Timeline for answer to Given present-day Earth as we know it, how could I fake a radio transmission as coming from a distant star? by RichS
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| May 31, 2016 at 20:34 | comment | added | Seeds | Right, make it convincing enough upfront, then yell "Government coverup" and watch the fun. :) | |
| May 31, 2016 at 15:53 | comment | added | Jason K | Sure, but since this is just a scam maybe the transient signal is alarming enough that the billionaire can use his PR machine to get the reaction he wants despite scientific opinion to the contrary. Kinda like the climate change debate :) | |
| May 31, 2016 at 15:29 | comment | added | RichS | @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. | |
| May 31, 2016 at 15:09 | comment | added | Jason K | What if the transmission is very short and only 1 antenna is conveniently looking in the right direction? Then when other antennas try to corroborate the signal it has already passed? How many antennas are looking/recording a particular star at one time? Is it possible the number is small enough to target each of them with a short signal? | |
| May 31, 2016 at 7:43 | comment | added | user | @RichS Semi-related to your comment about jamming an AM station (it's about amounts of power needed for interstellar communications), but if you have the time, I would love some expert attention to my answer to How far away would an alien civilization need to be for us to not notice them? | |
| May 31, 2016 at 7:32 | comment | added | user | @RichS I think Jonas Dralle is referring to amateur radio Earth-Moon-Earth (EME) communications. That's actually possible, using: very narrow-band transmission modes (JT44, slow CW, etc.), quite high power (at least 100-1000 W from the transmitter; a common ham setup is 100 W), and on both ends considerable antenna gain (tens of dBi) with antenna arrays steerable on both horizontal and vertical axis, to point them at the Moon. I wouldn't go as far as calling it common. I can't even imagine the kind of equipment that would be required to do something similar with a distant star. | |
| May 31, 2016 at 7:07 | comment | added | BlueWizard | @RichS i havent written a complete answer but a comment to RichS answer about parallaxes. | |
| May 31, 2016 at 6:43 | comment | added | RichS | @JonasDralle Not just unreachably high for the average person, but many times greater than humanity's entire energy annual consumption. | |
| May 31, 2016 at 6:26 | comment | added | BlueWizard | @RichS the energy consumptions is incredible high. Unreachable high for john doe | |
| May 31, 2016 at 6:25 | comment | added | RichS | @JonasDralle Please clarify. Do you want to bounce a signal off Vega and have it come back to Earth? If so, do you know the energy calculations to do that? For fun, I once calculated how much energy it would take for a transmitter in our outer Solar System to jam an AM radio station on Earth so listeners on Earth would receive the jammed signal instead of the AM station. It's billions of times more energy than Arecibo, the world's largest radio dish, can project. And you want to bounce a signal off Vega which is 1,644,000 times further away? | |
| May 31, 2016 at 6:19 | comment | added | RichS | @JonasDralle We don't use Earth's moon to bounce messages around. It's not like the ionosphere of the Earth where you can bounce messages off it. Besides, have you done the energy calculations for what it would take to project a message to the moon with sufficient janksys to bounce the message off for it to remain a coherent signal? Let's put it this way. A corporation once asked what it would take to project their logo on the moon. Astronomers told them the energy calculations made their advertisement idea silly. | |
| May 31, 2016 at 6:10 | comment | added | BlueWizard | We use the moon (and various other things) to bounce messages around. When you can calculate the position of vega in 26 years you can pretty much fire a signal to it, it will bounce and then will come back to us. Of course we're moving too and the signal will be spread very very thinly but I dont think someone could determine weather or not it was send by you 52 years ago or not | |
| May 30, 2016 at 20:56 | comment | added | user | @DonaldHobson It's not even "a km/s", it's approaching 10 km/s. Earth orbital velocity starts around 7-8 km/s, depending on the exact altitude. Let's say (just to pick something) that a satellite is in low Earth orbit, where it has an orbital period of 90 minutes or so. If my math is right, that means the satellite's radial velocity is 360°/90min = 4°/min = 4'/sec. I don't know off hand the beamwidth of radio dishes commonly used for these purposes (maybe RichS can fill in there) but I suspect it's well below even the arcminutes range on any reasonably interesting frequency to even -10 dB. | |
| May 30, 2016 at 16:37 | comment | added | RichS | @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/… | |
| May 30, 2016 at 11:46 | comment | added | Donald Hobson | If you have a satellite over each telescope then they will both get a signal. | |
| May 29, 2016 at 21:27 | comment | added | RichS | 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. | |
| May 29, 2016 at 21:15 | comment | added | Mołot | 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. | |
| May 29, 2016 at 11:17 | comment | added | user | 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. | |
| May 29, 2016 at 11:15 | vote | accept | user | ||
| May 29, 2016 at 6:09 | history | edited | RichS | CC BY-SA 3.0 |
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| May 29, 2016 at 1:53 | history | edited | RichS | CC BY-SA 3.0 |
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| May 29, 2016 at 1:46 | history | answered | RichS | CC BY-SA 3.0 |