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Offline Judge

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« Reply #25 on: 02/02/2008 07:37:03 »
There is one unicersal way in which all beings that we consider intelligent could communicat. If we found aleins that we considered intelligent there is an extremely high probability that they would know about atoms. Thus we could communicate using atoms. Both us and the aliens would need to be able to detect various atoms. We could then develop a language like this

Hydrogen could be the equivalent of Hello.

If we detected Hydrogen being emitted by an alein this would be 'Hello'. However this would requiere both side to be coincidently using this metheod.

Another possibility is that because of the extremely long time scales of the universe it is also extremely likely that any aleins we encounter will be millions possibly even billions of years a head of us in terms of technology. Such an advanced species will most likely have encountered other life and may have ways of communicating with aleins.

Yet another way that would be a little more difficult is using the positions of stars. If we send them data with the position of a particular constelation with positions of that constelations stars relative to earth and sent them data of earth's position relative to their locations and maped out the stars we gave them relative to their position we could use various grouping of stars as communications. for instance:

Equuleus star constellation means the equivalent of 'Hello'

Another way we could communicate with aleins is by communicating using universal constants. However this may be a bit more risky because many universal constants are constantly changing. Such as the grvitational Constant which has changed some over extended periods of time.

Another way, which would be unblievably difficult and requiere computers so powerful that its like nothing we can imagine. In about 600 hundred years it has been predicted that we will have computers that will be able to simulate the universe. Also this last one here is pure theory. Now using this computer we would enter everything we know about these aleins that is naturally occuring about them, such as their quivalent of DNA and the environment of their planet, moon, star, or whatever other object they live on then have a the computer run a simulation giving data on all possible combinations of what this species could come up with. And I am everything down to at least one of these simulations would give us the exact date they discovered the atom. Then amoung this data would be there language. Then this next part would take a very very very long time depending on their computing power and wether or not they are attempting to communicate with us to, which if we know about each other they may be interested in doing so. We will send them a steady stream of all this data we communicated from our simulation then if they responded using lets just say radio waves to keep it simple we would look for that peice of data amoung our database from the simulation and match it up. At that point we could confirm that to be some kind of a word. After that this process would be reapeted until we discovered many more of their words or rather word equivalent. Then once we have a reasonable number like at a point that we stop discovering additional words then we start sendng the words back to them that we discovered in random orders. Then we wait for a response. If the response sent back contained the same words only in a different order then we could know that their response was the correct order of the words. We keep on doing this until we get more snetances. Then we plug these sentances back into the data we got from the simulation. The simulations would have picked up the positions of the aleins lifeform at everystage of their timeline. We then try and look for situation in which one of these sentances that are correct was spoken by one of the aleins when first interacting another another alein after a period of time. Such as a 'Hello' you may give to a co-worker when arriving at work. Then after all that we will have successfully discovered what is MOST likely some sort of a greeting. At least in theory. However this metheod requires that the aleins have a greeting perhaps the aleins do not greet each other.

I can think of many other possible communication methods and at the same time I can think of holes in any of the above communication methods. That is why if we truly wished to communicate we would need to attempt hundreds of methods.
 

another_someone

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« Reply #26 on: 02/02/2008 13:29:38 »
The only meaningful conversations across interstellar distances would be between 'aliens' that had a much longer lifetime than us and a vastly different concept of time.
There is a remote chance that if we were in the right position between two systems that were communicating we might eavedrop on such a conversation but would we recognise it as such ? as the data rate would be very low by our standards 

The problem is that this leads to something of a paradox.

Ignoring the lifespan of an individual organism (not sure it is as critical as you suggest - but I'll get back to that later), but you are correct that they must have a different notion of time, insofar as they can send a transmission, and wait a couple of centuries or more for a reply, and regard that reply as still pertinent, it implies that not a lot has changed over the couple of centuries or more to allow the continued pertinence of the answer.  This is in marked contrast to what we imagine a high technology society to me doing.  It would imply that we might be dealing with a society that was once rapidly developing, but has reached a plateau, or else a society with a far longer period of technological gestation than we have had.  It implies a society that is inherently conservative, where social change is extremely slow.

As I indicated above, this need not tell us much about the lifespan of an individual organism, only of a social entity.  In an ultra conservative society, it is quite plausible for a man to send a message, and know that his grandson will receive the reply, and know exactly what kind of life his grandson will live (for his grandson will in all probability inherit the social position he himself holds today), and so the reply will be meaningful to the family (in such a society, it is the family that holds a place in society, rather than the individual), even if the particular family member who sent it is long dead by the time the reply returns.
« Last Edit: 02/02/2008 13:48:14 by another_someone »
 

another_someone

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« Reply #27 on: 02/02/2008 13:53:10 »
There is one unicersal way in which all beings that we consider intelligent could communicat. If we found aleins that we considered intelligent there is an extremely high probability that they would know about atoms. Thus we could communicate using atoms. Both us and the aliens would need to be able to detect various atoms. We could then develop a language like this

Hydrogen could be the equivalent of Hello.

If we detected Hydrogen being emitted by an alein this would be 'Hello'. However this would requiere both side to be coincidently using this metheod.

Another possibility is that because of the extremely long time scales of the universe it is also extremely likely that any aleins we encounter will be millions possibly even billions of years a head of us in terms of technology. Such an advanced species will most likely have encountered other life and may have ways of communicating with aleins.

Yet another way that would be a little more difficult is using the positions of stars. If we send them data with the position of a particular constelation with positions of that constelations stars relative to earth and sent them data of earth's position relative to their locations and maped out the stars we gave them relative to their position we could use various grouping of stars as communications. for instance:

Equuleus star constellation means the equivalent of 'Hello'

Another way we could communicate with aleins is by communicating using universal constants. However this may be a bit more risky because many universal constants are constantly changing. Such as the grvitational Constant which has changed some over extended periods of time.

Another way, which would be unblievably difficult and requiere computers so powerful that its like nothing we can imagine. In about 600 hundred years it has been predicted that we will have computers that will be able to simulate the universe. Also this last one here is pure theory. Now using this computer we would enter everything we know about these aleins that is naturally occuring about them, such as their quivalent of DNA and the environment of their planet, moon, star, or whatever other object they live on then have a the computer run a simulation giving data on all possible combinations of what this species could come up with. And I am everything down to at least one of these simulations would give us the exact date they discovered the atom. Then amoung this data would be there language. Then this next part would take a very very very long time depending on their computing power and wether or not they are attempting to communicate with us to, which if we know about each other they may be interested in doing so. We will send them a steady stream of all this data we communicated from our simulation then if they responded using lets just say radio waves to keep it simple we would look for that peice of data amoung our database from the simulation and match it up. At that point we could confirm that to be some kind of a word. After that this process would be reapeted until we discovered many more of their words or rather word equivalent. Then once we have a reasonable number like at a point that we stop discovering additional words then we start sendng the words back to them that we discovered in random orders. Then we wait for a response. If the response sent back contained the same words only in a different order then we could know that their response was the correct order of the words. We keep on doing this until we get more snetances. Then we plug these sentances back into the data we got from the simulation. The simulations would have picked up the positions of the aleins lifeform at everystage of their timeline. We then try and look for situation in which one of these sentances that are correct was spoken by one of the aleins when first interacting another another alein after a period of time. Such as a 'Hello' you may give to a co-worker when arriving at work. Then after all that we will have successfully discovered what is MOST likely some sort of a greeting. At least in theory. However this metheod requires that the aleins have a greeting perhaps the aleins do not greet each other.

I can think of many other possible communication methods and at the same time I can think of holes in any of the above communication methods. That is why if we truly wished to communicate we would need to attempt hundreds of methods.

All sorts of possibilities exist, but as you have subtly indicated, they are only meaningful once there is an agreed code as to how one should use these symbols.  If a word (whether it be a hydrogen atom, or the position of a star, or anything else) that we believe says "I come in peace", they interpret to mean "I will kill you", then you have problems whatever you are using (even assuming they and us do ascribe any meaning at all to particular tokens).
 

Offline opus

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« Reply #28 on: 02/02/2008 16:35:02 »
What will they make of The Beatles' "Across the universe" - an all-out declaration of war???? Have NASA really thought  this thru??
 

Offline JnA

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« Reply #29 on: 03/02/2008 08:08:56 »
What will they make of The Beatles' "Across the universe" - an all-out declaration of war???? Have NASA really thought  this thru??

the aliens might already be fans of 'earth music'...


http://en.wikipedia.org/wiki/Voyager_Golden_Record
 

Offline Pumblechook

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« Reply #30 on: 03/02/2008 14:27:03 »
----There has been threads on radio communication over vast distances and the calculations show that transmitters thousands of times more powerful than we have now would be required.


Are you sure about this?-----

Absolutely.  You can calculate received signal to noise ratio given transmitter power, frequency, receiver noise figure, bandwidth,  aerial gains and distance.   There are even on-line 'calculators'.   

I am familiar with boucing signals off the Moon with large antennas arrays and 400 - 2000 Watts of power at mid VHF.   Path loss is over 250 dB and special transmission techniques are used these day which improve the situation by a few dB only.   Signals are pretty weak. There is a limit to which special transmissions and processing at the receiver end can improve the situation.


Path loss over just one light year at 150 MHz is 336 db ...  another 86 db  which is 400 Million types greater in power times. 

So you would need 400 Million times more power than the minimum 400 Watts for the Earth-Moon-Earth path....with the same antennas.   =  160 Billion Watts (about double the output of all the UKs' power stations?) ....for just one light year to get a weak signal.  The antennas would melt in seconds.

The problem of using lower power and large dishes or arrays is the narrow beam angles.  It make the chances of two aerials being aligned by chance extremely small. 
 

another_someone

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« Reply #31 on: 03/02/2008 15:38:09 »
There is a limit to which special transmissions and processing at the receiver end can improve the situation.

This is the key issue I was wondering about.  Are these theoretical limits, or merely technological limits?

Bear in mind that we are talking about radio signals that may have to travel several hundred light years, thus to receive a reply would take twice that, so if the message too 1 year to transmit, that may mean a signal that might take 10 seconds worth of actual transmission, and the rest of the year merely sending error forward correction signals, that is a massive amount of redundancy that can be introduced into the signal, and so a very high noise immunity.
« Last Edit: 03/02/2008 15:54:29 by another_someone »
 

Offline Pumblechook

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« Reply #32 on: 03/02/2008 16:36:34 »
I would have though once a signal is well below the noise there is nothing you can do no matter what you do.   Integration of a period of time will have its limits. 

There are suggestions that the only way you could communicate would be to float huge dipoles (1.5 Million km) which have massive aperture in space and use carrier frequencies of the order 0.1 Hz.  Data rates would be very slow indeed.   Very large dipoles would have very wide acceptance angles and collect a signal of the order a dish of the same diameter working at VHF and higher.
 

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« Reply #33 on: 03/02/2008 21:05:19 »
I would have though once a signal is well below the noise there is nothing you can do no matter what you do.   Integration of a period of time will have its limits. 

I don't see this is the case.

Noise is the random fluctuation of a signal.  Information is a meaningful variation from that randomness.

If you look at the noise as a series of events over a period of time, then the signal you are looking for is a subset of those events.  The likelihood of the noise being inseparable from the signal is dependent on how probable is it that the events you are looking for are created by random chance within the noise you are receiving.  The larger the number of possible events are in what you are viewing, then the less likely that any single event is one of the events you are looking for, so the greater your certainty that the signal you are receiving is meaningful and not merely a manifestation of random noise.  Thus, if one has one years worth of signal, that signal amounting to 1 billion events per second, then you have 3.155x1016 events; which, if they are treated as binary events, are 23.155x1016 combinations of events.  If one is looking for 10 seconds worth of signal within that one years worth of transmission, then one is looking for any one of 21010 combinatorial events within a space of 23.155x1016 possible combinatorial events.
 

Offline Pumblechook

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« Reply #34 on: 03/02/2008 21:58:24 »
Take it from from there are no working systems which can rescue signals which are well below the noise.....and we are talking 60 - 80 - 100 dB ++ below noise.  100 dB is 10 billion times in power terms below noise.    You can dream up fanciful schemes to extract a tiny bit of info from a signal with massive redundancy and take a 1000 year to do but it wouldn't be much use would it?

There are other problems with long distances which space agencies have to deal with. Even at the record distance we have received a signal fom a spacecrft which is only 1/600 of a light year signals tends to arrive garbled due to group delay.  There are very slight differences in the speed of popagation at different frequencies so bits of a signal (which apart from sinple 0n-off keying - Morse has a spreed of frequencies) arrive before others. 
 

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« Reply #35 on: 03/02/2008 23:54:11 »
Take it from from there are no working systems which can rescue signals which are well below the noise.....and we are talking 60 - 80 - 100 dB ++ below noise.

Not doubting this, but that is a technological limit, not a theoretical limit.

You can dream up fanciful schemes to extract a tiny bit of info from a signal with massive redundancy and take a 1000 year to do but it wouldn't be much use would it?


But as has been said above, if you are dealing with hundreds of light years distance, you are not talking about real time two way communication, whatever you do - the limitation is not about getting the signal through, it is simply about how long the signal takes to get there.  It is more like sending a letter to Australia in the days of clipper ships , or maybe more like the Pope trying to communicate with the Emperor of China in the Middle Ages - probably even worse than that.  It is not as functional as we use radio communications today, but if it is the best you have available, but if it the best you have, it is still better to use it than not to.

There are other problems with long distances which space agencies have to deal with. Even at the record distance we have received a signal fom a spacecrft which is only 1/600 of a light year signals tends to arrive garbled due to group delay.  There are very slight differences in the speed of popagation at different frequencies so bits of a signal (which apart from sinple 0n-off keying - Morse has a spreed of frequencies) arrive before others. 

Agreed - so you have to make compensations for that either on the transmission or receiver side (this is something that network engineers have had to deal with continually - reshaping signals).
« Last Edit: 03/02/2008 23:57:41 by another_someone »
 

Offline Pumblechook

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« Reply #36 on: 04/02/2008 14:36:42 »
It is getting too esoteric and too 'science fiction'.  I am just making the point that huge transmitter powers would be needed to communicate at distances of the order of one light year never mind hundreds of light years. 



 

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« Reply #37 on: 04/02/2008 16:36:53 »
It is getting too esoteric and too 'science fiction'.

If we are talking about interstellar communication - ofcourse its science fiction - we don't do it, so however we might do it must be regarded as science fiction with regard to current capabilities.  The only issue is to understand what is plausible and what is implausible science fiction.

I am just making the point that huge transmitter powers would be needed to communicate at distances of the order of one light year never mind hundreds of light years. 

I am just not convinced that that is the only way (although clearly it is one way) of achieving that end.

Incidentally, no matter how big the transmitter, it makes not the slightest difference for the group propagation problems (in fact, that is probably not totally true, as increasing signal strength to the point where the signal could change the properties of the medium it is passing through, could make it worse).

On the other hand, it does not appear that group delay is so bad a problem that we cannot temporally resolve signals from millisecond duration pulsed quasars, although this clearly we would hope for better signal resolution than that if we are trying to transmit real communication signals.
 

Offline Pumblechook

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« Reply #38 on: 04/02/2008 18:02:37 »
Group delay is a separate question and there is a considerable difference between the 'rough note' pulsar etc and a communications signal.

To think there could be any technique that could retreive signals which are millions of times below noise...not only receiver noise but cosmic noise is a bit like me saying that I could make my ordinary car do 100,000 MPH and 50,000 MPG (at the same time).   Anyone looking towards Earth  would also be looking at our Sun and receive its radio noise.   

At some point there will be no signal..at some distance..when there are just no electrons being stimulated in a aerial by our Earth transmitter. 

 
 

another_someone

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« Reply #39 on: 04/02/2008 18:19:33 »
Group delay is a separate question and there is a considerable difference between the 'rough note' pulsar etc and a communications signal.

http://en.wikipedia.org/wiki/Pulsar
Quote
Owing to their extraordinarily rapid and stable rotation, MSPs can be used by astronomers as clocks rivalling the stability of the best atomic clocks on Earth. Factors affecting the arrival time of pulses at the Earth by more than a few hundred nanoseconds can be easily detected and used to make precise measurements.
 

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« Reply #40 on: 04/02/2008 18:29:36 »
To think there could be any technique that could retreive signals which are millions of times below noise...not only receiver noise but cosmic noise is a bit like me saying that I could make my ordinary car do 100,000 MPH and 50,000 MPG (at the same time).

Who is talking about 'ordinary'?

We are talking about what could be done with novel technologies, not how we can convert what we have today to achieve this.

Anyone looking towards Earth  would also be looking at our Sun and receive its radio noise.   

This is true, but it is all about the discussion about signal to noise.  Ofcourse our sun will contribute to the noise, but that is not to change the nature of the underlying problem.  Ofcourse, the majority of that noise will also be out of band, but there is no doubt that it will contribute to noise across the spectrum.

At some point there will be no signal..at some distance..when there are just no electrons being stimulated in a aerial by our Earth transmitter. 

So what would be happening to the photons in the wave?  Do the photons lose their energy?  To what would they lose their energy?

Yes, the number of photons you detect would reduce, but it will never go to absolute zero.
 

Offline syhprum

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« Reply #41 on: 04/02/2008 19:14:01 »
I think too much emphasis is being put upon the dispersion of the signal, the aliens that I visualise communicating over tens of light years would be quite happy to use a bit rate of 10^-6 bps which would enable the use of very narrow band receivers (computer simulated) to recover a much weakened signal.
I don't think we that have a 'snow balls chance in hell' of eavesdropping on such communications let alone joining in!.
 

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« Reply #41 on: 04/02/2008 19:14:01 »

 

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