Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 10/05/2016 15:18:14
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Jeff asked the Naked Scientists:
The question that I have is if we received an accidental message from space that was encrypted would we be able to recognize it, and would we be able to realize that it was encrypted?
I say accidental because I would assume that an intended message would be clear text, but an accidental message, such as an alien telecom signal would be encrypted so that it could not be intercepted. Think of HBO, in the seventies and eighties people bought large satellite dishes to receive it for free. When HBO realized that it was losing revenue due to this issue they began to encrypt the signal. Would we be able to recognize such a transmission from an alien civilization?
What do you think?
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Well, it depends. If the encryption is really good, it might not be distinguishable from thermal noise or cosmic microwave background radiation. But for keeping TV signals from nonsubscribers, that is not necessary. You can still have an identifiable carrier frequency. That sort of thing would be easily detected, even if not decipherable. This assumes, of course, that an alien signal would use principles that we would. That is, however, not necessarily assured, and they could choose some peculiar broadband method, for example, that might not be recognizable by our equipment.
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Claude Shannon was a pioneer of information theory (https://en.wikipedia.org/wiki/Information_theory) - how to communicate efficiently.
One result of his analysis is that if aliens wanted to communicate as efficiently as possible, their signal would be indistinguishable from white noise. So we may not even recognize it as an artificial signal.
We can expect that the signal would use some form of coding to improve the ability to extract a clear signal from the random noise and interference with which space is filled. Our methods of coding messages has become much more sophisticated in the past 50 years or so. Current methods use large amounts of memory and computer power that would have been simply uneconomic even 20 years ago. So Aliens with technology even 100 years more advanced than our own may produce messages which cannot be decoded, even if we could recognize it as artificial.
However, aliens who wanted to be heard would try provide some very clear signal that their potential audience could identify as being notable.
But since we don't know of any aliens, where they are, or what they would be like, or what technology they would use (or even what technology they would expect their audience to be using), then it is pretty hard to guess.
But the most difficult aspect of decoding a message would be to understand its content. If you were played a message from the Inuit people, the message would be incomprehensible. Knowing that it is a human voice does not help much, despite the common context of humans across the planet. What hope would we have understanding aliens with whom we have no common context?
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We discussed this question on our show
Emma Sackville put this question to Dr Duncan Forgan at the University of St Andrews...
Duncan - If we received an encrypted message from space, it depends on how good the encryption is. If a message is very well encrypted, we wouldn’t be able to understand it as an artificial message - it would look just like noise. Just like the kind of noise you see in the cosmic microwave background or the noise you see on your old fashioned television set.
If the encryptions not quite as good then there are certain things we can do to understand the quality of communication. We do this with communication from animals. For example, we can give it a rating to say how much information is contained in the signal and so we could certainly say this is very informative. But what the information actually is, is going to be very challenging to figure out.
Emma - Have we ever had anything similar in the past that could have been a message that people were excited about?
Duncan - The one that everyone remembers is what’s called the “wow signal,” which came in , I think, the early 70s, and it was a very strong, narrow band transmission being sent to the Earth. We think now that it was a natural signal; it was actually something bouncing off something else, but that signal had no information in it, it was just a pulse. But then even if the signals just a pulse, that still tells you something because a single pulse is basically “hello.”
Emma - Ooh, that could be interesting. Okay - ultimate question. If we got a message, and if we could understand it, do you think we should respond to it?
Duncan - Well, the issue is we don’t have a legal framework for figuring out what to do next. We have what’s called the reply protocols that SETI scientists wrote down saying well, this is what we should do, but not-ones going to follow those protocols because they’re not in international law. So, if a message was received and say, for example, America wanted to respond but China didn’t - tough - America could still send the message on behalf of all of Earth, which is not great.
My personal opinion is that we shouldn’t send any replies because, speaking as a human being, I’m not particularly impressed with how well human civilization copes with its responsibilities as a steward of the Earth. A little bit of time maybe before we become more respectable as a galactic civilization.
Click to visit the show page for the podcast in which this question is answered. (http://www.thenakedscientists.com/HTML/podcasts/naked-scientists/show/20160510-1/) Alternatively, [chapter podcast=1001343 track=16.05.10/Naked_Scientists_Show_16.05.10_1005152.mp3](https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.thenakedscientists.com%2FHTML%2Ftypo3conf%2Fext%2Fnaksci_podcast%2Fgnome-settings-sound.gif&hash=f2b0d108dc173aeaa367f8db2e2171bd) listen to the answer now[/chapter] or [download as MP3] (http://nakeddiscovery.com/downloads/split_individual/16.05.10/Naked_Scientists_Show_16.05.10_1005152.mp3)
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My personal opinion is that we shouldn’t send any replies
A message to ET has already been sent ... http://www.physics.utah.edu/~cassiday/p1080/lec08.html
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One way to differentiate a signal with noise versus one with information is to take a histogram of if its "bits".
If you take any book and went through each sentence and plotted how often each word appears. Say keep a tally how many times the word "the" appears, how many times the word "if" appears, and do this for every word and then order the histogram from largest tally to lowest tally. You'd get a negative sloping curve showing the highest occurring words down to the lowest occurring words.
On the other hand, imagine a random number generator that outputs words. If you run the generator for a long time and plotted how many times each type of word pops out, like before, you'd get a flat distribution, that is, each word has about the same tally, meaning its just noise and contains no information. This is one way to differentiate between a noise signal and an information signal. (I think this has already been done to analyze the dolphin's squeaks [:)] ).
But of course this has one immediate problem: how do you know which are the words? How do you separate one word from the next? ... and so on.
These problems are interesting.
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Advanced Aliens would probably communicate by modulating gravity waves so no we wouldn't be able to listen with our primitive radio dishes.