As I’m just finishing up Richard Holmes’ The Age of Wonder (Pantheon, 2009), the Royal Society had been on my mind even before the two-day conference on SETI that concluded yesterday made the news. If you haven’t read the Holmes book, by all means do so. It’s a fascinating study of the development of science and the imagination in the late 18th Century and into the Romantic era, with cameos by the likes of Shelley and Keats and in-depth discussions of everyone from Pacific voyager Joseph Banks to the chemist Humphry Davy. It’s a cliché to say I couldn’t put the book down, but this one fully deserves the compliment.
With the Royal Society now in its 350th year, a conference steeped in SETI and questions of astrobiology seems made to order as we track the data from our far-flung space observatories. I wanted to mention that Paul Davies’ public lecture at the conference, called “The Eerie Silence: Are We Alone in the Universe,” will be made available at the Royal Society video archive within a week or so. Davies (Arizona State), a physicist and popular science writer, argued at the conference that we should look here on Earth to see whether life has appeared on our planet more than once. A ‘shadow biosphere,’ one representing forms of life entirely different from our own, might be present in isolated ecological niches.
Addendum: The Davies talk is now available here.
Davies is thinking of places like the dry valleys of Antarctica, or lakes saturated with salt, or volcanic vents. It’s an idea we’ve examined here before, and one you can follow up on in Davies’ article “Are Aliens Among Us?”, which ran in late 2007 in Scientific American Vol. 297, No. 6, pp. 36-43 and is available online. Davies’ book The Eerie Silence: Renewing Our Search for Alien Intelligence, is to be published by Houghton Mifflin Harcourt in April.
Pondering Davies’ ideas, London’s Times Online notes that a US Geological Survey team led by Felisa Wolfe-Simon is investigating places like Mono Lake in California, where arsenic contamination might support life-forms that use arsenic the same way other life-forms use phosphorus. Not everyone agrees, of course, and the article quotes Colin Pilinger, leader of the Beagle 2 Mars landing attempt, as saying that looking for arsenic-based life is ‘wildly science fiction,’ and ‘you’d be off your trolley’ to look for it.
I wish I could have been at this conference to have heard Pilinger’s own talk, not to mention Alfred Harrison’s. The latter, from the University of California at Davis, took on the huge question of how humans would react to the reception of a signal confirming the existence of extraterrestrial intelligence. Here’s his response to the Times:
“It is easy to imagine scenarios resulting in widespread psychological disintegration and social chaos. But historical prototypes, reactions to false alarms and survey results suggest that the predominant response to the discovery of a microwave transmission from light years away is likely to be equanimity, perhaps even delight.”
And the Guardian‘s coverage of the conference looks at the parallel some people make with the famous 1938 ‘War of the Worlds’ broadcast of Orson Welles, which caused some in the radio audience to panic at the thought of an invasion from Mars. Harrison dismisses the idea:
“The public reaction was overstated. Most people who thought the broadcast was real took sensible actions to protect themselves,” Harrison said. “Surveys suggest most people think they will be fine, but they worry about others freaking out.”
I’m not sure which surveys Harrison is referring to, but one that supports him was presented as far back as 1996 at the OSETI II conference in San Jose (CA), where Miguel Sabadell and Fernando Salamero (University of Zaragoza, Spain) demonstrated that there was widespread public interest in extraterrestrial contact. Asked whether contact with ETI would be good for mankind, an overwhelming 79 percent answered Yes, and 77 percent agreed that if we receive a SETI signal, we should answer.
Also supporting Harrison were the results of a 2002 Roper poll that concluded:
“Most Americans appear comfortable with and even excited about the thought of the discovery of extraterrestrial life. Three-quarters of the public claim they are at least somewhat psychologically prepared for the discovery of extraterrestrial life, and nearly half are very prepared.”
This story in Nature News looks at Simon Conway Morris’ contribution to the conference. Morris, a paleontologist at Cambridge, points to examples of convergent evolution in Earth’s biological history to make the case for there being a limited number of ways to organize a sensorium or a society. The lives of intelligent aliens could, in other words, be every bit as violent as the lives of beings on Earth. Whatever the case, Martin Dominik (University of St. Andrews, UK) notes that no government has plans for what to do if intelligent life is confirmed elsewhere in the universe. One hope for the conference is that it will persuade policy makers to take the matter into consideration as the numerous imponderables of such contact are examined.
Off-topic, but interesting and relevant: according to the Extrasolar Planets Encyclopaedia, the Magellan Planet Search Program has just turned up 5 long-period planets, of which 4 are Jupiter like in Mars-Jupiter like orbits around sun-like stars:
– HD 129445 (1.6 Mj, 2.9 AU, G8 V star)
– HD 152079 (3 Mj, 3.2 AU, G6 V star)
– HD 175167 (7.8 Mj, 2.4 AU, G5 IV/V star)
– HD 86226 (1.5 Mj, 2.6 AU, G2 V star)
It looks like with increasing observation time, we are now entering an exciting period of increasingly solar-system type analogs, at least with regard to (sub)giants with long-period orbits.
Submitted for the Astrophysical Journal: “ARRIAGADA P., BUTLER P., MINNITI D., LOPEZ-MORALES M., SHECTMAZN S., ADAMS F., BOSS A. & CHAMBERS J. , 2010
Five Long-period Extrasolar Planets in Eccentric orbits from the Magellan Planet Search Program”.
Yeah, I don’t think there would be wide spread panic or pandemonium as a result of receiving a legitimate ETI signal. I think that is more hollywood than anything else. I am sure that nut cases of various types would make spectacles of themselves, but I think that most people would be able to go on about their business without hysterics.
As for me? I would probably cry with joy, relief, and yearning.
A paper by Davies, Wolfe-Simon, and others on a shadow biosphere:
You might take a look at my poll running at the PI Club website.
It is by no means an exact survey, but as far as I am looking at the figures from time to time (no, I don’t have systematic notes about the development along the time axis), it seems to me to show a rather stable distribution. The poll is actually about Messaging to ETI (called also active SETI) – note that this formulation is irrespective of having got a signal to answer or not.
Slightly more than the halft of the votes goes to “METI is beneficial, since we shall learn from ETI”, almost a fifth does not really care about messaging efforts (either they think we are alone or ETI does not care), and, a bit less than a third is anxious, stating that ETI could do harm to us.
Tibor’s poll misses out the option “this issue may potentially have a lot of ramifications that we should probably sit down and assess more thoroughly, before just going ahead and blasting messages out into the cosmos on behalf of all of humanity”…
If we discover ETI signals from ‘way Out There’ I’d be worrying about relativistic missiles following close behind them… dang that book!
and so the dreaded paralysis by analysis raises its ugly oversized head again.
Even if there are many (or any), it seems unlikely to me that out of the blue we’ll suddenly detect an unambiguous ETI signal. I suspect a more likely scenario is a number of ‘Wow signal’ type events as our detection methods improve. It may be a long time before we detect something that we can absolutely verify.
I read Simon Conway Morris’ book. It is quite good and well worth the read. His contribution to the subject is to approach biological forms from a design engineers perspective. He goes on to describe the enormous range of possible combinations that proteins can take, but notes that only a tiny fraction of those combinations actually exists in nature, suggesting that these may be the only functional forms of proteins. He takes the same approach, along with examples of convergent evolution to suggest that the range of potential alien life may actually be quite limited and that it would look much like Earth life.
I think this argument is valid. However, Morris walks off the map when he discusses about how natural evolution is not sufficient to explain the life on Earth and that there must be a teleological “force” driving it. Of course, I see no reason to believe this. I think he is peddling ideology as science. Much of this is done in the last few chapters of the book. Despite this, it is still a good book and I highly recommend it.
Religion could survive discovery of ET, survey suggests
21:49 26 January 2010 by Jessica Griggs, London
For similar stories, visit the Astrobiology Topic Guide
Could the world’s religions survive the discovery of extraterrestrial life? Or would their beliefs be so shaken that they would eventually collapse?
A survey (pdf) discussed on Tuesday at a meeting on the search for alien life at the Royal Society in London suggests religion would survive.
The survey, designed by Ted Peters, a professor of Systematic Theology at the Pacific Lutheran Theological Seminary and the Graduate Theological Union in Berkeley, California, asked 1300 people whether they thought the discovery of extraterrestrial intelligence would shake their individual belief, the strength of their religion as a whole or would adversely affect the beliefs of other religions. The survey included both religious and non-religious people, and most respondents were based in the US.
Full article here:
I do like the T_U_T bridge-building company. They don’t sit around, they just go ahead and build the bridge. It doesn’t matter how many workmen get killed because they didn’t think through the safety procedures, it doesn’t matter whether the bridge falls down a week after it was built, taking the lives of everyone on it at the time, what’s really important is the T_U_T company didn’t sit around doing tedious boring analysis but just went ahead as quickly as possible. No paralysis by analysis in the T_U_T company.
I think the average person would be able to handle news of ETI just fine. I think the problem will arise in who gets to make the reply. Assuming the source of the transmission is within the range of terrestial transmitters then almost any country, or organization on the planet could make the reply, and the first to make the reply will be the first to be heard by the ETI.
I can see it now, various religions leaders stating their devine right to reply, or various political ideologies racing to be the first to construct a message and transmit. Then what? Do the oposing factions send replies dismissing the message of the other parties? So rather then the ETI receiving a unified message of all the people on Earth, perhaps they will receive the squables of our various nations.
As to discovery of ETI shaking religion, well, note that the same tabloids feature both aliens and angels.
As to the bridge analogy, the issue is not whether the message will be badly constructed, but whether we want any bridge at all. For the bleating of the kid to attract the tiger, it doesn’t really matter what the kid is saying.
Nice straw man, though, what do you want to analyze about a binary go/no go decision about an leap into the unknown ? Unknown that can be turned into known only by trying ?
Either you go, and consequently have to deal with what ever you find there, or you don’t go, and risk that the ‘what ever is there’ will come down to deal with youf on its own terms.
This is a question of courage, not analysis.
Phil said on January 28, 2010 at 8:33:
“So rather then the ETI receiving a unified message of all the people on Earth, perhaps they will receive the squables of our various nations.”
At least it will be a honest if potentially confusing response regarding
the current state of our species.
bemusedoutsider said on January 28, 2010 at 11:13:
“As to the bridge analogy, the issue is not whether the message will be badly constructed, but whether we want any bridge at all. For the bleating of the kid to attract the tiger, it doesn’t really matter what the kid is saying.”
Please provide a list of serious reasons why an advanced ETI might
want to harm or destroy us.
Even your own metaphor fails you –
If the child yells, a tiger may come, but adults coming to help her are far more likely ( a tiger may not be hungry, may not risk eating an unknown animal, an generally, predators are up the food chain and thus rarer than their potential prey, while even strangers tend to come to help the helpless ).
If the child remains silent, then well, scavengers finding her by smell don’t need any sound to come, and adults will almost surely not come to fend them off until it is too late.
As I said. It is a matter of courage, not analysis. ( because the analysis tends to be very short, given the by definition lacking information in such circumstances. And anyway, usually leads to the conclusion that doing something is better than waiting till someone else does something to you )
Do you want continued human existence to depend on your understanding of hypothetical alien psychology? Perhaps they are incredibly territorial, and consider this galaxy as their own. Perhaps their religion (or whatever equivalent they may have) views other intelligent life as abhorrent. Perhaps they are coldly rational, and recognize that, advanced as they are, we have nothing to offer them except future competition. Perhaps they are making way for a new hyperspace bypass.
The history of humanity is littered with advanced civilizations essentially wiping out less technologically able ones for a host of reasons, and that’s where both parties are the same species.
Yeah. Like staying where we are would be any help in that case.
If there are more advanced aliens than us out of there then our contact with them is inevitable. And we will depend on alien psychology anyway.
So we better find them first, because that would give us at least some time to understand them, to prepare for what ever they may have in store for us. Because if we see an alien caravel aerobraking above our head, there will be no time for us to ponder alien psychology left.
I’m just glad people were not that phobic when they were sending the first radio or TV signals. Ditto sailing, exploring etc. Now where did I leave Chip, Penny and Used Napkin?
I constantly notice the same contradiction in these discussions about either or not sending out signals to ETI’s:
– con contact: it might be dangerous to contact ETI’s.
– pro contact: if advanced ETI’s exist, they know we are here already and either they cannot reach us or there is no escaping anyway, so we can only benefit by contacting them.
There is a joke by a Dutch stand-up comedian, which goes something like this:
“I am against contacting alien civilizations, because if they are truly advanced they will find us first and if they are not I want to have nothing to do with them”.
This isn’t just funny, I think there is some truth in it, which may render the whole idea of METI rather harmless, but also rather pointless, like Amazon indians, Congo pygmies or Papuas trying to contact the US govt. or the UN (not meant discriminatory or degrading BTW). If they really have global ambitions, they better develop (other) technologies. Most likely they will be found first anyway.
If there is a significantly advanced ETI anywhere in our MW, even some centuries or millennia ahead of us technologically, they will almost certainly know that we are here. If they want to contact us, they will do so. If the ETI is significantly less advanced than us, they will not be able to contact us nor receive messages. An ETI at approximately the same level is also interesting but statistically very unlikely.
This may even be a universal rule: the more adanced civilization will first find the less advanced and decide whether to contact or not.
As I have said before, first things first: we do not even have a good idea of (types of) planetary systems around us, let alone a complete database of planets (and their spectroscopic biosignatures!) in our (part of the) MW galaxy, something that should be quite doable this century or the next.
BTW: courage is not in contradiction with careful study and analysis. And a reason for ETI’s to mean harm to us: the most universal biological one: fear of (future) threat and/or competition. Also known as the galactic pecking order.
Ha! An excellent Sponge Bob aside, Bounty! Anyone else get it?
But if we do broadcast a message, it will probably take at least 10 years to reach it’s target. It’s quite likely Einstein was right, and FTL is impossible, so any violent response would happen 20 years later at the least, after the original message.
If people are so worried, that’s enough time for them to build up a solar fleet for defence. In the probable event it all turns out to be needless worrying, we’ve colonized our system and are on the way to the stars ourselves.
Or we could just sit around and not send a message. That way, when we *are* found by other means, we get obliterated, and if we aren’t found (because ET isn’t there), we don’t have a solar wide civilisation. The first instant is a draw-win, and the last situation is a lose-draw.
Yeah. That one worked really well for native americans. we have found them first…
You think things would have gone differently if the indigenous Americans had contacted the Europeans about the wonderful, resource-rich land they lived on?
Yes. For example the Inca empire would more likely acquire iron than collapse and would most probably be capable to fend off the few conquistadors exhausted by the long journey.
Seriously, solar defence fleets? The universe does not run on Star Wars rules. Far safer for the aggressor to use relativistic missiles, which give you very little warning (since they arrive very shortly after the photons which set out when the missile was launched), and wouldn’t be stopped by a fleet of spaceships anyway.
(since they arrive very shortly after the photons which set out when the missile was launched)
Where ‘shortly’ means something between months when launched from a nearby stellar system, and years when launched from greater distances.
And all it takes is just a few sand grains on its path to turn a relativistic ship into one flash of light and radiation and a quickly expanding and thinning plasma cloud.
How would they have gone about it? Holler into the woods? Smoke signals? Pick up the phone?
Fact is, they tried very hard to communicate, but their choice of intended recipients (their gods) and their methods (sacrifices, etc.) turned out to be ineffective. Nor could they have done any better, no matter how hard they tried, given their limited understanding of the world.
About the resource-rich land, I think the conquistadors would not have bothered to come at all if they had known in advance how little gold they would find.
System defense from relativistic weapons could be as simple as grinding up a few asteroids to make “ablation walls” for incoming projectiles to ram in to. Questions: How much mass would it take? and how long would it last for?
The second is due to dust erosional effects like the Poynting-Robertson effect and solar wind effects. Dust needs renewing on millennial time scales, at least in the inner system.
The first needs an estimate of how much we’d need to disperse to destroy reasonable sized projectiles. If we had long-range sensors and very high acceleration missiles we could have an AISM (Anti-InterStellar Missile) defense, but may be dust would be easier.
How massive a missile would be reasonable to use if you were attacking another system? To total a planet requires several trillion tons of mass-energy equivalent, but more economical would be to cause a massive heat-pulse and bake it – turn the crust into a magma ocean. If the crust is 17000 metres thick at 2800 kg/cubic metre and a target planet is 6.4 megametres in radius, and we want to raise the crust to ~1400 C hotter than it currently is, then the total energy needed is ~2 E+28 J. That’s roughly 2E+11 kilograms of energy equivalent, which seems kind of ‘unstealthy’ and energy intensive.
What if we boil the oceans? One Earth ocean mass is 1.35E+21 kg of water, at an average of just 5 C. Thus we need an input of ~95 x 4200 J per kilo of water to get to boiling point and about 2.3 MJ/kg to make it steam. If we call it 3 MJ/kg to be on the safe side, then the total input is ~4.05E+27 J or ~4.5E+10 kg of energy. Call it 45 million tons moving at 0.87c.
Perhaps that’s excessive. A thousand ton impactor at 0.87c would be the equivalent of ~22 million megatons of TNT (9E+22 J), which is rather frightful. But what is it spread over the whole face of the Earth? Every second the Earth absorbs ~1.22E+17 joules of energy from the Sun, so the 1,000 ton missile is equivalent to 8.5 days of the sun’s energy. Everything on land might burst into flames… or would it? We have 10 tons of gas above every square metre of the planet. All that energy, in one burst, would raise the gas temperature by ~30 degrees, making one face rather hot, but not utterly lethal.
So 1,000 ton missiles – what is needed to blow one into atoms? Say it’s a refractory metal like tungsten. Its heat of atomization is ~4.67 MJ/kg, thus a 1,000 ton missile needs to absorb ~4.67 TJ to be destroyed, minimum. If the missile is doing ~0.87c then the impactor needs to mass ~52 mg. A 1,000 ton sphere of tungsten is ~4.6 metres across, thus 16.8 squares metres of target. If we imagine the defensive ‘perimeter’ as a literal thin shell around the solar system (radius ~50 AU) then it masses 2.2E+21 kilograms, minimum. Roughly the mass of the asteroid belt. Grind up a few outer planet moons or Eris, and we’d have plenty of dust in the system.
That mass of dust surrounds some 523,600 cubic AU of volume. Around the Earth, thanks to the Zodiacal dust there’s already ~1E+16 kg of 100 micron specks of dust. Are we already surrounded by a sufficiently dusty shield?
The other point about this is you see it approach at (apparently) superluminal velocities. Given the object is going to be small, for most of the time it is too far away to spot – and by the time it is close enough it is too late. This makes figuring out just where the object is heading (in order to intercept it) very difficult indeed.
Point with a relativistic missile is it is small, and you try to minimise the cross-sectional area. You’d need quite substantial amounts of sand to get in the way if you don’t know where one is coming from.
In any case I strongly doubt METI will result in relativistic missile attacks, but then I suspect that technological intelligence is very rare (based on my reading of the evolutionary history of our planet). Nevertheless what the discussion needs is more input from biologists, anthropologists and historians… I suspect they’d have something to say about the notion of how if the Incas had advertised America to the Europeans they would have somehow ended up with enough iron technology to repel the conquistadors…
‘…and 77 percent agreed that if we receive a SETI signal, we should respond.’
Ha! That made me smile. :)
See Adam’s comment too.
But I caution that we should be listening for any signals–not sending them first, as though we were whistling in the dark or cackling in the trees like twits; this sort of tactic works for monkies in treetops. And the things that look for monkies, DO know where the monkies are at. The problem is; if spaceships were trees, we’re sort of…DEFORRESTED! <– That means we'er exposed. And we STILL don't even have an igloo on the moon! Monkies are clever, and when they are not, they'er something elses dinner.
I'm smiling again :)
Here goeth I, happily to my fate!
The point was really that the big space fleet probably isn’t a good way of defending the system… if you want to cause large amounts of damage at long range you don’t have to send in your own invasion fleet (which is what building our own space fleet would be defending us against), there are other ways you can contemplate of doing it, most of which don’t involve big wasteful Star Wars style space battles.
Those relativistic missiles are going to require some very impressive interstellar target shooting: there will be no opportunities for course correction. And then there’s energy input; every joule of kinetic energy it hits with will have to be put into it at some point by the aggressor. Interception is also a problem since even with a shield of similar rest mass (and placing it accurately!) there will still be considerable kinetic material that reaches the target.
One wild guess I have to make the attack more tractable is to use a shotgun approach: a large quantity of microscopic projectiles. Take a large mass, pulverize and ionize it, then feed it into an EM mass driver. You get the benefits of keeping the larger power plant fixed in one location and able to operate at a moderate power level over a long period. To adjust down the resulting long bombardment period, simply ramp up the muzzle velocity slightly over time to have the total mass arrive at the target within a short time interval. This technique can also spreads the missile mass over a larger area, making it more difficult to deflect and should also compensate for small trajectory errors.
It won’t make one big kaboom but it does dump the same amount of total energy into the target, which seems to be the point of a relativistic missile as I understand it.
Given that a relativistic missile can fly for all practical purposes only straight ahead, and you want to intercept it only if it is going to hit earth, all you need is to see a flash of light from its engines when it accelerated to almost eactly know, where it has to be if it is heading for earth.
And, also, a relativistic missile would glow pretty brightly because as it slams into interstellar gas an occasional dust grain, the resulting plasma outbursts will shine bright with and gamma ray flashes.
As I said above. An engine that can accelerate a craft to relativistic velocities would be clearly visible from all other stellar systems around. And a relativistic missile can not turn without being visible again. So you will exactly know where it is, because you know where it was launched, you know where it is heading, and you know it comes at a straight line.
And to the second part, fortunately debris clouds are neither difficult nor expensive to produce. Just nuke an asteroid in the right position so that the radiation pressure from the sun blows the dust in the right direction and you will get a several million kilometers wide barrier that a relativistic missile can neither go around nor pass.
I suspect they’d have something to say about the notion of how if the Incas had advertised America to the Europeans they would have somehow ended up with enough iron technology to repel the conquistadors…
They could beat them with bare hands, as they were ~100 000 , facing 168 conquistadors exhausted from the long journey. If they just knew ahead that the conquistadors are no gods.
Agreed about relativistic missiles being rather useless, due to the extreme tracking needs. If you aim for the center of Terra, but are off by 7000km (considering it’s just travelled several light years at the least, an easy mistake), it will carry on past Terra… if it doesn’t hit the zodiacal dust, that is. If it did, the resulting gamma ray burst might sterilize a hemisphere, but the other half should be fine.
You are assuming that you know it is a relativistic missile to start with, that you reduce your survey data in time, don’t get distracted by trying to model it as yet another freakish neutron star phenomenon…
That then raises the question of whether given a month or two’s notice it is possible to launch a mission to an asteroid that happens to be in a convenient enough orbit that it will be able to move it into the trajectory, pulverise it in such a way that a sufficient proportion of the debris cloud is still going to be in the right general area when the relativistic missile is there…
Ok let’s suppose the Incas or the Aztecs or whoever vanquished the conquistadors. The European powers are still there and having control of vast areas of land on a new continent is still an appealing prospect for the ruling classes.
There is just no way someone could mistake a relativistic ship engine for something else. Putting aside the fact that only a few known processes can produce that amount of energy confined to that small space, the doppler shift as it accelerates would be a dead giveaway.
You would have to piss off the Na’vi enough to abandon their paleolithic lifestyle and go on a technology rampage to have only such short warning time. The ship would need to constantly accelerate at 20 G all the way to 97 % c to give a 2 month warning time. The energy required to do that would be so ridiculously high that even if they strip-mined all unobtainium from their moon tehy would not have enough fuel to launch such a missile.
A more realistic attack would be for example 0.8 c impactor over 20 ly distance, giving say 6 year warning time.
No power in europe could deploy tens of thousands of soldiers at that distances to get their empires down by brute force. Not enough ships, not enough money for that tour de force. A a few colonists and outcasts on the border would be at worst a nuisance, at best a good way for the natives to test out what works best against them. So the inca and aztec empires would have decades perhaps centuries to adapt to new technologies. Maybe that would be not enough for them, but they would at least have a chance.
You know what, I don’t particularly care about relativistic missiles, the entire argument we’re having here is just because I foolishly mentioned them when I pointed out that space defence fleets are a silly concept because invasion fleets are not the only conceivable way to attack another civilisation.
Incidentally I’m glad these Incas and Aztecs in your faintly ludicrous alternate history of the Americas where the native inhabitants are saved by telling Europe that there’s a great big inhabited continent are able to bootstrap their medical science to the level where no-one gets wiped out by smallpox, for example…
Sorry I mentioned the damned things. But it’s one of those post-Cold War/post 9/11 horror scenarios that sticks in one’s head in this context, because we’ve had such graphic evidence in the last ~20 years of how blood-thirsty even a ‘civilized’ species can be. Robert Freitas has some rather hair-raising papers on these sorts of issues online…
…this one especially could give one sleepless nights if SETI ever gets a real hit.
On the observability of starships heading our way: I think it is entirely plausible that there would be no signal at all. If the starship is driven with on-board reaction mass, the exhaust will be directed in the opposite direction, at least until the ship decelerates. In addition, there will be a shield in front, shielding all engine radiation. The cross section will be small and the distance enormous, all factors making it extremely difficult to detect something, no matter how intense the ISM bow shock might be.
@andy. Nice to see you retreating from the “don’t go out or the
snipersrelativistic missiles will get you at the moment you leave the door.” argument against active SETI.
To the second part. AFAIK no empire was ever wiped out solely by an epidemic.
@Adam. I just wonder how you manage to leave your bunker, you know, armies around the world control several gigatons of TNT equivalent, you barely a few gram or even zero, they may nuke you accidentally, or just for fun. Or may take you and process you to hamburgers. Because humanburgers are tasty and you are powerless against them w/o any nukes.
No engine can be 100 % efficient. And given the grotesque amounts of energy expended by an engine that accelerates a ship to relativistic velocities, there is just no way how to prevent at least a tiny fraction of it going forwards. and the tiny percentage would be still a HUGE amount of energy.
It would seem to me, that this argument is completely pointless. Just considering the possibility of someone going through the struggle to build and launch a relativistic missile/ship, cross enormous interstellar distances just to bomb a planet witch dominant species aren’t even able to get to the moon, has to make one laugh!
If, in fact, we would be so interesting, or such a threat for someone to come over, it would defenitly not be with relativistic speed, but something much more advanced, probably so advanced that it would render any discussion about defence pointless.
Besides that it is also inappropriate to compare interstellar contact with our own past, because it wont happen with sticks and stones. Any civilization witch would achieve space travel would be dealing with such enormous amounts of energy, that they would have to be much more evolved in an ethical way as well in order to not destroy themselves. Witch in case would mean that, most likely, they just wouldn’t care about such primitive species as us.
A bit further to Kris’ post, I think that this whole idea about ETI as potential threat may also be a bit too pessimistic for two other reasons:
– First of all, there is probably nothing that unites people as much as a *perceived* external threat, as long as it doesn’t get too crazy (i.e. not imminent destruction resulting in hysteria, fatalism, fanaticism). This is what united Western Europe and North America (against the former Soviet Union) and what now (very bumpily) unites the European Union (formerly fear of another great war and presently of other economic powers). Besides the often mentioned cosmic awareness, being part of something greater, a perceived potential threat, the awareness of the reality of other, greater powers, also creates a strong ‘togetherness’, an ‘us and them’ feeling, which may actually enhance world peace and hasten solutions to our often puny political problems.
– Innovation often takes place in times of stress and threat. A lot of technological innovation took place during the 2nd WW and even more so during the Cold War. Not that we need conflict, and we or any civilization should never ever, but a potential threat, any threat (famine, disease, enemies, ,meteorite impacts, climate stress, …) does make people inventive and resourceful. Civilizations arose and developed where the conditions were favorable enough to build up ample reserves (beyond the daily survival level), but at the same time not ideal either, so that people kept searching for better alternatives to achieve their goals. For development, in nature as well as in civilization, (natural) conditions are required that offer both the opportunities (niches) ánd the necessity (pressure).
There is no innovation in paradise.
T_U_T: The “grotesque amounts of energy” produced by a star-drive would nevertheless be negligible compared with those produced by the nearby star, would they not? So negligible, in fact, that we most definitely would have a hard time resolving it, even if it was directed right at us.
Otherwise, I am entirely with Kris on this one.
The problem, T_U_T, is that you are arguing as if there is a binary choice between “civilisation gets totally wiped out” and “nothing happens, everything’s peachy”.