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Shouldn't we have heard alien radio signals by now? Why not?


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Rather dispiriting, but thought provoking:

World-leading Physicist: "ET Artifacts Could Be Camouflaged as Natural Objects in the Universe"

My personal belief / suspicion too. :rolleyes:

Stephen Wolfram is certainly brilliant, but sometimes does not exercise sufficient self criticism, if I may be blunt. His argument has a very simple flaw, even though he is right that signals look more and more random as more compression is applied. My analysis is the following:

I assume some discrete form of transmission (binary or otherwise) because we know that this is more robust to noise than analog transmission. It is also much harder to see how we would compress an analog signal.

Due to compression, the signal appears to be more random at the "bits and bytes" level. Communications would also be asynchronous, i.e. the receiver is not expected to acknowledge receipt of the signal, simply because of distances involved.

If I transmit a highly compressed signal, I have to be very careful I do not introduce errors, because compression removes redundancy, and that means an error in one bit propagates further through the signal than in the case of an uncompressed transmission. Because we cannot ask for retransmission of faulty signals, we need some form of error detection/correction which is highly robust against noise. This implies adding back some redundancy. Discrete transmission also superimposes a clock-like signal over the transmission, because we need some timing which is detectable without sending acknowledge handshakes for every bit of data. This too imposes a form of regularity. Thus, I do expect regularity in an alien signal distinguishable from noise even if we only study the signal at the frequency of transmission. Information theory has quit e a bit more to say on this topic.

Finally, and most importantly we look at the spectrum of transmission. Natural sources such as thermal or synchroton emitters have very characteristic spectra. The superimposed regularity of the signal will give a very different line+side-band type of spectrum, reminiscent perhaps of natural masers (but these have spectra dictated by the molecules involved). Aliens would prefer to avoid natural maser frequencies to avoid interference (which depresses possible bit rates, see Shannon). Natural masers, like pulsars before, were initially mistaken for alien signal.

So, though Wolfram is right in stating compression reduces regularity of signals, noise in real transmissions limits the redundancy that can be removed. Besides, spectral signatures may still differ significantly.

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There are approx 3 million different types of animals on Earth (I asked Jeeves), of those, only 1 (us) has developed any type of technology.

The odds that there is another planet in the goldilocks zone, with the correct type of intellegent life, at the right time in their evolution, are just too remote.

Also, the human race can't get along with each other, so why do we want to find other life-form out there (unless they've got some oil left, and want our western/capitalist views).

I don't think I agree with part of this. Consider the dams and artifical semi-underwater bunkers built by beavers, the nests built by birds, the complex habitations constructed by insects...

If we are going to say 'that's not what we mean by technology' then aren't we in danger of defining technology as 'our kind of technology' and so falling into tautology?

Olly

Edited by ollypenrice
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In addition to Olly's comment, there is also a danger of classifying life as "our kind of life" in "our circumstances".

If a technological civilisation were to emerge on Europa, they would be under a layer of ice several kilometers deep. How would they even know there was a whole universe out there.

Radio technology can not be taken as a positive or negative indicator of intelligent.

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How fast do radio waves travel through space? Do they travel at the speed of light?

If so, how far have the oldest radio waves traveled? Have they even left the Orion Arm of the Milky Way?

I agree with what other people are saying about what is technology. Humans are never satisfied with where they are evolution-wise, and always seem to be progressing. (This can be seen as both a good and a bad thing).

There are monkeys using sticks to get ants out of an ant nest, and using rocks to break open nuts, but they have not progressed further. They get the food they want, and thats enough for them.

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How fast do radio waves travel through space? Do they travel at the speed of light?

If so, how far have the oldest radio waves traveled? Have they even left the Orion Arm of the Milky Way?

Yes, they tarvel at the speed of light.

If we assume excellent detecting ability on behalf of the little green men, then the first broadcast would have been Marconi's transatlantic broadcast in 1901 (there were others before this, but very short range)

So, we are in the centre of a sphere of radio transmissions emanating from us that has a diameter of 200 light years at maximum.

Rob.

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Yes, they tarvel at the speed of light.

If we assume excellent detecting ability on behalf of the little green men, then the first broadcast would have been Marconi's transatlantic broadcast in 1901 (there were others before this, but very short range)

So, we are in the centre of a sphere of radio transmissions emanating from us that has a diameter of 200 light years at maximum.

Rob.

not far at all really, infact, does it even count?

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not far at all really, infact, does it even count?

Does it count? Of course it counts. Might not be much to an astronomer but it's still in the range of several systems with exoplanets, some of which may be in the goldilocks zone.

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Fifty years ago a gentleman named Frank Drake quantified "communicating life" in our galaxy. (google the Drake Equation) Observations have bolstered many of the assumptions he made in 1961.

His bottom line is there should be 10,000 communicative civilizations in our galaxy. That means we should find 1 such civilization in every 20 million stars. Although I think we should have to look at up to 40 million for the first, as we are the 1 civilization in the first 20 million stars. After that it goes back to 20 million.

Our radio waves have only passed the first 13 stars so we may still have a way to go before someone hears us.

Edited by MisterBill
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QUOTE=Nexus 6;1923830]Very interesting thread, was good reading and then I read about Edgar Cayse :)

agreed!

I sometimes like to think about the question in a slightly different way and think about all the possible intelligent life out there that may have been looking for other life and been long gone or extinct. As well as the universe being unimaginably large , it has also been around for a hell of a long time, so similar to the possibility we are the 1st,how about us being the only intelligent life at this moment in time? Other civilizations could easily have existed and been long gone!

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The Drake Equation may be interesting but it's far from reliable. Basically it's just the best we've got based mostly on guess work.

Well actually the Drake equation is fine - its what you put into it that is subject to doubt! The first 3 parameters are getting more settled, but the rest is anyones guess!

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Well actually the Drake equation is fine - its what you put into it that is subject to doubt! The first 3 parameters are getting more settled, but the rest is anyones guess!

The thing is that even then the equation itself might be omitting a huge factor that we just haven't thought of yet, or including ones that are moot. It gives us a number but the worth of that number is very up in the air.

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The thing is that even then the equation itself might be omitting a huge factor that we just haven't thought of yet, or including ones that are moot. It gives us a number but the worth of that number is very up in the air.

I don't think it can be missing a huge factor, people have looked at it fairly hard over the years. It's likely some of the parameters may eventually be split up in the light of new knowledge.

At it's simplest, the equation can be expressed as

N = Rb * T

Where Rb is the rate at which broadcasting civilizations appear and T the time they broadcast for.

So Rb can be expanded into some factors and we get the traditional Drake list of parameters.

Once we understand more fully how life appears, you might well split the probability of life appearing term into some other terms maybe (e.g., if some form of panspermia is significant then proximity to an existing life supporting planet might be a factor - but as it is we just have an encompassing probability). Similarly with the probability of intelligent life appearing, as we learn more we might well make that into a better equation.

Actually it may be by the time we know with fair certainty all the parameters in the equation, it will be a moot point as we'll probably have explored the galaxy by then :)

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Stephen Wolfram is certainly brilliant, but sometimes does not exercise sufficient self criticism, if I may be blunt.
He does seem to have annoyed LOTS of people though? Shame in a way... :(
... Nobel laureate and elementary particle physicist Steven Weinberg wrote, "Wolfram himself is a lapsed elementary particle physicist, and I suppose he can't resist trying to apply his experience with digital computer programs to the laws of nature.
My Emphasis - Ooer, Missus! But a bit more creative than some of his critics. :D
So, though Wolfram is right in stating compression reduces regularity of signals, noise in real transmissions limits the redundancy that can be removed. Besides, spectral signatures may still differ significantly.
Good stuff, Michael. Can't see any contrary argument. Even encrypted & compressed aliens may be unable to hide amidst more natural processes. Rightly or not, I was reminded that, with practice (Without a BFO!), one can recognise the general structure - Even get the vague gist of SSB transmissions... Many other modes too. :) Edited by Macavity
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He does seem to have annoyed LOTS of people though? Shame in a way... :(

My Emphasis - Ooer, Missus! But a bit more creative than some of his critics. :D

Good stuff, Michael. Can't see any contrary argument. Even encrypted & compressed aliens may be unable to hide amidst more natural processes. Rightly or not, I was reminded that, with practice (Without a BFO!), one can recognise the general structure - Even get the vague gist of SSB transmissions... Many other modes too. :)

Thanks for that. Wolfram is doing some sterling work, but his physics based on cellular automata was just fundamentally flawed. It does not include even basic symmetries such as rotational symmetry (which basically means the world looks the same, regardless of your viewing direction). I am not criticizing the man, I am criticizing his arguments.

Edited by michael.h.f.wilkinson
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