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    08 Feb '13 14:2012 edits
    Given unlimited advances in technology and unlimited resources, is it possible to have a single-photon detector that can detect, say, 90% of the radio photons that strike an area of, say, a one square km area of an aperture?
    Or would that just be physically impossible because there is just too little energy in each radio photon to ever make it practical to have such a 90% detection of radio photons?
    And, if so, exactly why would such little energy in each radio photon make them too difficult to detect photons with that 90% level of efficiency?

    Also, given unlimited advances in technology, is it possible to make something like a maser but which emits radio waves instead of the shorter microwaves and emits radio waves that stay in parallel i.e. the emitted radio beam does not significantly spread out with distance (just like with a laser beam)?
    And, if so, given unlimited advances in technology, would it be physically possible to have one that is, say, 99% energy efficiency and converting electrical energy into radio energy? And, if not, why not?

    P.S. there is a point to all my questions -I am trying to determine what determines the absolute maximum possible energy efficiency of radio communication and, also, given unlimited advances in technology and almost unlimited resources, whether it would ever be practical to have radio communication between the star systems within our galaxy or even between the galaxies.
  2. Standard memberDeepThought
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    08 Feb '13 14:412 edits
    Originally posted by humy
    Given unlimited advances in technology and unlimited resources, is it possible to have a single-photon detector that can detect, say, 90% of the radio photons that strike an area of, say, a one square km area of an aperture?
    Or would that just be physically impossible because there is just too little energy in each radio photon to ever make it practical to ha ...[text shortened]... 99% energy efficiency and converting electrical energy into radio energy? And, if not, why not?
    It's possible to build detectors that can pick up on a single photon. To get a large aperture then you'd simply need a lot of them. It would be unfeasibly expensive though. Also if you are thinking about long wave then you may need a single detector that big which is probably too much of an engineering problem.

    I don't see any problems with a radio wavelength laser provided you can find a lasing medium - or some way of stretching the wavelength of the coherent emissions of a maser.

    There aren't any fundamental limitations to converting electrical energy to electromagnetic energy like there is with heat engines. How feasible it is is another matter.

    Communication between stars is tricky because the interstellar medium is ionized, which attenuates the signal. Between galaxies it's just too far. These difficulties pale into insignificance compared with the difficulty in setting up a communication protocol with aliens.
  3. Subscribersonhouse
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    08 Feb '13 15:46
    Originally posted by humy
    Given unlimited advances in technology and unlimited resources, is it possible to have a single-photon detector that can detect, say, 90% of the radio photons that strike an area of, say, a one square km area of an aperture?
    Or would that just be physically impossible because there is just too little energy in each radio photon to ever make it practical to ha ...[text shortened]... ave radio communication between the star systems within our galaxy or even between the galaxies.
    I worked up a possible way to communicate at interstellar distances. It would take an advanced propulsion system but this is the idea: Just for illustration, suppose you had two tightly focused laser beams say a half LY from the sun and the beams graze the surface of the sun and have a wavelength that can go through the corona. the beams are in parallel but separated by say 1 million miles. So the beams are aimed in such a way as to be 'above' the sun for one beam and 'below' the sun for the other.

    The illustration is to show that because of gravitational lensing, the beams would deflect inwards at that famous 1.75 arc seconds or so, inwards and at some point out in space the beams will intersect.

    That distance happens to be around 80 billion Km out, a bit under 1000 AU.

    That is just to illustrate the principle.

    The idea would be to have a beam of RF at some useable frequency, say 10 Ghz just to pick one out of the hat, could be 10 Thz just as easily. The beam would originate at 1000 AU on the opposite side of the sun that you wish to send the beam and so you would need to have a beam that could focus most of its energy in a volume a bit larger than the sun. If you do it right, the beam, being circular in area would begin to focus, but if you make the beam large enough, say 10 million miles wide when it passes by the sun, then you would have in fact a converging beam line where some of the beam would focus on a line starting about 1000 AU on the opposite side of the sun where continuing on it would be going in the direction of whatever star you wanted to communicate with.

    The interesting thing I figured out about that is the beam can focus on a line that can go a long ways out and if you play with the diversion angle you can get a nice focused beam that could be 40 or 50 light years long before it peters out.

    That is using the sun as a lens more than 10 million Km in diameter.

    The lens effect does not stop at the surface but extends out to infinity.

    Of course after a few million miles the amount of gravitational bending gets really small but the lens is not limited to just the size of the sun.

    There is a lot more in that but that is the main idea. Of course you would have to have the same thing at the target sun if you wanted two way communications.

    I have seen system designs that would place a 600 mile wide lens out in space and a super powered laser sending energy to the lens to power a solar sail for an interstellar probe but you can do the same thing with powerful lasers and just using the lens effect of the sun to power interstellar solar sails also.

    This is stuff that won't be seen in our lifetimes but just a thought experiment to show what COULD be done maybe a couple hundred years from now given continuous technological development in space propulsion and high powered RF, Thz, or laser beams for such projects as communications and solar sail power.
  4. Wat?
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    08 Feb '13 17:12
    Originally posted by sonhouse
    I worked up a possible way to communicate at interstellar distances. It would take an advanced propulsion system but this is the idea: Just for illustration, suppose you had two tightly focused laser beams say a half LY from the sun and the beams graze the surface of the sun and have a wavelength that can go through the corona. the beams are in parallel but ...[text shortened]... h powered RF, Thz, or laser beams for such projects as communications and solar sail power.
    You don't think this mass accelerated development, by man, in technology, will decelerate on day in the next 200 or 300 or so years?

    If man keeps inputting as naievely as he does, you don't think computers will work out for themselves one day, especially if robotized, they can think for themselves, and take power? Of all banks, financial institutions, forces of power and the end is listless, that is dependant upon computers?

    Orwell's 1984 may not have been that far wrong. 😉

    Or will man always be in control?

    -m.
  5. Joined
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    08 Feb '13 21:1312 edits
    Originally posted by mikelom
    You don't think this mass accelerated development, by man, in technology, will decelerate on day in the next 200 or 300 or so years?

    If man keeps inputting as naievely as he does, you don't think computers will work out for themselves one day, especially if robotized, they can think for themselves, and take power? Of all banks, financial institutions, for ...[text shortened]... rwell's 1984 may not have been that far wrong. 😉

    Or will man always be in control?

    -m.
    Personally I think, when the inevitability AI singularity is finally archived and AIs become vastly more intelligent than us humans, we will quickly cease to be in control control because the AIs will take over -but not because of the paranoid reason some people assume. I think it would be far from being too assuming to think that we would not be so stupid to fail to carefully program the AIs so that they would not want to forcefully take over us or do us any harm. BUT, I think we would still loose control to the AIs anyway because we would choose to do make that happen! That is because we would quickly notice that, as a result of the AIs being vastly more intelligent than us, they could run schools, universities, science research, industry, engineering projects, businesses as well as the whole economy and even diplomacy vastly better than we, the comparatively stupid humans (esp the politicians), can do and, one people notice that, they would, in self interest, demand that the AIs take over control! After that, any economic problems would evaporate and there would be no more world poverty -it would be a friendly takeover.

    Just a thought though; would that really mean the end of any meaningful democracy? -because, the way I see it, the only thing left for the elected human politicians to do would be to deal with things that don't really matter such as the arts and sports -then might as well get rid of this last vestige of democracy that would what have, at best, become deduced to a mere pretense of real democracy and be done with it.
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    09 Feb '13 05:23
    Originally posted by humy
    Personally I think, when the inevitability AI singularity is finally archived and AIs become vastly more intelligent than us humans, we will quickly cease to be in control control because the AIs will take over -but not because of the paranoid reason some people assume. I think it would be far from being too assuming to think that we would not be so stupid to f ...[text shortened]... ld what have, at best, become deduced to a mere pretense of real democracy and be done with it.
    We all got our dreams humy.
  7. Cape Town
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    09 Feb '13 07:39
    Originally posted by DeepThought
    Communication between stars is tricky because the interstellar medium is ionized, which attenuates the signal. Between galaxies it's just too far. These difficulties pale into insignificance compared with the difficulty in setting up a communication protocol with aliens.
    Actually, establishing a communication protocol would not be that hard unless we were deliberately trying to keep our communications secret.
    The real difficulty is the time factor. If it takes anywhere between 4 years or 1 billion years to get a reply to any message (depending on the distance), communication is mostly one way.
  8. Standard memberDeepThought
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    09 Feb '13 11:255 edits
    Originally posted by twhitehead
    Actually, establishing a communication protocol would not be that hard unless we were deliberately trying to keep our communications secret.
    The real difficulty is the time factor. If it takes anywhere between 4 years or 1 billion years to get a reply to any message (depending on the distance), communication is mostly one way.
    You have to be able to recognize that you are being sent a signal in the first place. A highly compressed signal has high informational entropy and so is not easily distinguished from background noise. They may use something other than binary to encode signals - maybe even analogue. Any species we could talk to would have to be similar enough to us to use radio-telescopes, so let's assume it's a radio signal and not sent by some method we haven't thought of and so can't detect. You also have the problem that their natural signaling methods (language for us) could easily be very different to ours - so that they aren't easily mappable - unscrambled Navajo was used as an effective cipher during World War II and those were messages sent between humans in a context that meant the Axis navies knew it was a military communication they couldn't decode.

    Our methods of encoding images are based on how to trick our own physiology into responding as if the real thing was in front of us - if they send us their civilizational equivalent of a home video we may not be able to make any sense of the signal because our senses don't work the way theirs do - for instance sharks have this extra sense for electro-magnetic fields we don't have. So if the message is based on getting their sense organs to get their signal processing organs to respond in a particular way we could have real problems decoding it.

    If they send the equivalent of a text message then assuming they use an alphabet encoded in binary or another scheme we can cotton on to - is the encoding fixed length? If they've compressed the message and use some kind of entropy coding it's more difficult to extract the original message if there is a standard codebook they haven't sent, as we don't know how many symbols are in their alphabet (if they have such a thing) and in range coding a repeated input symbol doesn't just give you a repeated output symbol (which it does with Huffman encoding).

    Even if you isolate a signal you'll be doing well to work out how their error correction codes work. Never mind decoding the actual message - it might be in a medium we don't have a sense for.
  9. Standard memberDeepThought
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    09 Feb '13 11:281 edit
    Originally posted by DeepThought
    Assuming it's possible to get a signal through, and the round trip is 20 light years so it's possible to get 2 way communication in one lifetime, then first you have to establish that a signal is being sent or received. Step one is recognizing it as a signal, as opposed to background noise. They may use something other than binary to encode signals - m decoding the actual message - it might be in a medium we don't have a sense for.
    Clicked reply instead of edit...
  10. Subscribersonhouse
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    09 Feb '13 14:245 edits
    Originally posted by humy
    Personally I think, when the inevitability AI singularity is finally archived and AIs become vastly more intelligent than us humans, we will quickly cease to be in control control because the AIs will take over -but not because of the paranoid reason some people assume. I think it would be far from being too assuming to think that we would not be so stupid to f ld what have, at best, become deduced to a mere pretense of real democracy and be done with it.
    Well, the advent of super intelligent AI may or may not get here but if it does it will not stop the arts. I don't think AI's would even WANT to produce Beethoven level music or Picasso level art, they would leave that to humans, probably thinking it too primitive to even discuss but WE would still love it.

    They might have a couple of 1 nanosecond discussions to the effect of 'how cute, for a pet'.....

    What I see happening in that case would be a very subtle use of birth control, perhaps a new virus that limits human reproduction to get our population down to a few million or so, letting the planet recover. It would be done in such a way as to not even be noticeable by humans. We could be programmed to accept the fact that we can't reproduce in that era like we do in ours.
    It might be humans could leave the solar system and make a colony say, on Alpha Centauri, although they might think 4 light years separation would be a bit too crowded from an AI world and the AI might even build the spaceships for us🙂


    Getting back to interstellar communications, perhaps there really is a encyclopedia galactica, deliberately one way or maybe not, a real encyclopedia would be interactive but of course the time scales would be immense.

    Here is a report from the Seti bunch, first directed search coming up totally empty:

    http://phys.org/news/2013-02-seti.html

    Only 86 stars searched over a 3 month period but it's a start.
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