Flagging Down Aliens with World’s Biggest Laser Pointer

As you’re no doubt aware, humans are a rather noisy species. Not just audibly, like in the case of somebody talking loudly when you’re in a movie theater, but also electromagnetically. All of our wireless transmissions since Marconi made his first spark gap broadcast in 1895 have radiated out into space, and anyone who’s got a sensitive enough ear pointed into our little corner of the Milky Way should have no trouble hearing us. Even if these extraterrestrial eavesdroppers wouldn’t be able to understand the content of our transmissions, the sheer volume of them would be enough to indicate that whatever is making all that noise on the third rock orbiting Sol can’t be a natural phenomena. In other words, one of the best ways to find intelligent life in the galaxy may just be to sit around and wait for them to hear us.

Of course, there’s some pesky physics involved that makes it a bit more complicated. Signals radiate from the Earth at the speed of light, which is like a brisk walk in interstellar terms. Depending on where these hypothetical listeners are located, the delay between when we broadcast something and when they receive it can be immense. For example, any intelligent beings that might be listening in on us from the closest known star, Proxima Centauri, are only just now being utterly disappointed by the finale for “How I Met Your Mother“. Comparatively, “Dallas” fans from Zeta Reticuli are still on the edge of their seats waiting to find out who shot J.R.

But rather than relying on our normal broadcasts to do the talking for us, a recent paper in The Astrophysical Journal makes the case that we should go one better. Written by James R. Clark and Kerri Cahoy,  “Optical Detection of Lasers with Near-term Technology at Interstellar Distances” makes the case that we could use current or near-term laser technology to broadcast a highly directional beacon to potentially life-harboring star systems. What’s more, it even theorizes it would be possible to establish direct communications with an alien intelligence simply by modulating the beam.

A Laser to Rival the Sun

At interstellar distances, it’s very difficult to discern a planet from the star it’s orbiting. This is why we’ve only been able to directly image a small number of exoplanets; the only reason we know they are there is by watching for dips in the light output of their host star. The same is of course true in reverse. An alien intelligence that has a telescope pointed towards our solar system is really just going to be looking at our sun. That means any laser we fire out into space with the intention of getting somebody’s attention would need to appear brighter than the sun, otherwise it would be like somebody on the Moon trying to get our attention with a flashlight.

This would require a laser in the megawatt range that could be fired continuously or at least in bursts of several seconds. Admittedly it’s a pretty tall order, but not beyond our current level of technology. The US Air Force explored using an aircraft mounted megawatt laser as an anti-missile weapon in the mid-1990’s, which culminated with the development of the Boeing YAL-1. In 2010 the YAL-1 demonstrated it was possible to track and destroy ballistic missiles during their boost phase using its chemical oxygen iodine laser (COIL), though ultimately the project was canceled due to the tremendous costs involved in building and maintaining an operational fleet of the aircraft.

Regardless of its failings as a practical weapon, Clark and Cahoy cite the YAL-1 as proof that a similar laser could be constructed for interstellar communication. If the military can develop a megawatt laser that can fire for long enough to destroy a missile while still being small and light enough to mount in a modified 747, there’s no technical reason it couldn’t be done in an observatory on the ground.

As an added bonus, the COIL technology pioneered by the Air Force produces an infrared beam with a frequency of 1315 nm. This is particularly advantages for signaling purposes as our sun doesn’t produce much light at this wavelength, so the laser’s beam intermixed with light from the sun would be seen from a distant observer’s perspective as a star with a wildly fluctuating spectral output; an anomaly no alien astronomer could ignore.

Bringing it into Focus

As Clark and Cahoy explain, the megawatt class laser is only half the puzzle; it would still need similarly supersized optics to deliver the beam with the optimal divergence. But even here the hardware they have in mind, namely a 30 m to 45 m telescope, isn’t beyond our reach. The paper specifically mentions that the Thirty Meter Telescope Observatory (TMT) currently in the planning phases and scheduled to be operational by 2030 could provide adequate beam characteristics if it were paired with a 2 MW laser.

Artist’s impression of TMT primary mirror

Somewhat counterintuitively, the paper argues that a tightly focused beam is not the ideal choice for flagging down our celestial neighbors. For one, such a beam would need to be aimed and tracked with exceptionally high accuracy to hit a target tens or even hundreds of light-years away. More importantly, our ability to detect distant planets is still too rough to produce models of their orbits with sufficient accuracy; we simply don’t know where to aim the laser.

The solution is a beam that has a large enough divergence to compensate for our poor aim. In fact, Clark and Cahoy suggest a beam wide enough to illuminate large swath’s of a star system could be ideal in some scenarios. Multiple planets within a star’s habitable zone would be able to see our laser at the same time, greatly reducing the amount of repositioning we’d have to do on our end.

Against the Odds

Of course, there’s still plenty of variables in play that make such an attempt a very literal shot in the dark. For instance we can fire our laser towards Gliese 667, where Kepler previously detected a planet within its habitable zone, but its possible that the organisms who reside on that planet are insectoids with no appreciable technology. So whether it’s a rerun of “I Love Lucy” or a blast of infrared light from across the cosmos, they aren’t likely to pay it much mind and we come away with no more knowledge of our place in the universe than we had before.

But paling in comparison to technological or logistical hurdles is the most obvious problem: the economics of such a system. If even the United States Air Force didn’t think it was cost effective to continue operating a megawatt laser that proved it could destroy incoming ballistic missiles, who would possibly pick up the tab for an even more powerful and elaborate long-shot that arguably has no practical function other than to placate our yearning for exploration? Missions to the Moon or Mars can be argued to have practical benefits to mankind that offset their multi-billion dollar price tags, but shining a monstrous laser into the eyes of alien creatures that may or may not even exist for nearly the same price is a much tougher sell.

In the end, James R. Clark and Kerri Cahoy make a compelling and well-reasoned argument for interstellar laser communications. That the idea could work, and that it’s within humanity’s capabilities to bring such a system online within the next few decades is difficult to refute. But like so many great ideas, it seems unlikely it will ever see the light of day without the sort of concerted global effort that to date we’ve been largely unable to muster.

86 thoughts on “Flagging Down Aliens with World’s Biggest Laser Pointer

    1. I hope they figured out if their signal was going to be detectable above the noise. Lot of R squared to deal with. I doubt that I Love Lucy is reaching the LGM out there.

      (Little green men)

      1. In reality our 100-year-old radio transmissions aren’t really decipherable beyond a certain distance because the amount of time needed to tell the signal apart from the noise, or just to detect that there is a signal, is far too long to then make out any of the information.

        As your S/N ratio drops, your bandwidth decreases to the point that the information contained in the original signal is lost.

        1. Well, not your bandwidth but your channel capacity, but you get the point. After a point, all you can tell is that there is a signal at frequency X with a likely range of deviation Y and all the other information is smeared out to unrecognizable noise.

          You could still use that to send Morse code incredibly slowly, but again the further out you want to send, the slower you have to do it for the receiver to be able to pick it up.

      2. Since we’re talking about noise, I’d like to point out this paper:
        http://tuvalu.santafe.edu/~moore/ajp.pdf

        Assuming we’re trying to make contact via cold-call directed towards some random part of the sky, then surely we’d want to use very obvious and sub-optimal encoding. But if we’re planning on overhearing advanced communications between aliens on their own planet, or depending on them overhearing our own digital radio–it’s unlikely it would sound any different from noise unless they’re being purposely inefficient for some reason.

        Our old radio signals were like that, but we’re using bandwidth far more effectively nowadays.

      3. From a long enough distance, our Solar System acts as a point source of emissions. So, all of our TV and radio would be mashed in with the Sun, Jupiter, Saturn and the other gas giants which are pretty strong sources of RF noise. To pick out an episode of “Gilligan’s Island” from all that would be equivalent to hearing a mouse farting on New Years Eve at Midnight in Times Square while listening from Hong Kong….. sorry Lrrr and Ndnd… you will never get to see “Single Female Lawyer”

  1. Could we try to detect reflections to our pulses from the distant planets and try to estimate their orbits beter due to runtime differences / doppler shifts? At least we’d learn something about the targeted system even if there are now lifeforms to answer

    1. Jeez, we’re talking about making a light that’s noticeably brighter than our star… but imagine how bright a star is… now imagine how bright we’d have to be in order to reflect a detectable amount of light back at us! If there were a civilisation living in the targeted system that might justifiably be an act of war >.<

        1. I would still be like a whisper among starlight.

          The likelihood that we can ever communicate meaningfully above the din of interstellar radiation using our tiny machines is pretty far-fetched. The megawatt laser mentioned in the article would be the barest minimum, hardly detectable with even the most ideal of circumstances. And that of course depends on both perfect timing and perfect aim on the part of the receiver, which would be pure luck. Luck against odds that make the lottery look like a game of rock-paper-scissors against a man with no fingers.

          The vastness of space can only be known intellectually; it’s impossible to properly contextualize. Travel to another star would be outrageously difficult, more comparable to a religious miracle than mere engineering. But even simple communication is more ambitious a goal than anything humanity has yet attempted. These are seriously ballsy dreams, and even though I don’t have any hope for success I have to respect the people working on them for their sheer audacity.

  2. « There are forms of intelligent life out there. We need to be wary of answering back until we have developed a bit further » said Stephen Hawking in his book « Brief Answers to the Big Questions »

    1. Especially because the ability to respond in and of itself would amount to a civilization-destroying level of energy. Any interstellar capability whatsoever would be tantamount to a cosmic weapon of mass destruction; one that makes our defenses look like brief motes above a campfire.

      The Kzinti lesson: An engine’s effectiveness as a means of propulsion is directly proportional to its effectiveness as a weapon.

      1. “the ability to respond in and of itself would amount to a civilization-destroying level of energy” – that’s only true if “respond” means “come here”. A response could be anything from the amount of power we use upwards. A megawatt laser is pretty powerful, but it’s not going to end a civilisation.

        1. I doubt Hawkins said that by thinking in terms of energy and/or power. The simple cohabitation of two civilizations at unequal stages of evolution is likely to result in the disappearance of the least evolved. Even if no aggressive attitude has been shown on both sides

          1. The point is rather that being able to communicate doesn’t mean they’re coming over.

            There’s still the speed of light to consider. If we send out a gigawatt laser pulse to a place 100 light years away and they take it as a hostile measure, they’ll probably take at least another 1000 years to get here by any means.

            Even if they shot a laser beam of unimaginable magnitude back in our direction, it’s not going to hurt us because of the distances involved. The beam would have to be so tight and dense to start with that it rips space-time apart, or it must come from a stellar-size object which would take millions of years to construct.

            Anything they could do to harm us would take such a long time that we would either evolve out of the way, or kill ourselves by accident before they are able to. The quickest thing they could do to us is send another light pulse back and do the equivalent of shaking a fist.

  3. Why are stupid people in charge. Just a few centuries ago we didn’t have cars, computers, and so on. We can barley handle the tech we have new. Nukes and so on. These people with the quest for more knowledge from possible other intelligent beings is simply stupid until we have learned how to control ourselves. We are no more than children playing with big toys, and no where near ready for any kind of real power.

    1. Don’t worry, the limits of physics have all but made sure we won’t say hello to anyone else out there, let alone meet them or share technology with them. We’ve essentially hit a wall–it hardly matters how far we advance in the face of such distance and time. It’s an extremely non-trivial problem. Even with lasers.

      Unless we make some really, really good Von Neumann machines. Even that is doubtful. After all, carbon-based life on Earth essentially represents bajillions of highly advanced and durable Von Neumann machines that have been replicating for billions of years, yet we haven’t taken over the galaxy yet. Not even the solar system. Hell, not even the Earth. There are still vast portions of our own planet that would appear lifeless to a cursory observation. I think the simplistic estimates of exponential growth spanning the galaxy in a few million years are pretty absurdly optimistic. Which is, once again, a good thing. If building machines like that was possible, all matter would have already been converted to those machines. Perhaps billions of years before we even had a chance to evolve. Obviously that didn’t happen. Permanent exponential growth is impossible for a good reason.

      And FTL is about as likely as a genie appearing and granting us a wish. There are advances which may come in the future, while on the other hand there is baseless fantasy and logical nonsense. FTL certainly falls within the latter category.

      1. The exponential assumption always assumes that energy and materials are exponentially available as well, which they never are, and where energy is very abundant, it’s too much to handle. The replicators break down because they are physical entities that are limited by their mechanisms of action, which come apart if you try to make them work faster than they can.

        It’s just a matter of bad science fiction, where people forget that there’s no such thing as a free lunch. They imagine machines, let’s say, a robot that is ten times faster at running than a man – but when the robot is pounding its legs down at 100 mph they quickly realize that the robot’s feet are being hammered to bits and it can only sustain the motion for a few miles before it utterly breaks down.

      2. Totally agree with one work-around. Machine intelligence, or “immortality” for improved humans or human mind/machine, means trips of hundreds of thousands of years are reasonable. No food, etc. needed. You can turn yourself off or slow down, or play in VR and all that stuff.

        1. Humans already outlive virtually all our machines, even ones many orders of magnitude simpler than ourselves. I don’t see why we make this assumption that machine intelligence would somehow be timeless and immortal. The more excessively complex a computer is, the less time it lasts and more maintenance it needs.

          I think we should assume that four billion years of mother nature’s best care did an extremely good job at maximizing the longevity of the outrageously complex and powerful machinery which is responsible for consciousness, and that it would be cosmically difficult for us to exceed that.

    2. Stupid people are in charge because stupid people vote for them. They win the vote, because there are loads and loads of stupid people. It will ever be thus, at least on a relative scale. And even across time, is the average, or dim, or smart person now, all that smarter than their counterpart 300 years ago, or 2,000?

      We’ve learned more, we have better technology, thanks to an absolutely tiny proportion of the human race. I suppose some of the others did work in producing food and clothing for the smart ones. But they hold us back by falling for stupid manipulations and propaganda, and once you give the silly bastards a way to easily form groups, they start believing in a flat Earth. For the first time in history! Even the Greeks knew the world is spherical! Prior to that, maybe some dim Stone-Agers thought the world was flat, and the sky was flat above it, but they didn’t have the benefit of knowing about other planets, or the laws of gravity, or the vast, huge panoply of other knowledge.

      Many people now are stupid on purpose. It goes alongside people being arseholes on purpose. And voting for that right.

      1. ” And even across time, is the average, or dim, or smart person now, all that smarter than their counterpart 300 years ago, or 2,000? ”

        The answer is no. Knowledge and intelligence are two different things. The average intelligence may have changed over that time though. Idiocy begat idiocy. It’s the basis of the movie “Idiocracy”.

      2. “”Many people now are stupid on purpose. It goes alongside people being arseholes on purpose. And voting for that right.””

        The most correct thing I have heard all year.

    1. “Once there were three tribes. The Optimists, whose patron saints were Drake and Sagan, believed in a universe crawling with gentle intelligence — spiritual brethren vaster and more enlightened than we, a great galactic siblinghood into whose ranks we would someday ascend. Surely, said the Optimists, space travel implies enlightenment, for it requires the control of great destructive energies. Any race which can’t rise above its own brutal instincts will wipe itself out long before it learns to bridge the interstellar gulf.

      Across from the Optimists sat the Pessimists, who genuflected before graven images of Saint Fermi and a host of lesser lightweights. The Pessimists envisioned a lonely universe full of dead rocks and prokaryotic slime. The odds are just too low, they insisted. Too many rogues, too much radiation, too much eccentricity in too many orbits. It is a surpassing miracle that even one Earth exists; to hope for many is to abandon reason and embrace religious mania. After all, the universe is fourteen billion years old: if the galaxy were alive with intelligence, wouldn’t it be here by now?

      Equidistant to the other two tribes sat the Historians. They didn’t have too many thoughts on the probable prevalence of intelligent, spacefaring extraterrestrials — but if there are any, they said, they’re not just going to be smart.

      They’re going to be mean.

      It might seem almost too obvious a conclusion. What is Human history, if not an on going succession of greater technologies grinding lesser ones beneath their boots? But the subject wasn’t merely Human history, or the unfair advantage that tools gave to any given side; the oppressed snatch up advanced weaponry as readily as the oppressor, given half a chance. No, the real issue was how those tools got there in the first place. The real issue was what tools are for.

      To the Historians, tools existed for only one reason: to force the universe into unnatural shapes. They treated nature as an enemy, they were by definition a rebellion against the way things were. Technology is a stunted thing in benign environments, it never thrived in any culture gripped by belief in natural harmony. Why invent fusion reactors if your climate is comfortable, if your food is abundant? Why build fortresses if you have no enemies? Why force change upon a world which poses no threat?”

      -Peter Watts, Blindsight

      1. “Technology is a stunted thing in benign environments, it never thrived in any culture gripped by belief in natural harmony. Why invent fusion reactors if your climate is comfortable, if your food is abundant? Why build fortresses if you have no enemies? Why force change upon a world which poses no threat?”

        Good thing we got kicked out of that particular garden.

      2. >”Why invent fusion reactors if your climate is comfortable, if your food is abundant?”

        Because it’s a Malthusian trap. There is no such thing as “abundant food” – populations will increase to the point of war anyways, and war leads to armaments, armaments lead to technology, technology leads to improved exploitation of your resources, which leads to faster population growth, which leads to another trap and the whole thing starts over. War, peace, war, peace…

        If a species fails to advance, they fail at the stage where they’re still animals without abilities to plan, by getting stuck in an local evolutionary maximum and dying out. Even under stable ecological conditions, life isn’t, because life abhors stability – if everything remains the same, a virus will eventually evolve that kills the whole lot.

        1. If war is not possible, human sacrifice – child sacrifice. Or very structured hostilities that stop (for a while) after a single death and resulting ceremonies and mourning, as seen in closed valleys of Borneo, or East Africa before Shaka Zulu.

        2. “Because it’s a Malthusian trap. There is no such thing as “abundant food” – populations will increase to the point of war anyways, and war leads to armaments, armaments lead to technology, technology leads to improved exploitation of your resources, which leads to faster population growth, which leads to another trap and the whole thing starts over. War, peace, war, peace…”

          Ah! Yoda logic.

          1. Conflict is more likely to arise in competing for mates. The source of human intelligence is very likely competition with other humans. Nothing else I know of produces the steady pressure to be more clever. When this ended, evolution stopped – probably pretty much with the invention of agriculture. Now it waits for managed improvements instead of accidental, which has had to wait for “reverse engineering” the most complicated stuff ever seen.

        3. And that is exactly the point. Anything which has fed all mouths despite the limitations of the natural environment for such a great length of time–anything that persists past its local evolutionary maximum and makes it into deep space–would necessarily be warlike. And meaner than a maced viper on PCP to boot. Sort of the way we are to almost every other species. Domineering. Enslaving. Merciless. Causing unparalleled slaughter throughout our environment.

          We want to be extremely careful when poking around for aliens. We don’t know what a culture would look like after a few millennia or even millions of years post industrial revolution. But we could make a very educated guess and say they would be more vicious than we can easily imagine.

    2. They probably won’t. Somebody noticed, a few years ago… The theory was that, as technology advances, we’ll produce more and more radio waves that are obviously artificial, eventually lighting our sky up enough that aliens will be able to see us. But that was the old analogue days.

      For one thing, we have data compression. And it’s some law or other, that the more efficiently data is compressed, the more it resembles noise. Any redundant information or repetition is coded away, so removed. There’s also things like QAM, where the more distinguishable levels of power you can send in a signal, the more data you can fit in. Practically every form of computer communication uses this now. Mobile phones, and TV, certainly.

      So data looks less and less like data. And sure there’s probably more noise than there was, but not much more compared to the background of a planet in space.

      So it turns out a civilisation, ours at least, only uses detectable radio waves for perhaps 100 years or so. It starts out from nothing, then sparks and big beams, then back towards noise again as the data rate goes up. This is particularly relevant for things like SETI, it’s likely only ever to pick up signals deliberately coded and aimed at us. Though that was true anyway.

        1. Some designs are highly optimal and won’t change much, even with thousands of years of unknowable advancements.

          Radio waves are one of the most ideal methods of communication the laws of physics makes available to us. We’ll probably develop other methods to augment radio in certain niche situations, but it’s incredibly doubtful that we’ll ever abandon radio as a useful tool no matter how godlike our tech becomes. There will be vastly more advanced radios, but they will still be radios broadcasting EM through some kind of antenna at some frequency or combination of frequencies.

          E.T. will probably use encryption or compression schemes that make their data nearly indistinguishable from noise, though. We already have that issue ourselves–our modern transmissions are way less obvious than in the olden days. If we intercepted an advanced alien communication, we probably wouldn’t recognize it for what it was unless we’re lucky enough to snatch one of those messages optimized for communicating the very concept that it is a message. Like broadcasting primes using plain binary signals in the hydrogen absorption frequencies. A bit contrived, but it would perk up some ears if it was strong enough.

          We did that a couple times in the last century (at utterly pathetic amplitudes) then went back to encrypting and compressing everything. I don’t think aliens are going to be any more diligent when it comes to trying to get the attention of unknown strangers. And hella nobody is going to pick up an omnidirectional signal. Channel 2 is all but gone forever once it leaves our solar system. It must be directional if it’s going to have even the slightest chance of being received at another star. So the laser sounds like a good plan, but it’ll still be a long shot–both physically and figuratively.

          1. Any data we send can’t be arbitrarily close to noise – otherwise it would BE noise to us as well.

            For example, here we’re sending UTF-8 characters to each other, which don’t span the entire space of possible combinations there could be. I’m not sending you the number Pi from a random location onwards, I’m sending you sentences in English, and that necessarily creates some pattern that can be distinguished no matter how this information is compressed.

          2. @ Luke of course I could be wrong, but I’m mentioning it because of studies I’ve read:
            http://tuvalu.santafe.edu/~moore/ajp.pdf

            Without knowledge of the encoding details, highly efficient transmissions are necessarily identical to random blackbody radiation. Mind you that this is talking about a raw signal–the analogue readout of a certain frequency band. Which is what we listen to with a radio telescope, since we don’t and can’t know what kind of encoding is being used.

            We’re communicating using UTF-8, sure, there’s an obvious statistical pattern–but we’re talking more fundamental than that. Obviously we don’t know what E.T.’s version of UTF-8 is. The raw data being transmitted–the strict binary which all digital communication gets encoded into before going over the network–this would be indistinguishable from random noise if the usage of the available bandwidth was optimized.

            The pdf I linked mathematically demonstrates that if there are distinguishable differences from noise, then bandwidth is being left on the table. If they were trying to make an interstellar contact, sure, they would probably use less-optimal encoding to try and make it more obvious; but eavesdropping on advanced, digital, internal communications would likely sound identical to the CMB.

          3. >if there are distinguishable differences from noise, then bandwidth is being left on the table

            This deals with the idea that you’d be sending the maximum amount of information per channel, which would indeed look like noise because it would very much BE noise that requires detailed knowledge about the message to decipher. Ultimately, we could be sending just index references to a huge book of data. The point I’m making is that when sending a meaningful message, you’re never sending the maximum amount that you could be sending.

            To condensetheinformationinthissentencewecanskipsomeredunantcharacters. Starts to look like noise. But that’s not what is being done.

          4. Or, to put it in another way: the bandwidth may be optimally utilized by some type of encoding and data compression, but the data we are actually sending contains redundancies, and thus bandwidth is never optimally used.

          5. That’s the nature of compression, though. redundancy is slimmed down into fewer, unique bytes. Any redundancy at all indicates a sub-optimal compression algorithm.

            It’s not “condensetheinformationinthissentencewecanskipsomeredunantcharacters.”

            It is:
            01100011011011110110111001100100011001010110111001110011011001010111010001101000011001010110100101101110011001100110111101110010011011010110000101110100011010010110111101101110011010010110111001110100011010000110100101110011011100110110010101101110011101000110010101101110011000110110010101110111011001010110001101100001011011100111001101101011011010010111000001110011011011110110110101100101011100100110010101100100011101010110111001100001011011100111010001100011011010000110000101110010011000010110001101110100011001010111001001110011

            That’s your spaceless string of text run through an ascii-binary translator. Getting any meaning out of it without knowing how our binary AND ascii encoding works (through statistical analysis perhaps) might still be possible–assuming you already know at least some human language and grammar. Without even that, you’d be very hard-pressed to differentiate that from noise at all.

            And this still assumes far too many clues. If we transmitted this through a radio, the boolean digits would be transformed into arbitrary analogue levels of amplitude at an arbitrary frequency over an arbitrary baud rate, or even worse into frequency modulation between two arbitrary frequencies across an arbitrary bandwidth–again with an arbitrary baud rate and threshold between boolean values. And this doesn’t even get into compression. That data was still compressible.

            Add in several light-years of bad SNR, fade, doppler shift, etc and it would be heroic to decode any meaning–or indeed the mere EXISTENCE of meaning at all–even with knowledge of the natural language, machine language, encoding scheme, compression scheme, DAC scheme, and transmission scheme. But we will have none of those.

  4. The idea of flashing light on a dying boat in a sea potentially full of pirates. What could possibly go wrong ?
    Even if the target specy is peaceful, why on ea…**ahem** space would it answer?
    This would reveal their existence to a species that can be peaceful or not. It’s extremely easy to destroy a planet (we can already do it with only 10% of our nukes), would you bet your only planet just to meet your “neighbors” ?

    1. So far we can’t even reach another star. We’ve no way of getting a nuke there, and certainly not the fleet you’d need to destroy a planet. Assuming they don’t have defenses against missiles. And even we have that! We’re no risk to anyone. It’d be great to talk, though.

    2. The number of nuclear weapons needed to “destroy a planet” has been greatly exaggerated. We couldn’t do it with all our nukes at the peak of the cold war, let alone 10% of what we have now. We couldn’t even wipe out our biosphere completely. We’d ruin our civilization, though. That’s for sure.

      Now a relativistic vehicle, on the other hand… If aliens can manage to get themselves from where they are to where we are, destroying us would be about as hard as neglecting to apply the brakes, or throwing a few tons of cargo out the airlock while they zip past. If you’re going fast enough to get anywhere out there, any kind of warhead at all is just redundant. Anything that could travel that distance would be far, far beyond our ability to resist. It would be like a cockroach trying to prevent a meteor from falling. Or something. I don’t know, I’m not a poet.

      1. That’s a good point. For perspective, consider that the “dino-killer” asteroid struck Earth at maybe 0.01% of light speed, and remember that kinetic energy increases by the square of the velocity. A relativistic kinetic weapon would certainly be capable of planetary-scale destruction.

  5. Hmm, if you look at what happened to the native populations of countries that were discovered by our explorers (eg the Americas, Australia, the Arctic), you get a bit wary of being a native population attracting attention from interstellar explorers…

    1. No, those are all omnidirectional signals. It would have to be focused, some kind of convergent beam of energy. At interstellar distances, the inverse square law basically amounts to total isolation. A directional antenna (or laser, like the article says) gets around the inverse square law somewhat, but it’s still going to be tough. Even putting all our nukes at the focus of a huge parabolic reflector would likely never get noticed.

      Don’t forget, we’re right next to a gigantic fusion reaction that is the equivalent of 1,000,000,000,000 one-megaton nukes going off per second. That’s one trillion. Around a hundred and twenty-five nukes for each man, woman and child on Earth. That kind of nuclear cacophony is happening every. Single. Second. And that’s just one star. At the distances we’re talking, even that is difficult to see clearly, to extract meaningful information out of. The distance is unthinkable.

      In a cosmic sense, we are barely separated from the sun at all. From the vantage point of another star, there would be no way to detect a thermonuclear war happening on our planet because billions of thermonuclear wars happen non-stop just next door. And everywhere else in the universe.

      Space kind of makes our affairs look forgettable by comparison.

      1. The amount of Solar radiation, across its emission spectrum, that hits Earth in one second is likely more energy than humans have created since our first generation of electricity.

        One hurricane like Katrina unleashes in its week or so of existence more energy than the entirety of humanity generates and uses in around 15 years. No wonder the storms generate gamma radiation bursts. They’re natural cyclotrons.

        The human caused climate change contingent pooh-pooh’s the natural variation in total insolation over the course of the Sun’s spot cycle as an insignificantly small percentage. Well that ‘small’ percentage of yottawatts is still a very enormous amount of energy, far more than our species generates.

        1. Totally with you–up until the climate change part. Anthropogenic climate change is still caused by the energy from the sun–humans only contribute the rarefied catalyst that causes that energy to run amok. This doesn’t mean it’s not our fault, nor does it mean the consequences are insignificant or inevitable.

          https://xkcd.com/1732/
          If you put the data in proper perspective, it’s clear that it isn’t the effect of sunspots. Do sunspots effect climate? of course. But for it to change this much so quickly is unprecedented. The data is in, it’s reliable, and it has passed exhaustive multinational independent peer review which would have ruled out a conspiracy or mistake decades ago. It’s real. We don’t get to ignore it anymore. Not if we want to have a future.

  6. The thing that bothers me about either receiving a message, or sending a message is something I have heard neither camp address: planetary motion, solar system motion, and galactic motion- to whit: the earth is rotating 15 degrees per hour, while orbiting in another axis at a little over a degree per day (360/365.25), and our solar system is moving in another orbit in the Milky Way at some degrees per second, in yet another orbital plane, and then there’s the galactic motion of the Milky Way, through the universe. Just taking our planetary human emissions (radio and TV waves, microwaves that can transit our atmosphere, etc.) into account- there’s the plane of polarization of the launches radio waves- vertical, horizontal, left circular polarized or right circular polarized, and the fact these beams are being swept about into the universe with a given beamwidth. Think about the dwell time any given signal will “illuminate the surface of some remote planet. Seconds? Fractions of seconds? Can a civilization detect the signal? If so, can they determine that brief blip of energy actually contains information? If they could do the foregoing, could they demodulates the signal and determine the signal is voice, or video? What if that part of signal was a recording of tree leaves rustling in the breeze or rain fall, or the babbling of a brook, or the road of a tornado? If they wanted to receive another signal from Earth, could they? Their planet is spinning in some eccentric axis like ours, inclined in its orbit, like ours, in a given arbitrary plane of rotation about its star, in a given orbit about its galaxy, with its own galactic motion. How can anything intelligible be detected? How long to wait until the transmitter and receivers are aligned again? Think of the melange of spectrum being emitted from our little planet- which time segment of signal goes with which other time segment?
    A LASER system, regardless of power or columation, is going to sweep through space in the manner of radio waves, but be an even smalller angular subtended angle than a given radio wave, so it’s dwell time on the remit planet probably won’t be as long as the radio wave discussed earlier. Maybe that is a good thing- maybe we don’t want to be found. After all, God is said to protect fools and innocents… Which are we?

    1. If we were able to build an absolutely perfect laser, it would be known as diffraction-limited; that is, there are still laws of physics which will cause those parallel beams of light to spread no matter what we do. It’s a fundamental quality of light. It depends on the wavelength of the light you’re using.

      In reality, we’re probably not going to get even that good of a beam. By the time the laser reaches a star that’s appreciably far away–the closest is four light-years, and it’s probably not going to just happen to be an ideal target, it’ll probably have to be much further off still–the beam will spread to become cosmically large. As in even a planet whirling around its sun will still stay within the beam for an appreciable amount of time.

      https://physics.stackexchange.com/questions/279872/how-well-can-a-laser-be-focused-over-interstellar-range
      Note these calculations are for one light-year, so you’ll have to multiply the beam width by the distance to the receiver.

      The original article suggests we should actually use a diverging beam to increase our chances of hitting the target with sub-optimal tracking, but this strikes me as unrealistic optimism. I don’t want to be arrogant–I’m sure the person doing the math knows more than I–but somehow I suspect that even our best laser paired with our biggest and most precise optics would spread out too much over so many light-years. I think they’re speaking from a perspective of ideal engineering, of sub-atomically perfect mirrors, rather than a realistic design tempered by experimental measurements.

      Of course this also means those two megawatts of laser energy is going to be spread very thin. This is still an extremely difficult contact to make. Outrageously sensitive receivers must be pointed at precisely the right part of the sky to pick up a couple feeble photons of that once-mighty laser beam. The RX equipment will almost certainly need to be optimized for just the wavelength being used by the TX equipment. And of course that kind of equipment loadout, timing, and calibration on the other end will depend entirely on luck.

      Not to poo-poo all over the concept. I have extreme respect for these people–engineers and physicists who devise daring ways to approach the impossible. It’s almost certainly doomed, but sometimes it’s more about the journey than the destination. What little amateur radio work I’ve done leaves me utterly dumbstruck by the difficulty of an interstellar contact.

  7. Hm… use the Voyager probes’ cameras to test if it’s working. Then fire the laser at their RTG to extend the probes’ lives.
    (if not, and the power for the experiments runs out but still enough for the computer – let’s reprogram them to mine Bitcoin :-) )

    If little green men were hostile and advanced, they would’ve overrun us ages ago.

    Dr. Evil reference, anyone?

  8. Broadcast towers transmit their signals outward in a sphere, which falls under the inverse square law. The strength of the signal decreases massively over distance. By the time you’ve gone a few light years, the signal is almost non-existent.

    The intensity of radio waves over distance obeys the inverse-square law, which states that intensity is inversly proportional to the square of the distance from a source. Think of it this way: double the distance, and you get four times less power.

    1. Hoo boy. I want to disagree, but somehow I think the laser they think they need now won’t be within an order of magnitude of the laser they really end up needing. That’s how things usually work when we go from ideal astrophysics to real engineering. But logic that also applies to such a nutso-bismol bonkeroo idea as building a Dyson swarm. That’s gonna be seriously hard.

      I wonder just how much of the sun’s light you’d have to block to send a useful, unambiguous signal that wouldn’t be mistaken for natural phenomena or noise. It would be a hell of a lot of satellites. Hell of a lot of mass. Absolute shitload of energy to get them all placed into the proper orbits. Even timing the modulation across all of them would be a huge challenge, considering the signal lag between them and clock changes inherent in a quadrillion objects all traveling at such different relative speeds.

      Maybe instead of a full swarm, you could just have a few statites held up by photon pressure on the side of the sun facing the target star. And in addition to opening and closing shutters to block light, they could also charge up solar batteries and fire tight beams of collimated light at the target when the shutters are open–just to push the two values of light and dark apart as far as possible when viewed from that specific direction. combine both systems for maximum SNR.

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