{WARNING: The next three paragraphs are buildup to the actual idea, for those unfamiliar with the subject. If you understand the Fermi Paradox, skip past the next three paragraphs.}
The Drake Equation (sound in principle, although any numbers you try to plug into it are suspect.) states that there should be loads of extraterrestrial life. After all, we live in a galaxy with an enormous number of stars, many of which (based on known statistics, which are admittedly sketchy) have planets. And some fraction of these planets ought to be able to support life. Judging by how quick life sprung up on Earth, it seems reasonable to assume that many of these life-supporting planets support life of some kind. (as well as can be judged from a sample size of one) Even after all this, there should be a massive amount of life in are galaxy. At the very least, one would expect more than one intelligent lifeform out there (although I admit that, with a sample size of one, nobody's really in a position to expect anything.)
So, why haven't we noticed a single sign of it? Not even a single wayward transmission has been detected to date. We would expect the Galaxy to be teeming with life, and yet we have never seen a sign of it. This is known as the Fermi Paradox. Although one could argue that we haven't been looking long enough (which we haven't), that we're looking at too small a band for transmissions (which we are), and any number of reasonable arguments, these can be solved only by time, technological advance, and whether society decides to care about this apparent pipe dream. However, one other solution to the Fermi Paradox is this- that everybody's listening , but nobody is talking.
It takes deliberate effort to send intelligible signals to the stars. Relying on stray transmissions from our radios and cellphones won't work- even our most powerful transmitters are pointed at other people, not the sky, and the spread of compression algorithms makes the sound of Earth almost indistinguishable from radio noise. Besides, technologies that leak away signals to the void tend to be outmoded and replaced, because (unless that's what they're meant to do) it's just a waste of power. Judging by our society, even under the best conditions, the window when civilizations are visible without deliberately making themselves so is small indeed.
Therefore, if we want to contact other civilizations, somebody has to be talking for the other to hear. Since they don't seem to be screaming out into the void, we might as well do it.
As such, I propose to build a solar statite. A statite is a device that uses a large solar sail and photon pressure to balance out gravity, in this case, the gravity of the Sun- they've been proposed, and we could actually (if we wanted to) build one without invoking any technology we don't have already or conceivably develop in a few decades. There's nothing actually new about them, we just don't have the architecture in place to build them.
This statite will be placed in a slow orbit out of the plane of planetary orbit, so as not to block the signal. Supported by the statite will be what essentially amounts to a Hubble-or-larger scale telescope, pointed so that the "eyepiece" is toward the stars. The telescope will also have a vane array, similar to Venetian blinds, on Sun end of this "reverse telescope." The basic effect of this is that, while open, this would make our star much, much brighter than normal to all observers in the beam, which itself will remain visible over a much larger range than the Sun itself would be. The vanes would be used to shut the beam on and off in some clearly intelligent pattern that couldn't be mistaken for a pulsar or something. Pi and the Fibbonaci sequence just sound like nonsense if you come in in the middle of the transmission, so probably we'd transmit something like one pulse, wait, two pulses, wait, three pulses, and repeat.
We’d probably also want to put some method of propulsion on the statite, in case we want to move it so that it points at some star system we preferentially want to signal at, like a star with Earthlike planets. In this case, we would tilt the solar sail, and photon pressure would cause it to go kiting off to a new orbit.
One advantage of this method of signaling is that it’s very simple and low-power. The enormous nuclear inferno of the Sun provides all the energy we need, all we’re doing is focusing it with a few mirrors. It has few moving parts, being largely reflective foil and optics, with the only electrical parts being a few solar panels to power the vane array and a simple, programmable circuit that modifies the sequence. It’s also low-maintenance, as we can pretty much stick it out there and forget about it. And it also gives us a target, because we can focus on preferentially scanning the skies for transmissions from stars in the path of the signal.
The only major disadvantage of this is that we’re essentially screaming our location at God-knows-who, or –how-hostile.-- Hive_Mind, Sep 25 2010 What Floats Their Boat http://www.foxnews....air-force-officers/ [Grogster, Sep 25 2010] I don't believe it's that they haven't heard; from what I gather what we've had to say so far has been so colossally boring that it's hardly worth their trip to drop by and ask us to turn it down. What does float their boat appears to be our nuclear programs: <link>. So, if you want more action out of them you might blast a few more tidbits from our cadre of nuclear physicists...-- Grogster, Sep 25 2010 // So, why haven't we noticed a single sign of it? //
Because we wear burkhas when we walk amongst you, stupid.-- 8th of 7, Sep 25 2010 I got kinda fuzzy wading through the first three paragraphs, then I really started blinking at "heliostat". ("You keep using that word....") Solar power people use it to mean a mirror which moves so as to keep reflecting the sun onto one spot.
I understand the concept of using a solar sail to hover in one spot--look up "statite"-- but I don't know if you do. First, you don't have to. A solar sail in any solar orbit will be nicely placed for reflecting light at any one star for a month or so at at time at least--unless you plan on bothering the frack out of one particular star, moving on will be fine.
Second, if you are going to use a solar sail, you want it as light as possible, so ditch the scope and just use the sail as a reflector, and tilt it a bit to flash on and off.
Speaking of light, the ion engine is not. Keeping it up will take a damn-lot of sail. And, if the sail were in a stationary hover, using the method you described, all you would have to do is tilt it the least bit, and it would go kiting off to another location, at least as fast as an ion engine could push itself.
I must give credit for a good concept--using solar light to signal--and for a solar statite, which was new to me. But I won't give a croissant. [ ]-- baconbrain, Sep 25 2010 I apologize. The first three paragraphs were meant to be a sort of buildup, as to why the hell we'd want this thing in the first place.
I don't know where the hell I got the idea that "heliostat" was the word I wanted. Again, my apologies. I suppose it just sounded right.
The ion engine was a late addition, because realized I wanted to move it. My fault for not actually thinking about it, or doing the research and the math on solar orbit.
I still think that the reverse-telescope focusing device is necessary to make the signal clearly visible over the vast, possibly Galactic-scale distances I want. I know that lasers as bright or brighter than the Sun, if fired through a telescope, would be clearly visible across interstellar distances, which is why I thought the telescope would be nescessary. I'll do the research and check.
Mistakes duly edited and fixed.-- Hive_Mind, Sep 25 2010 Low Earth orbit is good. Keep it below about 500 miles (800km) of altitude or you'll need to provide your solar sails with some means of maintaining their position. Above that you are out of the little atmosphere Earth has at that height and increasingly subject to "solar wind" (see below)
There are two components to "solar wind"...Solar photonic pressure (radiation pressure or electromagnetic radiation) and Solar wind pressure (about 1/1400 of photonic or radiation pressure and composed of charged particles rather than light). Both will will push your sail away from the Sun, slowly at first but with a steady, constant acceleration that will soon have it travelling at a fair clip.
Google IKAROS if you want to see the first working solar sail spacecraft.-- infidel, Sep 25 2010 I likes it better now, [Hive], and will give you a croissant. You might want to save it for when your aliens have captured us all--it'll be a nice break from Soylent Green.
I didn't mean to sound snarky in my previous anno, but the flash drive in my pocket is named something I derived from "statite", and I have put a lot of work into an idea that turned out to be preempted by one bit of a very obscure NASA-funded research project (which is probably another guy who is working out of his house). Mine's better, of course, but it won't get off the ground. So "rrrr".
I agree with the reverse telescope part. A narrow beam will be crucial. I do recall a discussion where I argued that getting the light from an apparent disc, like the sun, to stay in a tight beam was impossible, but others argued that a focus at six light-years off was the same thing.
A 'scope as you describe could be made quite light, and a light sail could keep it moving.
[Infidel], a light sail that is orbitting in any part of the earth's upper atmo, no matter how thin, is going to slow up and drop.
I am still a bit fuzzy on how sunlight gets funneled into the 'scope, but [+].-- baconbrain, Sep 26 2010 [Infidel]: The thing's not even in Earth orbit. It's orbiting the Sun.
Secondly, it's placed and sized so that gravity cancels out radiation and "wind" pressure, keeping it in a state where it's much harder to fall out of its slow orbit. So no rocketing off from photon pressure.
[Baconbrain]: I'd assumed that light was funneled into the scope simply from sunlight entering the "eyepiece," but if that is insufficient and it indeed is necessary to funnel it in by some other means, I'd probably use a Fresnel lens or something.-- Hive_Mind, Sep 26 2010 //is going to slow up and drop//
Unless it is under the action of another vector. In this case, sunlight.
//It's orbiting the Sun//
My bad, I misread that part of the idea.-- infidel, Sep 26 2010 Um, [Infidel], it seems to me that a solar sail is so light and fluffy that sunlight can push it. The atmo is either so heavy and dense that sunlight cannot push it, or it is gone away as single and free molecules headed for the Oort cloud under solar pressure. I think that any atmosphere that meets any definition of atmosphere is too dense for a solar sail to travel through.-- baconbrain, Sep 26 2010 If there is sunlight and atmosphere on one side of it and just atmosphere on the other then it will begin to move away from the sunlit side, in a straight line unless there is another vector extant... gravity might have some effect but 500 miles altitude will have neutralised it to a large extent.
Of course, I'm presuming the physics are the same on your planet as on mine.-- infidel, Sep 26 2010 My planet doesn't have laws of any kind, let alone physics.
But I cannot see a light sail in orbit in the upper reaches of the atmo doing anything but burning up or stopping really fast. If it is not in orbit, it must be forced upward against gravity by sunlight coming from below it.
My planet tends to block sunlight, but we are kind of dense.-- baconbrain, Sep 26 2010 random, halfbakery