This paper has received a new title since being put online. It has had two comments over on Space.com and I now realize that the title gave the wrong idea as to contents and intent. I would like to thank _a_lost_packet_ for being one of the few people to read and reply to my post over at Space.com, but his comments uncovered what I realized would be a common misconception with my essay given its original title (which had the word Supernova in it) and likely few people did more than read the title and jump to some erroneous conclusions about the content. This essay has NOTHING to do with triggering or harnessing Supernova explosions. It is about exploiting the natural occurrence of Supernovas to facilitate the initiation of communications between extraterrestrial civilizations much in the same way fireflies my all flash in unison when lighting strikes. The fireflies don't cause the lightning nor are they close to it, but you would know they would all flash in unison to it. Now replace lightning with Supernova and ET with fireflies and given the immense distances between stars we would see the resulting 'simultaneous' signals spaced years apart (except in certain rare situations outlined below).
_a_lost_packet_ also posits that waiting around for Supernovas isn't what Extraterrestrial civilizations would do -- in this case we would be one of those civilizations waiting around. Since we have already waited 40 plus years without contact, this isn't necessary a matter we have control over. ETs are probably using more than one method to try an communicate with us and others, this would be one more method that if exploited would be long in coming, but efficient and productive when available. If there is more than one civilization within signaling distance, then the times between observable signals would be roughly 100 divided by the number of civilizations within signaling distance (assuming they too participate in this signal synchronizing strategy).
Again with emphasis - this strategy while exploiting the occurrence of Supernovas for reasons of timing does not require the triggering of Supernovas, the channeling of Supernovas nor being close to Supernovas by ether the senders or receivers, they are merely timing aids to narrow search parameters.
There is a large camp, perhaps a majority of people that see SETI research as a waste of time and effort. Considering the world changing implications of finding an ET signal it is hard for me to see this as a waste even if it hasn't as yet provided results. Of course the search itself has provided results and knowledge, just that the results so far have pushed the boundaries of where near technological societies might be farther. How much farther? Well that is a little hard to quantify and is made murkier yet by the problem of synchronicity. Stated simply we have to not only be looking towards where they will be transmitting from, but during a window of time when they will be transmitting -- and this is the problem this paper hopes to address. Many or most people probably think that SETI has been listening to all planetary systems in the Milky Way Galaxy on a more a less continuously for the last 40-50 years and come up with nada. The truth is we have only scrutinized a relatively few close star systems in any great depth and only for relatively limited amounts of time. There are a larger general sky surveys, but they are piggy backed on other general astronomical research and also suffer from problem of synchronicity.
The core problem is the amount of energy needed to send signals across light years of space is quite large, especially omni-directional continuous signals. Even with megawatts of transmitting power, reception is problematic beyond a few dozen of light years distance, and it is only beyond these distances we are likely to encounter other technological civilizations, even if the Milky Way has thousands or millions of such civilizations. Even assuming conventional SETI and being generous and assuming ET could have detected our early radio broadcasts 75 years ago (a very big assumption) then the round trip reply would be possible from less than
If it were possible to look in the right direction at the right time things would be far simpler for both sender and receiver. But how to determine the best look and send times before communications have been established? Fortunately the universe has provided such synchronization assist mechanisms in the form of various astronomical events; the most familiar and spectacular of these being Supernovas though there are probably others that might also be exploited.
For ETs to make their presence known they would wait for such a spectacular event and set off a large Electromagnet Pulse (EMP) or other highly energetic signal carrier when observed. Assuming we know the distance to the Supernova and the distance to target star systems we can work out when their respective signals would arrive and thus know when to look for them.
While the core concept is simple there are a lot of problems remaining to be ironed out, the chief one would be working out accurately when to observe each target star system. Unfortunately we do not have the distance to even relatively close stars known with great precision as the data below from the Hipparcos satellite shows.
accuracy level -- stars known -- light years
1 percent -- 400 stars -- 30 light years
5 percent -- 7,000 stars -- 150 light years
10 percent --28,000 stars -- 300 light years
Since there are approximately 100 billion stars in the Milky Way, this means we know the distance with 10% accuracy to less than
Cosine to the Rescue
If we assume an ET on a star system 300 light years away sent a signal 300 years ago, naïvely we would have to observe the system continuously 30 years to detect the signal event if we knew it to coincide with a Supernova event. Even with only
Supernovas are not only rare, but also most likely to be tens of thousands of light-years distance from us. If we assume the Milky Way is relatively densely populated with ETs then some star systems will lie close to the line along which the Supernova's light is travelling to us. Take the case where a Supernova goes off 2000 light years from us, and there is an ET civilization a mere 1 light year off this line at 1000 light years (I have kept the numbers simple for purposes of illustration). The pulsed signal sent when ET observes the Supernova would arrive 1/3 day later.
Most likely ET will not lie so close along the line we observe the Supernova from, but this does illustrate how powerful the concentration of time can be for signals not too many arc seconds off its path -- whether we know their exact distance or not. If we do know the distance then we can work out the likely window of observation needed, the closer to this line, the much less time is needed.
We can use the Law of Cosines to work out the arrival times for candidate star systems (assuming reasonable guess as to distance, which for even very distant systems can be worked out by various methods, though with very large error bounds).
b^2 == a^2 + c^2 - 2*a*c*cos(B) (where a, b, c are the sides of a triangle and B is the angle opposite side b).
If we keep distances in light-years, then the final delay off a Supernova event is given by: T == d1 + sqrt(d1^2 + d2^2 - 2*d1*d2*cos(B)) - d2 Where d1 is the distance to the target star system, d2 is the distance to the Supernova, B is the angular separation between them and T is the time in years (when B is small, T will probably/hopefully be a small fraction of a year).
It is my hope that Supernova events would trigger a flurry of activity galaxy wide. Not only would this activity be useful in alerting potential fledging civilizations where to concentrate their observational energies, but such signals would be useful as a cosmic surveyor's aids, helping pin down the distances to star systems with greater accuracy.
Assuming dozens if not hundreds or thousands of civilizations take this opportunity to signal their place in the heavens, it would appear as an expanding disc of flashes around a Supernova. While we may not know exactly wherein the disc the flashes might occur, we can still work out statistically the circular arc where 95% plus of the flashes could occur. Observing this disc while it is still small and synchronicity is at is best is probably our best chance of bagging an ET signal. Though we may never be able to communicate directly with the first ones we observe, as they will likely to be many hundreds or thousands of light-years distant -- observing just one such synchronistic event might be proof enough we are not alone -- two or more a dead certainty. More targeted observations can be made of the few hundred thousand stars within say 200 light years. A synchronization signal from them would justify building huge new space based observatories in multiple EM bands to try and detect not just simple hello pulses, but any directed message or stray EM leakage, even it is just reruns of "I Love Lu-C-Prime".
I have the Power
During the Reagan Presidency there was an exotic missile defense scheme posited employing the use of X-Ray lasers to knock out intercontinental ballistic missiles in mid-flight. Such exotic devices were never built, but exist in theory. The X-Ray lasers proposed were essentially focused atomic blasts. A nuclear devise was to be placed in orbit and affixed to it where several long pipe like attachments each one of which could be pointed at an individual incoming missile. When the nuclear devise was detonated the immense initial EM pulse was focused, converted, or caused lasing in the X-Ray portion of the spectrum along these beam pipes. A short intense X-Ray beam would then have streamed out before the devise was obliterated by the blast-wave to follow scant milliseconds later. Here then in theory is at least one devise that could send a strong unmistakably technological in origin signal. I'm not suggesting this is the only way to send a strong pulsed signal on cue, just positing one devise that could work -- though it obviously would be too dangerous a contraption to build in low Earth orbit.
It is possible to generate ultra strong EM pulses with conventional explosives, I imagine they could be focused and harnessed in much the same fashion as the proposed Cold-War X-Ray Laser if needed. In any event we need not obsess on how such signals are generated, we know that they can. Truly gargantuan EMPs could be detonated on the far side of the moon, thus shielding the Earth from any unintended electronic damage fallout. Our intended recipients would of course be seeing a signal many orders of magnitude smaller given the immense distances.
Depending on the technological level of the sending society they may just use some brief omni-directional brief pulse and not worry about focusing on likely candidate worlds. If it is a society with high enough technology to know with certainty which worlds harbor life, they may use directional beams for greater efficiency and signal strength. The signal may last milliseconds or a day or two. Regardless, the onus in now on the receiving world to listen at the right time and in the right direction.
Where to Look Now
While not in the Milky Way proper, but in the Large Magellanic Cloud, Supernova 1987A might still be worth investigating for transient SETI activity in star systems not far off its coordinates. 21 years is a relatively short time astronomically, and with this Supernova being 170,000 light years away there are lots of candidate systems relative close to its sight line that would just now be having a visible synchronized pulse. Similar to our previous example a civilization at 85,021 years away could be 1890 light-years off the Supernova 1987A's sight line and its beacon or pulse would just now become visible. (note 85,021 was chosen so the light would arrive now, 21 years later, so 1890 is the result of sqrt(85021^2 - 85,000^2) )
If we truly want to join an intergalactic community we should put some effort into creating and EMP signal of some sort. I imaging a few million dollars would buy a firecracker of sufficient size to serve as a beacon. More importantly what I hope to emphasize, is we need to be working out what we should be look for and where in the aftermath of a Supernova explosion. The Supernova itself will be a wonderfully informative event, but I hope this paper stirs to action possible tangential discoveries potentially even more important. I speculate we could get some dual use research out of this search. It is likely in the few years after a Supernova it's light will briefly illuminate the interplanetary dust clouds of systems close to it, providing additional astronomical information and a means to refine our galactic yard sticks. Since we might be looking in this direction anyway, we should be alert to the possibility of extremely transient events that might be intelligent in origin.