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Making It Hard For Extraterrestrials To Hear Us
quaith writes "US astronomer Frank Drake has told scientists at a special SETI meeting in London that earthlings are making it less likely that we will be heard in space. In the past, we used huge ground stations to broadcast radio and television signals which could be picked up relatively easily — according to astronomers' calculations anyway. Now we use satellites that transmit at 75 watts and point toward Earth instead of into space. In addition, we've switched to digital which makes the transmissions even fainter. Drake has concluded that very soon, in space no one will hear us at all. I guess we'd better keep listening."
This issue was already known to Drake when he formulated his famous equation -- a key parameter is the time window during which a civilisation is broadcasting radio signals.
So if a sufficiently advanced civilization (like ours) eventually develops radio technology that doesn't get far beyond their own planet, could this severely limit how much we would detect from other planets in the way of radio signals?
It reduces the probability that earth could be quickly located.
We gotta consider the possibility, that any extraterrestrials close enough to hear our signals in any reasonable amount of time, and with the sophistication to pinpoint us....
Might have the technology and desire to invade earth.
E.g. Consider earth itself... fast forward a few dozen generations...... massive overpopulation, lack of resources, land, severe overcrowding.
Extreme desire for another habitable place to live.
And then you detect an alien signal.. a foreign world. You step foot there, and you're greeted by basically an aboriginal species (compared to your civilization).
Habitable world, massive resources, very primitive 21st-century level technology, nothing compared to your 23rd century tech.
Oh.... so some colonists start travelling from earth to 'the new world' for a better life.
Settlers VS the Natives all over again.
It's happened before, it could happen again. Except us earth inhabitants could be the primitive natives / "Indians" / etc.
Scary, huh? :)
The possibility of extra-terrestrials intercepting our signals, being interested in them, replying before humanity has run its course, and something good coming of it, are so remote that it's not worth constantly wasting energy for the purpose. If you look at Earth from space you realize what a tiny, limited, fragile place it is and how important it is that we do all we can to make us "live long and prosper". Hoping that aliens are going to help us in any way is counter-productive.
And this is a possible answer to the Fermi paradox. Well, after you accept that interstellar travel is not economically feasible.
Broadcast is not a great communication strategy. On-demand point-to-point communication takes over most things. Advanced civilizations go silent from the outside within a blink of them transmitting their first broadcast signals. There's no reason to think that we'll ever put serious effort into sending signals into the black given all the other things on our plate. And there's no reason to think that any other civilization would have such extra resources either.
Cheers.
This is good news. And overdue.
We've been a stupidly noisy duck for far too long.
kartune85 : Incapable of reason, observation or learning. A kind of dim, drab, flightless parrot.
the closest aliens are at least thousands of light years away, they haven't "missed" our radio signals, they still haven't heard them yet. And they'll have like 100 years of signals to figure us out.
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Stay tuned for some shock and awe coming right up after this messages!
Considering how the meeting between two civilizations, one more avanced than the other has generally gone badly for the majority of human history, it may not be such a bad idea to keep ourselves quiet until their intentions are shown to be peaceful/cooperative.
Sigs are too short to say anything truly profound so read the above post instead.
Since we still pump large amounts of light into space from street-lighting around the world would that not be easier to detect than a few encoded radio signals?
Even if they detect a digital signal they still have to demodulate it to this obscure 'base-2' encoding we use over here because it works well with our equipment they have either grown out of or never discovered, after that they might decide to visit asciitable dot com to find out what it actually means.
Maybe we can buy out Arecibo and continuously waste a few megawatts at broadcasting a "Hello?! Can you hear me now?" analogue recording
If any alien civilization were capable of communicating or visiting here, I doubt these issues will be a problem?
~don't feel threatened by my pineal~
I was under the impression that historically, our radio and tv signals didn't even make it to Alpha Centauri. Unless we suddenly discover extra-terrestrial life inside of our solar system, does the switch to digital really change anything? Correct me if I am wrong, please.
I don't like Linux. This doesn't make me a troll.
Considering that most aliens are hellbent to destroy Earth (according to a reliable media source in Hollywood), maybe going silent would be a good idea?
Do we WANT to be detected? Oh it would be wonderful if we could communicate with intelligent life somewhere other than earth (I am assuming there is intelligence here). But what if the species we contact are not peaceful? What if they're out looking for worlds to enslave? There certainly would be an advantage in staying quiet and being the first to "discover" a new civilization without giving up our own presence. That way we could study these new beings before deciding whether to risk contact or not.
Likewise, the same logic can be applied to an alien species. Why would they trust us? Why would they carelessly beam their presence out into space, not knowing who was going to listen in? It is certain, given our past history (you know, that part about strong humans usually ending up wiping out weaker ones through conquest), that we ourselves aren't exactly trust-worthy. Maybe they have heard us, and we failed the test, and we will never meet our neighbors. That is one possibility the "Drake Equation" fails to account for. Maybe we will be permanently assigned to the universe's "time out" box, because of our bad behavior - and we'll never know.
Seven puppies were harmed during the making of this post.
Has anyone considered the historical evidence of what happens when superior civilizations encounter lesser ones? The Native Americans, the Mayans, the Incas, the Australian Aborigines, the tribes of South America, the natives of Pacific Islands, to name a few, all cry out to humanity to avoid at all costs encounters of the first, second, and third kinds. We have no reason to expect anything but annihilation from advanced alien races- either they are truculent and violent like we are, or they will destroy us as a service to the rest of the galaxy. We do not wants aliens to find us!
I guess they should have paid their TV bill.
So if the trend of our communications technology is to become less noticeable to space people, and we assume aliens follow a similar course of technological development, does SETI have any hope of finding anything?
I keep asking this question: Why can't we detect ET's transmissions?
DRM'ed, no doubt.
There have been several attempts at sending radio messages into space specifically for communication purposes. Whether we keep that up or not is independent of our use of radio for intraplanentary communications.
Would pretty much suck if it were Vogons.
I keep asking this question: Why can't we detect ET's transmissions?
Now I know. They do digital as well.
Not just that.
They've realized what we will also eventually realize.
They use cat6 cable.
Especially after we started sending all those damn microwaves into space and their wifi stopped responding.
Why are so worried about finding aliens right now? Its like a child trying to throw a paper plane to the top of a mountain. We need better technology and it will be here soon. Best not worry where we're pointing our signals at the moment.
In nature, young defenceless animals which make too much noise and bring attention to themselves often get invited to dinner by predators. Discuss.
The freespace loss from Earth to anywhere outside of the solar system is so incredible that fretting over a couple hundred dB out of literally trillions seems ridiculous, especially with the enormous noise source of the sun practically on top of us (in a galactic sense).
I've always thought the idea that an ET would detect our Radio/TV signals to be romantic at best. This is also why SETI is pretty much pointless.
I read the internet for the articles.
Military over-the-horizon radars put out a lot of power.
If you're an alien dude who wants to score with the alien chicks, you might just impress them by collecting humans. You could embed a human in a chunk of pure carbon-12 diamond, mount that in an iridium ring, and slip it onto her tentacle. She might have thousands of tentacles.
Maybe you collect humans to sell as an aphrodesiac. You puts the heads on top of a snack, kind of like sea urchin eggs on sushi.
Maybe you lay eggs in the humans. Ever see that movie with the pods? The aliens take over human bodies. An infected human passionately embraces an uninfected human, and then the alien penis-thing (an ovipositer maybe?) bursts out of the infected person's forehead and stabs right into the uninfected person's forehead.
Maybe you even mate with the humans. You keep them in your flying saucer and rape them with **all** your tentacles in every oriface. When the alien babies are ready to be born, the humans explode.
I can't beleive i'm the first person to think of/post this, but:
In space, nobody can hear you stream.
I can't believe this came from educated scientists.
Our communications signals are getting weaker, sure, but we still have other sources of clearly artificial radiation that are just as powerful as before. For example, military and weather radar. We regularly send out radar pusles powerful enough to compute the range to other planets in the solar system. Similarly, the Deep Space Network sends out powerful signals on various frequencies using highly directional beams when communicating with space probes.
To think that aliens will be using radio is like Geronimo thinking the people in Europe used smoke signals.
Wish I could tell you what they are using, but as we haven't invented or noticed it yet, your guess is as good as mine.
(For my guess I'll say they're using Quantum Filament Transmission Sequencers. Whatever that is.)
I don't begrudge the idea of searching for alien radio signals, we might luck out and find one and actually recognize it for what it is, but I'm not holding my breath.
(Besides, foreign art film reruns are bad enough, do you really want to see alien ones?)
I've been critical of SETI efforts for this reason. Much SETI effort was focused on looking for "carriers", big constant-frequency RF sources. Broadcast AM, FM, and analog TV (which was AM video, FM audio) have strong carriers, but that was hugely inefficient. About 80% of an analog TV station's power output wasn't conveying any information other than "We're here". As receivers improved, new RF technologies used weaker carriers, then suppressed carriers, and finally, with spread spectrum, dropped the whole concept of carriers. Many modern RF signals appear to be noise unless you understand the encoding. (The same thing happened to modems decades ago; at 300 baud, you heard tones; at 9600 baud and up, it sounded like white noise.)
I once pointed out to a speaker at Stanford promoting some SETI scheme that they couldn't detect any emission that the FCC would now license for a new application. He admitted that was true. For our civilization, there was less than a century of high-powered carriers. That's a narrow window to hit for SETI purposes.
Arguably, though, any sufficiently advanced civilization will monitor all RF passing through their solar system and will be able to detect anything which has a pattern which can be synched up. Although carriers are going away, all signals between distant points need some form of synchronization information. The synch information may be a tiny fraction of the transmitted data, but there has to be something upon which the receiver can lock.
We have large synchronized power grids. They'll get a signal that's 2x the line frequency. As the Earth turns, you get modulation of various sorts: frequency, phase, amplitude.
Amplitude goes down for oceans, and up for land. You get more 100 Hz for the Old World, and more 120 Hz for the New World. As different country-sized areas with the same line frequency pass into view, you get phase change.
It all has a nicely repetitive 24-hour period.
The smart aliens will use full encryption anyways so no way to tell any transmission apart from background radiation noise anyways. Think TrueCrypt plausible deniability ;)
Don't you worry! With technologies advancing and our "social skills" improving, we'll have figured out how to turn our planet into a giant cloud of rapidly expanding burning gas - or something like that - in no time. Everybody in the galaxy will be able to see us ;)
Curses! Yet another victim of the new AT&T's wireless service!
lasers could easily out shine the sun
I keep asking this question: Why can't we detect ET's transmissions?
DRM'ed, no doubt.
Dude, if only that were true! You'd find aliens just by searching the pirate bay!
These posts express my own personal views, not those of my employer
Economically, it might be more expensive keeping the invasion fleet at home - better to have them wander the galaxy picking fights under the aegis of securing inter-galactic democracy - nothing worse than having trained killers hanging out in the 'burbs. Or they might even be space nomads looking for suitable planets to stop off at to eat, get sexy and reproduce before carrying on through space. Or, Earth might be home to a resource that is exceptionally valuable, such as haemoglobin(?!) or raw brains, to their sprawling empire making the journey potentially profitable for inter-galactic venture capitalists. So there are plenty of reasons why we can expect aliens to come calling - in fact is is surprising it hasn't happened already.
People throw massive amounts of RF at the Moon, with high-powered transmitters and highly directional aerials. Using the same highly-directional aerials you can receive the very faint echo of your signal reflected off the Moon. The reason it's faint is that most of it misses, and when it reflects off the convex curve of the Moon most of it diverges into space.
Now, while this used to be used by various government and military comms people, it's mostly done by radio amateurs now, using equipment that wouldn't take over much of the average suburban back garden. If you threw the resources of a large radio telescope at it (like for example CAMRAS) then you could detect very tiny signals indeed.
I just love how everyone on Slashdot thinks that they know what some alien race is thinking, as if they themselves were from some alien race and have the key to their rationale.
What if the race is on a generation ship and just so happens to stumble across us on its interstellar cruise? "Hey, there's a planet with a whole lot of tasty looking critters and a chance for us to resupply" would be my inevitable first guess.
And that's just one of a quadrillion different scenarios we could postulate for an alien encounter. You should put away your absolutes and your thoughts that 'humanity is superior', because we have no evidence to either. We can make plenty of good guesses, but if the Hungry Hippos of Halcyon 9 arrive on the cruise ship Horatio and they have a taste for the flesh of mammals, I hope they eat you first.
"Victory means exit strategy, and it's important for the President to explain to us what the exit strategy is." G.W.Bush
Extraterrestrials are advanced beings who lead by example. In particular, they obey FCC Part 97, which states that one must use "the minimum power necessary to carry out the desired communications." We should follow their lead.
Currently gives the number of civilization with which is possible a contact equal to 2.31.
This assume the parameter L (the expected lifetime of such a civilization for the period that it can communicate across interstellar space) equal to 10000.
If now L has a value of 100 instead, the the number of civilization with which is possible a contact would be 0.0231.
Time to move the funds from SETI to something that has a greater chance of producing results maybe?
I believe there is a general principle here that goes beyond the technology at hand: any sufficiently advanced intelligence is indistinguishable from white noise.
I think it's safe enough to beam out messages that advertise ourselves to any potential ETs that might at best ruin our civilization with contact, at worst invade and steal our resources.
If a advanced civilization develops the ability to colonize space and cross interstellar distances... why exactly would they need anything from a biosphere at the bottom of a gravity well? Presumably they would be well adapted to space, have all they might need in terms of energy and resources, and no doubt would be more than capable of staying hidden from us if they so chose.
Of course they may just come here out of scientific curiosity, which would necessarily mean a non-interference approach to data gathering.
Simple economics, getting into and out of a gravity well is expensive.
I'd sooner believe a Dyson sphere suddenly popping up around our star, or our gas giants being strip mined for useful elements (and the earth being taken out as colateral damage) than I would alien hordes showing up just to say "hi you're not alone" or to steal all our biomass and our beer recipes.
So this brings me to one of Douglas Adams astute observations hidden in his sci-fi comedy. In Hitchiker's we have the parable of the Vogons destroying earth to make way for a hyperspace bypass. Which was really pointing out that advanced spacefaring species might have absolutely no economic interest in our biosphere.
After logging in slashdot still does not take you back to the page you were on. It's been that way for 20 years.
"Stultz, I wonder if there is actually life out there. We've been centuries monitoring the neno-kurflichsk time-fabric disturbance detector that any technologically advanced civilization should be sending out if...if... they sentients do exist. I mean, it is third grade stuff, anybody knows that time-fabric can be disturbed instantly, we keep doing it simultaneously to all the atoms of the universe, and still nothing for CENTURIES. Can you believe it?"
"Professor, I wonder... I have this crazy idea... maybe other other advanced civilizations use... radiowaves?"
"Stultz, you are an idiot or what?"
"I...I am just saying, maybe some less advanced civilizations..."
"Pluuhlease, that is enough! Are you serious? You should go back to elementary school. Have you forgot that radiowaves travel at the speed of light??, it is more than obvious that it is not the most convenient way to communicate with other civilizations... unless you want to wait another lifetime to send your response, and to where should we point the antennas, huh?. Have you forgot that we are talking about ASTRONOMICAL DISTANCES?? It would take centuries! Or even worse, those electromagnetic waves would be absorbed by black holes, bounced, even hit by the breshanistok matter! We would get nothing or everything scrambled, indistinguishable from white noise! Your question is simply retarded. We are trying to contact sentients, not idiots!"
And professor Breshanistok stood up upset and the graduate student Stultz watched the glowing monitoring holoscreen scratching his head.
If aliens ever landed and they tell they have been monitoring our transmissions for years, they'll probably get promptly arrested by the RIAA for not paying the content... :p
> Not too long ago, it was deemed completely impossible
Yes, but this is a much different matter than faster-than-light travel. Ordinary flight wasn't deemed impossible because we had a model of the physical universe where the impossibility of ordinary flight was an axiom. That would have been pretty stupid if physicists had thought that, considering that birds are also heavier than air.
If there were anybody out there *half* as interested in communicating as we are, they'd have found a way to contact us by now.
Cut that out, or I will ship you to Norilsk in a box.
Its about time those oval-eyed, crop-circle forming, et b*st*rds stopped eavesdropping on us. They should pay for their own cable.
Basically what Frank Drake is complaining about is the disappearance of the carrier wave (the large spike of energy at the center of most broadcasts). Most broadcasts are indeed moving to a suppressed carrier, as the carrier carries no information.
That is not, however, true for radar, at least for civilian radar, which typically has a very strong carrier for detection of the returned signal. While planetary radar from Arecibo (1 MegaWatt, 305 meter antenna) is without doubt our strongest signal, in most cases a distant receiver would only be in the beam for order 1000 seconds - a single signal lasting less than an hour is unlikely to be detected light years away.
I think that our most detectable signal right now is the NEXRAD Doppler Weather radar, and similar systems in other countries. These are fairly dense arrays (159 in the US) and scan the horizon continuously with (for NEXRAD) a 750 KW beam from a 8.5 meter dish. While the Arecibo radar would appear roughly 1700 times stronger to any distant alien receiver, for roughly 6 hours twice per day any alien receiver anywhere in the Northern sky would be scanned over more or less continuously by one or more NEXRAD beams as it rose or set across the NEXRAD array. This large duty cycle makes it much more detectable than the planetary radars, which are highly unlikely to illuminate any particular point in the sky, ever. (This beam, being directed, is also a much better signal than TV broadcasts, of comparable power, but uniformly directed to the entire horizon at once.)
So, I think that Frake Drake is worried a little unnecessarily. We are still pumping out a lot of power for aliens to see, if they are there and care to look.
Good. Maybe people will stop wasting their time on SETI and putting their processors to use for something that's actually an immediate and local issue, like Folding@Home.
(The same thing happened to modems decades ago; at 300 baud, you heard tones; at 9600 baud and up, it sounded like white noise.)
BEEEEEEP, CHIRP, CHIRP, KTWANG, shhhhhh, SHHHHHHH!!!
we need to use sub space like the SGU uses to send data over space.
If we knew were to point them, and somebody was watching for exactly the right frequency at wherever we pointed it, for the absolutely microscopic amount of time (again in galactic sense) that we point it there.
I read the internet for the articles.
...in space, no one can hear you scream?
I'd rather we become the ones who find other intelligent life and eat/enslave/probe/hybridize them, rather than the reverse.
In a cosmic nanosecond or two (couple hundred years or less), kids will be learning in history class how the ancients (us) used radio to communicate. We'll be moving on to gravity wave communications pretty soon, and radio will be history, forever. That's why we're not hearing anything. No one in the cosmos is using radio any more.
If I didn't have absolutely NOTHING to do, I wouldn't be here.
I don't think you understand how dB work.
Here is an example - we communicate easily with spacecraft at a distance of 1 Astronomical Unit (AU). The nearest stars are a little less than 300,000 AU away, and so the signal from the same DSN transmitter would be about 10^-11 as weak there as it is a 1 AU. That amounts to 110 dB.
Even at the Andromeda galaxy, this same signal would "only" be down by 224 dB as compared to 1 AU.
So, yes, 100 dB is a big deal. It is comparable to the difference between the planets and the nearest stars, or the nearest stars and other galaxies.
I agree that it's stupid to imagine aliens coming here to take our resources. However, it might still be perfectly rational for them to come and destroy us. If we survive long enough, we might start an era of galactic colonization, where we jump from star system to star system, grinding up whatever material we find into gigantic orbiting space stations.
Any radio-trasmitting civilization has the potential to become a galactic colonizer. So suppose that you belong to a society who also intends to colonize the galaxy and is perhaps a little bit more advanced. Then you notice a potential rival 100 light years away, who just entered their broadcast TV era. You realize that in the far future there might well be a great, catastrophic confrontation, as your wave of colonization bumps into theirs. But there is a cheap way to prevent this calamity: You send a giant sterilization machine or some such thing. Maybe it would drop a small black hole into the sun's gravity well, or maybe it would be a factory to assemble a robotic army from the material in the asteroid belt. In any case, if they could wipe us out before we settle other solar systems, they would save themselves a lot of future grief.
If they're nice, they'll want to study us a bit before they kill us, and they might even keep several thousand of us in some kind of a zoo. However, that would add significantly to the expense of the extermination. At its cheapest, they could just calculate how long we will remain stuck in the solar system - suppose that in our case it will be another thousand years - and then send their mechanical destructive commando to us at a languid 10% the speed of light. That would be the smart thing to do... so expect it to arrive in about 900 years.
In space, no one can hear your stream!
Shiny. Let's be bad guys.
The Predators come to Earth to hunt humans. Just like rich Westerners go to Africa to hunt game. They don't really need it but enjoy it.
__
Men with no respect for life must never be allowed to control the ultimate instruments of death.
GW Bu
Considering how the meeting between two civilizations, one more advanced than the other, has generally gone badly for the majority of human history.
I for one, am confident the space alien's relief agency will take a junket to Earth on a fact-finding mission and decide we Earthlings are living in poverty, our old are dying needlessly and we have wars with each other.
The 1st wave of emergency relief, will arrive in the form of advanced medicines, large quantities of food and clean water, thus destroying the local market for our bio-tech firms, farmers, grocery chains, food manufactures and clean-water engineers. Student will lose incentive to study things like thermodynamics and would rather jack into the Alien mp7 porno players.
The 2nd wave of relief will be to beam power, point to point to each building. thus wiping out the local market for power generation and transmission. (No more nasty CO2! Look at how much help you're being provided!)
The 3rd wave of relief will arrive in the form of galactic peace-keeping security forces with funny, bright-purple helmets of a highly reflective surface ideal for protecting their heads from advanced beam weapons, which, over a pint of Romulan Ale, the aliens will privately share with us makes it feel like they wearing targets for protection. They'll ask us "why don't your mal-contents use proper beam weapons instead of the lead-throwing tubes? Our reflective helmets were designed for beam defence and your kind just ruins these advanced systems."
A 4th wave of relief will come in the form of briefcase carrying, champaign-sipping representatives of the Galactic Bank. They'll tisk-tisk at how dependent we've become on foreign galactic aid, roll their eyes and moan "When will these poor earthlings ever become self-sustaining?"
Earthlings will want to buy the advanced alien mp7 porno players and gizmos upgrades, but will have only paper-backed currency and not the gold-pressed latinum the rest of the civilized universe uses.
As a solution, the Ferengi delegation to the Galactic Poverty Relief Bank will lobby to offer our politicians access to EZ credit...secured by the planet.
Perhaps, if we just held the Planetary Deed...we could generously increase your government's credit line.
Sure, it may sound scary, but it will be okay, because our confident-sounding politicians will promise us "change."
They'll tell us that "they have a plan" and will work tirelessly to "restructure the global economy to be competitive in the galactic economy" and will borrow the money to get it done quickly. There is no time for debate. They'll publicly promise that the borrowed gold-pressed latinum will absolutely be spent wisely. Unlike every other time we've promised that...this time, we really-really mean it!
They'll promise "complete transparency" when making legislative sausage. They'll promise the economy won't be re-structured behind closed door sessions with the Ferengi lobby. All elected officials thinking of funding their next campaign, they just loath lobbyistsand will work tirelessly with them to reduce their influence. Also, if you still like your paper-backed earth currency...in a way, it could be said that you'll be allowed to keep it. After all, the leaders say they can always borrow more gold-pressed latinum to print more paper currency. They'll just quietly hold more frequent bond auctions to raise the cash needed to meet the required down payment to borrow the gold-pressed latinum to spend on the influential and growing slashdot group known as "I for one, welcome our new peaceful and generous Overlords."
I'm not cranky...I'm just drawn out that way.
There has been a surprising number of comments in this discussion about the threat of invasion by an alien species. Since I can't tell if these people are joking, I have to assume they're serious. So let the record show that it's highly unlikely that earth is going to be invaded by aliens. This is for two reasons:
1) Interstellar travel is expensive, probably even for an advanced species.
2) We have nothing they want.
I think it's safe to assume that point (1) is correct. We know very little about how interstellar travel will be conducted, but we do know that the energy cost of moving things between stars is extremely high.
As for point (2), Earth is nothing special. If aliens want to take our minerals, they can acquire anything they can find on Earth in much higher quantities at a much lower cost from asteroids. They will have no logical reason to enslave us either. Any civilisation with interstellar capability is not going to have a huge demand for manual labour. It's also not likely that they will come here to colonise Earth, because we can't assume they will be anything like human. They may look like hundred legged spiders the size of buses who will be crushed in our gravity, or maybe sulfur based sea slugs who won't be able to live in our atmosphere. This brings me to my next point:
Aliens, in all likelihood, will be nothing like us. Meaningful communication* with them may be impossible. This doesn't mean that we shouldn't try, but it does mean that we shouldn't use examples from human history to argue against contact. Just because every time a technologically advanced civilisation has come into contact with a less advanced civilisation has resulted in disaster in the past doesn't mean that contact with aliens will.
On the other hand, there are 'illogical' reasons why aliens might invade. One is religion. It's unlikely that any alien philosophy will be anything like religion as we know it, but they may have a code of conduct of a single philosophy that underpins their actions. This is the sort of thing that we can't predict, but considering the cost of interstellar travel, any civilisation that makes a habit of sending ships to other worlds for the sole purpose of killing aliens isn't going to last very long.
But then again, aliens are alien. Try as we might, we may never be able to fully understand their motives. This is all speculation, we will never know for sure if I'm right until we actually meet some aliens, which is yet another good reason to look for them.
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*by 'meaningful communication', what I mean is an exchange of philosophies or ideas. More fundamental things like exchanging knowledge of chemistry may be more possible. (yet still difficult)
I think it's safe to assume that point (1) is correct. We know very little about how interstellar travel will be conducted, but we do know that the energy cost of moving things between stars is extremely high.
The energy cost of a round trip is zero, unless your spaceship has friction against ether, or something. Besides, even if you use more wasteful ships, an advanced civilization is supposed to be able to afford their use if they make them in the first place.
As for point (2), Earth is nothing special.
You offer many guesses, but miss the one that several posters already mentioned. The aliens may want to simply destroy us as future competitors. They indeed don't need us or our planet or anything in between. They might just want us gone, like you want mice gone from your home. Just a guess, of course, but it has its place among others. And don't forget the hyperspace bypass theory too.
considering the cost of interstellar travel, any civilisation that makes a habit of sending ships to other worlds for the sole purpose of killing aliens isn't going to last very long.
You may be right, and when Earth starts shaking and falling apart under their destructor beams we should be sure that those aliens won't outlive us by much - a few million years, top.
The assumption here is that we'd want to be heard. Can we assume the ETs would as well? And it seems based on a further assumption that any unEarthly culture will be of uniform benign disposition. Could they say the same about us? What is the point of such an assertion in any case? Are we expected to intentionally stunt improvment and energy efficiency of communications just so's we'll be easier to find? Look at the Drake equasion. Fascinating to think about it but purely assumption based, every segment of it. Plug in whatever you want, depending on your own predisposition. Better, for now, to keep a low galactic profile.
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Apart from the one about dinosaurs.
Call this the Over 40's Relationship Theory of First Contact. In this theory, the term "advanced civilisation" refers to one which is over the self-important, self-destructive, self-unaware phase, having achieved relative peace, equity and opportunity for all its citizens.
Would such a civilisation bother responding to radio waves from a world such as ours? I imagine their response would be: sure, you can go all night, but the conversation sucks. No, I imagine they'd bookmark us for later, and keep on looking.
For one thing is certain - if there's more than one intelligent species out there, there will be many more. So what's so special about us, in this point in our history, if any species out there is advanced enough to directly contact us?