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The search for extraterrestrial intelligence

Can information theory help us talk to aliens? Created by Brit Cruise.

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  • hopper jumping style avatar for user Shruthi Prabhu
    If people thought that there are intelligent species somewhere out there and would send out radio waves, couldn't it be possible they have gone beyond the radio wave signals and send out something far more advanced? They could be more or less intelligent than us instead of the same.
    (74 votes)
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    • male robot hal style avatar for user Cameron
      Indeed, this is one of the issues with attempting to contact alien civilizations.
      Often stars within our "neighborhood" of the galaxy are over a billion years younger or older than our star. This would tend to suggest that, if evolution occurs at similar rates on other planets, that if we contacted one of these stars with an alien civilization, the gap in intelligence would be equivalent to the gap between humans and bacteria. If the star is younger, they are the equivalent of bacteria. If the star is older, we are the equivalent of bacteria.

      The gap in technology could be enormous, and the desire for the more intelligent party to communicate with the other could be very small.
      (74 votes)
  • leaf blue style avatar for user GoldenApple황금사과
    Are there a way to find a more efficient language?
    (15 votes)
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  • primosaur ultimate style avatar for user Aaron Pennington
    Do we see these same patterns in music?
    (13 votes)
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    • winston default style avatar for user Sim
      With lyrics, yes. It's speech, so it has some of the same probability of words and characters. You can type the lyrics into the Markov text exploration applet to see that in action.

      If you're talking about patterns of notes in music, I would also say yes, definitely. Different genres of music tend to use certain scales, only using some of the available notes on a keyboard, and typing in random notes within those scales can make something that still sounds like those genres of music.

      Going even further, certain patterns in music are repeated many times, and moving up or down on a scale can make a pattern that elicits happiness or sadness. In fact, because of the predictability, you should be able to take a midi file, input the text into the Markov text exploration app (adding spaces) and come out with something that sounds like music.
      (14 votes)
  • leaf yellow style avatar for user Neels Grobler
    How would data compression affect our ability to find anything? Assuming the following:

    1 - Data compression will increase entropy. Maximum compression results in data that appears perfectly random.
    2 - Any intelligent life form that discovered radio waves also discovered electricity.
    3 - A civilization that uses electricity would then inevitably discover computers.
    4 - Electronic communication tends to replace all other radio communication as it becomes more and more advanced
    5 - As electronic communication becomes more sophisticated, data is more likely to be compressed

    Based on the above, it seems like we have a really small window of maybe 100 or 200 years of evolution where a civilization is advanced enough to use radio waves, but not so advanced that we would not be able to distinguish between their communication and just random natural radio waves
    (10 votes)
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    • male robot hal style avatar for user Cameron
      Generally, orgnaizations like SETI are not looking for just random alien communications (most of these signals would degrade and blend in with the background radiation by the time they reach us). Instead, they are looking for a signal targeted at earth for the expressed purposes of trying to contact us. It is believed that such a signal would contain sufficient information to decode/interpret it. This would include the decompression algorithm for any compressed information. This is based on how humans would try to do it, and a belief that our way of thinking and logic is somewhat universal (It is important to note that there isn't really any evidence to support or counter this belief).

      Hope this makes sense
      (8 votes)
  • blobby green style avatar for user BERNARD BLOCK
    It seems there are really two postulates here and the consequences of each is of significance.
    The first postulate is that the potential exists for other life within the universe. That certainly requires that we continue searching.

    However the more important postulate is that life on earth is the only life within the universe. This postulate is of great significance because it implies that once life ends on this planet when our sun burns out all life within the universe will cease.

    Having this alternative postulate requires a much higher significance than the first proposed herein as it means that every effort has to be made within the time limitation of our sun to insure that life continues in the universe.

    That significantly impacts on the behavior on our planet and civilization's behavior in insuring that life continues beyond the lifespan of our own planet. If we only are guided by the first premise it entails that we somehow are not driven by the need to perpetuate life within the universe because we are making the assumption that somehow it exists elsewhere.

    This is not to deny the need to continue the search for xlife but rather to underscore the need to work to see that life continues beyond earth's inherent mortality. I am curious what others think of these notions.
    (7 votes)
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    • mr pink red style avatar for user Varun
      Before we think about moving to other worlds and Earths mortality, we might want to consider that humanity is in a big mess right now and might kill itself off long before Earth's mortality ever becomes a problem.
      (10 votes)
  • winston default style avatar for user Sim
    Is it really safe to assume that extraterrestrial communications will be predictable? If information is compressed completely before its sent, like it is on the internet sometimes when downloading large files, then any radio signals would seem completely random.
    (8 votes)
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  • primosaur ultimate style avatar for user Dale Brosius Jr
    I had a thought and was wondering what others think about it. So a lot of ET belief extends from the belief that aliens have already visited Earth. Now if they had the intelligence to visit us then they would have the intelligence to know what to leave behind to prove their existence in the future on Earth. Since that proof don't exist you have only 2 conclusions. 1.) they didn't want us to know or 2.) They where never here. So keeping with the ideal that they where here we have to conclude they don't want us to know of their existence. Now if they don't want us to know of their existence then they can easily hide from any primitive method we use to try to find them.

    As I see it this all leaves it to be proven that their is no purpose of wasting time or money to search for ET life. Because either they are smarter then us and are hiding from us or they are dumber then us and we will never find them since they are billions of years from creating radio waves.
    (5 votes)
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    • leaf red style avatar for user Shawn
      Before I start, I just wanna clarify that I don't believe aliens have visited (or will visit) us in the past or in the foreseeable future, although I do agree with the statistics that extraterrestrial life - probably microbial - is most likely out there somewhere. I'm just responding cause I hate to see a good point go unanswered.
      That argument assumes the alien life cared about what we think. If we assume the visiting aliens were billions of years ahead of us, like you said, then why would they bother to leave some sort of message for us? It would be like a human leaving a memory card in an anthill; they'd be relying on the facts that:
      a) evolution would take us in the right direction
      b) we'd survive long enough to grow to understand the message
      c) they'd survive long enough for us to understand the message
      c) by the time we'd understood the message, the alien life would still care about us (they'd be a few billion years ahead too, remember)
      d) the message would have any significance to us, even if we did understand it
      it seems like a lot of 'ifs' for hypothetical planet-hopping green men to worry about, to me.
      (2 votes)
  • piceratops tree style avatar for user Srikanth Musti
    Considering that each individual person has a different sounding voice, (some being deeper than others) how did they decide that some frequencies are produced more than others?
    (4 votes)
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  • leaf green style avatar for user Lucie le Blanc
    At , how did the scientists differentiate between the different dolphin clicks and sounds? Doesn't that require a lot of complex technology?
    EDIT: what I mean is, how do they know which sounds are made by one dolphin and which sounds are made by another dolphin? Don't all the sounds blend together?
    (3 votes)
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    • blobby green style avatar for user Dean Smith
      Well yes but know, you need to record the sound and analyse its frequency spectrum. Depending on the frequency distribution you can distinguish between the sound of a voice, instrument or an explosion. A discrete frequency distribution indicates a periodic sound wave signal such as the sound of a violin with its correspoding characteristic overtones. A continuous irregular frequency distribution indicates ugly sounds...the mathematical framework is Fourier analysis.
      You can record the sounds and give every signal its corresponding sound which you can keep a data bank on.( I guess the concept relates to the bookkeeping of IR spectra of chemical compounds in the pharmacy industry.)
      (3 votes)
  • male robot hal style avatar for user Abel Sousa - (Brazil)
    What does that mean alien? (the word alien).
    (1 vote)
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    • eggleston orange style avatar for user Jennifer J
      In this context, it means not just "from another country," but "extraterrestrial" (coming from or existing outside the planet Earth"). At , you hear physicist Philip Morrison talking about the question "are we alone, as conscious beings, in this entire... galaxy." At , Brit talks about "the modern search for extraterrestrial intelligence." At , Brit says, "the study of information theory will continue to play a key role in our technological and social innovations on earth, and perhaps beyond."
      (6 votes)

Video transcript

Philip: What I would like to know is the answer to a very simple question. Are we alone as conscious beings in this entire buzzing 400 billion star galaxy, one of 10 to the tenth other galaxies? It seems pretty implausible. Voiceover: The modern search for extraterrestrial intelligence, or SETI, began in 1959 when two Cornell physicists, Giuseppi Cocconi and Philip Morrison, published an article in Nature that outlined the possibility of using radio and microwaves to communicate between the stars. In order for this to work, researchers assume that any intelligent civilization will have discovered the ability to transmit radio waves. This assumption is based, in part, on the fact that it took human beings only 80 years to figure out how to do this following Alessandro Volta's discovery of batteries and electric current. The premise is quite simple. We can create radio waves by sending short pulses of electric current through wires. These waves can then travel beyond our atmosphere and out through space with little interference. Once these radio, or electromagnetic, waves are sent out, they can be received using antennas and turned back into electrical pulses. In 1960, Frank Drake conducted the first search for radio signals from other solar systems. Much like turning a radio dial, Drake was trying to scan the sky in order to tune in to faint radio signals that might be coming from other worlds. Though this first attempt did not result in any noteworthy findings, researchers have been scanning the stars ever since. Carl: So, there is some chance that in the next few decades we will get a signal from some spectacularly distant, spectacularly exotic civilization, and everything on earth will, as a consequence, change. That is possible. Kent: The interesting thing about the SETI search is that although we claim that we're looking for extraterrestrial intelligence, we can't actually define what an intelligent signal is. A starting point is to say we look for a signal which nature will not produce by any mechanism that we understand. Voiceover: An important question emerges. How can we ever know if such a signal is coming from an intelligent source? At the first SETI meeting in 1961, John Lilly proposed that researchers study dolphin languages to help them learn more about what extraterrestrial signals might be like. Much of this early work culminated in the research conducted by Laurance R. Doyle and Brenda McCowan. Doyle and McCowan's work is based on the assumption that if there is some common trait in both human and nonhuman communication systems, then extraterrestrial communication systems should also share this trait. They analyzed a long sequence of vocalizations from both adult and baby humans and dolphins. In the case of dolphins, this was a set of whistles and clicks. Human babies learn to speak through a process of vocal imitation, slowly amassing a larger and larger set of sound signals. (baby babble) However, during what is known as the babbling phase, the sounds produced are more or less random, or unstructured. To see this, Doyle and McCowan plotted the different sound signals against their frequency, or how often they occur, then they ordered the symbols in the graph according to frequency, with the most common symbols on the left and the least common on the right. With human babies, the slope is nearly level as all sound signals produced occur fairly evenly or randomly. However, as children learn the language of their parents, they narrow their sound repertoire to fit the model to which they are exposed. As a result, structure is imposed on our speech patterns. Consequently, the slope of this graph converges towards a 45 degree angle, or a -1 slope on a log-log chart. This is known as Zipf's Law. What's interesting is that this same slope appears in different human languages, and seems to be a pattern all humans share. Even more surprising is that this pattern also emerged when Doyle and McCowan analyzed nonhuman communication. They found that the whistle sounds produced by baby dolphins seemed to be distributed in a pattern similar to human babies during the babbling phase. At first, the dolphin whistles are more or less unstructured. By the time they reach adulthood, the graph converges on a slope of about -1, which is the same as humans. (dolphin cries) But this sort of analysis looks only at individual signals, or words, and doesn't say anything about the deeper linguistic structure of either human or dolphin communication systems. Let's clarify what we mean by deeper structure with an example. If I select a random word from a book and ask you to guess what it is, you will have no clue what it might be and will have to simply guess. If, instead, I give you a random word from a book and ask you to predict the word that follows it, you will still have to guess, however, you'll notice it's likely easier to guess this word. If I give you a sequence of two words from a book and ask you to predict a third word, it becomes more predictable still. If you are given a sequence of three words, this trend continues. The ability to guess is even easier. It seems that as a result of the structure of language, the freedom of choice decreases as we look at longer and longer strings of words. Intuitively, this is why we can finish each other's sentences. Now, to quantify this, Doyle and McCowan borrowed Claude Shannon's measure of entropy, which, as you recall, is a measure of surprise. Entropy can be thought of as the number of yes or no questions, or bits, required to guess the next word. As predictability increases, the information entropy decreases. Doyle and McCowan calculated the entropy for different depths, or orders, so single words is first order, groups of two words is second order, groups of three words is third order, and so on. Then they plotted the value of information entropy against this depth. For adult humans, as we may expect, they found that the information entropy decreases as the depth increases. This is a result of the rule structure in our communication systems. Amazingly, Doyle and McCowan did the same thing with dolphin languages, and found the same pattern. Dolphin communication systems display decreasing information entropy as we look at longer sequences of sound signals. This means that in dolphin communication systems, there is a rule structure which emerges, and arguably, this also allows dolphins to finish each other's sentences, too. (dolphin cries) Contrast this to just a random sequence of symbols, which has a flat line on this information entropy graph since there is no conditional dependence between symbols. Because this pattern emerges in both human and nonhuman communication systems, Doyle and McCowan have suggested that this decreasing of entropy is essential for the transmission of what we might call knowledge. As Doyle puts it, if we get a narrow band signal, a -1 slope on the Zipf plot, and higher order Shannon entropies, we've nailed it. All of this rests on a simple premise, that aliens, too, can finish each other's sentences. Dark-haired man: How can I help you to communicate with us? Alien: How I am able to speak. By assimilation of former photosynthesis. I have been able to incorporate certain of Dr. Wyman's functional processes. Dark-haired man: Was Dr. Wyman's death necessary? Alien: Through his sacrifice, I can communicate. Voiceover: Without even understanding the language or culture of the other human or nonhuman species, Claude Shannon's entropy is a unit of measure that can allow us to detect the presence of these structural rules regardless of meaning. Claude Shannon's model of information was born out of a desire to save time over the telegraph wires. This led to the global unit of information, the bit, a single difference, now the backbone of our information economy. The increasingly digital and network technologies that drive our modern world point to the power and persistence of Claude Shannon's ideas. The bit is here to stay, and the study of information theory will continue to play a key role in our technological and social innovations on earth and perhaps beyond. Carl: I think even if there's a plausible argument for a few we ought to keep looking. I'd even go further than that. If there's a plausible argument that there isn't anybody out there, bearing in mind that we can be wrong, we ought to keep looking, because the question is of the most supreme importance. It calibrates our place in the universe. It tells us who we are. So it is worthwhile trying to find other civilizations, I would say, no matter what.