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Radio and other electronic signals in space?

  1. Apr 11, 2016 #1
    Not sure if this is the right section or if this might be better off over at Cosmology... or...?

    So this is actually around a story concept I had, and while I would like to get the science as right as possible, I expect a certain amount of hand-waving to get past some of the difficult and difficult-to-explain points.

    Humanity has FTL travel.
    Alien (radio or other electonic) signal (microwave? probably not laser?) can be detected in space, and can be decoded to play back on human technology.

    How difficult is it to direction find an early radio signal in space?
    Would the signal still hold its data/coherency, say 1000 light years from its source?
    As technology advances, signal technology jumps from say radio, to microwave, to...?
    Are there other iterative steps I'm not aware of between those two?
    I recall reading radio travels at light speed, are there other transmission methods that travel slower (causing gaps in the communication)?
    Making smallish micro-jumps closer to the source, how hard would it be to find a related signal and reorient on its source?

    any advice and assistance appreciated.
    This is kind of my first post to wrap my head around the problem, which would help shape the story.
  2. jcsd
  3. Apr 11, 2016 #2


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    no different to direction finding using radio on earth, except working over greater distances

    the signal strength of the signal at a given distance in space from the transmitter would be mainly dependent on the transmitter output power and how directional its antennas(s) are.
    Considering how weakly received on earth massive natural transmissions are from pulsars etc even from within our own galaxy. The chances of a strong enough transmitter on, say earth, reaching 0.5 - 1 light year distance and still be detectable and still be able to be demodulated is probably unlikely.

    radio and microwave are the same thing ... you are not the first to err on that one :wink:
    microwave generally refers to radio frequencies 1GHz and higher

    sound does, but wont travel in the vacuum of space.
    ALL EM radiation travels at the speed of light radio waves through to, strangely enough, light ( lasers)

  4. Apr 11, 2016 #3
    How are you going to detect signals if you are travelling faster than the signals are?
  5. Apr 12, 2016 #4
    Stop in ordinary space and listen before making the next FTL jump?
  6. Apr 12, 2016 #5
    In the case that you have faster than light travel, it makes sense that faster than light communication would also be preferred. Electrical wires wouldn't be used if men on horseback happened to be faster, therefore radio signals would likely not be used if messenger probes were faster. I'm not sending critical signals through to a space station orbiting Neptune that'll take 4 hours at the speed of light if I can send a messenger probe that'll get there in 20 minutes. If radio will be used at all in your universe, it'd be for ship to ship communication over very small distances.
  7. Apr 12, 2016 #6
    Interesting. Sooo... what I'm hearing is it's exceedingly unlikely to hear (by way of comparison) WWII transmissions 1000LY from earth.

    Yeah, but I should have realized. Thinking about it further, it makes enough sense that I feel a bit like a moron. :sorry:

    Sound: Well, yes.
    Haha, you funny guy: Light traveling at the speed of... light..
    I guess what I was leading to was the thought of: Are there any transmission methods outside of the EM band and sound that are known or theorized? (I suppose I can do a google search for that)

    Dave: Thanks.


    I reject your premise: Snail mail still exists even though we have radio, cell phones, and email, with a comparable rate of days vs seconds of delivery time. Also, not what I'm trying to ponder here.

    To make an analogy for what I'm looking at:
    This is someone in a jet-car stopping to get gas and while there, finding a member of the original pony express still trying to deliver their message.
  8. Apr 12, 2016 #7
    Oh ok, so you're looking for civilizations that are technologically behind us or communications that leak from planets rather than direct messages to starships. In that case, I see no reason that this is beyond even todays abilities: a radio telescope in space. Have a wide field capability to scan the entire sky for signals, then a high powered one to hone in on signals once they are seen, no different than how SETI listens now.

    I'm not sure how dim the Earth's broadcasts are compared to stellar objects, but they should appear very very different. Communications use narrow bands, cosmic events don't. They also use spectrums that almost nothing in nature uses.
  9. Apr 12, 2016 #8
    Yes, that. But from what Dave above said, it sounds like leaking em band communications would be difficult to find at the 1000 light year mark - no?
    SETI was going to be a question I was going to bring up a little later - if signal strength and degradation causes the signal to die so (relatively) quickly, how is it we expect something SETI to work... ever?
  10. Apr 12, 2016 #9
    Try this: http://www.setileague.org/articles/range.htm A 5 meter telescope has a range of about 650 light years.

    SETI does a lot more than just listen for radio signals. Remember, they also have arrays of telescopes, not one.
  11. Apr 12, 2016 #10


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    that isn't going to work ....
    consider you are moving out from earth using FTL travel and stop at a 4 LY distance from earth ( Alpha Centauri)
    you would have to sit there and wait 4 years for the radio signal to get there as it is only travelling at light speed
    Now you do another FTL jump of another 6LY, and now you are a little less than 10 years ahead of the travelling radio signal

  12. Apr 12, 2016 #11


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    gotta have a giggle here and there :-p life is too short to take it too seriously :smile:

    other things ... ummm .... gravity waves

    no, for reason, see my previous post

    yes, all star trek and some other sci fi all rely on subspace comms to cover great distances quickly
    and even then I recall several occasions where it has been mentioned that the enterprise etc was so far out from earth that
    response time was still going to be hours to days

    absolutely miniscule .... the energy put out by, say, the Crab pulsar is more than all the energy generated on earth at any given instant

    no, far from it, natural EM emissions are right across the spectrum from ELF, through microwave, to light

  13. Apr 13, 2016 #12
    Yes, if you are listening to a signal sent out from Earth after your departure.
    However, you could hear other stuff:
    You could hear signals sent out from Earth 4 years ago;
    stopping, say, 0,15 ly distance from Alpha and Proxima Centauri, you could hear signals which would only be heard on Earth 4 years later;
    you could hear signals that are too weak to hear on Earth 4 ly away, but which you at 0,15 ly can detect.
  14. Apr 13, 2016 #13
    In the case of Voyager, they were so far out that even subspace transmissions would never make it back to Federation space.

    I've heard respectable scientists (NGT, Hawking, Sagan) express concern that we are broadcasting our position out into space, do you mean to tell me that all those transmissions from earth wouldn't be identifiable as a civilization at all? I always thought that Earth is drowned out by the sun in some frequencies, but lights up like a spotlight in others.

    I've also heard that we're searching very specific frequencies because they're not natural, such as 4.46GHz (pi times the hydrogen line?)
  15. Apr 15, 2016 #14
    Sure - if you're listening for your own civilization's transmissions.
    What if you're listening for another civilization's transmissions?

    My thought is that you might hear a transmission, figure its direction (would you know it's exact point of origin?I suppose so because of how empty space is and you could probably do the math to calculate how long the signal has been traveling) Jump 2-10 LY in that direction and listen for another transmission, re-orient, jump another few light years towards it... lather, rinse, repeat.

    Doing so would be important when following a newly found civilization - my thought is that you might hear the first transmissions, jump a couple years towards the origin, suck up as much information as possible, make another jump, etc... The ultimate result would you end up with an overview of their history and media as you jump "forward" in time. If it's a long distance to the target system, you could pick up an overview of a few hundred to a few thousand years of history by the time you arrive. When you get within say, 0.5-1 LY (depending on the quality of your sublight drive) you could then spend several months processing that data and learning about them as you slowly creep up on their system, ultimately determining if you want to contact the aliens or not (assuming they have not surpassed you in technology).
  16. Apr 15, 2016 #15
    That would give you a very complete and condensed history of the species. However, if they've also invented FTL travel, those signals may be out of order.
  17. Apr 22, 2016 #16
    ...I think that's what I said/implied.
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