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Space Science

Optical SETI 116

Posted by Hemos from the look-into-the-light dept.
R3 writes "BBC News is running this story, about SETI's renewed efforts to find ETs who might be flashing us with light, instead of radio-waves:"
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Optical SETI More

Optical SETI

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  • You are so full of it. (Score:1)

    by Anonymous Coward
    And then you get modded up?
    Kind of telling, considering the moderators around here are barely literate.
  • Sure, they are the same if you aren't concerned about things like how much energy is required to create them, how they interact with matter, and how one might build a (presumably matter-based) transmitter/reciever.
  • laser beams are the most common ones

    Which is, in reality, pretty stupid.

    In space all you'd have to do is to punch a hole in the hull of the enemy vessel. The most effective way to do that is to shoot something hard and fast against it. A gatling gun would be much more devastating weapon than a silly laser beam.

  • Drug mysticism (Score:1)

    by Anonymous Coward
    And of course the most simple explanation is that these "contacts" are nothing more than drug induced imagery created by the brain.

    You people seem to believe that because the imagery is similar from one person to another, it must mean something. Well, you're partially right. It means that human brain works in the same way in everyone. In other words, if Jack and Jill take the same amount of the same hallucinogenic drug, they're bound to have similar dream imagery. Alcoholics who are having delirium tremensis are known to hallucinate about snakes, insects and small, grey people. According to your logic, these should be real because so many people share the same hallucination. Bollocks.

    As far as "expanding the mind" goes, you're only expanding the empty space in your head.

  • hah (Score:3)

    by Anonymous Coward on Tuesday July 24, 2001 @11:42PM (#62928)
    Flash lights from nearest planet millions of lightyears away (boy their arms must get tired). A few million years later, humans discover the light. Too late, aliens died.
  • > First of all, that laser beam would only sweep
    > a circle, not a sphere.

    True enough. And even multiple lasers all up the mountain at different angles wouldn't help us here (imagine they're aimed 1 degree of arc apart, there'd be huge gaps between them at the range you're talking about).

    > How long would Earth stay in such a beam?

    Yeah, I missed that :) I read the article which says they're looking for 'very brief flashes of laser light' and assumed that this 'beaconing' was the reason. In retrospect, I imagine they're using a laser that provides a very short, very high intensity beam. Compare a flash gun with a lamp bulb for instace...

    Of course, if they manage to modulate their sun's output, we'd see that... And this is being considered by some SETI enthusiasts, just as Dyson Spheres are. If you alternately dim & brighten the sun's output in a clearly non-natural way, that's a good sign of intelligence. Just don't ask me how to do it - ask your local science fiction author!

    Mark

    Keeper of the Wedding Shenanigans Home Page

  • Re:optical detection sounds hard (Score:5)

    by Mark Hood ( 1630 ) on Wednesday July 25, 2001 @01:16AM (#62930) Homepage
    > wouldn't we have to depend on the fact that
    > the other civilization know that we are right
    > here, and that we are able to pick up their
    > signals?

    Yes, that's true if we assume they're trying to contact US specifically. If they've just got a huge laser on the top of their local Everest-sized mountain & are relying on their planet's rotation to turn it into a beacon we have a better chance of spotting it.

    If we try to pick up radio we can (in theory) spot their TV signals, satellite communications & Star Wars ABM radars :)

    > No matter what kind of transmission ET is using
    > he will have to hope that we are able to pick
    > up the signals

    Of course - and that's why the Seti League (http://www.setileague.org/) advocate lots of smaller dishes. Their argument is that while an Arecibo size dish can look further, this comes at the cost of seeing a smaller area of the sky. Their favourite statistic is 'even if we're looking on the right frequency at the right time, there's a 99.999% chance that when the call comes in, we'll be looking the wrong way'.

    Of course, they're talking about radio waves, but the same argument holds for optical SETI.

    Mark
    Keeper of the Wedding Shenanigans Home Page
  • I vaguely recall that an experiment to bounce laser light off the surface of the Moon determined that the light's "footprint" had spread out to several km over the distance between the Moon and Earth. Your mileage may not vary.
  • Lasers are just a concentrated light beam, and aren't immune from the effects of the inverse square law - so as the distance was doubled, the area that the laser would hit would be squared and thus the intensity would be greatly reduced.

    Go you big red fire engine!
  • Surely there hasn't been enough time for them to have read rthille's comment [slashdot.org] in the recent "Ask Slashdot" wireless serial adapters article, much less for the resulting signals to have made it back to us already.
    --
  • Yes, light does obey the Inverse Square Law. A laser does not because the light has been manipulated to make the photons travel parallel to each other, thus it does not "spread its influence equally in all directions".

    Your laser beam diffracts as it passes through any finite-sized aperture (the laser mirrors count as apertures for this). This causes the resulting beam to diverge (think back to the single-slit diffraction experiment in high school physics class).

    A diverging beam can be thought of as a cone. The area of a cone's cross-section goes up as the square of the distance from the origin, so the intensity of the laser light will indeed go down as the inverse square. In a real laser beam, the distribution vs. angle is gaussian instead of uniform, but the same principle applies.

    Using a wider beam would result in a narrower cone, but your aperture would have to be at least 10 km wide to have a spot size as small as a planet at a distance of 10 light-years. So, any practical laser would spread out like a cone that covers a lot more area than the target.

  • Re:How do ET aim at a moving target? (Score:3)

    by Christopher Thomas ( 11717 ) on Wednesday July 25, 2001 @07:07AM (#62935)
    What do you think? Are we (Terrans) currently able to target a laser beam on a planet 1, 10, 100 light years away?

    Short answer: Yes, but it would be expensive.

    Long answer:

    Stars and planets have (relatively) easily-plotted courses. Spend a few months with a big telescope, and you can do any fine-tuning you need to in your model of the planet or parent star's trajectory. Put a big beam splitter in front of the telescope, fire a huge, very expensive laser at the beam splitter, and you can send the laser beam to the target system while using the telescope to make sure it's going in the right direction.

    Target _system_?

    Well, the problem is that your laser's aperture is small enough that diffraction prevents you from focusing it on something as small as a planet over interstellar distances. So you'll probably end up bathing most of the inner system of the destination star in weak laser light. Your laser has to be quite bright to be picked up (even if you pulse it), which means very, very expensive.

    Alternatively, you can build an array of many lasers in space, and pull evil tricks to keep them all in phase with each other. This gives you a very large synthetic aperture, which would let you target the laser at a single planet. Of course, you'd need a synthetic aperture optical telescope of comparable size to _track_ the planet, but if you can build the laser, the telescope is within reach also.

    This is "stupidly expensive", as opposed to merely "insanely expensive", but it could be done. We'd have to do something similar if we wanted to easily launch sailcraft over interstellar distances.
  • What people fail to acknowledge here is the time scale that another civilization may be at when trying to signal us. They may very well have the capability to resolve Earth from a distance of light years by building an extremely large telescope.

    I see the lack of communication passing through our galaxy as evidence that we simply haven't figured out THE practical medium for communication. Maybe laser pulses for a billionth of a second are exactly how civilizations are communicating. The chances of there not being intelligent life elsewhere in the galaxy are just too small. If we determine this, then I'm going back to church.
  • The nearest planet is not millions of lightyears away, its millions of miles away. *BIG* difference. We don't have the ability to detect something on that scale at a distance of millions of light years.

  • And, we'd also like to build a bypass.

  • well we do not risk much because US government will probably prosecute & jail Aliens because they reverse engineered the DTV Codec, or anyone has licensed it to them ?
  • so how could we use lasers to measure distance to moon ? the distance was twice the atmosphere height. If we could use a laser to do that, aliens will probably be able to do better. Sorry, you'll get fried ;-)
  • in a David Brin book (excellent writer), stars cans be made to explode into supernova. Then you have not a omni-directional light stream. Your signal can be detected from any point around the supernova & traces last for some time. So, why not study data signal from supernova ?

    Ok, we do not know how to make a supernova send informative data, but we don't know either how to transform good old Sun into a supernova ;-)
  • There are also interesting testimonies from Near Death Experience victims. It is far cheaper than psychedelics and it may prove to have better results since the experience (and "contact") become permanent...

    Well, please try none of these experiments and concentrate on praticing relationships with your beloved :-)
  • A laser sends out a cone of light, not a straight line. At the distances at which you normally use that laser pointer of yours, you don't notice this, but if you were sending a message to a different solar system you'd take this into account. (Either that or you'd have some explaining to do when your grant comes up for review.)

    You'd also take into account the fact that your planet moves, if indeed it does in your frame of reference. There is no such thing as being stationary in space (i.e. there exists no absolute velocity, Mr. Michelson), and in any case an advanced alien civilization or a high school student would be smart enough to calculate the direction of a laser beam as a function of relative locations. Given reasonably precise astronomical tools (beyond what we have currently built AFAIK but IANAA) it shouldn't be hard to figure out from a reasonably distant solar system that the third planet around our star revolves through a certain orbit, and that our star is moving through the galaxy with a certain velocity relative to the alien body. Yes, that body might indeed rotate, but if the transmitter were actually on the surface it would be simple enough not to broadcast when the target body is beyond the horizon... or use multiple transmitters, or just launch the transmitter into orbit. If the aliens really were so dumb as to not figure that out, would we really want to communicate with them? They'd probably be OS zealots anyway, or maybe just wanting to sue Adobe for using their patented ROT13 encryption.

    Now suppose that within, say, 30 ly of Earth has picked up on our radio transmissions and has used some simple triangulation to figure out that our planet is the source of these transmissions. If they wanted to make contact with us, they could send us a message encoded in a laser beam. Yes, they might have to do some simple math, but I think they could do it. And that beam, if it exists, could be visible today.

    --
  • Sucks you got modded down for that comment; you actually have a good point. But then considering the other electromagnetic spectra they're listening for can't travel any faster than the speed of light either, it's sort of the same difference.

    I don't think the point is whether the aliens are still there, but whether they were there at all. The other idea is that the signal may not have to have travelled all the way from another system, but may be broadcast locally by travellers.
  • According to the mathematics, yes, "infinitely wide" is needed -- and size 0 is undefined.

    In practice, a laser is formed by the photons which happen to bounce back and forth between two mirrors (a miniscule percent leaks through the beam mirror to create the usable beam). In most designs, photons going in other directions may contribute to the energy level but will not themselves emerge in the beam.

    The geometry for a photon-as-a-particle requires the largest divergence angle to be from a photon which begins travel toward one edge of a mirror, and bounces between the mirrors umpteen times before escaping at the opposite edge of the mirror. Basically, draw a line from one side of one mirror to the opposing side of the other mirror, and that's the maximum for a photon with one pass at both mirrors. Most photons have to bounce back and forth a huge number of times, so the angle has to be much smaller in order for the photon to bounce back and forth "enough" times. Photons at too large an angle hit the wall and never come out as the beam.

    Photon-as-a-wave doesn't use the same line-drawing geometry, but the above shows why the beam is narrow and the photons are nearly parallel. There are other effects due to the lasing medium and optics outside the lasing chamber.

  • Inverse Square Law (Score:3)

    by SEWilco ( 27983 ) on Wednesday July 25, 2001 @02:06AM (#62946) Journal
    Yes, light does obey the Inverse Square Law. A laser does not because the light has been manipulated to make the photons travel parallel to each other, thus it does not "spread its influence equally in all directions". A laser is following the geometry applicable to parallel lines (depending upon accuracy of construction), not a sphere.

  • Am I the only one to think that a full range radio wave analysis includes light waves ? Just because the Human kind uses them for different purposes doesn't imply a split between the two.

  • Using patters of light to indicate intelligence? (Score:3)

    by AtariDatacenter ( 31657 ) on Wednesday July 25, 2001 @04:17AM (#62948)
    Wow. It's been in front of us all along, and we haven't seen it. They ARE communicating with us via regular flashes of light. And it takes a very advanced level of technology to create.

    They're called pulsars. ;)


  • SETI with an emphasis on CETI (where the emphasis is on the expectation of 'communication' transmissions) is based on assumptions, fundamentally flawed IMO, that advanced civilizations will not evolve to the limits imposed by physical laws. If they do, then solar systems should contain in excess of 10^50 bits. You cannot communicate even a small fraction of 10^50 bits across interstellar distances (several l.y.) in the age of the universe even if you use all the bandwidth from radio to UV-radiation.

    Advanced technological civilizations do not communicate across interstellar distances because you can never get off the first page of Encyclopedia Galactica. This discussed more in my paper from the OSETI III conference, Life at the limits of physical laws [aeiveos.com] which is part of the Matrioshka Brains [aeiveos.com] papers.

    We can conduct "SETI" (where the emphasis is searching for 'signs' of advanced technological civilizations) but it requires gravitational microlensing studies, infrared and occultation astronomy -- not listening for radio or optical transmissions.

  • ah, wonderful, i never understood was the meaning of carriage return was before this post either..


  • The scope of vision for most people when contemplating alien life is woefully narrow. Would our ancestors succeed in contacting alien life through smoke signals and drums? (maybe)

    Nothing contradicts the possibility that hyper-advanced beings could manipulate the universe at will, perhaps even modify or conjoin with the fabric of the universe. Our bodys and minds are made up of this fabric, so is it really so far fetched to look within our selves to contact other beings?

    In fact, some people believe they have already contacted [erowid.org] alien beings through the use of the hallucinogen tryptomanes, like DMT and Psilocybin (mushrooms). A large percentage of DMT "travellers" all experience the same contact with elf-like beings that can control the nature of reality. Some also believe that they have contacted [erowid.org] insect like beings through the use of psychedelic mushrooms.

    Psychedelic research has a number of distinct advantages over SETI, though I am not saying that the SETI work should stop. First, it's cheap. Psychedelics are available to most people, if they try to find them. Also, hallucinogens get results, and they are testable, if you have the mental stability to handle the large doses required. If you don't believe it, you can try it. And, they also have the capability to expand your mind in ways unimaginable.

    LS
  • Ok Mr. AC, what unshakeable foundation, what absolute truth do you posess that informs you that your perceptions of reality aren't complete hallucinations? Inductive reasoning? A gut feeling? I don't know if you've tried to alter and test your mind, but I have a feeling that you haven't. Go ahead and live within your Windows box of a mind. I've personally had experience on hallucinogens that were more real that my day to day experiences. But I guess you'll just have to experience that for yourself.

    LS
  • I'm scratching my chin at the profundity of your statement.

    You're looking at the syntax of my words, and not the meaning. Perhaps I should have said "aware" instead of real. But doesn't the beginning of my statement, that no one has an unshakeable foundation of truth, mean essentially what you are saying?

    I post in all seriousness about a touchy subject, and get modded down as flamebait and only ACs respond. Fuck, I hate anonymous cowards...
  • Just be sure you detect it from multiple points at once.
    problem with that is, if the source is many light-years away, if you get those multiple readings from points that are relatively close together, you'll be seeing it at the same point. so even if we could see this light from Earth AND from a sensor on Mars or even a probe on the edge of our solar system, we wouldn't be able to triangulate anything more about the position. sure we'd have the direction, but no measure of distance unless it could be observed over a length of time. guess you'll have to find some other use for those missiles.

  • Great! (Score:2)

    by vrt3 ( 62368 )
    Now the only thing left to do is tell the aliens to stop sending radio waves and start pointing their powerful lasers at Earth.

    Shouldn't we better start to emit that kind of laser beams ourselves? In case another civilization has a similar kind of SETI project running?

    I mean, what are the chances of aliens sending exactly the kind of radiation we are detecting? How can we be sure they are sending any radiation at all?

  • The way this would work is that the sender would flash his laser at any reasonably nearby star. There aren't *that* many close by. Then, just make sure diffraction spreads the beam to a width of a few AU. It's not so unlikely a hit. Plus, he'll flash us a few times just for good measure, maybe over a period of years.

  • Re:hah (Score:3)

    by BlueUnderwear ( 73957 ) on Wednesday July 25, 2001 @12:24AM (#62957)
    > Actually, we won't be sending out noise for that much longer. Digital radio/communication with encryption and compression should be completely entrpic (random). In other words, no distinct signal coming from us unless they know the DTV CoDec. And we're not even that noisy a radiation source.

    So we better stop those SETI type projects. Or else an alien ship might destroy the earth to punish us for violating their equivalent of the DMCA...

  • It's some of each, or realy neither... the duality of light. First we thought one thing, then disproved that and went with another, then Planck and Einstein had fun poking at the photoelectric effect and Einstein settled on photons. (Millikan's experiments helped Einstein win the Nobel prize, and Millikan got one of his own later)

    So what's the answer? Is light a wave, or is light a flow of particles? Well, the bottom line is that it's neither one. Light is are you ready? a "quantum vector field." That phrase doesn't give you much of a mental picture, does it? I actually kind of know what a quantum vector field is, and it doesn't give me any mental picture. The fact is that the true nature of light defies mental picturing, because it's not quite like anything we can lay our hands on. Under certain conditions, such as when we shine it through narrow slits and look at the result, it behaves as only a wave can. Under other conditions, such as when we shine it on a metal and examine the spray of electrons that comes off, light behaves as only particles can. This multiple personality of light is referred to as "wave-particle duality." Light behaves as a wave, or as particles, depending on what we do with it, and what we try to observe. And it's wave-particle duality that lies at the heart of the Heisenberg uncertainty principle.

  • Gravity waves expand in all directions and don't dissipate in something as silly as an atmosphere or something. They can go on FOREVER! Wouldn't a really intelligent species be communicating with gravity?

    OK, it's maybe a cheap plug for the LIGO project [caltech.edu], but can you blame me?

    No, really, though, we should be looking at a multitude of sources for contact with intelligent life. Besides, according to Neuromancer, we've already picked up a bunch of signals from the 70s.

  • Laser light travels in a precise, straight line; it's not like a flashlight that beams an ambient cone of light..

    Actually, lasers aren't all that straight. They get pretty "flashlightish" at long range.

  • Incidentally, the Ford Prefect is no more - we now also have the Ford Escort (though I think it's a bit different to the US model [no, not just with the steering wheel on the other side]). Oddly, Escort is also the name of a pr0n mag over here. Not really worthy of note, except we also have the Ford Fiesta, which is also the name of a pr0n mag. Weird, huh?
  • If only the Independence Day aliens had though of shooting us with a laser from outer space - then Will Smith would never have whipped their butts.
  • Didn't Ford do something like this? IIRC he beamed a "pencil-thin" signal from the speaking clock that he'd picked up off the sub-etha net back to Earth as a practical joke.

    Don't have my copy of The Guide to hand though, so I can't verify this I'm afraid - anyone else know?

  • Wow. You said it much more clearly than I did. And to think; all this technical discussion came from a rubbish joke I made....

  • Don't think so (Score:3)

    by Dr_Cheeks ( 110261 ) on Wednesday July 25, 2001 @12:59AM (#62965) Homepage Journal
    Um, really. I know the beam spreads out a bit, but is it according to the inverse square law?

    For example - take a laser pointer. Hold it about 30 cm (approx 1 foot) away from a surface and make a rough guess what sort of area the beam is covering. Let's say a circle with a 1mm radius to make things simple. Now stand 3m (about 10 feet) away. You're now 10 times as far away, and 10^2 is 100. Is the beam now hitting an area 100 times in size? Following the inverse square law, the area that the beam hits should go from about 3.1 square millimetres to 301 square millimetres (or 10mm radius). If it is then your laser pointer is broken.

    I'm afraid I can't remember the physics of why lasers work this way, but they do.

  • >If they've just got a huge laser on the top of their local Everest-sized mountain & are relying on their planet's rotation to turn it into a beacon we have a better chance of spotting it.

    Erm, no. First of all, that laser beam would only sweep a circle, not a sphere. So unless we just happened to be exactly on the plane of their planet's rotation, we'd miss it. Secondly, even if we did happen to be lined up perfectly, we'd never notice it since the beam's path (not the photons) would sweep past Earth at a velocity far exceeding the speed of light. Consider that if they are 100 light years from us, then their laser would be painting a circle that is 2*Pi*100ly in circumference every one of their days. Assuming their day is the same as hours (24 hours), that would mean that at our distance their beam would be sweeping 70,000,000,000km a second. How long would Earth stay in such a beam? Not long enough for your detector to see more than a single photon. And that's assuming we just happen to be lined up.

    No, the only way that laser communication would work is if it is directed straight at us.
    --

  • Re:Accuracy (Score:3)

    by FTL ( 112112 ) <slashdotNO@SPAMneil.fraser.name> on Wednesday July 25, 2001 @03:01AM (#62967) Homepage
    [...] stars cans be made to explode into supernova. [...] Your signal can be detected from any point around the supernova & traces last for some time.

    Blowing up a star to say "Hello there!" (or "First post!", or "All your base...") seems like a rather expensive way to communicate. Plus you then have to travel to another star to send your next message.

    Green Peace would have a cow if we started blowing up neighbouring stars for fun.
    --

  • Ordinary Citizens + Small Arms + time = Terrorists?

    regardless of how one feels about private gun ownership, I think we can all agree that this proposed bit of logic is seriously flawed, and reeks of hyperbole. I am reluctantly willing to agree that some european nations which ban small arms have managed to avoid sinking into despotism. Ordinary Gov't + Ban Small Arms+ time= Despotism : the corresponding argument of the 'gun nuts'. Neither argument is really true. You have to remember, the NRA is not really a secret society of evil child killers. That's just your propaganda. When you start to believe your own propaganda, that's really sad.
    Not that this is anything but flamebait.

  • I was under the impression radio waves WERE light? Ahh well, I'm not sure it would make sense for an alien race to see things in the same visual spectrum as humans. There's no logical reason why they might not see radio waves, or infrared, ultraviolet or any other segment of the light spectrum. So it seems a bit silly to set up optical equipment with a "human bias" on what qualifies as "optical".

  • Re:What known source in space gives off laser beam (Score:3)

    by ozbird ( 127571 ) on Wednesday July 25, 2001 @02:03AM (#62970)
    Lasers ain't natural. If you find lasers, you find life.

    Not so - there are natural lasers; all you need are the right conditions.
    Examples from space: ultraviolet lasers [stsci.edu], Microwave lasers (masers) [achilles.net] and near infrared lasers [achilles.net].
  • ...then how come we are not shining laser light into space with our own encoded messages?
  • If they really wanted to get our attention they'd be sending us gas coupons, or something like that, since we are a collective bunch of morons who figure freedom comes from sitting alone in our planet-destroying vehicles and they'd most likely figure that any civilization who hadn't figured out how incredibly stupid fossil fuels are in this context all deserve to die anyway.

    Boy, that paragraph took a turn. I wonder were that came from? I guess I'll have to think about it when I ride my bike to work.

    Thimk!

  • Mmmm....lets see our planet is 5 billion plus years old, millions of species have evolved, only one arose out of all that time to become sentient enough to be curious about the universe to engage in technology endeavors. 5 Billion years? Millions of species? Obviously this intelligence thing is a complete FLUKE, a one in a 5 billion years stab in the dark. Doesn't anyone find that odd? The chances of intelligence happening on another planet seems extremely remote too me given this evidence (or lack there of aka SETI.).

    Your evidence to one or other direction is rather minimal; we have so far managed to detect just the first few tens of exoplanets that happen to be relatively near us and have very little knowledge about them; in practice, we know only our own solar system in any meaningful detail at all. That is not sufficient to analyze the situation galaxy-wide or even within the closest 100 lightyears IMO.

    However, in the next few decades the situation might be changing with the planned projects that could actually be able to give us glimpses of the other worlds.

  • Of course - and that's why the Seti League (http://www.setileague.org/) advocate lots of smaller dishes. Their argument is that while an Arecibo size dish can look further, this comes at the cost of seeing a smaller area of the sky. Their favourite statistic is 'even if we're looking on the right frequency at the right time, there's a 99.999% chance that when the call comes in, we'll be looking the wrong way'.
    Unless you're using a antenna like this. [osu.edu]

    Of course, the data requirements are high...

    When completed, Argus's 64 antennas will generate 2.56 gigabytes of data -- the equivalent of 4 CD-ROMs -- per second, and there's no economical physical connection that can carry that much data for any great distance, Ellingson said. So the engineers will process all the data just as it emerges from Argus, and throw away all but the most important signals. Ellingson's team of graduate students is building a mini-supercomputer out of PCs to process the data.
    The "mini-supercomputer" mentioned above is, of course, a Beowulf cluster.

    Milalwi

  • It's not that hard. Even a laser beam spreads out over distance. If we wanted to beam a message to a planet circling a star 22 light-years distant, we would design the laser so that the divergence covers the habitable zone around the star (~ 4 AU's). Then we just lead it enough to account for stellar drift, and fire our laser. The calculations required aren't all that difficult -- we know the stellar drift for most of the nearby stars, and can make a pretty good estimate of how big the habitable sphere of a given star will be. Actually, building a laser that ONLY diverges 4 AU's over 22 light-years is probably beyond our capabilities. Having more divergance makes it easier to hit our target, but it also means that we have to put out a lot more energy to maintain the same intensity at the far end.
  • Think of the answers the detection would give....

    Every UFO nut will say "Told you so", and abductions will become the new fashion.
  • We might have to use all avaible energy know to mankind. But who cares, as long as we send a really cool massage. Like "Drink more Coke" or "This place for rent".
  • who might be flashing us with light, instead of radio-waves:

    They're flashing us?? Hooray! Free alien pr0n!

    *Grabs camera and dashes outside to take pictures of the sky*
  • Ford first incapacitated the Sirius Cybernetics Corporation salesman who was too stingy to let him make a long-distance phone call to Earth, then he called up the time recording on Earth. Then he re-broadcast the time signal over POLS (plain old light speed) service back to Earth, the idea being that the long-distance and time service charges would continue to rack up until the ship was found. The pencil-thin POLS signal was the only radiation coming out of the ship, so it would be some time before the ship was found.

    Moral of the story: always let people named after Ford Escorts (called a Ford Prefect in England) use your phone.
  • I have no idea. I read somewhere, though, that Adams was quite disappointed in America for not getting this riotous joke. Apparently the Ford Prefect enjoyed monumental success for a time.
  • Absolutely preposterous.

    Using Lasers to send messages. How dorky.

    Let me get this straight, a billion dollars later, a couple decades worth of enourmous computing power, and ZIPPO, no radio signals.

    Now we are doing lasers?

    Mmmm....lets see our planet is 5 billion plus years old, millions of species have evolved, only one arose out of all that time to become sentient enough to be curious about the universe to engage in technology endeavors.

    5 Billion years? Millions of species? Obviously this intelligence thing is a complete FLUKE, a one in a 5 billion years stab in the dark.

    Doesn't anyone find that odd?

    In any case, most scientists believe there has to be many intelligent beings out there, yet they completely ignore the fact that we are IT on our own world and it NEVER happened previously!!

    The one and only Darwinian trait, intelligence/technology arose in one and only one species in 5 BILLION years time, half the age of the know Universe!

    There have been millions of species before us, that lived a lot longer and from all accounts of the fossil record and were a LOT more successful than homo sapiens. They didn't need intelligence either!

    I think intelligence is so rare, that I am inclined to believe some of these spacemen stories that say we were visited and were modified in some way from domestic species. That seems much more likely given the fossil record.

    The chances of intelligence happening on another planet seems extremely remote too me given this evidence (or lack there of aka SETI.).

    Even if I do buy into the fact there is some intelligent civilization out there, they will have an understanding of physics, space and time that we as labratory rats can't possibly comprehend.

    They most certainly won't be using Lasers or electromagnetic energy to communicate.

    What is so dorky about the logic in this is that SETI admits that traveling to distant stars even at the speed of light would be impractical.

    So what do they base there search on? The very impracticality of what they say can't be done!

    Electromagnetic Radiation.

    How STUPID.

    hack

  • Re:hah (Score:3)

    by bentini ( 161979 ) on Wednesday July 25, 2001 @12:12AM (#62982)
    Actually, we won't be sending out noise for that much longer. Digital radio/communication with encryption and compression should be completely entrpic (random). In other words, no distinct signal coming from us unless they know the DTV CoDec. And we're not even that noisy a radiation source.
  • Mote in God's eye [scifi.com] by Larry Niven and Jerry Pournelle features an alien race that manage to send a beam of light to a nearby colonized planet.

    Though they were not stupid enough to send a laser beam in small angle spotting just one measly starsystem just to contact someone else. (even though the manage to feed the laser for years!)
    If you want to contact someone you'd better look for radio signals, anyone that can manipulate stars as a semaphore will probably decide for themselves whether they will come here or not. Btw, the aliens in the book used the laser to propel a large solar-sail vessel.
  • As if non-directional radio signals would ever reach the stars above the noise treshold. In fact the most likely item we could find is a directed radar or similar.

    Kjella

  • ...but wouldn't we have to depend on the fact that the other civilization know that we are right here, and that we are able to pick up their signals?

    Or at least hope they take the time and effort to flash every star system within, say, a 50 light-year radius. But this strikes me as a specific example of a more general problem: our SETI efforts are directed towards detection rather than transmission; we seem to be doing a lot more listening than talking. If the aliens take the same attitude, then it's obvious no-one will ever contact anyone else.

    Of course, a lot more effort is necessary for detection than for transmission, but AFAIK there aren't any transmissions going out specifically related to contact (our own EM noise probably doesn't count, simply because it doesn't have the oomph to travel interstellar distances). Are there any major efforts underway to ensure continuous transmission of "Hi there!" messages from good ol' Mother Terra?

  • lol we could call it the b.u.n.s (blowing up neighbouring stars) protocol.


    If the only tool you have is a hammer, you tend to see every problem as a nail.
  • Actually, we won't be sending out noise for that much longer. Digital radio/communication with encryption and compression should be completely entrpic (random). In other words, no distinct signal coming from us unless they know the DTV CoDec. And we're not even that noisy a radiation source.

    Your first point illustrates nicely the difference between COMINT and ELINT. They don't have to be able to understand us to see that there is a message. If there is "noise" on a narrow waveband, it will be interesting in its own right. If there is noise on a whole group of narrow wavebands, that is very interesting.

    Of greater concern is that all our comms will go over fibre and leave none to leak out into space.

    Paul

  • Just makes you think, though... What if they're using 1000 bit encryption on a scrambled frequency that changes every few nanoseconds... How would we ever detect them?

  • SETI is against intergalactic law (Score:3)

    by Junior J. Junior III ( 192702 ) on Wednesday July 25, 2001 @02:48AM (#62989) Homepage

    Earthlings:

    This is the Intergalactic Police. Intercepting and attempted decoding of encoded signals is a violation of the Digital Milky Way Copyright Act (DMCA). This is a Class II Felony according in your sector according to Intergalactic Planetary Law.

    We have your planet surrouned. You will agree to hand over all conspirators and contributors in this crime to our awaiting vessel.

    We consider a conspirator or contributor to be:

    • Any scientists involved in the study of Astronomy, Cosmology, or Astrophysics.
    • Anyone using or distributing the Circumvention Device known as SETI-At-Home
    • Anyone involved in the industry which manufactures the devices which enable the SETI-At-Home program to run and function. This would include computer manufacturers, retailers, end-users, and research and design engineers.

    If you do not respond and comply to this writ within 48 hours, your planet will be subject to immediate seizure for processing into raw materials according to Andromedean Law (ref. Victims of Crime Restitution Act, Article III, Section 2, Paragraph 500.23.

    You have no chance to live. Make your time.

  • Laser. Light Amplification by Stimulated Emission of Radiation. Lasers ain't natural. If you find lasers, you find life.
  • Okay, so I got modded down for asking an honest question about the IBM CRT's and if they easily break. Sheeesh...! Well... here's another honest question that I think is very valid for this topic...

    Like the subject says, what known source in space gives off laser beams? SETI searching for signals in RF and light is fairly well-known, and subsequently, those sources are well-documented. But... I honestly have never heard of anything in space giving off laser beams. I was hoping the article would at least mention an example, but it did not.

    Anyone care to enlighten us/me?
  • How would you propose that we triangulate the source using only one signal? And on that matter, why would you have to triangulate at all, given that it's a single coherent beam of light. Why not just look along it.

    And then, since light takes considerable time to travel from AlienWorld, and that planets, systems etc. are all moving, the place that the laser was sent from is almost certainly not where the planet is now, and it's tough to accurately predict the current location of a planet when you can't be sure how far away it actually is.

    No, I think that the Intergalactic Destructo Missiles(tm) would probably head off into space and hit some poor sap who was just looking for radio waves. And then wouldn't your face be red!

  • But you can't detect a laser beam in multiple points at once - it's not like it radiates outwards from a central source like radio. A laser beam is just that - a beam. It only goes in one direction, and by definition can only be picked up in one place.

    You're also assuming that Lord High Master Gjo'rgW hasn't forseen your attack, and implemented the Son of GalacticWars program.

  • Either way, it'll be coming in straight to the Earth somewhere (apart from the short time when it's in the atmosphere at a tangent). As soon as the earth moves into the beam it'll be clear which direction it comes from.

    But my point was that it's only going to one place, since it's essentially a line from 'them' to 'us'.

  • But you make the point yourself that you don't know how wide the emittor itself it. You also don't know how scattered the beam is going to become, since photons won't deviate without reason (hitting atoms of hydrogen or some such in space) and the effects will be, if not totally random, then at least close enough that you can't predict it.

    So if the emittor was a foot wide, and your assumption came from the idea that it was a meter (for all the nasa fans out there), any distance estimate is going to be lightyears off.

    And I'm not sure that what you're talking about is triangulation, either. Triangulation is measuring the signal strength from a transmitter at three points, and calculating from that the grid coordinates. The signal strength is a measure of the distance. What you're trying to do is calculate the distance to the source from several points, and I'm not convinced that this method could work. Maybe something to do with redshift...

    Either way, I agree that it's rather pointless (although the idea of our sublight missiles hitting this poor planet a thousand years after we've become allies is rather amusing). Still, I'd have to think that firing a laser of high enough power to get that far at a planet could be considered a bit rude ("We come in peace, sorry about vapourising your lab").

  • So in summary (Score:3)

    by L41N14L ( 205602 ) on Tuesday July 24, 2001 @11:46PM (#62996)
    They're looking for aliens firing lasers at Earth. I can see how that'd be useful.
  • Actually, you would have a better chance claiming that they are in violation of an Intergalactic FCC. I'll bet that not a single soul at SETI has their Intergalactic 128 digit call sign! That being said, I'll bet that Sending short waves over to the edges of the Milky Way would make for one helluva moon (to moon to moon) bounce! Perhaps they have local repeater stations sitting on various planets. I'll bet that we are listening to the wrong frequencies!
  • I always wondered - besides the nice screensaver - why people should search for alien signals. As long as we do not find wormholes, I don't think we can gain a lot by knowing that at just 1000 parsecs there is somebody (er... let's say someBEING). Neither think I that it is possible to get from the beginning the broadcast of the hit "how could you build a FTL spaceship". I prefer to waste my CPU searching for Mersenne numbers: at least everyone knows that's useless. ciao, .mau.
  • Isn't the goal of the SETI project to search for extraterrastrial intellicence? Whether the aliens are dead or not is really irrelevant to the aim of the project.

  • They're looking for aliens firing lasers at ANYTHING. Most likely earth was in the way. Once you find the laser light, triangulate the source of the transmission, and send our Interglactic Destructo Missles(tm) to blow them up. Look, the bottom line is that coherent light sources(aka lasers) are as unnatural as sequenced radio waves, and a dead giveaway of intelligent alien life.
  • Lasers are subject to distortion just like any other light source. Gas clouds, crystals, even gravity will spread and distort the beam like a wet noodle over large enough distances. Also the beam will spread out the further from the transmission point you get simply as a function of the optics aiming it. Aim a laser pointer at a house a few hundred feet away and you'll see what I mean.
  • I concede that finding the original source would be difficult, what with celestial bodies moving about all the time. However, triangulating the original source isn't hard at all. Just be sure you detect it from multiple points at once. Since the origin is a single point(or near enough to one), the difference in direction recorded is enough to give you a fix on the location. Now if only those pesky aliens would sit still for a few millenia, my missles might have a chance! :)
  • Your forgeting that the beam isn't made up of a single stream one photon wide. It will spread as a function of the precision of the optics transmitting it so that the beam that may have been say, a foot wide at the transmission point becomes much wider by the time it reaches us. So assuming then that multiple points on earth(there's no need to spread them out far enough that relativity comes into play, given instruments sufficiently precise) pick up the beam, triangulation becomes a matter of simple geometry. Also, if the detectors lock onto the beam for any length of time it becomes possible to figure out the source's motion relative to the earth.
    Not that this really matters. Anything sent to get there at sublight speeds will still be obsoleted by the FTL craft developed a few centuries later. Leading some poor, confused guidance program lightyears from home only to have it blown up and/or arrive years after first contact is just silly.
  • Something doesn't seem quite right here. What we call "radio waves" are just light in a certain band of wavelengths. So they're going to look for messages transmitted via light of a different wavelength. That doesn't seem like a big deal for me.

    Seems to me that if they're going to search for extraterrestrial light-based communications, they should be searching the entire spectrum--not just the groups of bandwidths into which we subdivide the spectrum.

  • Don't have my copy of The Guide to hand though, so I can't verify this I'm afraid - anyone else know?

    What, you don't have your copy of The Guide an you??? And I suppose you don't have a towel either?

  • what? when did lasers start travel in a straigth line? my lasre pointer certainly sends out a cone shaped light (It is really easy to see when you aim at a target about 100 metres away).

    And what is all this about having to send a beam the size of a planet?

  • optical detection sounds hard (Score:3)

    by tantrum ( 261762 ) on Tuesday July 24, 2001 @11:51PM (#63007)
    I thought that we had enough problems with discovering meteorites close to the earth, not to mention the fact that we have never really seen a planet outside of our solar system.
    It should be a lot easier to detect a laser beam directed directly towards the earth, than spotting a planet, but wouldn't we have to depend on the fact that the other civilization know that we are right here, and that we are able to pick up their signals?

    No matter what kind of transmission ET is using he will have to hope that we are able to pick up the signals. For how long have we been able to pick up that kind of signals, fifty years, maybe. I don't think that the aliens would bother to communicate with such a primitive rase as the humans.

    umm.. that was all for now. lunch time.
  • Right now, on another planet they've constructed a similar device to listen for light signals. Of course they like us haven't bothered sending light signals... (its like trying to find out if someone is on the telephone when neither of you talk.)
  • has picked up on our radio transmissions ... If they wanted to make contact with us, they could send us a message encoded in a laser beam

    What is the logic of responding to a radio transmission with an optical one? Wouldn't it be much more promising to answer a call with the same technology? Of course they could but is it probable?

  • Well, a couple things. First, the Sun is a G3 V star, and a fairly inactive one at that. (This is a good thing, BTW, because around an active star, you get lots of intense flares and other activity that would make life, if not impossible, no fun.) Thus good ol' Sol emits very little in the radio part of the spectrum. Thus, it doesn't take much radio emission for Sol to stand out in the kind of cross-spectrum mapping that astronomy has been doing for a long time. So any radio telescope within 100 LY of us will see our system as odd ... "A G3 main sequence star putting out that kind of radio emission? Let's write a proposal to get the funds to look closer."

    There are three strong source of radio emission in our solar system. The sun, of course, plus Jupiter and Earth. The sun's is typical of the emission in a quiet star. Jupiter's is what you would expect from a planet with an intense electromagnetic field, and it's Doppler shift has a periodicity of 5.2 years. Earth's emission is largely from mankind's technology and would show a Doppler shift of 1.0 years (of course).

    As long as there is enough radio and tv transmission, the signals can be picked up. That they can't decode it won't mean a lot, that it can be detected as a radio spectrum that can't be explained by natural phenomena will make it worth a look-see.

  • They don't know Morse code.
  • Note: this of course assumes Earth-like chemistry and biology

    Surface (or near-surface) dwelling beings would be exposed to a tremendous amount of 'visible' light. Most of the rest is either too long of a wavelength (infrared light just doesn't have the resolution of our visible wavelengths, never mind radio), or too short, and would either be filtered out by the atmosphere (UV and the higher wavelengths like Xray or gamma), or would kill anything with body chemistry similar to ours.

    Someone did a paper on this a long while back, basically his conclusion was that the wavelengths that we call 'visible' light are just a natural result of our chemistry.

    Besides, just imagine a primitive race that *could* see UV very well. It's not like they can just start a fire that produces copious amounts of UV radiation :)

  • However, in the next few decades the situation might be changing with the planned projects that could actually be able to give us glimpses of the other worlds.

    Could you please tell more about what projects are planned that might reveal more about those exoplanets?

  • Accuracy (Score:3)

    by Omniarch ( 317112 ) on Tuesday July 24, 2001 @11:51PM (#63014) Homepage
    How accurate would you have to be to aim a laser directly at the earth from who knows how many light years away? Personally, if I was an alien, I would stick to radio, or some other non-targeted communication if I was trying to contact any other life in the universe.
  • There's a lot of talk on here about the slim odds of finding a directed light beam. Isn't the whole SETI project about slim odds? - finding the needle in galactic haystack? Until we actually search, the argument over how any potentially technologically advanced civilisation might try to contact us is just pure conjecture. It's kind of like debating whether anyone is going to call when the telephone is unplugged. Surely we should investigate all possible avenues - this is science after all. Any technique that increases the likelihood of finding alien civilisations is a good thing...we need to know who is out there and whether they are friend or foe... In addition to its more noble goals, SETI could/should also be viewed by the more reality-focussed as an early warning system. Maybe the Pentagon should cough-up some greenbacks! Then we wouldn't have to rely on Will Smith.
  • Either that or you'd have some explaining to do when your grant comes up for review.

    Damn, you mean aliens have to go through grant procedures too?

    Miko O'Sullivan

  • You can just see it already:

    Mr. Smith! We have confirmation of an extra-terrestrial signal!
    Well? Can you decipher it?
    It seems to be in. . . . .english, Sir!
    And?
    It says "I send you this file so I may have your advice", sir. After that it just has this first_contact.doc file attached.
    Damn! And we just installed outlook!

    Yeah, I know it's a lame joke, but it had to be done.
  • What about ET's who might be flashing us with their asses, instead of radio-waves or light?
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  • It only goes in one direction... That assumes we catch the laser when "they" started firing it. If the Earth happens to stray in the path of the beam, how the heck will we know which direction it's travelling? (Is it moving right-left or left-right, so to speak?)
  • Most stars emit electromagnetic radiation with peak intensity in the visible light band. If eyes on Earth evolved/were created to be sensitive to the peak of the Sun's emission spectrum, why shouldn't the eyes of another world be tuned to the peak emission of their sun? It might be redder or bluer than ours, but the wavelength would differ by less than a factor of two.

  • How do ET aim at a moving target? (Score:3)

    by ThinWhiteDuke ( 464916 ) on Wednesday July 25, 2001 @01:18AM (#63031)
    ok, let's assume ET is 100 light years away. While the laser beam travels, earth revolves around the sun and the sun itself moves within the milky way. Of course aliens could compute the movements and target where earth will (should) be when the beam reachs us. But chances are that gravity wells would slightly bend the path or dust clouds would slow the light. Again truly superior aliens could take all of this into account. But reliance on such a huge collection of initial conditions would make the system pretty chaotic.

    What do you think?
    Are we (Terrans) currently able to target a laser beam on a planet 1, 10, 100 light years away?

    I will fight for the right to be right
  • I am not a subject-matter expert, but I was doing some reading today about various forms of communication and transmission media, and the pros/cons of each...

    For beings from another planet to contact us with focused optics, they cannot use a 'broadcast' approach (one source sent out to many users, a la radio stations). If they were trying to use a focused laser, this implies they'd have to know where we are in the first place (and would have known for the years the light had to travel)... or, if from far enough away, they would have had to sent the light to us before we existed!
    I dunno, it seems to me that anyone out there would be far more likely to send a broadcast signal that finds us by chance, rather than a focused one, given the very short time we've had the technology to send/receive these sorts of communication. Thoughts?
  • I fully agree with you. Besides that, what makes them think they will be more successful hunting for light? I mean, Earth is sending out radio waves into space (as a side-effect of radio wave based comms) but I never heard of any project sending laser pulses into space just to let aliens know we are there. So why would ETs do it?

    I believe one of the rare occurences of Earth sending laser light into space was to measure the distance to the moon, using reflectors placed on it. So those beams didn't get very far (from an interstellar point of view).

    ---

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