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I Can aliens hear us?

  1. May 1, 2017 #1
    To date we have not picked up any signals from aliens. Some take this as a sign that we are alone in the universe or that intelligent life and culture, if it exists elsewhere, is rare.

    What I am not clear on is what we are expecting to find.

    Reversing the argument, if aliens were searching the heavens for us how close would they have to be to be able to deduct the electromagnetic radiation we have been inadvertently sending over the past 100 years or so?
     
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  3. May 1, 2017 #2

    phinds

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    Well, how far do radio waves travel in 100 years?
     
  4. May 1, 2017 #3
    There is no possibility they could detect e.g our television signals, these become indistinguishable from background noise within a few light years. Signals such as military radar are more powerful, but they exist within such a narrow beam that the aliens would have to be in exactly the right place and time to detect them.

    So the chances of detecting us electromagnetically are almost nil. But if biospheres are rare, then we have already been sticking out like a sore thumb for millions of years, and aliens with sufficiently powerful telescopes will know of our planet's unusual properties. How they choose to respond to that is a matter of pure speculation.
     
  5. May 1, 2017 #4
    So you are saying that aliens would be able to detect our signals at 100 light years?
     
  6. May 1, 2017 #5
    This is what I've suspected. So our only realistic chance of picking up a signal is if aliens are deliberately beaming a powerful signal at stars they think could have planets that are home to civilisations. So absence of signals could also be a deliberate policy of non communication.
     
  7. May 1, 2017 #6

    phinds

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    Not exactly. What I am saying is that there is NO possibility if they are farther away. Although I think Walton overstates the case regarding the difficulty of radio waves being detected at various ranges, I absolutely agree w/ him that there is likely about zero chance at the full range of our signals. Normal radio/TV signals are not DESIGNED to be detected much beyond their designed broadcast range which is, after all, right here on Earth.
     
  8. May 1, 2017 #7
    We could in principle develop telescopes that could filter out the background noise.
     
  9. May 1, 2017 #8

    tech99

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    Analogue transmission lasted for only about 100 years, the Twentieth Century, which is negligible in the timescales of the universe. Digital transmissions are designed to be noise-like, because that is the most efficient way. Without knowing the code, digital transmissions are difficult to distinguish from noise.
    My rough figures (may be wrong) tell me that, using a 100m receiving dish, signals from a UHF TV station with 1 MW ERP would fall to the noise level in about 100 hours. This assumes 1 deg K for the Cosmic Microwave Background at 1 GHz and 10 kHz B/W.
     
  10. May 1, 2017 #9
    Don't forget, even if they did get a signal distinguishable from the background noise,they may not see it as it is. As it is very possible they communicate in different ways. Sound(speech)is a human form of communication,what is to say they don't communicate by colour,taste or touch,even pheromones like hive insects such as ants? I am no xenobiologist but I'm sure the old of means of communication will be the same. They might even talk outside of the pitch(right word?) we are capable of hearing.
     
  11. May 1, 2017 #10

    russ_watters

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    I'm pretty sure you are answering the wrong question. The OP isn't asking how far away our radio signals could be detected by now, he is just asking how far away our radio signals could be detected....as a way to judge if we could detect an alien species with a similar level of technology to what we posess today.
     
  12. May 1, 2017 #11

    russ_watters

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    There is also the Arecibo message, which demonstrates that it is possible in principle to send a signal, with meaningfule data, that has a chance of being detected and disciphered at 25,000 light years, with 1970s technology.

    https://en.m.wikipedia.org/wiki/Arecibo_message

    The Aricebo message was a one-shot deal, but using some game theory logic, one could examine the possibility that a civilization might be sending such a message our way.
     
  13. May 1, 2017 #12

    russ_watters

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    While more or less true (but extremely unlikely), no such society would be of a sufficient level of technology to pique our interest in the context of the question.
     
  14. May 1, 2017 #13

    phinds

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    Fair point, but double-check the last sentence in the OP
     
  15. May 1, 2017 #14
    Yes this is exactly what I was asking
     
  16. May 1, 2017 #15

    russ_watters

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    Yes - I think you are reading something in the last sentence that isn't there; Timeframe of emission is mentioned, but timeframe of receipt is not.
     
  17. May 1, 2017 #16

    There has been much speculation on what sort of signal or code we could send that would be discernible by ET intelligence. Prime numbers are a very popular idea and I also think it is a good bet. If there is one universal science that can be transmitted and probably understood by a vastly different culture or civilization I think it would be mathematics. So, yeah: pulses at intervals or maybe duration (in seconds?) that reflect prime numbers.

    As far as how long for them to hear us, we must remember the vast distances involved. Any intelligent life is going to come from outside of our own solar system, so that means the nearest star system is the binary Alpha Proxima/Centauri system, which is some 4.3 light years away. So even if the ET's were this close (which is a small chance) you're looking at close to nine years for us to recieve a message that they got ours and then decided to respond. I personally am of the opinion that the Universe is teeming with intelligent life. But I also do not believe that we have been visited, like these UFO apologists do, becasue of, again, those mind-numbingly vast distances. Just think: our own little MIlky Way galaxy is about 100,000 light years across! And this is only ONE of billions of galaxies. So even if there was Intelligence in our own "Local Group" of galaxies, it could take longer than your entire lifetime for us to receive ans answer to a signal we transmitted.

    For this reason, the "needle in the haystack" dynamic, the US government cancelled the SETI program a few years ago. It is not that they don't think there's no life out there, it's just that they know the distances make the chances of contacting them while anybody here is still around very small. I tend to think the odds are better that we one day recieve a signal or even get visited by a very advanced civilization than they are of somebody out there getting one of our signals.

    This latter idea of course opens up a whole new debate: would it be a good thing for us to be visited by ET's? Many Cosmologists don't think so. Including Stephen Hawking.
     
  18. May 1, 2017 #17
    I think life is relatively common in the universe, but intelligent life? I'm not so convinced. And to take that one step further, intelligent life with sufficient technology to make themselves known to us? And yet further, intelligent life with the technology, thought pattern, that can make themselves known to us, WANT and TRY to make themselves known to us, and exist in their technological age in timespans comparable to ours, at distances close enough to be relevant and detectable? Yea...no. These chances IMO are so close to zero they can be considered zero.

    Think about what all has to go right for this scenario. A suitable planet close enough to us with a star similar in age to our own, a planet in the habitable zone with a stellar environment stable enough to allow life the chance to evolve for billions of years, an environment similar enough to our own for that life to have evolved similar thought patterns to our own, a planet with sufficient resources to develop electrical technology, a stable neighborhood free of an over abundance of asteroid impacts, a possible need for them to be aligned in such a way to detect us by transit, and have this occur in nearly the exact same miniscule timeframe as our ability to receive, understand, and acknowledge a signal? This seems a near impossibility.
     
  19. May 1, 2017 #18
    Much as I would like to believe that instellar travel is possible and that we will be visited by ET I think the distances involved are just too far for living beings. Despite the incredible technological advances of the last fifty years the reality is that those advances have been predominantly about computing and control of the small scale. There were BMW adverts boasting about how the 7 series had more computing power than the Apollo space craft. True but what was not said is that the 50 year old Saturn 5 rocket is still the most powerful rocket ever launched and the fastest aircraft is still the Blackbird from the 1960s. Despite our advances we are not at all close to visiting the stars. I think ET will face the same problem. If we are ever visited it will be, in my view, by inorganic AIs for whom thousands or millions of years travelling between stars is no problem.
     
  20. May 1, 2017 #19
    [QUOTE="Schnellmann, post: 5752935, member: 596904]If we are ever visited it will be, in my view, by inorganic AIs for whom thousands or millions of years travelling between stars is no problem.[/QUOTE]

    And even that has its own significant technological and circumstantial hurdles.
     
  21. May 1, 2017 #20
    Our universe is almost 14,000,000,000 years old. Humans have existed maybe approx. 200,000 years. We have been using radio waves for just over 100 years. I think it is somewhat pointless to try to figure out what the other intelligent species (if any) can see, hear or do, as they have most likely been existing and communicating much much longer than us. Speculating is always fun, though!
     
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