Could we communicate via radiowaves through interstellar space?

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Profile Patrick HummelProject Donor

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Message 1860731 - Posted: 10 Apr 2017, 13:30:23 UTC

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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Message 1860749 - Posted: 10 Apr 2017, 15:42:36 UTC

Two issues with inter-stellar communication
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.
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.
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Message 1860762 - Posted: 10 Apr 2017, 16:18:36 UTC

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.

Random or sporadic flipping of a binary digit by noise would be unlikely to corrupt most data blocks, or to corrupt the same digit in most blocks. The predominant version of the data block, among the repetitions , could be assumed to be the correct one.
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.
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Message 1860769 - Posted: 10 Apr 2017, 17:33:36 UTC - in response to Message 1860762.  

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!
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Message 1860775 - Posted: 10 Apr 2017, 17:57:47 UTC - in response to Message 1860749.  

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.
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Message 1860781 - Posted: 10 Apr 2017, 19:07:23 UTC

Error correcting, parity checking or Hamming codes (minimum distance three) must be inserted at the source. Sender and receiver must agree on the scheme used.
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Message 1860788 - Posted: 10 Apr 2017, 19:56:19 UTC

William's right. It is far easier to just detect a signal from an intelligent source, than to worry about what it says.
Suppose aliens about 50 light years out are just detecting I Love Lucy.
Most likely all they would recognize is a signal coming from somewhere near our sun that was not natural.

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Message 1860794 - Posted: 10 Apr 2017, 20:39:36 UTC - in response to Message 1860769.  
Last modified: 10 Apr 2017, 20:42:42 UTC

Math expert, I'm not, by far, but I think it might not be too difficult to indicate a simple form of error correction. Let's try an experiment.
What would you make of the following sequence, sent repeatedly? Dashes inserted merely to indicate a timing space.


0000--- 0000
0010--- 0001
0100--- 0001
0110--- 0000
1000--- 0001
1010--- 0000
1100--- 0000
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Message 1860798 - Posted: 10 Apr 2017, 21:23:04 UTC - in response to Message 1860794.  
Last modified: 10 Apr 2017, 21:23:33 UTC

Alien Signals--intentional or otherwise might not be digital.
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Message 1860808 - Posted: 10 Apr 2017, 22:16:22 UTC - in response to Message 1860794.  
Last modified: 10 Apr 2017, 22:17:30 UTC

The left column is counting by 2's in Binary. The right column makes no sense. Aliens schooled in Base two arithmetic would dismiss the sequence until they saw that it was repeated then they would scratch their heads and probably conclude that there was no useful information encoded. They might conclude that this was a purposive beacon and might scan this section of their sky to see what they might see or hear.
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Message 1860809 - Posted: 10 Apr 2017, 22:22:26 UTC - in response to Message 1860794.  
Last modified: 10 Apr 2017, 22:24:42 UTC


0000--- 0000
0010--- 0001
0100--- 0001
0110--- 0000
1000--- 0001
1010--- 0000
1100--- 0000


Left column is a simple binary count in the three leftmost bits with the least significant bit not used (or just counting by twos), the right column is an odd parity bit.
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Message 1860968 - Posted: 12 Apr 2017, 2:20:46 UTC - in response to Message 1860809.  
Last modified: 12 Apr 2017, 3:16:14 UTC

Quite correct! Since this was so readily perceived, perhaps it would be perceivable, too, by mathematically minded extraterrestrials. Would anyone care to devise a comparable cluing method for the use of a check sum?
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Message 1861185 - Posted: 13 Apr 2017, 10:42:12 UTC - in response to Message 1860968.  

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:
https://www.youtube.com/watch?v=NRv3HMEyuDE

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.

@SciManStev
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).
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Message 1861416 - Posted: 14 Apr 2017, 10:38:18 UTC - in response to Message 1861376.  
Last modified: 14 Apr 2017, 10:52:07 UTC

We have not heard an eavesdropping style of alien signal now for 50 years and we are not likely to find one in the future.

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.

Here is what we would (should) do if we found a strong signal of apparent non-Earth origin:

    Hopefully we will have recorded the damn thing and it's position in the sky--it may be a one time blast from a slewing beacon.
    Use auto-correlation techniques to raise the signal up out of the noise. Guess at the pulse form (square wave ?) to enhance this
    Look for a modulation scheme and message type: Am, FM, Side band, ON-OFF
    Demodulate to look for: --video raster, picture, audio, counting out numbers.
    look for repetition within the message.
    Look for a primer either of language or number representation

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Message 1861556 - Posted: 15 Apr 2017, 3:05:59 UTC - in response to Message 1861488.  

Huh ?
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Message 1861609 - Posted: 15 Apr 2017, 7:17:02 UTC

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. We are used to "talking" in near real time, not with a many year delay between calling our presence and getting the response, this makes communication, as opposed to broadcast, which is when the sender just shouts into the ether", and does not expect (or require) any response from any receiver of the message.
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Message 1861612 - Posted: 15 Apr 2017, 7:23:19 UTC
Last modified: 15 Apr 2017, 7:55:26 UTC

I think we humans not only will communicate but also explore the universe beyond interstellar space.
The means of doing that is quantum communication, i.e through entanglement, and sending small robotic spacecrafts. Probably also Van Neumann probes for planetary research whose information can be relayed home by quantum satellites.
That will give us the tools of observing and collecting knowledge in near real time regardless of distances long before we can travel ourself.
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Message 1861627 - Posted: 15 Apr 2017, 9:01:22 UTC
Last modified: 15 Apr 2017, 9:03:41 UTC

Interstellar is the matter that exists in the space between the star systems in a galaxy, beyond that is intergalactic space between galaxies. The nearest star in our own Milky Way galaxy is Alpha Centauri 4.4 light years from earth. To explore even the nearest star would take space probe 4 years to get there at light speed.

The recently discovered Canis Major dwarf galaxy, is 25,000 light-years away, and the Andromeda full size galaxy is 2.5 million light years away. So unless we can break the speed of light barrier we ain't going to be sending probes to other stars outside our Solar System anywhere soon. And is Einstein was right, we never will either.

How we communicate with a probe when it gets there is another matter of conjecture.
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