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Setting: Western world nation, Earth as we know it, May 2016, Gregorian calendar. Eccentric billionaire, large multinational corporation or similar; lots of money, and ability to enlist the help of some really smart people.

Let's say that I, for some nefarious or benevolent purpose (doesn't matter) want to make it seem like there is intelligent life out in the universe, and that they have something important to teach us Earthlings. Let's say that I have determined that the best way to do this is to transmit a signal of apparent extraterrestrial intelligent origin toward Earth at a time when I know that someone will be listening in that direction.

I have figured out the details of what to transmit, how to modulate the signal, which frequency to use, how to masquerade the launch so as to not attract unwanted attention, and every other such preliminary item on the checklist.

I have the ability to launch spacecraft (maybe myself, maybe by paying a commercial launch services company). I also have the ability to design and build a satellite or probe to make the transmission, and make it seem sufficiently legitimate to (again) not attract unwanted attention. I have the money for several such spacecraft and am willing to spend it if doing so significantly improves my chances of success. I can make things happen in such a way that it's very hard to trace it all back to me.

There's just one tiny problem left.

Given that I have all this down pat, in the face of a reasonably expectable level of scrutiny, how can I make the transmission appear to originate from a distant star?

I don't really care which star, but if possible would like for it to be one that is something like 20-60 lightyears away. Ideally one that is known to host a planet that is potentially at least non-hostile to life as we know it, but that is less important than that the transmission will genuinely appear to originate from well outside of our solar system.

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    $\begingroup$ Eccentric billionaire wants to fake an alien signal from a star about 20-60 light years away? And wants to do it for benevolent purposes? That sounds like a plot point from the movie, Contact. $\endgroup$
    – RichS
    May 29, 2016 at 6:10

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No, it is not possible to fake it. The simple one word reason is parallax.

Let's say you try to fake a signal from Vega (to borrow an example from the movie, Contact). That's 26 light years away, so within the range you mentioned.

You can put a satellite in orbit around Earth and make your satellite transmit a signal, and pretend the signal is from Vega. A radio dish could pick up the signal when your satellite is in the same position in the sky as Vega. All a radio astronomer has to do is ask a technician at a different radio telescope a few thousand miles away to point their dish at Vega. When the other dish points at Vega, it won't be pointing at your satellite, so it won't get the fake message from your satellite.

It's a simple parallax test.

Radio astronomers do this all the time. Every day. They might get some transient signal. The signal is not necessarily an artificial signal, but something from either a nearby source on Earth, something in orbit around Earth, some automated unmanned aircraft flying over their dish's controlled airspace, or perhaps a weird natural phenomenon hundreds of light years away. How do they filter out Earth based (or Earth orbiting) signals from astronomical events? They just ask their buddies at a different radio telescope to do a quick check. This check only takes a few minutes. If their buddy a few thousand miles away gets the same signal, they know the source is not from Earth. If their buddy does not get the signal, they know the source is Earth based.

I'm surprised the main character, Eleanor Arroway, did not mention this very simple test at the end of the movie when National Security Director, Michael Kitz, asked if Hadden could have faked the signal.

How do I know this? I've been an astronomer. I published peer-reviewed articles in astronomical science journals. There is a reason why my profile picture shows a radio dish.

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  • $\begingroup$ The question was very much inspired by Contact, yes (but I did my best to make sure that it could stand on its own). Frankly, this is exactly what I expected that the answer would be, but it's always interesting to see what the Worldbuilding SE community can come up with. I've been surprised before. $\endgroup$
    – user
    May 29, 2016 at 11:17
  • $\begingroup$ Have you ever looked at hologram? It makes us see light coming from point far beyond it's surface. Holograms can pass parallax test all right. $\endgroup$
    – Mołot
    May 29, 2016 at 21:15
  • $\begingroup$ That's not how holography works. Holograms require a specially prepared surface so an observer can see different images from different angles. (Usually different views of same target object.) Holography needs a single observer at a single location turning a holographic surface to see different images. Parallax is when 2 observers at 2 different locations looking at the same object and seeing different backgrounds. $\endgroup$
    – RichS
    May 29, 2016 at 21:27
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    $\begingroup$ @DonaldHobson And when those satellites pass overhead at a kilometer per second, they will not be between the dishes and Vega. It would take from a few minutes to over an hour depending on the satellite's orbit. That's another reason why you can't fake an alien signal with a satellite, and I considered that as a different answer, but chose to post about parallax instead. You can post that as a separate answer. I recommend doing the math for satellite orbits first. Here's a site for that. physicsclassroom.com/class/circles/Lesson-4/… $\endgroup$
    – RichS
    May 30, 2016 at 16:37
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    $\begingroup$ @JasonK Transient signals are not useful signals. If you can't get other observatories to see the signal, and you can't even get a repeat of the signal after a few seconds, it's just noise that clutters up what you were observing in the first place. Astronomers consider most transient radio signals as Earth-based signals. $\endgroup$
    – RichS
    May 31, 2016 at 15:29
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What you need is synthetic hologram, only in radio spectrum, not visible light spectrum. But EM is EM, it is doable, at least in theory, and it is possible to create wave front that would look exactly like if it originated at arbitrary point (for example, distant star).

Earlier answer about phase array is neat. Indeed, phase arrays can be considered form of holography. But they are bit too simple, sadly. You would want to create holographic emitter the size of Earth. This means, you would need to put quite a lot of satellites, and make sure that during emission window they are sufficiently close to each other.

Good point is, if you can cover half of the globe with satellites, and make sure no two are too far apart (think wavelength distances), you would no longer need to care who is watching.

Or simply sell IT equipment to all radio-telescope teams, and fake data directly in their database. Just make sure only "your boys" are looking when you do this.

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  • $\begingroup$ What about @richS' s comment on his answer regarding holograms? $\endgroup$
    – JDługosz
    May 30, 2016 at 7:33
  • $\begingroup$ @JDługosz Hologram creates wave front as if it came from arbitrary shape. Point is simplest case. If "surface" is otherwise transparent, this "point" will look exactly as a light source placed where you want it to. Look here at one angle, stick is behind squirrel. At another, it is visible. As if these objects were there. Two observers, everything looks real. Limited to single wavelenght, but for purpose of one signal, that's enough. $\endgroup$
    – Mołot
    May 30, 2016 at 9:17
  • $\begingroup$ @Mołot Several problems. A holographic surface does not emit radio waves; a hologram only exists by reflected light. Your "surface" would have to be thousands of kilometers across to fool the hundreds of radio dishes on Earth that are sensitive enough to receive alien radio signals. Such a surface would be visible to the unaided eye. $\endgroup$
    – RichS
    May 30, 2016 at 16:48
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To really do a job you'd probably have to have a [minimum of a] couple of precisely linked craft either is really high orbit, or on an outbound trajectory. They'd beam coordinated signals at either side of the earth to simulate a parallax of an source father away. You'd probably want to pick a candidate that could reasonably expect some gravitational lensing from an object on the path between here and there, to cover any inconsistencies.

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  • $\begingroup$ Won't work with even dozens of satellites. Or hundreds of thousands of satellites. Why not? There are hundreds of radio dishes on Earth capable of receiving signals from light years away. How will you keep all those satellites over all those dishes all the time? The satellites will fly overhead at a km/s and would move in and out of your field of view every few minutes. Any radio dish technician will figure out within minutes what your plan is. They will soon track every orbit of every satellite and then start ignoring your signals. $\endgroup$
    – RichS
    May 30, 2016 at 16:43
  • $\begingroup$ Outbound trajectory means: on a course out of the solar system. A message doesn't have to be continuous, but it always has to appear to come from the same part of the sky, obviously. I don't know if you can make an orbit where the object in question can appear to be in the same part of the stellar background all/most of the time. It's probably simpler to just make the craft move out system. $\endgroup$
    – Seeds
    May 31, 2016 at 20:15
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Maybe a phased array can trick the antenna into thinking that the beam is coming from some specified direction, different from the real source. That can fake the effect of the moving earth and actual position of the source.

You might need different "trick" signals for each receiver. If the signal requires special equipment or only the elite observatories can do the job, that can help with the plans.

You will need to keep an eye on any plans for variations in the observations, such as deciding to observe from a different position or with different equipment. And, the transmitter will need to cope with these changes on the fly, when it's already way out there.

So, you will need some insiders helping you, as well as equipment capable of contingencies.

You might have the signal come and go with poor reliability. Then it's not too suspicious when you have to cut it after the observatory makes an improvement, before you can compensate for it. Compensating might even require the inside man to do something at the receiving end, as well as reporting on the details of the listening post.

To summarize, you can't fool all possible observers all the time. But you only need to fool the actual observations that are made. You can prevent observations that could not be handled, and adapt on the fly.

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  • $\begingroup$ Care to explain the downvote? Downvotes indicate "egregiously sloppy, no-effort-expended post, or an answer that is clearly and perhaps dangerously incorrect." and I fail to see how that describes this answer. So, please include a comment. Or comment first and see if the post is improved. Downvoting here is not to indicate "not what I'd do". ... hmm, looks like every answer has a downvote, which is suspicious. $\endgroup$
    – JDługosz
    May 31, 2016 at 8:48
  • $\begingroup$ I assume by "phased arrays" you mean a group of satellites all programmed to deliver the same message so a single receiver gets the entire message in sync. That's very technically challenging. Very tricky! No groups of transmitters do that today to my best knowledge. That's the opposite of using several receivers as a radio interferometer so the entire group of receivers acts as a single antenna. The trick for radio interferometry is getting the signals lined up when the receivers are in different focal planes. The focal planes can be off by several hundred meters or even kilometers. $\endgroup$
    – RichS
    Jun 1, 2016 at 6:01
  • $\begingroup$ So if the focal planes are off by several km, the signal is not received in sync. Each difference of 30 cm is a nano-light-second. A photon travels about 30 cm in a billionth of a second. Radio dishes look for signals from .5 cm to 11 m because that's where Earth's atmosphere is transparent to radio waves. en.wikipedia.org/wiki/Electromagnetic_radiation#/media/… If your radio dishes are 3 km apart, they will receive signals out of phase by an order of 10,000. (3 km / 30 cm) $\endgroup$
    – RichS
    Jun 1, 2016 at 6:10
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    $\begingroup$ During my last visit to a radio dish in Goldstone, California, I inquired whether anybody was researching how to make several radio transmitters stay in sync. Goldstone would want to solve that problem because they transmit signals to space probes in the outer Solar System. If they want to use multiple dishes to do that, they want the probe to get a coherent signal, not a bunch of garbage caused by overlapping out-of-phase signals. The answer was that some physicists and mathematicians at JPL and CalTech are working on it. $\endgroup$
    – RichS
    Jun 1, 2016 at 6:17
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    $\begingroup$ Explaining why the phased array idea is wrong takes more knowledge than explaining why other answers here are wrong. Your answer is much more sophisticated and touches on a complex problem the other answers don't. Your idea is similar to another idea of using "precisely linked craft in orbit" to "beam coordinated signals". I wanted to give the more sophisticated comment to that answer as I did to yours. Nice try, but your phased array in orbit won't work. If you get it to work, you can make some scientists really happy! $\endgroup$
    – RichS
    Jun 1, 2016 at 6:20
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Yes, Easily. A couple of men walk into the observatory in engineer type cloths, carrying a toolbox. They fiddle around and measure some things then attach a small box of electronics to the direct input, the system contains a microprocessor and is programmed to add its own signal to the incoming one.

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    $\begingroup$ That won't work at many sites. Even when I visited other observatories, I needed a visitor badge. There are hundreds of radio observatories, military radio dishes, and radio communication sites for talking to spacecraft. You would have to get your guys to fool them all because it only takes 1 site to show your signal is a hoax. As Lincoln once said, you can fool some people some of the time, but you can't fool all the people all the time. $\endgroup$
    – RichS
    May 30, 2016 at 18:46
  • $\begingroup$ And of course, next thing you know, someone gets curious because the signal is slightly out of phase with what it should be given the frequency and expected linear distance on a path toward the star, because whatever system you designed isn't totally perfect when run in synchronization with dozens or hundreds of other similar ones. And before you think I'm making that up, while I don't know if this is regularly done on random signals, remember that interferenometry is a real thing. A signal of apparent extraterrestrial intelligent origin would likely be subjected to quite some scrutiny. $\endgroup$
    – user
    May 31, 2016 at 7:35

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