial capability in a system, you can transmit any additional data for other purposes, including seeding and colonization.

The motivation isn't there, and the finance definitely isn't, but I think the technology is.

I think advanced life would most likely be interested in other intelligent life, but only if it wasn't a peer competitor. If we arrived at a distant star with god-like technology, our first instinct wouldn't be to vaporize the cavemen living below, they are no threat and their development can be monitored and observed. We'd be interested, we'd want to engage in a positive way.

If, however, we encountered another alien race with similar capacities to our own, we'd be terrified. We could not assume they would be friendly, in fact, considering the stakes, namely the possibility of our own extermination as a species at the hands of a superior competitor, a fate we ourselves have inflicted on countless species on our own planet, we'd have no choice but to assume the worse and attack, as would they.

So I think the biggest risk is running into something like us. If we encounter gods or cavemen, then they are either no threat to us or we no threat to them, but statistically, the chances of meeting another species at the same point of development is an infinitesimally small percentage of an already infinitesimally small number.

Plus, the idea that we'd find traces of a visiting probe a hundred million years after it had been and gone is utterly laughable. How big is space, exactly? Come on.

"If intelligent life evolved elsewhere it should have happened far enough back in time that these aliens would have spread out over much of the galaxy by now."

Why should it have? Maybe intelligent life takes billions of years to develop. Perhaps the amount of time it took us to develop is not unique, and other intelligent species out there are at roughly the same level of development as us. Heck, maybe we're the first!

Joeseph, you said "Perhaps the amount of time it took us to develop is not unique, and other intelligent species out there are at roughly the same level of development as us."

With all due courtesy, I want to call your attention to the fact that our Sun is (at least) a second-generation star - one that was formed from the debris of a previous generation of stars in our galaxy that went supernova. The astrophysical evidence for this is compelling and readily available through any search engine - it is not speculative in any way. I think the implications of this for your argument that we may be the first intellignet life, or even nearly so, are obvious.

Boogliodemus,

Your arrogance on this subject is eclipsed only by your ignorance.

As an objective scientist I have no personal bias in this matter - other than the profound implications if it turns out that we are indeed being observed by an extra terrestrial species.

However for you to dismiss top insiders and whistleblowers such as U.S. Astronauts Aldrin, Cooper, and Mitchell as New Age wannabees, and for you to be too narrowminded to even look at the radar data and radio communication evidence that backs up several trained observers testimony, as well as the numerous U.S. and foreign Govt. case study compilations that conclude that intelligently controlled vehicles of unknown origin have been observed, just shows your inability to accept evidence which contradicts your own dogmatic world view.

Until you are willing to educate yourself on the topic of UFOlogy you will remain in the same intellectual blindfold that handicapped geocentrists for hundreds of years before Copernicus.

Feel free to continue to bury your head in the sand while those of understanding do the hard thinking for you.

(and for those who think an alien race would need to take any mineral resources from Earth - please - by the time they can reach Earth they are likely more than advanced enough to either create such substances themselves or mine them much more efficiently in their local galaxies)

A brief discussion of this occurred at my blog:

http://onestdv.blogspot.com/2009/07/why-people-believe-in-ufos.html

We don't know enough to really even speculate (though it's fun). We know one planetary system fairly well (our own), and are learning about others, but until we get more data it's mostly pointless speculation. (Not unlike the stories about Mars and Venus having life, Mars with it's canals and deserts, Venus with it's swamps and dinosaurs and such)

That said, my take is that it is quite possible we're the only ones nearby, if not the galaxy. From what we know, our solar system appears to be something of a freak. Most extrasolar planets seem to be several times the size of Jupiter, but much closer to its sun. We also happen to have a gigantic moon (relative to the size of the Earth), which has has a huge impact on us.

Of course, some of that probably has to do with it being easier to detect huge planets. But still, our solar system seems quite rare, possibly unique.

Then you have to factor in our location in the galaxy. Because of radiation, much of the inner galaxy won't be too habitable.

>Heck, maybe we're the first!

The first, and quite likely the only. Freeman Dyson points out that even at rather modest sub-light speeds, the amount of time required by a space-faring species to colonize every star system in our galaxy is quite brief compared to the Milky Way's age.

In five million years our post-human descendants wil be bitching about how celestial over-development along the spiral arms has spoiled their view of the galactic core, and even the Magellanic Clouds will be getting a little crowded.

I don't know whether to be exhilarated at the thought, or vaguely depressed.

This topic has come up periodically at science venues I work at.

There are several criteria that rarely seem to be discussed in this, or, more accurately, are glossed over. The very first is, even if there are extant alien civilizations present within hailing distance of us, it is sheer anthromorphism to believe that they would be interested in us, or the region near them. They may not; actively seeking out other life may be a thing only our species shares. Or we may not be nearly as "interesting" as we believe.

Another criteria is the time-in-existence issue. Civilizations rise; they fall. There well may have been other highly technological civilizations within our Galaxy, but as is the nature of things, they may no longer be in existence; a miss of even 5,000 years would mean they are no longer present for us to communicate with. Only in Star Trek and popularized fiction is there a Galaxy teeming with life, that exist at precisely the same technological level, all at the same time.

Yet another is the "Uranium problem." Any civilization that may arise will inevitably discover nuclear physics, and with it the ability to develop nuclear weapons. It's been noted that this is a fairly simple discovery, so it seems likely that any civilization will discover fission quite early on, at a time when they may not be yet stable and developed enough to handle the challenge. One may wonder how many might have existed that failed the challenge, and destroyed themselves before being able to communicate with us.

And finally, all of this would depend on just how many civilizations might exists at the appropriate technological level, at the same moment, in a Galaxy. If there are only a few, we would quite possibly be separated by many thousands or hundreds of thousands of light years, and so be effectively too far away for us to communicate with.

The Drake Equation is entirely based on guesswork and some hopeful assumptions, none of which has a single piece of evidence to back it up. I certainly hope Drake's more hopeful assumptions turn out to be the correct ones, but in the utter absence of any evidence (that we know of), all we can do is wait and keep listening.

So, re: these ancient artifacts, are we looking for a multi-million year old golden phonograph record that plays at 16-2/3 rpm (not 16 or 17...16-2/3) or something really advanced--more along the lines of an iPod, complete with the latest hip-hop/rap on it?

http://voyager.jpl.nasa.gov/spacecraft/goldenrec.html

I like the comment that says aliens won't contact us until we get an all-powerful world-wide central government. Been watching a little too much Star Trek, eh?

That's even better than calling for a world central government to stop the dreaded CO2.

I can see the campaign now: "Give up our national sovereignty so the aliens can feel comfortable!"

Sherlock,
Actually Joseph may have it right. Maybe life only forms with stars that are the remnants of supernovas...thus maybe we are the first.....

Technologically advanced civilizations are a fluke, and so our galaxy isn't likely to contain more than a few at a time, and maybe just one. I've said this before, and I'll say it again. Science as we know it arose only once. It didn't arise everywhere spontaneously. It arose only once. And even in that one case, there was nothing guaranteeing it. A semblance of science arose in ancient Greece, but anything could have sabotaged it along the way. The Persians could have crushed Greek culture. The Romans could have crushed Greek culture. Greek culture might have died out after Rome fell, but it was kept alive. Eventually, Europeans figured out how to do science as we know it, but even then the Church could have crushed it.

Look at what the Muslims did with Greek culture. At first, they preserved it. But then al-Ghazali came along, a man who used his brains to argue that faith is more important than reason. That was 900 years ago, and Islamic civilization still hasn't recovered.

Being anti-science and anti-reason is the default mode of human culture, and I would argue of any ET culture, too. We humans are very lucky that somehow science and advanced technology got developed. And there are plenty of people who don't like it. Enjoy it while it lasts.

Your arrogance on this subject is eclipsed only by your ignorance.

Ah, the irony...

"It is my personal opinion that no Alien culture, if they are observing us, is likely to make contact before we have a centralized world government system - to me that is logical"

I have it on good advice that they are simply waiting (seven decades now) for universal health care reform in the U.S. which is logical to me...and there is a little-headed big-eared alien right now sending signals out to them to get their rectal probes ready...

Probes may have already visited Earth. Why would an advanced civilization utilize manned vehicles when they could use automated craft? Life in the universe is very rare, but there is probably more out there that is much more fascinating than a bunch of near apes on a small planet in an otherwise unexceptional solar system. If a far more advanced civilization is out there, we are probably no more than a negligible blip on their radar or a novel curiosity and nothing more.

Kudzu Bob,

I'm already scheming on how I can find a nice solar system and somehow engineer it to make it look inhospitable from a distance so that tons of colonizers won't move in and destroy my neighborhood.

How to make a nice solar system with a planet near 1G and good atmosphere look like a really lousy place? I need to get started on this before lots of probes mark my planet as desirable.

Koblog,

If Obama gets reelected the aliens will invade. Spread the word.

Amabo Amoeba,

The aliens want to be first in line to get the free health care. They'll probably start landing as soon as the program gets funded. They'll want to get theirs first before the United States goes bankrupt.

There is much to be said about the theory that civilization requires heavier metals and minerals - ones that would not be available to a first-generation star (since these things can only be produced within supernovae). Thus, the first several billion years would be hostile to life. Then, obviously, a series of second and possibly third generation stars were produced, from the corpses of the previous novae. But, having said that, there should be other second-generation stars with civilizations. And if they are only a few thousand or a million years older than us, they should have already colonized the galaxy. Why can't we find them?

theories:
1. The conditions for life are rare: second generation star + planet with lots of minerals + liquid water + carbon + stable orbit + strong magnetosphere + Jupiter/Saturn-to-sweep-away-asteroids == incredibly rare - we're a huge statistical outlier
2. Life isn't uncommon, but we're one of the first to get this far
3. Some future technology that we haven't stumbled upon yet (or can only theorize) will accidentally wipe us out
4. The galaxy is teeming with life, but we can't comprehend it,so we can't detect it, and they haven't bothered us because they don't care to
5. The Berserkers are on their way, so it's only a matter of time before we are consumed
6. Some sort of high-powered being/civilization is deliberately protecting us from interference
7. Some future technology renders the concept of living in a physical universe to be hopelessly primitive - i.e. the aliens have "sublimated" into a new dimension/universe/something
8. We are part of a simulation, whose parameters preclude the existence of other civilizations
9. We are characters in a "game" or some form of artistic entertainment or historical "what-if" simulation, where the introduction of an alien civilization is specifically directed to occur at a certain time
10. Aliens have already colonized our planet and used technology/etc to render themselves (mostly) imperceptible to us

These are all the primary theories I can think of. In terms of plausiblity to me, I rank them: 8, 7, 3, 9, 5, 4, 1, 6, 10, 2

Weren't all or most of these questions handled in the various incarnations of Star Trek? Personally, I believe that since a machine can ultimately be programmed to only do what it is told, and we'll never get to true AI, as defined by the scale. We might reach 4th level, however, that's still not a machine that can 'think' for itself.

An idea that I've been having for some time is the following: Alien life must obey the same laws of physics that we do. Also, alien life has generally similar psychology to ours, that is based on survival, spreading one's genes, costs and benefits of war and cooperation, etc.

So to answer the question "what would aliens do?" just ask "what would we do"?

Why has SETI not discovered any powerful microwave transmissions? Well, who says that the aliens are building transmitters for our benefit? They're probably building transmitters for their own benefit! Since interstellar flight is pretty well impossible over reasonable time spans, but interplanetary flight is, then the aliens need enough transmitting power to communicate at interplanetary distances, NOT interstellar distances. Why would they do otherwise? Money may not be universal, but "resources" and "energy" are, and why would they waste resources?

Therefore, if our SETI cant detect signals that are intended for the aliens to speak with themselves, then it's hopelessly too small. The Arecibo telescope could not detect Earth's transmissions (that are intended for other humans) over light years. Therefore it's unlikely to work.

The same thing is likely true of space travel. A given civilization may have a thriving colonization program of it's own solar system, but why bother to send colonists or robots to other stars? Waste of resources.

You might answer that aliens might live much longer than we do, but earth's animals have a limit on how long they live. The oldest animals known live 200 years, still not enough for interstellar travel. Remember, the laws of physics are the same on other planets as here, including aging and metabolism, so much older animals are not likely.

So you put this together, and even though life and civilizations are very likely to exist in the universe, the aliens are hopelessly far away to be detected.

Robert Pickar

Andrew Cutler of Energy Science Laboratories in La Jolla wrote a paper on detection of ancient earth colonization by looking for depletion of various key hydrothermal ores. He claimed he found such depletions corresponding to the Cambrian explosion and that the asteroid belt could be explained by a planetoid being dismantled for its nickel iron core around the same time.

James,

Some "alien" nuclear reactors for ya:

http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor

Aliens with interstellar travel capability are going to use some kind of nuclear technology, either for energy production or for making materials via transmutation processes. So, maybe the Oklo reactors were made by aliens. Mars and the asteroid belt would be good places to look for artifacts. All of this makes for sense to me than the SETI approach of trying to listen in to the aliens' cell phone conversations or their reruns of MASH.

As long as the Berserkers don't arrive; those things are bad news.

>Since interstellar flight is pretty well impossible over reasonable time spans

Already we can dimly imagine ways to get to the nearer stars that don't violate the laws of physics, such as generation starships and so on. For this reason I find it hard to imagine that we won't develop some sort of manned interstellar capability in the next several thousand years, assuming that scientific knowledge continues to increase at some modest pace.

To mention Freeman Dyson yet again, he once pointed out that interstellar travel is not a problem of engineering, but a problem of biology. Perhaps greatly increased longevity or suspended animation will allow us to reach the stars. Or maybe we will figure out some way to boost human intelligence to such a level that we will be smart enough to master new sorts of physics that are, in a quite literal sense, unthinkable to us today.

I think the biggest assumption made by those actively looking for ETs is that they use technology similar to ours, or even within our grasp. It has only been a few hundred years since we relied on candles and torches to provide light, and if we find an efficient alternative to electromagnetic communication in the next few hundred years, it would imply that the window for detecting ET life via electromagnetic transmission is ridiculously small. We're just not technologically mature enough to expect to find ET civilization.

I think the biggest assumption made by those actively looking for ETs is that they use technology similar to ours, or even within our grasp. It has only been a few hundred years since we relied on candles and torches to provide light, and if we find an efficient alternative to electromagnetic communication in the next few hundred years, it would imply that the window for detecting ET life via electromagnetic transmission is ridiculously small. We're just not technologically mature enough to expect to find ET civilization.

I think it was sf writer Sheffield who had a good throw-away line about spotting alien tech in one his novels: a human explained the concept of "solar eclipse" to an alien, and when he got up to the part where our moon is exactly the same size as the sun from our persepctive on Earth, the alien said, "And it never occurred to you that you were living on an artifact?!?"

:)

the alien said, "And it never occurred to you that you were living on an artifact?!?"

Then the human replied that the moon/sun similarities were explained away as mere coincidences by teabaggers protesting a new government space program.