Posts by Patrick Hummel

1) Message boards : SETI@home Science : Could we communicate via radiowaves through interstellar space? (Message 1862327)
Posted 19 Apr 2017 by Profile Patrick Hummel
Thanks for all your feedback so far! Personally, I think this is an interesting topic.

First of all, the main topic of this thread was the question of whether or not it would be technically possible to communicate over very large distances (between stars) via radio waves, because cosmic radiation might corrupt the message in a signal so much that it is unreadable by any recipient. This is purely theoretical (at the moment), since we have yet to find a communication partner.

@William Rothamel
Now: for high powered purposive "we are here" types of signals we would not expect them to be encrypted nor using any type of error correcting code.

I agree, if we only want to broadcast the fact that we exist, then we do not need any type of error correcting code. This is because there is no information we want to transmit and we simply hope that other intelligent species can detect the difference between "natural" and "man-made" signals. And the steps you discribed that we should follow in case we detect something seem like a good solution. But as I stated in my previous response, if the signal gets corrupted or changed by cosmic radiation too much the language or number representation will be jibberish even after you "clean" it up. Although I don't know how bad this corruption is, which is why I opened this thread.

I read your long response even though I had a hard time trying to understand your point. Whether or not the big bang was caused by a "god" or "creator" is not really relevant in this discussion. No matter how the universe got its fundamental constants and physical laws, we are unable to change them and therefore need to use what we have. Of course it is hypothetical if there is other life in the universe, but for the sake of argument we accept the possibility. I'm more interested in how we could effectively communicate with other intelligent life forms via the current technology that we have, and by that I mean via radio waves.

@rob smith
Communication implies that the two ends of the link "talk" to each other. This is irrespective of what the modulation and encoding of the message.

Communication implies that both sender and recipient have agreed upon an encoding. The symbols we use in the english language is also an encoding. That means that we both are currently communicating using the agreed upon code (the english language). If you started to answer in japanese, I would not be able to interpret the information no matter how fast or how good the quality of the message is, therefore we would technically not be communicating. Computers depend on this even more, if you just send streams of bits (101010001) there is no way for the recipient computer to figure out what you were trying to send. A broadcast is still a form of communication, the opposite you may be referring to is a unicast (only between two parties). As stated above, I am curious about the plausibility of a direct communication (unicast) with another species, which includes an agreed upon encoding for the information itself and also the error correction that encompasses the message for a safe transmission. It may take a long time, but that does not mean that it is not possible. For example, you could theoretically slow down the TCP connection-oriented network protocol, and it would still be considered unicast communication.

Of course communicating with other lifeform is only possible after we have actually found one. This includes finding "unnatural" signals and identifying them as from other intelligent beings. My question was more about what we do AFTER we have found others (that may also have noticed us) and about how we could communicate with them and if this is actually technically possible with all the distrubance by radiation. Does anyone of you know how much cosmic radiation influences / corrupts / alters / changes radio waves? Does it only affect it a little bit (f.e. max 25%) or does it completely corrupt anything we try to send outside our solar system?
2) Message boards : SETI@home Science : Could we communicate via radiowaves through interstellar space? (Message 1861185)
Posted 13 Apr 2017 by Profile Patrick Hummel
Interesting little experiment, I read your answer just now but I agree with the others on the interpretation. I found this youtube video that explains the problem and solution using error correcting codes really well:

Parity checking and other methods (such as a checksum) work well to find out that there are errors, but to actually be able to correct flipped bits we would probably need more extensive codes. In the video, the professor talks about simply sending a greyscale picture of mars, which basically means sending a numbers between 0 and 63 back to earth (color of a pixel). The coding experts thought there would be up to 25% (!) corruption or flipped bits, which means they needed to send 32-bit messages for just 6 bits of information (2^6 = 64) with a distance of 16 (-> 7 bits can be corrected, as he calculates in the video). There is a part 2 of this video, and he explains that you can scale this, f.e. sending 64-bit messages with even more error correcting possibilities. But the longer you make a message, the more likely it is that it gets corrupted at all.

Now what concerned me here was that they calculate with 25% corruption just between mars and earth (depending on how far apart they are at any given time). Now think about how much corruption you would have to think about on a mission to pluto or even outside our solar system. I'm not very advanced in astrophysiks but as far as I know there is a lot of cosmic radiation beyond the limits of our solar system. If we would need to correct 75% or more errors, the error-correcting codes would need to be massive. But I'm not sure how much of an effect the radiation actually has on radio signals, which is also one of the reasons I opened this thread.

Therefore it may be more difficult to agree upon error correcting codes exceeding 32 or 64 bits. An example of a 64-bit message:
0110 0000 0010 1001 0101 1100 1100 1111 0100 1101 1010 0101 0011 1110 0100 1100

@William Rothamel
Alien Signals--intentional or otherwise might not be digital.

Sure, they may not be digital. But as far as I know it is easier to send a 0 or a 1 using radiowaves than lets say 0, 1, 2, and 3.

It is far easier to just detect a signal from an intelligent source, than to worry about what it says.

Sure, I would be very happy to just detect a signal that is not from a natural source. My question was more hypothetical and discusses what we could do after we actually get a signal from a nearby star (or they found our I love lucy signals and are trying to communicate with us).
3) Message boards : SETI@home Science : Could we communicate via radiowaves through interstellar space? (Message 1860775)
Posted 10 Apr 2017 by Profile Patrick Hummel
First, dispersion. Over the distances involved radio waves will be scattered, and thus be less readable when they get to the far end of the communications link. Digital communications can go some way to overcoming this.

Agreed, I would think that a bit is less likely to be flipped or wrongly interpreted when the signal weakens. But if we knew where exactly our communication partner is, wouldn't we be able to focus the waves better? Although that might depend on how far away the other solar system is.

Second, time lag. Our nearest star is 3 light years away, radio waves travel at the speed of light, so any dialogue would have a six year delay between initiation and receipt of acknowledgment. Not exactly conducive to ready conversation. Digital technologies don't help here.

Exactly, these long transmission times are why the error-correcting codes are so important. We couldn't just ask for a new version of the data because the one we received is corrupted. Personally I think that even though it might take a long time, a conversation would still a great goal. At the beginning it would probably be very simplistic because there is no common language, maybe some numbers or relations. Then some instructions on how to decipher more complicated information. It might take many generations, but I think it would be worth it simply because that would be a great achievement for a lifeform such as ourselves. Also, without some sort of faster than or close to light travel, that might be the only way to interact with them.
4) Message boards : SETI@home Science : Could we communicate via radiowaves through interstellar space? (Message 1860769)
Posted 10 Apr 2017 by Profile Patrick Hummel
Repetition codes, though very inefficient, have the advantage of simplicity. If each block of data is sent repeatedly, a consistent number of times, this scheme will soon make itself obvious.

Thank you! I didn't even think about the option of just sending the same block of data lots of times. Since the possibility of corruption is already a problem for interplanetary communication, I thought the radiation beyond our solar system would be an even bigger problem and thus making "raw" data without error-correction generally implausible. But as you said, even though there is a chance the same binary digits flip in sent blocks it decreases with an increase in the amount of repetitions.

Such a message could contain instructions on the use of a more complex and more efficient method of error correction, establishing a standard technique for a particular communications channel.

The missing agreed upon communication protocol was what worried me the most. Even though I suspect it would not be very easy to find a way to formulate the instructions in a way that some other lifeform can interpret it correctly, with enough time and dedication on both sides this could lead to actual corresponence. Your answer was very helpful, thanks!
5) Message boards : SETI@home Science : Could we communicate via radiowaves through interstellar space? (Message 1860731)
Posted 10 Apr 2017 by Profile Patrick Hummel
Hello everybody,

I'm currently studying in the computer science field and I came across some interesting topics concerning data transmission and coding theory. This may not concern the search for signals directly, but the ability to possibly decode or interpret them if they do exist. If I recall correctly, Mr. Seth Shostak (or perhaps somebody else) advocated the benefits of searching for signals in a talk, which included the possibility of listening to signals that encompass technologies that are more advanced than ours (and thus very valuable). But this question would also concern much simpler transmitted information, such as a sequence of numbers or other encoded data.

So as I read about communication with far away satellites and other exploring spacecraft that are in interplanetary space (f.e. mars orbiters, juno spacecraft, voyager, etc.) there are two things that grabbed my attention. First, due to cosmic radiation, radio signals seem likely to get corrupted while traveling through space. Second, if a corrupted data package (such as a photo encoded in binary) is received on earth, it is impractical to send a message back and ask the sender to send the packet again due to the time it takes (even though it travels with the speed of light). Therefore the need for error-correcting code (as part of the coding theory).

Perhaps my assumption is wrong, but if other intelligent life exists and has developed the technology to transmit radio signals, they may also have some kind of computer science theory as part of mathematics (which to me seems pretty universal). So the idea of bits (1 and 0, on and off, true and false, ...) may not be far fetched. And if they also send their data in binary, cosmic radiation might turn a zero into a one and the other way around. So no matter if they just send out the fibonacci series or broadcast images or music in binary, it probably wouldn't even make it out of their solar system without being corrupted.

If we do find a signal, I bet a lot of time and effort will be spent on trying to decipher or make sense of it in some way. But is this even possible? If they do package the information in some error-correcting code, how could we decode it without knowing what they used to encode it? If we were to broadcast anything, how will other lifeforms be able to decipher our error-correcting code? If a "nearby" advanced civilization notices us and we notice them, and want to communicate via radio, how could we agree on a common protocol and encoding scheme if the instructions for decoding would become corrupted in transit as well?

Or perhaps I misunderstood something along the way. Either way, I found this topic highly interesting and I thought this could be the right place to get some thoughts from you guys. What do you think? What types of signals are we expecting? How much does cosmic radiation affect possible signals? Of course I would be very satisfied with any signal at all, but actual interstellar communication would be a cherry on top.

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