Half a croissant, on a plate, with a sign in front of it saying '50c'
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Strobe Light Planet

To let them know we're here
  (+11, -1)(+11, -1)
(+11, -1)
  [vote for,

When looking for intelligent life in the universe, we look for patterns in signals. However, we haven't put much effort in generating such patterns ourselves.

I propose we use atomic clocks to synchronize all power plants. Of course, we'll all have to switch to the same frequency of AC power, but after that synchronizing our power plants should be fairly easy - it's more or less done anyway, within countries.

The result? Every fluorescent light will flash at the same time. Every incandescent light will have a bright pulse at the same time. Etc. Our entire planet will more or less flash at some frequency. That should show up quite well on some alien planet's version of SETI@home, then all they have to do is listen for our radio and TV signals, and we'll be on our way to having new friends (hopefully).

Worldgineer, Aug 30 2006

Flicker http://www.ccohs.ca...ghting_flicker.html
[Worldgineer, Aug 30 2006]

Intergalactic Morse Code Intergalactic_20Morse_20Code
[theircompetitor, Aug 30 2006]

Earth at Night http://antwrp.gsfc....ghts02_dmsp_big.jpg
The Australians aren't doing their part. [baconbrain, Aug 31 2006]


       + I think this idea is very bright.

xandram, Aug 30 2006



       + //new friends//? I didn't know we had any friends now.
baconbrain, Aug 30 2006

       The Earth has a mean radius of 6,372.797 km
Light travels at 299,792,458 metres per second (slower in the atmosphere, but let's factor that in later)

       This means that light emanating from the surface of the Earth nearest the aliens will arrive 0.21255 seconds earlier than light emanating from the edges of the planet.   

       In order to send a clean signal, we need to ensure that the frequency of strobation is lower than 5Hz, which is good, because it's almost exactly the value the British Health and Safety Executive reccomends limiting strobe frequencies to in order to avoid triggering epileptic seisures - although I'm not sure how many aliens they included in their studies.
zen_tom, Aug 30 2006

       //This means that light emanating from the surface of the Earth nearest the aliens will arrive 0.21255 seconds earlier than light emanating from the edges of the planet.//   

       Good point, though I think you're off by a decimal. I get 0.0213. That's about 50Hz, which is reasonable. Staging power plants such that the pulse moves across the surface of the earth at about the speed of light will result in a nice strong pulse from half of the earth followed by a weaker signal, as observed by the aliens.
Worldgineer, Aug 30 2006

       We could just carve our initials on the Moon, you know.
DrCurry, Aug 30 2006

       somewhere in deep space a predatory black hole on a fishing expedition alters course "§¶•o?7g? 8 u8uhyo7y7689©gt5 ugggg©¥©©??vƒ†¨¥??†??"" roughly translated : "hey Zuni - I think I got a bite" "Well reel her in Gooni, before she gets away, just look at all those croissants - tasty" (+)
xenzag, Aug 30 2006

       [Ling], [World] you're both quite right, I missed an 0 out. Unfortunately, while this is going to be ideal for the alien's SETI@bwaag'ahk'mahan'e*, it's not going to be great for the British Health and Safety Executive who are likely to be inundated now with calls from twitching epileptics.   

       *home being very much a planetist concept.
zen_tom, Aug 30 2006

       Isn't the UK already on 50Hz?
Worldgineer, Aug 30 2006

       You don't have to include the entire earth in the pulse length calculation, only half. The other half of the planet is effectively the dark side.
Galbinus_Caeli, Aug 30 2006

       50Hz - Ha, yes, it is - I guess the thing that stops the strobe effect being noticable must be the warm-up/down times of your average light filament/neon tube.   

       But [Galbinus_Caeli], if you don't know where the aliens are, how do you decide which side?
zen_tom, Aug 30 2006

       Just leave it to the aliens, they will figure it out.
Galbinus_Caeli, Aug 30 2006

       [zen] Actually, there's dramatic flicker that happens at 50Hz (or 60Hz, here), especially in fluorescent tubes. The reason we don't notice has more to do with persistence of vision in our eyes than the light source. I'd love to see a slow-motion film of the earth at night from space. You can probably pick out different power grids.   

       (link) It looks like lights flicker 2x for each cycle (of course!), so we really have 100Hz or 120Hz flicker. But with my staged power grid scheme we still should be able to get a good signal to space.
Worldgineer, Aug 30 2006

       I dont know but I suspect that every single light on earth pointed in the same direction at the same time would generate less light then is reflected by the moon, or even by the earth itself, Im just not sure how this would work, as the sun so radically outshines everything else in the solar system and it is not an even light, i think this would just get lost in the background of space.   

       Also SETI does not look for life in the visual spectrum, it is searching in the Radio(ultra low frequency) spectrum, which has a better chance of being recieved ungarbled.
jhomrighaus, Aug 30 2006

       /The reason we don't notice has more to do with persistence of vision in our eyes than the light source/   

       I think that phosphorus has a little something to do with it.
Texticle, Aug 30 2006

       Brains, too.   

       Isn't there some transmission delay over distances, so that lights further from the power source will blink at an equal but unsynchronized rate?
daseva, Aug 30 2006

       There has to be, but it's faster than you think. I can't find an exact number, but a quick search tells me that transmitted electricity travels at "nearly the speed of light", and is related to the resistivity of the conducting material.
Worldgineer, Aug 30 2006

       Turns out they're here already. Well, sort of :)
theircompetitor, Aug 30 2006

       Ok, so the poor aliens are looking for the pulses of light at 100-120Hz. This happens on the dark side of the Earth, of course, which is the opposite side to the Sun (no prizes for the bleedin' obvious). So the afore-mentioned poor aliens have to look for the light pulses against a background which consists of the Sun. Good job they have advanced technology.
Ling, Aug 31 2006

       //Good job they have advanced technology.//   

       If we go to all this trouble to get their attention, I hope their morals are equally advanced. (unlike the disturbing correlation between technological advancement and empathy shown in our own species - there may be "some" (I wish I could put that in italics) correlation to increased empathy, but I don't feel very safe extrapolating this to the capabilities of beings capable of near or greater than light speed travel). Maybe I should just watch the sitcoms instead of CNN.
Zimmy, Aug 31 2006

       [Ling] The sun looks much smaller out in deep space. If their optics are good enough to pick up our planet, the sun won't be a problem unless they are perfectly lined up.   

       [Zim] That's why I said (hopefully).
Worldgineer, Aug 31 2006

       Ah! sorry, [World], I didn't catch the meaning. They'd need some high quality telescopes to see the pattern on the crescent shadow if I understand. + anyway.   

       A light pulse might be something an alien SETI search routine might look for.
Zimmy, Aug 31 2006

       It might be difficult to synchronise the ends of long transmission lines; I'm no expert on power transmission though.   

       To see the flickering of flourescent lights, look at a point to one side of the light, then flick your gaze to a point on the other side. You see a series of narrow white bands, with a dark brownish colour between. Works well with outdoor lights because the background is dark. If you're keen, you can use this to estimate the transition time of your eyes.
spidermother, Aug 31 2006

       While this doesn't seem much of a beacon, I'm bunning it just for the pulse synch, a very halfbaked thought.
Shz, Aug 31 2006

       //Staging power plants such that the pulse moves across the surface of the earth at about the speed of light will result in a nice strong pulse from half of the earth//   

       That could be done concentrically to make this idea directional. I mean, it would be best observed from a particular point/direction above the center of that half of the Earth. Start at the perimeter and work inward, taking into account the sine or the cosine of the sphere, and do all the center at once. You could get a pretty good blip going in one direction.   

       All we need to do is to figure out where those alien jerks in all those bad movies come from, and signal the other way.   

       Um, after looking at a composite image of the earth at night, I think this idea is probably moot. There aren't that many continuously-lighted areas. The US could flash on and off, and Europe could, but they aren't close together.   

       Looking at a globe shows that the Pacific covers almost a hemisphere, so there's your dark side. Opposite that is Europe, surrounded by darkest Africa, the Arctic and central Asia. Everybody else is hidden by the curve of the planet, or by a great slice of atmosphere.
baconbrain, Aug 31 2006

       Re: [bacon]'s link. I love that image. Look at how bright the Nile is.
Worldgineer, Aug 31 2006

       And how dark Africa is.
ldischler, Aug 31 2006

       <squints at image> Note to self: I have left my porch light on again.
Texticle, Aug 31 2006

       Where's Canada?
Shz, Aug 31 2006

       Most of us in the US have been asking that question for years.
jhomrighaus, Aug 31 2006


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