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Rethinking Alien Encounter

by Larry Klaes

Larry Klaes wraps up his two-part essay on our attitudes towards extraterrestrials by looking at how the subject has been treated in the past, and speculating on the scenarios that might bring disaster. Do Earth-shattering depictions of space invasion reflect what people really believe, or are they merely a form of escapism? Either way, they tell us something about ourselves as we confront the possibility of contact.

For those who may still wonder and question just how much weight the words of the famous cosmologist Stephen Hawking hold for the concept of alien intelligences and their potential reactions to encountering humanity, consider this: A new science fiction film coming out this November titled Skyline has recently premiered its theatrical trailer, which you can view here. The trailer begins with the line: “On August 28th, 2009, NASA sent a message into space farther than we ever thought possible… in an effort to reach extraterrestrial life.”

Now it is true that a transmission was sent from Earth into deep space on that very date and it was indeed broadcast by a NASA-owned radio telescope located in Australia. However, the collection of messages sent into the Milky Way galaxy from people all over the world as part of the Hello from Earth campaign were aimed at a planet in the red dwarf star system of Gliese 581, which is only 20.3 light years, or 194 trillion kilometers from us. Now that may seem like a long way to Earth-bound humanity, but on a celestial scale the Gliese 581 system is a near neighbor. Besides, the transmission, moving at the speed of light (almost 300,000 kilometers every second), is just over one light year from Earth as of this writing. That isn’t even far enough to reach our closest stellar neighbors, the Alpha Centauri system at 4.3 light years distant, let alone be properly given the title of the farthest human message ever.

As a final point, we are far from certain if any life of any kind exists either on or near the target of Hello from Earth, the fourth world circling the star Gliese 581. However, astronomers now think at least one and possibly three planets in that system have the potential to possess water in a liquid state, a major ingredient for the formation of at least terrestrial types of life. Of course the transmission is not going to stop once it reaches that alien planet. The messages will spread outward and onward into the galaxy at light speed, which will give them an increased chance of being detected some day by an ETI, assuming any exist in the signal path.

Image: Alien devastation in the upcoming movie Skyline. Credit: Universal Pictures.

With this inauspicious beginning to the trailer, the viewer is then treated to some apparently real news broadcasts about Hawking’s alien warnings interspersed with images of strange bluish-white meteor-like lights dropping down upon the city of Los Angeles. In the news segments, former CBS Television news anchor Dan Rather intones that “if extraterrestrials visit us, the outcome might be similar to when Columbus landed in America. In other words, it didn’t turn out too well for Native Americans.” The trailer caps off this dire warning with the text “Maybe we should have listened.” And done what, I have to ask? Cover Earth in black tarp with some stars painted on the outside and hope nobody notices us?

Too late, the alien Columbuses arrive in their bizarre and menacing spaceships over the city, looking like some kind of gothic metal sculptures bearing down on the places where the lights had landed. A quick reveal is made to the audience of the name of this film being advertised and then the final scene: A close-up of one of the alien vessels hovering over LA, its underside open wide like the jaws of some immense beast, pulling thousands of tiny screaming, tumbling humans up through the air and into itself for reasons as yet unknown, but ones the audience has little trouble imagining may not be for the benefit of humanity.

A final text warning suggests that we “Don’t look up”, which is directly counter to what our society has been taught in terms of social progress and evolutionary development – to say nothing of what the recently deceased astronomy popularizer Jack Horkheimer said at the end of every episode of his PBS program Star Gazer, which was to “Keep Looking Up!”

More Than One Side to the Alien Encounter Debate

Aside from the more than likely possibility that Skyline will be little different or better than the majority of alien invasion stories of the last one hundred years, using the real words of a real scientist (and a cosmologist at that) to give a sense of weight and urgency to just one side of the concept of alien interaction with our species and our world ultimately blurs and overshadows the wider range of possible behaviors and outcomes for what may one day define the ultimate course of humanity among the stars.

While it is true that the primary overall purpose of Skyline is a material one – to line the pockets of its makers with money by appealing to the basic instincts of those who will provide said profits – the film (and Hawking) are nevertheless contributing to the debate on whether and how we should deal with other intelligences in the Cosmos. This is the case whether the filmmakers had any deep intentions of doing so or whether the idea is plausible or not.

Since so many science fiction stories about aliens tend to focus on the negative aspects of and possibilities for encounters between varied species, thus biasing (and reflecting) public thought on this topic, it is both fitting and important to take a look at just how plausible Hawking’s dire prediction and all the related ones truly are. There are of course certain limits as to how much one can reasonably determine what an ETI may or may not do in regards to humanity in its present state: Not yet knowing for certain scientifically if there is any life beyond Earth tops the list here. However, we do possess enough scientific and technological knowledge to make some plausible determinations on just how likely our greatest fears about our galactic neighbors might be true or not.

Image: Skyline‘s imagery portrays alien encounter as disaster. Credit: Universal Pictures.

Just as there has to be a set of solid parameters for current SETI on this planet to work, meaning that a society has to have both the means and a purpose which presumably is not willingly detrimental to itself to signal others across space and time, so too must there be some sense of foundation regarding an alien invasion or attack.

As SETI requires its hypothetical subjects to share some common elements with humanity in order to work, any beings who wish to do harm on us must also think and behave with some similarity to us. So when examining the types of invading alien beings, I am excluding the ones with abilities we would consider to be godlike: Able to appear at will anywhere or anytime and commanding so much knowledge and power as to make the act of rendering us extinct a quick and easy exercise. I make the presumption that if such superbeings wanted us gone, it would have been done by now. The fact that it has not happened could mean a number of things, such as they are much too smart and nice to harm lesser life forms, or they don’t care about us one way or the other, or they will destroy us but they just haven’t gotten around to it yet. As a result, I am staying away from speculating any more on the superETI, except to warn that beings which are given abilities to do just about anything blur the line between physics and supernatural magic. In addition, I make no pretense that my lists of alien motives and weaponry are in any way complete, so further ideas are welcome.

The Why of Alien Invaders

Assuming that invading another world across interstellar distances requires some serious time, currency, and resources, our hypothetical alien marauders will not be attempting to take down humanity and its home planet on a whim or to follow some cliché of galactic hegemony. Like the future humans in the 2009 film Avatar who travelled 42 trillion kilometers to reach the Alpha Centauri system moon Pandora for its mineral wealth to aid their ailing civilization, our invaders will have to come up with a very good reason for traveling all that way if they ever literally want to leave the ground.

Of all the “whys” for an alien assault on Earth, taking our planet as a new place to live and utilize because their homeworld is dying or destroyed for one reason or another, is at least as old as H. G. Wells’ The War of the Worlds.

Well’s 1898 novel was a combined reflection on how European colonizers of the era were treating the people and places they were colonizing and an extrapolation of the idea of advanced beings responding to the slow but inevitable demise of the habitability of their home planet, in this case the fourth world from Sol, Mars. The numerous astronomical reports of seemingly straight lines on the Red Planet since 1877 had led to speculation that they were artificial in nature.

One fellow, the wealthy American astronomer Percival Lowell, championed the idea that the lines were actually immense canals built by the Martians to bring water from the icy white polar caps to quench their drying and dying cities. While Lowell seems to have assumed the superior Martians would eventually accept the end of their species and become extinct with dignity, Wells imagined these same creatures not wanting to go down with their planetary ship, thus their invasion of Earth.

Image: This early issue of Hugo Gernsback’s Amazing Stories brought H.G. Wells’ War of the Worlds to a new audience.

Now of course one advantage Wells’ Martians had over just about any other species in the Milky Way galaxy was living so relatively near to our world. A conventional rocket can propel a spacecraft to Mars in a matter of months, as they have in reality since the early 1960s. However, it is an entirely different matter to send a ship between even the nearest stars. Unlike the vessels of science fiction which are equipped with fanciful warp and hyper drives or have a conveniently placed cosmic wormhole nearby, our current knowledge of what it would take to get from one star system to another is fraught with technological and celestial hurdles that make even a slow multigenerational ship a daunting task.

So even if say an alien planet was going ecologically, geologically, or cosmically south, would it be wise to say nothing of practical to send a fleet across interstellar space to take over another star system, when unless their sun was turning into a red giant or going supernova, it would be much easier to utilize the worlds in their own solar system for resources and settling. If, for example, an alien society was in desperate need of water like the Martians of Lowell (and presumably Wells), it would be much cheaper by comparison to mine the many, many comets that we know exist around other stars, just as they do at the fringes of our Sol system. And while we have yet to detect any exomoons, we do know that most of the moons circling the four Jovian planets are covered in water ice and in some case, like Jupiter’s Europa, likely have deep global oceans of liquid H2O.

The same goes for mineral resources. There are estimated to be many billions of whole solar systems in the Milky Way galaxy alone. Presumably they have lots of planetoids in addition to their major worlds and the comets, just like our celestial neighborhood. It is also probable that many of those worlds are uninhabited but rich in elements that a technological civilization would find useful. So even if our marauding aliens do want to journey all the way across the galaxy for gold or oil or whatever, with so many star systems to choose from, why focus on Earth and its environs when the pickings are so easy and plentiful elsewhere? Plus since hauling all those rocks home would be expensive as all get out, trying to colonize a solar system that already has one intelligent species, even if that species is just starting to explore and utilize space, might be more trouble than it is worth.

Now let’s look at another classic reason for an ETI to want to come to Earth: Dinner. It has become practically an old joke that some aliens would see all the teeming life forms covering our planet and consider us an open buffet. Not only do we once again invoke the question of whether it would be worth going to all that time and expense for a meal when there are probably much closer snacks at home, but it has been said that our biochemistries would be so different that Earth organisms would be pure poison to an alien creature (and vice versa). The vastly different genetics would also go for interspecies breeding, especially since it is considered unlikely that we and they will look anything alike. As for needing a race of slaves – robots would be so very much less expensive and far more efficient. This all sounds like some very old and very low-grade science fiction in any event.

Image: This classic episode of Twilight Zone featured Damon Knight’s short story ‘To Serve Man,’ in which the idea of humans as menu items made a sardonic appearance. Credit: Cayuga Productions/CBS.

If it is just too much to fly all the way here for rocks or a meal, are there any other reasons why an ETI might still want to exterminate us? We may not be a threat *now*, but perhaps some day if we do spread ourselves into the galaxy, there might be others who could see us as future cosmic competitors for all the places and resources previously mentioned. If the galaxy has beings who think and act in very long terms, certainly much longer than most present humans do, they may not want to wait until our descendants are arriving at their doorsteps and instead take us out now.

I for one would like to think and hope that a stellar island of 400 billion suns over 100,000 light years across with perhaps 100 billion galaxies beyond our Milky Way in a Universe 13.7 billion light years wide would be plenty for everyone. However, perhaps some cosmic real estate is more choice than others and its finite nature makes it a valuable target worth fighting for. One estimate I saw in a Scientific American article from 2000 said the galaxy could be conceivably colonized in just 3 million years – a very short time compared to the 10 billion year age of the Milky Way. The fact that our planet appears to be free of any alien conquerors/settlers may say something about that idea, or perhaps conquest and colonization is not as popular as we might imagine (and often do).

Even if we and others decide to be planetary homebodies for many generations, there will come a day when a home system’s main source of light and heat, their sun, will begin to die out. Our yellow dwarf star is no exception: Sol is expected to start making things pretty unbearable on Earth in just a few billion years as our sun begins to expand into a red giant star. Even if Earth is spared being swallowed up by this bloated monstrosity of hot gasses, our planet will be cooked into molten slag, killing anything living that remains. Earth will later turn into a frozen iceball as Sol shrinks into a white dwarf and eventually a dead, dark cinder of itself. Even if our planet survives all this in at least its physical presence, when Sol goes completely so will Earth, its icy battered carcass floating off into the depths of the Milky Way as a rogue world.

So while we do have several billion years to prepare for this event, the point is that eventually nature will force our hand and make us choose either flight or extinction. Even staying in distant parts of our system will pass once Sol starts collapsing upon itself. And this is the fate of every star some day, even the very long lived red dwarfs, though some suns will also turn supernova or collapse into neutron stars or black holes. I know things will be very different in those distant epochs, but doing more than briefly visiting Earth or anyplace else nearby in those eras seems infeasible at best and deadly at their worst.

Have other species around other suns realized this about their celestial hearths as well? Will they decide to stay at home and wait for the end, or will they pack up and look for worlds where their suns won’t be going out quite so soon? Will the fact that we have at least a few billion more years of relative safety be appealing to such refugees? What happens when it is our species turn some day? Perhaps there are many vague and hidden factors which will render all this particular speculation and prediction moot, but at least this idea has the merit of being a plausible reason why one might have to go interstellar voyaging.

Image: From the film Alien Invasion, strange craft fill the skies over Earth’s cities. Credit: Richmanclub Studios.

Another reason ETI might want to come to Earth is a religious one. Perhaps like certain segments of humanity there are alien beings who have very strong spiritual and religious beliefs and it is their sacred duty to share the Good News with everyone else, whether they want it or not. Will alien missionaries ply the stars seeking to convert other species to what they perceive as The Truth, perhaps affecting their “heathens” in the same way that missionaries affected the cultures of the Pacific in their zeal to save souls – settling in some very nice real estate in the process. What will happen when a human group and an alien collective of very intense and very certain religious missionaries encounter each other? Or is religion a primarily human concept? Well, so far we have not been forced to worship any strange alien deities by clergy from the stars. Unless some of our current religions were the direct result of an ancient missionary visit.

How Might They Vanquish Us?

Although we have now looked at the primary and most obvious motives (to us at least) for an alien species to want to crush humanity and found most of the feared concepts wanting, it is time to explore the ways that said alien marauders might still take us out of the galactic picture. Ironically, while the potential motives for invasion and destruction are often weak if not outright impractical or implausible, the methods that a smart but aggressive species might want us gone (or we they) are often even more likely and effective than the usual imagined scenarios for the conquest of Earth.

If asked to visualize how an alien race might come after humanity, the scenario that seems to jump to most people’s minds is the one of giant spaceships hovering over major cities (Skyline is just the latest incarnation of that scenario), or a whole fleet of shiny silver spinning disks carrying troops of alien soldiers wearing shiny silver spacesuits and gripping laser rifles in their clawlike hands.

Now while one cannot entirely rule out the possibility that one day Earth’s skies will be filled with large and dangerous alien vessels up to no good for us, the idea that more advanced beings would engage in a battle for Earth and against humanity in a manner similar to the scenarios described above seems about as efficient as targeting our world for its supply of water with all the much easier and more effective alternatives available.

If you want to get rid of the higher life forms on Earth and don’t care if most of the flora and fauna inhabiting our globe also gets destroyed in the process just so long as the planet remains intact, then all you need to do is attach some rocket motors to a collection of planetoids and manipulate them so their ultimate destination is Earth. Humanity could be doing this with some of the smaller varieties of space rocks in just a few decades if we choose to, so a species that has actually made it to our Sol system via starship would be able to conduct this activity too.

Depending on the size and mass of the planetoid and where the ETI would target it, our civilization if not our very species could be rendered helpless in short order in a style reminiscent of the dinosaurs 65 million years ago. Indeed, there have been a number of small planetoids which have come close to Earth in recent times that astronomers discovered just a few days before their close encounters, leaving very little to no time at all to develop any countermeasures had they been on an intercept course. And these objects were guided only by the forces of nature! A deliberate use of planetoids to smash us into submission or worse is a scenario that has been discussed and written about, but a real organized defense system is still decades away.

An even more frightening concept is using a starship itself as a weapon. A large enough vehicle moving at relativistic speeds, even a fraction of light speed, could hit Earth with more force than humanity’s entire nuclear arsenal at its peak in 1990 (55,000 nuclear bombs). Such a weapon would be very hard to track and virtually impossible to stop at our present state of things.

Image: Artist’s impression of an asteroid strike. Do we have any defense against this kind of impact? Credit: NASA.

The details on this scenario, along with a very interesting discussion as to why an ETI might do such a thing to us and others (take out any potential aggressors/competition before it does the same thing, in essence) may be found on this part of the Aliens chapter of Atomic Rockets from Winchell Chung’s fascinating Web site.

Keep in mind that while Chung does make some very compelling arguments, he is also a very big space war gamer, so having a galaxy full of mature, peaceful, and altruistic beings may make for a nice place to live on a cosmic scale, but a rather dull RPG. Going on the offensive with other species is also a pretty good guarantee that even an advanced ETI that gave up aggression and war ages ago may not like being threatened or seeing others in such a state and take action against such a paranoid and self-serving race.

Another method for taking us out is one that has probably happened naturally across the Universe since the first stars came along: Supernovae. An exploding star would not only vaporize the members of its system but spread deadly radiation for hundreds of light years around. Earth has obviously survived having its native life forms become completely extinct by any stellar explosions over the last four billion years (and we can thank a supernova for even being here in the first place, as astronomers say it was the violent death of an ancient star some five billion years ago that kick-started the cloud of dust and gas that became our Sol system, along with giving us the elements needed to make life possible), but if an advanced species knew how to make and control a stellar detonation, they could fry us and our galactic neighborhood. Other methods of sterilizing whole solar systems includes smacking two black holes together and directing galactic jets, which are streams of particles and radiation thrown out by massive black holes in the cores of some galaxies. One hopes it won’t be possible to harness such energies, but who knows what beings that can survive and grow for eons in this Universe might be capable of.

Another cosmic weapon which fascinates and frightens is known as the Nicoll-Dyson Beam. Dyson Shells are a fascinating concept in their own right: Freeman Dyson envisioned a society taking apart its solar system and building a vast swarm of communities around its sun to collect as much energy from it as possible (right now 99% of Sol’s energy gets “wasted” into space). From a distant vantage point, anyone monitoring such a system would see its star gradually dim in the optical realm and brighten in the infrared region of the electromagnetic spectrum.

Being able to collect and utilize so much energy from a sun has many benefits for an advanced technological society – and a few dangers for others as James Nicoll would later point out. Dyson Shells would be able to focus and redirect the solar energy they collect into tight and powerful beams called a phased array laser. The beams could easily destroy whole worlds many light years from the Dyson Shell.

Whether Dyson Shells actually exist and would their makers use them as galactic-scale weapons is another matter (though there have been actual SETI programs which attempted to find these astroengineering projects), but this page from the Orion’s Arm Web site gives an interesting visual and text description of this idea.

Is SETI Itself Dangerous?

There have been many who warn about sending greetings and other messages into the galaxy and beyond. The idea, called METI for Messaging Extraterrestrial Intelligences, is that since it may be hard for an alien species to find Earth and humanity among the 400 billion star systems of the Milky Way, we should increase the chances for detection by broadcasting into deep space towards what we think are favorable cosmic places for intelligent life. The main idea behind SETI is that alien beings are conducting their own METI programs, as that is likely the best and easiest way for humanity to detect another society in the galaxy at present.

The main and obvious issue with METI is that we do not know what other kinds of beings are out there. Folks such as Carl Sagan have speculated that aggressive species tend to wipe themselves out before they can achieve space travel. However, this has the flavor of painting an alien race with the traits and behaviors of our species. What if there were species which cooperated as a unit and still decided that other beings must go before they become a threat to them? Or what if they felt that other species, being viewed as inferior, were in need of a serious “makeover” that would effectively destroy whatever made the target species unique?

Some have speculated that an ETI might take out humanity and any other species at our stage of knowledge and development by operating a METI program that carried what we might call an artificial virus. The target species would pick up the alien “message” and in the process of decoding it would unleash a program that could do all sorts of dangerous and deadly things, from taking down our technology to giving us the plans for a superbomb that would detonate once we built it from the instructions given in the message. Other potential scenarios involve converting humans into their puppet slaves or replicating the alien species on Earth to take over and then aim more such messages at other potential worlds to continue their galactic conquest.

Of course it would seem easy to make sure that this never happens by simply keeping the alien message isolated or just never building the design plans. However, the combined excitement of detecting an ETI signal and the often wild, vast, and intricate nature of the Internet could bring about the spreading of the virulent message and be released by those who feel it is their right to have and know such information. In addition, as we see in the news on a regular basis, there are those groups of humans who might deliberately want to open up this cosmic Pandora’s Box to spread death and destruction across our planet for their own purposes.

Image: As iconic as it gets, this still from Independence Day highlights the menace from above. Credit: Twentieth Century Fox Film Corporation.

This Web site goes into detail about the possibilities for an alien species to take out Earth without ever having to leave home either in person or even through a robot vessel.

Final Thoughts

This essay began thanks to Stephen Hawking’s well-publicized views on alien intelligences which he thought would not be a good thing for us to encounter any time soon. While there is of course the possibility that we might encounter an alien species that is a threat, I was unsatisfied and disappointed with Hawking’s version of this scenario. It struck me as not only being one-sided, limited, and old fashioned in thinking, but far too reminiscent of numerous recent Hollywood-style science fiction plots – an industry not exactly known for its rigorous scientific accuracy.

Hawking’s take on alien life feeds into this negative, paranoid, and inward-looking attitude regarding the unknown that seems to be growing in human society these days. While it is prudent that we do not just jump into the galaxy without at least having some idea who and what is out there, focusing on the idea that all alien beings are hostile monsters and that we should dismantle our radio telescopes and hide under our beds is not exactly the actions of a healthy, maturing society. Besides, if an ETI were out to get us, remaining ignorant of the Universe and trying to be undetectable is not the way to go.

As I have pointed out in this essay, an advanced alien species will be able to destroy us in short order and we will have little recourse to stop them at present. The fact that it has not happened may mean they simply haven’t found us yet, but it may also mean that we are either lacking in large numbers of intelligent galactic neighbors or that taking out another species that has barely gotten its feet wet in the cosmic ocean is not the way to behave as a galactic society. We still have far more to worry about from members of our own species bringing down civilization than any hypothetical alien species anyway.

Another thing I do know about human nature: No matter how many warnings and precautions and even laws that get thrown up to control people when it comes to what society thinks is in its best interests, there will always be individuals and groups of people who defy these rules either because they disagree with them or because it is in their nature to go against the grain.

This will apply to voyaging into space as much as anything else. The only reason it hasn’t happened already is due to the technological difficulties in making a deep space mission a reality at present. However, I know once we establish a serious foothold in space in our Sol system, there will be groups who will not want to remain confined to our celestial neighborhood but want to venture to those countless stars surrounding us. This will keep happening for as long as humanity lasts.

This is the eventuality we must prepare for, because I will agree with Hawking on one thing: If life’s evolution is similar everywhere, then it is likely that some other species will also share our drive and desire to see what it out there beyond their home world. It may be only a matter of time before we are visited. How we respond to them depends not only on their intentions but how much we have learned and evolved when it comes to understanding the Universe as well. Hopefully we will not let our fears and hostility turn a potential friend into an enemy.

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Comments on this entry are closed.

  • Carl Keller October 6, 2010, 10:31

    Clarke advanced different views. The exoplanet Sagan Two was to be a home for humanity, with an eye to terraform it in his ‘Songs of Distant Earth’. Presumably it had no indigenous life to begin with, needing a shift in its orbit using the vacuum energies of the starship itself. http://two-words.info/index.php?page=458

    His ‘Childhood’s End’ was remarkable having an alien culture – though forcibly guided by a superior entity – coming to Earth to assist in human evolution.

    A very different alien encounter is found in Robert Silverberg’s ‘The Man in the Maze’, which is a likelier scenario of more mystery than continuous contact. Paul’s earlier suggestions that First Contact with a civilization may be so strange to us to the point of our inability to comprehend what we find is very possible.

    Whatever the future brings, we must think outside the proverbial boxes. I would include box offices in this one. Very thoughtful articles, Larry.

  • Scott G October 6, 2010, 11:44

    (1) I think the bottom line is that we don’t know who or what else is out there (as in, we have ZERO evidence), so there’s no point in assuming it’s a threat to us (by placing restrictions on what we broadcast into space) — because if it were, it’d likely be eons ahead of us, which raises the point: what could we do to stop it anyway? On a related note, I also hope that we never become so paranoid that we, ourselves, will preemptively find and wipe-out any newly forming technological civilization based on ‘The Killing Star’ principle (the fear that they’ll eventually do the same to us).

    (2) In considering the level of aggression of a hypothetical alien being… I can’t imagine any space-faring civilization hellbent on extinguishing all other inhabited worlds (or even just those with nascent spaceflight capabilities). Any species that makes it to the level of interstellar spaceflight probably has a healthy dose of altruism in its genes. That is, they probably wouldn’t have made it that far in the first place if they didn’t know how to cooperate or, conversely, if they trampled over all other living things on their home planet (which would likely have exhausted their food supply and/or natural resources before they could use them to achieve spaceflight).

  • Dreamer October 6, 2010, 12:19

    I agree with pretty much everything you wrote Larry. In the end, it’s little more than futile to be worried about the motives of the interstellar capable aliens that might be out there.

    There is almost certainly nothing we can do to stop anyone from (a) spotting that we are here and (b) doing what they like once they get here. I would add that even an extensive, aggressive METI program doesn’t add much, if anything, to whatever the risks of being discovered might be.

    With the Kepler mission—only the second of what is bound to be hundreds of exoplanet hunting missions—we are already capable of finding Earth-like planets up to 15,000 light years away. Even though that is only under the specific, fortuitous circumstances where the planets pass in front of their star when seen from Earth, that is still a rather amazing achievement for a civilization that has barely made it out of Earth’s orbit.

    Just imagine what the 100th exoplanet-hunting mission will be like in comparison, say 5,000 years from now. There will perhaps be a whole fleet of space telescopes working together to tease out images and spectral lines of exoplanets thousands of light years in every direction. This type of exploration is far easier to undertake than sub-luminal interstellar flights, and thus is the first (and maybe only) logical step for any civilization wanting to find out what else is in the neighborhood. Therefore the odds of an oxygen-rich bright blue ball called Earth being missed by a far more advanced alien civilization in our part of the galaxy are undoubtedly very small.

    So if there is anyone out there close enough to be a threat, they already know that Earth exists and likely sustains a thriving biosphere. Perhaps it’s too soon for them to detect signs of a technological civilization (the reflected light containing telltale signs of pollution hasn’t reached that far yet) but it’s only a matter of time.

    And so it’s really only down to one or two other factors whether or not they decide we’re special enough to warrant a visit—how common is life, and how common is intelligent life in the galaxy?

    If planets with life are common as muck, then Earth is nothing special, thus the odds of us being singled out for a visit are going to be very low. But if life is rare, or perhaps intelligent life is rare, then assuming the aliens have anything like the curiosity we have, they might make the long haul trip to come and see us.

    Either way, that decision to make the trip would almost certainly be nothing do with whether we have been sending out deliberate METI-like “We are here” messages. So if we’re doomed, we’re doomed, and there is nothing we can do about it!

  • Tarmen October 6, 2010, 12:30

    All survival and reproductive strategies will be used by various alien intelligences. The Milky Way is like a coral reef. Plenty of symbiosis. Plenty of harmless coexistance. Plenty of predation. Hawking is right to warn us that there is a chance of disaster. And it’s not zero % . Today mankind has all of our eggs in one basket. If we are sniffed out of our hiding place by the wrong kind of ‘others’, we might indeed go into the sunset. Kittens shouldn’t play near the street. When we are older and stronger, we can perhaps try to initiate relations.
    For now, caution is wise on this corel reef.

  • Mark Wakely October 6, 2010, 13:56

    The criticism often leveled at claimed first encounters is to question why aliens would travel trillions of miles to land in some remote farmer’s back forty rather than the White House front lawn. But unless they’re arriving en masse or have extraordinary defenses, a single alien ship on an exploratory mission might prefer a first encounter off the beaten path to avoid any overwhelming, coordinated hostile reaction, either out of fear or misunderstanding. Such an encounter might have already occurred, and if greeted with arrow, spear or gunshot, visiting aliens might have already decided that humans are poor candidates for inclusion in any galactic federation of planets. We might be in a “quarantine zone” and not even know it, with the aliens watching and waiting for some tangible proof that we’ve abandoned our warlike ways before risking a second encounter. If that’s the case, unfortunately they probably have a long, long wait.

    As to whether aliens came from the same primordial soup we did- and thus might share some of our traits- I still like the old science fictional theory that Earth was seeded inadvertently by visiting aliens millions of years ago, who found no life but left behind bacterial contamination as they wandered the ancient barren shores, bacteria which adapted and evolved. Maybe someday those aliens will return and be astonished at what their ancient ancestors wrought.

  • Tarmen October 6, 2010, 13:56

    I could imagine long long term voyagers, political refugees sleeping frozen in their alien caccons, until the automated sensors pick up something interesting. A place to hide from their oppressors.

    I could imagine perhaps 1 single individual ‘scientist’ alien like Charles Darwin mucking about in the Galapagos. Picking up samples. Perhaps that’s what UFOs really are.

    I could imagine contingiancy robo-wardens left in the Oort Cloud 10 million years ago, with their purpose to watch the ‘park’ planet ‘Earth’, in case the human population gets to large for the park. Maybe that’s what UFOs are.

    I could imagine a millions year old galactic federation, mistakenly sending troublesome alien races to live in this wrongly thought ‘uninhabitted’ little Solar system.

    I could imagine unintelligent automations or semi intelligent instinctual aliens, carrying frozen ‘pods’ with no other purpose than to spread their larvea onto ocean-worlds everywhere. Listening to the static, scanning for warm places.

    Perhaps some colony ship is even now correcting its timeless course to pass closer to this candidate planet 53237828811.984 , we call Earth.

  • Tarmen October 6, 2010, 15:13

    I often look up at Andromeda Galaxy, and I wonder how many forlorn and frozen colony ships are in my line of sight. Either attempting the long crossing from Milky Way to Andromeda or else attempting to cross from Andromeda to into ‘our’ Milky Way. There are 300 billion stars on either end. At say, 50% Lightspeed, it is a 4 million year journey. Some might even wake-up after the long eons. And likely a steady stream of robot exploror probes do attempt the crossing. Most crossings of 4 million years duration would surely never wake up, but some might. Some may have succeeded long ago .

    Are there a thousand ?? Or a million ?? Probably some . Many sleeping alien colonists must surely be in our nightly line- of-sight to and from the Andromeda Galaxy. It’s 2 million lightyears of space (and time).

  • amphiox October 6, 2010, 15:17

    The more common advanced ETIs are, I think, the less likely that there will be many aggressive ones. Because even the most peaceful beings will be likely to defend themselves when threatened. A warmongering ETI is obviously much more likely to provoke retaliation than a peaceful one, and if ETIs are common enough, such retaliation will more likely involve not a single retaliating civilization, but alliances of several. The aggressive ETI will thus most likely find itself outnumbered and outgunned. For the sake of self-defence, coalitions of the peaceful will snuff out individual aggressive civilizations.

    In this manner, aggressive ETIs could gradually get weeded out, until the majority of surviving ETIs are peaceful, for the simple reason that if you like to provoke fights, you are far more liable to eventually come up against someone or something just a little bit too tough for you, and get yourself squished by the counterattack.

    A similar dynamic has been speculated to have been at work in our own ancestors, leading to the “pacification” of humanity in comparison to our closest ape relatives, at least in the realm of interpersonal conduct – humans are far less prone to aggressive interactions, and far more likely to opt for cooperation, on the scale of individual one-on-one encounters than any other great ape (this of course, doesn’t include societies vs societies), and a possible reason might be that once we evolved sufficiently advanced planning and communication capabilities, the most aggressive and anti-social members of our communities found themselves suppressed by scheming coalitions of their more sociable and cooperative fellows.

  • Greg October 6, 2010, 15:41

    I would think that interstellar travel will be for most civilizations to be a huge energy expenditure, so the likelihood is very remote that another civilization would want to conquer us, just not worth the energy expenditure. With that said there’s only one real reason that they, as in several ships, would show up at our doorstep and that is for the sake of survival. Either sun gone bad or their civilization was threatened by a nearby super nova, or any other mechanism one can think of. If they are in the thousands, they could probably live in the asteroid belt, more resources there than at a bottom of a gravity well. If they are in the millions they probably would come to earth, it’s just to hard to support that kind of population while trying to carve out an existence in the asteroid field, eventually they could, but not right away, they would have to start there industries from scratch.

  • Tulse October 6, 2010, 16:10

    Given how common it appears planets are, and even potentially earth-like planets, it seems very unlikely that aliens would feel the need to utilize the earth for resources — there are plenty of other spots with similar resources that don’t have indigenous populations that might fight back. Indeed, with that consideration, it is hard to imagine that there is any solid practical reason for a more advanced civilization to visit earth. (There may be non-practical reasons, such as curiosity, proselytizing, and/or innate aggression.)

  • kurt9 October 6, 2010, 16:14

    Another alien invasion movie out of Hollywood. Oh boy!

    Unfortunately, the commercial success of “Avatar” has convinced a slew of producers and directors that SF is the way to go. SF is one genre that Hollywood should leave to novelists.

  • bigdan201 October 6, 2010, 16:54

    We’ve created alot of fiction about what aliens might be like. Their portrayals usually reflect some or other archetype or ideal. Most commonly there are the militaristic invading aliens bent on destruction, with no other subtleties. On the other end of the spectrum, there are the enlightened, spiritual aliens, who live in harmony and are only waiting for us to socially advance enough to join them in the cosmos.. or in the worst case, see earth as a threat to their paradise. Even in other depictions of aliens, they are always modeled after some recognizable archetype – noble savages in Avatar, and the oppressed minority in District 9.

    Chances are, when we do find aliens, they will simply be… alien. They won’t fit into an archetype or fill some basic emotional need. They may be more like ants, for example. Ants live right around us, but they could just as well be aliens for how completely different they are from us. We don’t feel a certain way about ants, and we can’t communicate – we can only study them from a detached distance.

    With that said, our science, physics and chemistry do apply just about everywhere else in the universe. They will have energy requirements just like us. It is also likely that they will be social and have the capacity for aggression, since those factors led to intelligence on earth. Predators naturally develop more intelligence, and a social nature does this too. Still, alien evolution may not be like us. They may be more like a colony of insects or some other species. Given the variety of planets and planetary conditions, wildly different turns of evolution are plausible.

    Life in general occupies every niche it possibly can, and the spread of life on earth is remarkable. It seems likely to me that very simple forms of exobiology will be relatively common, with more complex animals being less common, and intelligent species will be rare. This is a reasonable extension of our observations on earth, where there are countless simple organisms, with numbers going down as complexity goes up, and only one intelligent species (that we know of), us.

    It is hard to say how we will interact with aliens. Dazzling fiction about ruthless invaders or enlightened beings will continue to dominate popular culture, making it difficult to have a rational discussion outside of places like this. If they are aggressors, we probably shouldn’t be worried in the near term, since earth has only been radio-loud for about 100 years or so. Outside of 100 light years or more, aliens will not see much that indicates our presence on earth, unless they look very closely.

    It is hard to guess what they will be like, much less their motivations, although they will definitely need resources and possibly living space. As the article mentioned, the resources of earth can be found in many other places, unless there is some rare resource on earth we don’t know about.

    Aliens may well figure out interstellar travel at relativistic speeds. Perhaps they’ll even discover foldspace. But even if they do, the energy requirements of folding space, and the difficulties of traveling at even high percentages of c, will mean that they are not going to fly all around the galaxy within a short time. They will expand across the stars in the long-term, as we also must do.

    This comment is long so I’ll wrap it up here, and respond to any other comments that are relevant.

  • Eric October 6, 2010, 17:11

    Good essay and many reasonable points.

    As far as the issue of aliens detecting us, it’s an interesting point to consider. We’re probably pretty obvious. For the past billion years or so, alien observers of Earth would have noted lots of chemical disequilibria in the atmosphere. So we can be pretty sure that there aren’t too many “Berserkers” out there that want to snuff out all life. (Anthropic reasoning here). For all we can tell, Earth’s oxygenated atmosphere hasn’t even earned it a visit.

    However, it’s only in the past 100 years or so would industrialization (pollution) and radio be added to this picture. That’s a very recent (and fairly obvious) set of changes to Earth that can be noted by others. Perhaps these changes would give Earth more “special attention”?

    (Note, I agree with Larry that attracting alien attention should be ranked pretty low on list of worries, though I do believe it would be safest to keep as low a profile as feasible until we understand more about our galactic environment. I other words, I don’t think we should go out of our way shouting into the dark, even though there’s nothing we can do to really hide.)

    But it would be interesting as we develop better astronomy around exoplanets to see how many worlds have chemical disequilibria (and probably life). Understanding these issues may make it easier for us to see how much Earth would stand-out from the crowd at various stages of its history.

  • Adam October 6, 2010, 17:39

    Hi All

    Some SF reasons for alien invasion or bad Contact or just weird.

    Stephen Baxter’s Squeem conquered Earth because they had FTL and we didn’t. The Qax did it, some centuries later, because it made economic sense to enslave the planet for their Galactic business operations. The Gaijin, naturally evolved “machines” from a planet with iron carbonyl seas, didn’t conquer Earth, but the economics of Contact meant Earth got lazy and eventually was screwed over, to coin a phrase. Their patience was sufficient to manipulate short-sighted economics to their long-term advantage.

    Terry Dowling’s “Wormwood” is about an occupied Earth divided between several alien species, but with none of them actually invading. Their stargates or wormholes or whatever, just opened up one day and Earth was changed irrevocably. It’s unsure whether any of them were the source of the space-time bridges or were just commensal species following something larger and stranger.

  • duffer October 6, 2010, 18:59

    Another possible motive for alien invasion/destruction was hinted at by John Varley in ‘Steel Beach’, namely punishment for/prevention of poor planetary stewardship, or humans as vermin, if you like.

  • Dreamer October 6, 2010, 19:01

    (Note, I agree with Larry that attracting alien attention should be ranked pretty low on list of worries, though I do believe it would be safest to keep as low a profile as feasible until we understand more about our galactic environment. I other words, I don’t think we should go out of our way shouting into the dark, even though there’s nothing we can do to really hide.)

    But that’s the thing. There is nothing we can do now, or in the foreseeable future that is more likely to garner attention than the very existence of planet Earth itself.

    Any beacon or signal that would be strong enough and persistent enough to be considered “shouting” is far beyond our present means and abilities, and even if it was not, the time and effort it would take to build the device necessary would permit a lengthy debate about the wisdom of doing it well before it became operational.

    Note: I accept that we can already send signals that, in theory, could be detected at interstellar distances, but any civilizations capable of picking up these random whispers is going to be capable to detecting Earth anyway, and probably has already done so.

  • Tarmen October 6, 2010, 19:18

    That’s true about ants. Ants may as well be aliens. Their psychology is so weird. We can imagine quite a few scenarios that don’t add up to peaceful co-existence at a safe distance. Sure, there are many planets as good or better than already occupied Earth . Sure, there are many reasons why cooperation may be the rational evolution of intelligence. Maybe. But the good guys don’t always win. In Nature, in the woods, I see nothing about sweet reason. Reason doesn’t always win. There are accidents, happenstance, hunger, fears, lust. Hawking is right to warn us. Bad things happen to good people. And to good planets just minding their own business with the volume tuned up.
    Who will weep for us after we are 500 years gone into extinction, as did H.neanderthal before us?? Some freebooter alien Borla ‘bugs’ arrived and just Borla-formed our world right out from under us.
    The Borlabug ‘historians’ will white-wash us out. Simple primitives. We only had 1 planet. And we cried out like babes-in-the-woods. Life goes on.

  • Malcolm October 6, 2010, 20:01

    http://arxiv.org/PS_cache/physics/pdf/0512/0512062v3.pdf

    Beatriz thinks that it’s likely “the Solar System belongs to the territory of a non-aggressive hypercivilization,” and ” this civilization treats us as
    a protected species and cares about us.”

    I do not assign to her views a zero probability; and she does express herself clearly.

  • Tarmen October 6, 2010, 21:06

    Beatriz, she’s interesting. That’s a possibility Malcolm. Not zero probability. I know it would appeal to a lot of people who hope for guardian angels. A little too ‘feel-good’ for me. I’m still preferring us to hide in the murk until we are an older and stronger species with more colony planets. I admit I am fearful. Evolution has put fear into human animals for a good reason. Fear will never go obsolete. If we humans stay hidden, and some fateful shadow passed us by 9.7 light-years out, we will never know how right we were to be fearful. But if some nasty ‘others’ do squash us…
    ..we’ll know ( too late! ) we should have kept hidden.

  • ljk October 6, 2010, 21:48

    What I find amusing is that when the Stephen Hawking the Science Authority says that aliens might do us in, the general public goes “Oh my goodness, he’s right! We better hide!” without looking into whether or not his statement had any real validity.

    But when the same Stephen Hawking says in his new book that God wasn’t necessary to make the Universe, the same general public goes “SAY WHAT?!” and suddenly Dr. Hawking isn’t quite the Ultimate Authority Figure any more.

    I am suddenly thinking of this line from Monty Python’s The Life of Brian:

    http://www.youtube.com/watch?v=LQqq3e03EBQ

  • Eniac October 7, 2010, 0:08

    Excellent thoughts, Larry, on why it probably would not make sense for the aliens to come and get us.

    I have some concerns on the how, also. I believe even for very advanced intelligences it would be very hard to pull this off, for various reasons, for example:

    – A relativistic missile is much easier to detect and track than it is to aim. It can be easily vaporized by putting a pebble in its path.

    – To arrive here and act, they must decelerate. That will create a signal impossible for us to miss. We will know that they are coming. Every kilogram of payload has an enormous cost, so it will be a few small, light ships against an entire, prepared planet. They must have REALLY good and lightweight weapons.

    – Are they going to pick up the loot and then return? With what? They cannot possibly bring enough fuel to return, so they must stay and build an entire highly advanced technology from scratch. In effect, they will have to be colonists. By the time they are ready to return, they would be a completely independent civilization and might well decide to go back and destroy their original world for the same reasons they destroyed ours…

  • Eniac October 7, 2010, 0:51

    The idea that there is a “jungle out there” is patently absurd in the face of interstellar isolation. A jungle is idiomatic because it is a highly connected ecosystem of many densely interacting species. This is not what you could ever find in interstellar space, even if every single star system was inhabited.

    Space is more like a gigantic lifeless ocean with tiny islands sprinkled on it thousands of miles apart. Put a lion on one island, a gazelle on the other, and try to get a jungle going. And this image does not even do full justice to the true extent of interstellar isolation.

    The idea of war itself becomes absurd under these circumstances. “War”, at least in the usual sense, implies an exchange of attacks and counterattacks, and an intense flow of intelligence and counterintelligence. What would a “war” be like if even the smallest expeditionary force would cost trillions to mount, spend decades in transit, and have no way to return? If information on its progress would take many years to get back? Would anyone consider it worth fighting?

    As for “tipping over the anthill”, that again implies things are so densely connected that you might accidentally stumble over something. Ain’t going to happen in interstellar space. And Junior intentionally tracking down the ants and killing them for fun before lunch? Better take the lunch, and some serious equipment for a very long, boring hike during which there will be plenty of time to grow up and contemplate the wisdom of one’s action.

    Now, if we were talking FTL, things would be different, but I am under the impression that we are not.

  • Jonathan October 7, 2010, 1:29

    Another wonderful article. It pleasantly reminded me of a piece I saw some years ago detailing the mathematics of how fast Santa would need to travel in order to deliver presents to millions of well-behaved Christian children across the globe – and ultimately how he would not be able to complete his voyage due to disintegration at impossible speeds.

    Strange connection, I realize.

  • Dreamer October 7, 2010, 2:39

    Beatriz thinks that it’s likely “the Solar System belongs to the territory of a non-aggressive hypercivilization,” and ” this civilization treats us as a protected species and cares about us.”

    Well, frankly, if that’s the case, and they’re just watching millions of sentient being dying in abject poverty and miserly (over one million babies still die every year on this planet) then I’m not sure I want their care and sympathy. I want them to be doing something about it, or at least giving us the means to do something about it.

  • ljk October 7, 2010, 8:08

    Dreamer said on October 7, 2010 at 2:39:

    Beatriz thinks that it’s likely “the Solar System belongs to the territory of a non-aggressive hypercivilization,” and ” this civilization treats us as a protected species and cares about us.”

    Well, frankly, if that’s the case, and they’re just watching millions of sentient being dying in abject poverty and miserly (over one million babies still die every year on this planet) then I’m not sure I want their care and sympathy. I want them to be doing something about it, or at least giving us the means to do something about it.”

    This is why those “messages” to any aliens around Gliese 581d sent by the Hello from Earth campaign in August of 2009 often sounded a lot more like prayers to a deity than actual messages to another intelligence in the galaxy. Lots of requests to come and “save” us from ourselves.

    If other intelligent species out there are similar to us, why aren’t we going out there to help them? People really need to think about all the parameters not only when it comes to the idea of an alien threat but also from the idea of an alien species coming to Earth with the express purpose of “helping” us.

    Our best bet from an alien encounter is to learn more about the Universe from them, along with some new forms of biology and technology. But as for asking for them to save us, or the other way around well…. Maybe if they found out that a nearby sun was going supernova next month and they offered us a lift. Maybe.

  • ProtoAvatar October 7, 2010, 10:22

    About why an alien species would be agressive, why would this species attack us:
    To obtain ‘mineral resources’ or ‘habitable space’ – such reasons make no sense: the universe is filled with such resources (most of which are not deep inside a gravitational well) and Earth is specifically tailored to support Earth life, not aliens with different requirements.
    The only resource present on Earth that cannot be found elsewhere in abundance (most likely) is life and intelligent life (us).
    The aliens could be motivated by religious or political memes. What form these memes have is anyone’s guess.

    But I can think of at least one logical reason – it would be a preeemptive strike, wiping us out now, while we’re still weak and can be exterminated with minimal effort, in order to prevent us from posing a threat in the future, when our technological evolution will make us into a player to be reckoned with.
    I heard a possible counterargument – that any species with this kind of behaviour will wipe itself out. I find this counterargument weak – in our history, there were many examples of members of a culture believeing themselves superior to all other humans (which is why the latter had no rights) – apparently, racism is easy to rationalise even among the same species; it should be a lot easier among two different alien species.

    About the ability of interstellar faring aliens to destroy us – any propulsion system powerful enough to travel at relativistic speeds is also a weapon of mass destruction.
    For example, all these aliens would have to do is send a ship (roboticly operated or not) towards us – in order to decelerate near our solar system, put a relativistic engine on an asteroid and accelerate it towards Earth. We would have no way of deflecting this asteroid (it being too fast or too large). Perhaps we would see the aliens decelerating, even the asteroid – it wouldn’t matter.
    As for the cost of such an attack – an alien species may wery well regard it as well spent, if a future threat was thus neutralised.

    The probability of aliens thinking along those lines is not 0%. This possibility alone should impose prudence, stealth.
    Of course, there’s not much we can do to be ‘stealthy’.
    That does not mean there’s noting we can do – reducing our radio signature, for example, making it harder to detect us by this method.
    We could very well be detected by spectroscopically analysing Earth’s atmosphere? Yes – but only by some aliens who would go to the trouble of first finding Earth-like planets and then performing this analysis. The galaxy is gigantic – such analysis would take time and significant resources.

  • coolstar October 7, 2010, 10:52

    I have to agree with those who argue about “not shouting into the dark” especially when you have no idea what is out there. While it’s true on can’t hide the fact that earth is “habitable” it is pretty easy to hide the fact that it is in fact inhabited by sentients(evesdropping on radio signals is very hard and expensive and most of that radio leakage will be non-existent in just a few decades). So why take the risk, even if it is small, as seems likely? Small isn’t non-existent. As someone once said, the thing about aliens is that they’re alien. What’s irrational to one species may turn out to be the thing one just has to do, whatever the expense, for another (Niven and Pournelle coined the term “crazy eddy” in the Mote in God’s Eye that embodies something akin to that thought). Niven and Pournelle also, separately or together and often in multiple works (no sense in wasting a good idea, I suppose) have used most of the energy efficient ways mentioned here for eliminating a civilization. I think they also used one not mentioned here, simple bio-engineering. Presumably simple for an advanced civilization, that is: simply make the human race sterile. No fuss, no muss (for the aliens, there would be plenty of muss for the soon to be extinct homo sapiens, one imagines).
    Finally, in an otherwise very admirable essay, I think the author greatly underestimates the economic value of slaves. I can see that as quite a reasonable motive for nasty aliens. Though one would think that just harvesting “seed corn” and growing your own slaves would make more sense (given some live humans to get the “education” process going). Biology may turn to to be a much more economical (and perhaps even safer) way of acquiring servants than engineering. Niven and Pournelle again make use of this idea in their “war with the kzin” series, even before either side has ftl.
    One should also never forget that the present human life span would almost certainly not apply to members of an advanced civilization. Even one order of magnitude increase there makes lots of nasty things much more probable.

  • Darrell E October 7, 2010, 11:04

    From the OP.

    “As SETI requires its hypothetical subjects to share some common elements with humanity in order to work, any beings who wish to do harm on us must also think and behave with some similarity to us.”

    This does not make any sense. Unless you mean “think and behave with some similarity” in a trivial sense, or perhaps a tautology. In which case the claim is not useful for support of any further speculation.

    What exactly do you mean by “wish to do harm”? Do you mean that the aliens’ primary intent and goal must be to do us harm? Or, less directly, that harm to us must be an inevitable consequence of whatever it is that the aliens are intent on accomplishing?

    Either way, I don’t see any similarity or equivalence between the first part of this statement and the second part. I don’t understand why you would claim that aliens must also think and behave with some similarity to us”, in order to “wish to do harm on us”. And the first part of your statement does not appear to give any support to this assertion. This statement appears to be a key starting point for further speculation, but it seems to be a pretty weak foundation to build anything on.

    Am I being too picky about what may amount to no more than rhetorical style being given precedence over rigorous semantic clarity?

  • ljk October 7, 2010, 12:53

    Eniac, you bring up some excellent points. To address them:

    I will presume that anyone sending a relativistic missile our way will be aware of the problem even one speck of dust can do to such a fast craft and will find a way to compensate for it. Even Daedalus had a “dust bug” and a beryllium shield to keep from being destroyed on its way to Barnard’s Star. What else might work, and by this I mean real ideas, not Star Trek’s shields.

    I hope I am wrong here, but if there were an alien invader in our Sol system and they were planning to drop controlled planetoids on us (see the SF novel Footfall as an example), would we be able to stop them even if we did detect them and knew what they were doing? Launching nuclear missiles may not be enough and if it simply broke up a planetoid headed our way, that would just make an already bad situation much worse. Unless some government is currently hiding a space battle fleet on the lunar farside, I don’t see how we could stop such an attack at present.

    Thank you for bringing up a very important point that is often hard for people to realize being stuck on this one planet: Space is HUGE! Really, really huge. This more than any other reason is why we haven’t found any kind of ETI yet or why they aren’t popping by for a cup of tea.

  • Dreamer October 7, 2010, 13:34

    Our best bet from an alien encounter is to learn more about the Universe from them, along with some new forms of biology and technology. But as for asking for them to save us, or the other way around well…. Maybe if they found out that a nearby sun was going supernova next month and they offered us a lift. Maybe.

    I respectfully disagree. The assumption is that a “non-aggressive hypercivilization” would be in an excellent position to offer assistance in all kinds of ways. Even if they only provided advance low cost technology for our food, water, sanitation and energy needs, they would certainly save millions of lives.

    I accept that any intervention from an advanced, outside source probably has its risks, but unless by some extreme fluke we are the first such client civilization, then this would be a well rehearsed scenario–i.e. they would know what they were doing. I guess it’s possible that they have learned through bitter experience that the best solution is just to leave us to wallow in our squalor and ignorance, but I find it difficult to believe that there is no better way.

    As for comparing requests for to help with praying to God, well, you have a point. But probably the most difficult question concerning monotheistic religions like Christianity is “Why does a loving, caring God allow so many men, women, and children to suffer so horribly?”

    Now, substituting God with dispassionate or disinterested advanced aliens, would make providing a satisfactory answer much easier (e.g. they don’t care what happens to us since we are nothing but an anthropological science project to them) but if they had any empathic sense at all, they should feel some sense of duty to provide assistance. After all, what does a baby dying in pain and in squalor care about so abstract greater good of leaving us to our own devices?

  • kurt9 October 7, 2010, 13:48

    The things about aliens is that they’re alien. It might not be possible to ascribe human emotions or aspirations to them.

    The thing about most Terran life is that it is predatory. Life itself may be inherently predatory. Feeling some trepidation about the prospect of alien intelligence may not be unreasonable.

  • Eric October 7, 2010, 13:55

    @Eniac, @ljk

    Yes space is huge, and from the perspective our short life-times, what happens in other star systems seems impossibly remote and irrelevant to us. However, if you take a more “deep time” perspective, the Galaxy could be a jungle of competition, cooperation, and diversification. It’s just that it would happen at a glacially / geologically slow pace from our perspective. Remember, island ecosystems on the Earth don’t stay isolated forever.

    As far as hiding or worrying about alien invasion goes, I agree it’s mainly silly. They probably already know about the Earth if they bother looking. Since the Earth is still here, after 1 billion years of oxygenation in its atmosphere (a clear sign of life), we probably don’t have to worry about getting the attention of the wrong sorts of aliens. But we’ve recently changed the Earth would appear to outsiders. There’s a non-zero chance that the recent changes (industrial pollution, radio broadcasts) would attract attention from critters that ignore oxygenation or signs of an active ecosystem.

    Since it costs money and energy to send a strong broadcast out into space, and since there’s a tiny (but real) chance that it can attract negative attention, it seems to make sense that we should avoid “active SETI” until we understand the galaxy a bit better.

  • Dreamer October 7, 2010, 14:04

    But I can think of at least one logical reason – it would be a preeemptive strike, wiping us out now, while we’re still weak and can be exterminated with minimal effort, in order to prevent us from posing a threat in the future, when our technological evolution will make us into a player to be reckoned with.

    I find this scenario extremely difficult to believe possible. To make it work you have to assume that, as in many convenient scifi scenarios, we are going to make a whole bundle of amazing technological breakthroughs that will suddenly catapult us into becoming a galaxy-roaming civilization and clashing with advanced alien species. (Peter Hamilton’s Commonwealth springs to mind).

    In reality, it’s probably going to be many thousands of years (if ever) before we have any significant presence outside our of solar system, and tens of thousands of years after that before we even begin to venture more than a few dozen light years away, and we would still almost certainly be little more than a curiosity to an alien race that had been roaming the stars for millions of years.

    Of course, there’s not much we can do to be ‘stealthy’.
    That does not mean there’s nothing we can do – reducing our radio signature, for example, making it harder to detect us by this method.

    Anyone capable of detecting radio waves leaking into space from hundreds of light years away is going to be more than capable of detecting the presence of a life-bearing planet at the same distance, and unless life is extremely common, would be more than enough excuse for a close examination either at long range or close up.

    We could very well be detected by spectroscopically analysing Earth’s atmosphere? Yes – but only by some aliens who would go to the trouble of first finding Earth-like planets and then performing this analysis. The galaxy is gigantic – such analysis would take time and significant resources.

    So what else do you think we’re going to be doing between now and the time (perhaps not for another 5,000 years) when we can finally travel to other star systems? The only way to explore the solar systems around us for the foreseeable future is to study them through the end of a telescope, and even after we can travel to other stars, it’s still going to be many orders of magnitude faster and cheaper to continue studying exoplanets from our home system. You could probably build a million space-based planet hunting telescopes for the cost of one interstellar mission.

    The point is that no matter how big space is, the only cost effective way to study it is through the end of a telescope — even if you need to make that telescope the size of the Moon! Thus no matter how expensive in time and resources it is, it will always be the cheapest option, and thus it’s a pretty safe assumption that by the time any civilization takes it’s first steps into the interstellar void, they will have cataloged all but the smallest exoplanets within their reach, and that process will continue as they advance outwards.

    So if they can reach Earth, they already know we’re here (or at least that our ancestors were, depending on the distance).

  • Dreamer October 7, 2010, 14:29

    Finally, in an otherwise very admirable essay, I think the author greatly underestimates the economic value of slaves. I can see that as quite a reasonable motive for nasty aliens. Though one would think that just harvesting “seed corn” and growing your own slaves would make more sense (given some live humans to get the “education” process going). Biology may turn to to be a much more economical (and perhaps even safer) way of acquiring servants than engineering.

    History would suggest otherwise. Even without developing any form of artificial intelligence, we have created thousands of machines and devices that are far more economical to operate than any slave could possibly be. Throw even a rudimentary AI into the mix, and you have a complex, flexible, advanced machine that is designed specifically for the set of tasks at hand, never complains, never gets tired, and never decides that they would rather be somewhere else.

    The overhead of breeding, educating and maintaining a slave population would far outstrip any possible benefits they would provide over an AI-machine based economy, which would limit their use to vanity purposes only — like having a butler or something.

  • Tarmen October 7, 2010, 14:43

    “Remember, island ecosystems on the Earth don’t stay isolated forever.”

    That’s very true. There are thousands of ‘alien’ investations wreaking havoc on thousands of former Pacific island eco-systems, long isolated . Many extinctions are happening nowadays. A few islands are still ‘hidden’ in remotest Pacific. The local fauna (if they could think) never in a million years figured that one alien life-form, H.Sapiens, would ever visit their island in ships, and bring destruction and doom to all they had known . But it happened to them.

  • Tarmen October 7, 2010, 15:26

    Maybe we haven’t heard any SETI signals because surviving civilizations are indeed trying to keep hidden. Some discovered that there is an old predator culture and went quiet intensionally . Some others never knew about the predator culture, and so they went extinct (and quiet).
    We just don’t know enough to be heedless, careless about it.

  • kurt9 October 7, 2010, 15:59

    Another explanation is that sentient species evolve/degenerate into the “swarm” and eventually loose their sentience.

    Brains are like muscle. If you don’t use it, you loose it. We use our brains a lot because there are lots of discoveries to be made and lots of new technologies to invent. Once we reach the limits of technological innovation, life becomes comfortable and much less challenging. We might use our brains a lot less at this point. More and more behavior becomes scripted. Think of it as the bionanotechnological equivalent to the feudal system, but one where sentience becomes less and less important as people become more integrated in the bionano system. Give 10,000 years and you get something like Bruce Sterling’s “Swarm”.

    Perhaps this is the long-term fate of sentient intelligence in the galaxy.

    How’s that for making your day?

  • Dreamer October 7, 2010, 16:09

    That’s very true. There are thousands of ‘alien’ investations wreaking havoc on thousands of former Pacific island eco-systems, long isolated . Many extinctions are happening nowadays. A few islands are still ‘hidden’ in remotest Pacific. The local fauna (if they could think) never in a million years figured that one alien life-form, H.Sapiens, would ever visit their island in ships, and bring destruction and doom to all they had known . But it happened to them.

    Yes, but I don’t think you can compare the ignorant bumblings of 18th century mariners who had no concept of the fragility of an isolated ecosystem with an incredibly more advanced civilization that’s capable of crossing the interstellar void in large numbers.

    Even today, after only 300 more years, we have a much greater appreciation for the fragility of life in isolated places, and we take far greater precautions to ensure that it remains intact wherever we find it. For example, Surtsey, a new volcanic island that sprang up off the coast of Iceland 40 years ago has been a tightly restricted nature reserve ever since. Such an action of preservation would have been unthinkable only 100 years ago.

    I do find it interesting that when it comes possible actions and motives of other, far more highly advanced alien civilizations, we often seem to prefer to ignore the progress we have made over the last century or more. We have a far greater scientific understanding today of the long term benefits of cooperation and preservation (to name but two fields) compared with the destructive pillaging of resources that marks our past (and, sadly, still our present in many parts of the world), and we are barely getting started.

    Sure, the morality and ethics of an unknown species are impossible to determine, but we do know some of what it takes to become a successful technological species, and those aliens live in the same Universe we do with the same challenges and problems to overcome. So I believe there is good reason to expect that they will have at least overcome their worst impulses as we have already begun to do. (Admittedly there is still a long way to go, of course.)

  • ProtoAvatar October 7, 2010, 16:17

    ” ‘But I can think of at least one logical reason – it would be a preeemptive strike, wiping us out now, while we’re still weak and can be exterminated with minimal effort, in order to prevent us from posing a threat in the future, when our technological evolution will make us into a player to be reckoned with.’

    I find this scenario extremely difficult to believe possible. To make it work you have to assume that, as in many convenient scifi scenarios, we are going to make a whole bundle of amazing technological breakthroughs that will suddenly catapult us into becoming a galaxy-roaming civilization and clashing with advanced alien species. (Peter Hamilton’s Commonwealth springs to mind).”

    This scenario doesn’t require FTL, Dreamer.

    It only requires relativistic speeds and thinking ahead for hundreds/thousands of years. Considering the size of our galaxy, any enterprise that could be named ‘interstellar’ (colonization, contact, war, etc) is a long-term project.

    And any civilization that has “been roaming the stars for millions of years” will think extremely long-term.

    “‘Of course, there’s not much we can do to be ‘stealthy’.
    That does not mean there’s nothing we can do – reducing our radio signature, for example, making it harder to detect us by this method.’

    Anyone capable of detecting radio waves leaking into space from hundreds of light years away is going to be more than capable of detecting the presence of a life-bearing planet at the same distance, and unless life is extremely common, would be more than enough excuse for a close examination either at long range or close up.”

    Anyone capable of detecting radio waves from such distances is capable of determining the structure of a target solar system and spectroscopically examine the atmospheres of the planets if he dedicates substantial resources and time to a galactic survey of this type of 200-400 BILLION star systems in our galaxy.

    That’s an significant expenditure of resources.

    Plus, the results could be ambiguous regarding the presence of intelligent life: atmospheric pollution can result from natural processes, too – unlike radio waves.
    And aliens would be far less likely to send an expensive interstellar expedition based on ambiguous results.

    Realistically speaking, if some aliens are looking for us, they will find us eventually.
    But there’s no point in making it easier for them. This ‘eventually’ could very well be sooner or later, depending on our behaviour.

    “You could probably build a million space-based planet hunting telescopes for the cost of one interstellar mission.

    The point is that no matter how big space is, the only cost effective way to study it is through the end of a telescope — even if you need to make that telescope the size of the Moon!”

    You severely overstate the cost of an interstellar mission – even today, we could sent mini-sails on interstellar journeys with a lot less resources than would be necessary to build your telescope monstruosities.

  • ProtoAvatar October 7, 2010, 16:37

    “‘But I can think of at least one logical reason – it would be a preeemptive strike, wiping us out now, while we’re still weak and can be exterminated with minimal effort, in order to prevent us from posing a threat in the future, when our technological evolution will make us into a player to be reckoned with.’

    I find this scenario extremely difficult to believe possible. To make it work you have to assume that, as in many convenient scifi scenarios, we are going to make a whole bundle of amazing technological breakthroughs that will suddenly catapult us into becoming a galaxy-roaming civilization and clashing with advanced alien species. (Peter Hamilton’s Commonwealth springs to mind).”

    This scenario doesn’t require FTL, Dreamer.
    It only requires relativistic speeds and thinking ahead for hundreds/thousands of years. Considering the size of our galaxy, any enterprise that could be named ‘interstellar’ (colonization, contact, war, etc) is a long-term project.

    And any civilization that has “been roaming the stars for millions of years” will think extremely long-term.

    “‘Of course, there’s not much we can do to be ‘stealthy’.
    That does not mean there’s nothing we can do – reducing our radio signature, for example, making it harder to detect us by this method.’

    Anyone capable of detecting radio waves leaking into space from hundreds of light years away is going to be more than capable of detecting the presence of a life-bearing planet at the same distance, and unless life is extremely common, would be more than enough excuse for a close examination either at long range or close up.”

    Anyone capable of detecting radio waves from such distances is capable of determining the structure of a target solar system and spectroscopically examine the atmospheres of the planets if he dedicates substantial resources and time to a galactic survey of this type of 200-400 BILLION star systems in our galaxy.
    That’s a significant expenditure of resources.
    Plus, the results could be ambiguous regarding the presence of intelligent life: atmospheric pollution can result from natural processes, too – unlike radio waves.
    And aliens would be far less likely to send an expensive interstellar expedition based on ambiguous results.

    Realistically speaking, if some aliens are looking for us, they will find us eventually.
    But there’s no point in making it easier for them. This ‘eventually’ could very well be sooner or later, depending on our behaviour.

    “You could probably build a million space-based planet hunting telescopes for the cost of one interstellar mission.

    The point is that no matter how big space is, the only cost effective way to study it is through the end of a telescope — even if you need to make that telescope the size of the Moon!”

    You severely overstate the cost of an interstellar mission – even today, we could send mini-sails on interstellar journeys with a lot less resources than would be necessary to build your telescope monstruosities.

  • Duncan Ivry October 7, 2010, 17:07

    Larry, I agree with Eric: “Good essay and many reasonable points.” And interesting comments. But I have some objections.

    (1) In your final thoughts you say: “an advanced alien species will be able to destroy us in short order”. Quite the contrary. Interstellar travel is very difficult, expensive, and dangerous, much more than most other projects. The same is true for interstellar warfare. Controlling asteroids over interstellar distances? Forget it! Directing energy beams from faraway Dyson shells onto earth? Ridiculous! Alien species will *not* be able to destroy us.

    (2) You considered several science fiction stories. This gives nearly no insights, because, with very few exceptions, science fiction stories are — as most literature — about the concerns of human beings in human societies here on earth — and nothing else (this I say after having read thousands of science fiction stories). Avatar is exemplary for *not* having anything alien — except a little bit on the surface.

    (3) One important aspect is absent in your article, as it has been absent in all space oriented websites, I have read in about twelf years: the “higher” features of our civilization, i.e. what usually is subsumed under the humanities. People talk about resources aliens may want: rocks, meat, chemistry and biology of living beings, subjugation, life as such. People talk about aliens being advanced, and because of that they would or should be able to do fantastic things, and from the ability to leap over interstellar distances people leap to bold conclusions. Larry: “destroy us in short order”.

    Never someone said, some aliens may be so advanced, that they are first and foremost interested in the stories we tell, the music and the plays we perform, our paintings, our dances, our philosophy — our sense of humor.

    May be, aliens (some aliens) are so advanced, that they are much more humorous than we are. This would calm down the case, I think.

    Let’s imagine aliens contacting us some day, saying: “Hey, we want to offer those comedians of the Hello from Earth campaign a gig. We still laugh about their messages. Are they able to perform interstellar stand up comedy? … Oh, and, of course, if we ever recognize, that you have no sense of humor, we will destroy you … er … in short order … … hey, come on, we are kidding … you didn’t really think …”

    That’s my vision: aliens who are kidding.

  • amphiox October 7, 2010, 17:21

    I hope I am wrong here, but if there were an alien invader in our Sol system and they were planning to drop controlled planetoids on us (see the SF novel Footfall as an example), would we be able to stop them even if we did detect them and knew what they were doing?

    At present we would have less than the proverbial snowball’s chance in hell. Even a completely natural, accidental impactor would be tough for us to divert without several decades of warning. And all remotely feasible solutions aside from a massive nuclear barrage (which of course has its own attendant problems and uncertainties) require decades of lead time to set up.

    A deliberate “mass driver” assault isn’t going to be so kind. If the attackers use any intelligence at all, they will be launching multiple projectiles (with the resources of an entire outer solar system to draw from, they could easily overwhelm our defense capacity by sheer numbers, throwing more projectiles at us than we can hope to manufacture counters to), from multiple directions, with the majority probably coming from the sunward side to hinder our ability to detect them. They will also not be moving at normal orbital asteroid/comet speeds, but will probably be accelerated. And they will not give us years of warning, probably a few weeks at most.

    We’d be screwed. Completely and totally.

  • Eniac October 7, 2010, 17:55

    That’s very true. There are thousands of ‘alien’ investations wreaking havoc on thousands of former Pacific island eco-systems, long isolated . Many extinctions are happening nowadays. A few islands are still ‘hidden’ in remotest Pacific. The local fauna (if they could think) never in a million years figured that one alien life-form, H.Sapiens, would ever visit their island in ships, and bring destruction and doom to all they had known . But it happened to them.

    Quite true, and this is where my analogy fails. What you describe would be the situation with FTL. Without FTL, you have to modify the island analogy and restrict ocean travel to swimming.

  • Tarmen October 7, 2010, 20:09

    All this speculation borders on philosophy, and theology. All we know is that:
    -Nature on Earth is violent and variant.
    -There are hundreds of billions of planets and niches for life in our own galaxy.
    -We once thought we were the center of Creation. We’ve been wronger and wronger every century since 1500AD.
    -Some earnest Air Force pilots and policemen have seen unidentifiable flying objects. Here on Earth, in Europe, Asia, North Amer, South Amer.
    -We’ve advertised ourselves via radio, for less than 1 Earth century.
    -Maybe 50 000 star systems could have ‘heard’ us , in a 80 LY radius sphere.
    -We’ve search for ET signals for 30 yrs. So far, nothing.
    -We think Light speed might be that maximum speed to travel, even for aliens.
    -We ‘re not dead yet.
    -Rule #1 : -Nature on Earth is violent and variant.

  • ljk October 8, 2010, 6:07

    Duncan Ivry said on October 7, 2010 at 17:07

    “Larry, I agree with Eric: “Good essay and many reasonable points.” And interesting comments. But I have some objections.

    “(1) In your final thoughts you say: “an advanced alien species will be able to destroy us in short order”. Quite the contrary. Interstellar travel is very difficult, expensive, and dangerous, much more than most other projects. The same is true for interstellar warfare. Controlling asteroids over interstellar distances? Forget it! Directing energy beams from faraway Dyson shells onto earth? Ridiculous! Alien species will *not* be able to destroy us.”

    Wait, wait – on what do you base the idea of Dyson Shells as weapons being “ridiculous”? And as for using planetoids to bomb Earth, I was talking about an ETI starship in our Sol system conducting this, not from across the galaxy. However, you do prove my point that most reasons humans think aliens would come to destroy us are rather excessive at best due to the vast distances in interstellar space. And while I do consider the possibility of destruction by aliens remote, no one here can say it is impossible and I have already shown that it is quite doable at our present stage of things.

    “(2) You considered several science fiction stories. This gives nearly no insights, because, with very few exceptions, science fiction stories are — as most literature — about the concerns of human beings in human societies here on earth — and nothing else (this I say after having read thousands of science fiction stories). Avatar is exemplary for *not* having anything alien — except a little bit on the surface.”

    Go search for my Avatar articles on Centauri Dreams where I delve into why I was disappointed that the aliens in that film were hardly alien at all, as is the case in most cinematic SF.

    “(3) One important aspect is absent in your article, as it has been absent in all space oriented websites, I have read in about twelf years: the “higher” features of our civilization, i.e. what usually is subsumed under the humanities. People talk about resources aliens may want: rocks, meat, chemistry and biology of living beings, subjugation, life as such. People talk about aliens being advanced, and because of that they would or should be able to do fantastic things, and from the ability to leap over interstellar distances people leap to bold conclusions. Larry: “destroy us in short order”.

    “Never someone said, some aliens may be so advanced, that they are first and foremost interested in the stories we tell, the music and the plays we perform, our paintings, our dances, our philosophy — our sense of humor.

    “May be, aliens (some aliens) are so advanced, that they are much more humorous than we are. This would calm down the case, I think.”

    I did mention such a thing in another article published on CD here:

    https://www.centauri-dreams.org/?p=9489

    I too think some aliens could be as big a bunch of chuckleheads as us. It would explain so much.

  • ljk October 8, 2010, 6:10

    Tarmen said on October 7, 2010 at 20:09 :

    “All this speculation borders on philosophy, and theology. All we know is that:
    -Nature on Earth is violent and variant.”

    This is why I advocate more SETI programs and a push to make Orion a reality, as it is the only starship technology we can make happen now if we want to explore even the nearest stars in our galaxy in the next few centuries.

    Until then we are going to be stuck with one data point and a lot of more or less educated guesses.

  • Eniac October 8, 2010, 10:36

    We’d be screwed. Completely and totally.

    Maybe. But they would have to have some really miraculous technology, and miniaturized, too. There are very severe limits on payload for interstellar trips, because of the rocket equation. They would have no industrial resources when they arrive, and would be completely isolated from their home world. There would be no backup or reserve, and they would be vulnerable to nuclear missiles that we would have had decades to put in position.

    Asteroids are much harder to move around than most people think, except for very small ones. They would have to strap one of their star drives to one and operate it with leftover fuel. It would take a very long time of acceleration to budge an asteroid, and it would be clear for us to see. Our best option would probably be to try and nuke their drive before it can finish the burn.

    Instead of wasting years messing with asteroids, they would probably just bring a nuclear arsenal with the intention of selectively dropping it on Earth’s population and industrial centers. The same technology used in the star drive would enable much lighter and more powerful bombs than we have, permitting them to bring a sufficiently destructive arsenal to strip us of our own industrial resources.

    When we see their ship coming, we have to make the difficult decision about whether to hang out a welcome banner or send a full force of nuclear missiles (or both?). If they were hell bent on destroying us, and had no interest in talking or looking around first, they could launch their arsenal early during arrival, giving us no warning and no chance of preemption. However, we could by then be prepared to retaliate, having seen them coming for many years.

  • Tarmen October 8, 2010, 11:29

    Wolf may want to eat a turtle. Turtle should:
    A)The turtle can disbelieve in wolves.
    B)The turtle can tell itself that wolves don’t eat turtles often, if ever.
    C)The turtle can trust it’s shell to withstand the jaws.
    D)The turtle can run, if it sees a wolf coming.
    E)The turtle can smile friendly at the wolf.
    F)The turtle can swim and hide in the muck.
    G)All of the above.

    Correct Answer: F The turtle can swim and hide in the muck.

  • amphiox October 8, 2010, 13:24

    They would have no industrial resources when they arrive, and would be completely isolated from their home world.

    Basically I envision them harvesting the resources from the asteroids and comets themselves. Starting with small and relatively simple self-replicators and exponentially building up from there, working on multiple asteroids/comets in parallel. They could obtain all the fuel they need from cometary water. The idea would be that they would turn on the star drives only when all the planned projectiles are ready, so that even if we see them, we’d have to deal with many (maybe thousands) all at once.

    If they planned the trajectories properly, the stardrive burns will all be finished while the impactors are still out in the Kuiper Belt or Oort Cloud. With current tech there’s no way we’d get a nuke out in time to stop them.

    With stardive level technology they also have the option of using much smaller asteroids that are much easier to move, but accelerating them to much faster speeds for equal devastation.

    The key for us would be detecting them at initial insertion into the Solar System. Whatever means they use to decelerate would probably be theoretically detectable if we were looking in the right direction at the right time. But if we miss that signal (and currently I don’t think we have the capacity or resources to conduct the kind of continuous full sky surveys that would allow us to be confident of not missing that signal, and neither do we have sufficient knowledge of any of the surrounding star systems to be able to guess at what directions a likely attack might come from) everything after that up to the point when the comets flare up and start to fall inward would low-energy local activities that would be very hard for us to detect.

    And they could also employ misdirection – they could make a lot of visible and obvious activity in one direction to catch our attention and prompt us to deploy our defences there, and then smack us from another direction.

    It would of course take many years to set up, but this kind of attack would not require a very large spacecraft or huge invasion force to start with at all. A single probe weighing only a few kilograms containing a few of the initial replicators is all that would be needed. The aliens would in effect be trading time for size. It would depend on how willing they are to wait the required time.

    And for a culture willing to contemplate a non-FTL invasion of another star system, a few centuries for setup will probably not be a big deal.