lpetrich

As to how one would interpret a message from extraterrestrials, there are two main possibilities:

If the message is something that the ET's had created for their own use, then decoding it would be very difficult, because one has no context that would help us decode it. I know from direct experience how difficult it can be to reverse-engineer data formats, and I knew what the data was supposed to represent.

The only possible exceptions are if the data has some simple format, such as analog audio or analog video.

One could guess that some broadcast is of analog audio by doing a power-spectrum analysis and noticing lots of approximately-evenly-spaced lines from the harmonics of pitched sounds.

And one could guess that some broadcast is of analog video by noticing the horizontal and vertical sync signals, and then seeing if stacking the in-between signals gives a reasonable-looking image.

But even in those cases, further decoding would face severe difficulties, such as deciding which is horizontal sync and which is vertical sync, and the horizontal and vertical scan directions.

However, if the message is intended for others to understand, then the ET's would have carefully designed it so that its recipients can interpret its contents. It would likely start out with a long series of pictures illustrating a variety of concepts; these illustrations would contain examples of a language to be used later in the message. The later parts of the message may be mostly text in this language, but there would still be illustrations here and there, with various data formats being carefully described before being used.

It seems to me that a really good message would take up a large number of bits, meaning that it would take a long time to transmit. One can reduce the amount of background noise by reducing the bandwidth of the signal, but since (bitrate) ~ (bandwidth), one will have to transmit more slowly.

lpetrich

Also, in the 1980's, there was an article in Science magazine about detecting our TV stations from outside of the Solar System.

The article focused on what could be learned from the carrier waves, since this part of the broadcast is the easiest to see. This is because the TV signal proper has a bandwidth of about 10^7 Hz, while the carrier wave has a bandwidth of about 1 Hz. This means that picking up the broadcast content would require about 10^7 times the antenna area (linear dimensions 3000 greater). This reduces the antenna's (solid-angle) field of view by 10^7, reducing the interstellar-noise background by that amount, but not the broadcast (the noise is diffuse, while the broadcast is a point).

There are a variety of things that could be learned, such as the positions of the TV stations, the Earth's size, rotation rate, and spin-axis direction, and so forth.

With VLBI, it may be possible to get very precise positions in the sky, not enough to distinguish different places on Earth, but enough to be able to track its orbit around the Sun, at least if the observer is not too far away. This will enable finding out the precise distance of the Sun from the observer, the Sun's mass, and the Sun's light flux at the Earth (the "solar constant").

What further inferences could be made is an interesting question. The stations have only a few carrier-wave frequencies, suggesting some widespread standardization. They are clustered, suggesting that they serve a few special areas. The Earth has a radiation-equilibrium temperature that suggests that there may be liquid water there. ...

HallaK9

I remember reading somewhere that the most powerful radiowave emitters on Earth are the heavy duty radars used by superpowers to detect incoming intercontinental missiles. How easily recognizable as artificial would such a source be? For us or "them".

Antti

lpetrich

Shklovsky and Sagan had done some calculations along those lines in their classic Intelligent Life in the Universe. Some SETI site may contain some more recent calculation, though in my limited searching, I haven't found any precise numbers.

As to the radar signals themselves, they might be recognized as being artificial because of their being narrowband and precisely pulsed.

It would be hard for an extraterrestrial observer to learn much from those signals, but the detection of them would prompt them to scan the Earth's direction with greater sensitivity. This may lead to the discovery of Earth-TV carrier waves, which would tell the observers much more about us.

These also are narrowband, though they are continuous signals; this may help in recognizing that they are artificial.

[ April 08, 2002: Message edited by: lpetrich ]</p>

lpetrich

I think that the impact on our society will depend on what's in the message, or at least the parts of the message that can be decoded.

Picking up a carrier wave or a broadcast for internal consumption would tell us little, and the ET's would likely be relegated to the realm of interesting curiosities. I don't see how that might provoke a fundamental cultural shift.

One problem with an ET's broadcast is that we would not know the language that it is in. But ET's would be aware of that problem, and would carefully design a language-tutorial message, which would consist of introducing that language with abundantly-illustrated examples. These examples would be drawn from mathematics, the physical sciences, and related fields of engineering, because what they describe are universal features. There being no largest prime number and the periodic table of elements are shared across the Universe.

However, if we only got that kind of message, that would not tell us much more about the ET's. Although it would certainly help if they described how to quantize gravity.

The same could be said about their describing the planets of their home system, and their biology and engineering constructions; that would tell us lots of interesting things, but not what many of us might consider the really important things about them.

Those things are their society and culture; there would be lots of interesting things to learn from the ET's, at least to the extent that we understand what they are describing. And if they describe how to achieve certain forms of social organization, we might be able to put some of this knowledge to work. It is this sort of thing which I consider a likely cause of some fundamental cultural shift.

Bill

Those radars use a distinctive "chirp" pattern which could not fail to be detected as artificial. The "chirp" is necessary to gain full three-dimensional position, plus velocity information, from as few pulses as possible, given that "incoming missles" are "high dynamics" targets.

== Bill

Wyrdsmyth

I think it's highly possible that, if there is other intelligent life in the universe, contact could be entirely non-personal and one-way. For example, we might pick up a transmission and infer that it is a message (and even partly or wholly decode it), but not know how to reply or precisely where to reply to. Even if we know where to reply to (by deducing exactly where the message came from), we may not have an efficient means of replying.

Let's say the message originates from a star that is in the Andromeda Galaxy, over 2 million light-years away. How are we going to respond to something like that? Imagine this tantalizing but aggravating situation: we learn there is other intelligent life in the universe, but have no way of responding to them or of meeting them. And that intelligent life might even be long extinct. I think it's entirely possible that something like this will be our First Contact scenario. I also think it's entirely possible that what we learn in the future about other stars (and life forms) will come from long-range observation, and not from physically travelling there. Warp drives and hyperspace and stargates -- while great and entertaining in video games and sf movies -- may not ever come about. They might be impossible, even in principle. Or, they might be possible, but lethal, or impossible to navigate. Who knows. I just have a feeling the future isn't going to look anything like Star Trek or Star Wars, with fleets of hyperdrive-equipped starships hopping around the universe... I think it's going to look more like what we have now, but with more high-powered orbital telescopes and other long-range sensors that we build in space, and maybe a moon base and some terraforming on Mars, and perhaps eventually some terraforming and seeding of the closest star systems, like Proxima Centauri (4.2 ly), Barnard's Star (5.96 ly) and Lalande (8.11 ly), but nothing in the way of human beings travelling to other galaxies, or even significantly far across our own galaxy.

[ April 11, 2002: Message edited by: Wyrdsmyth ]</p>

fando

I'm so certain that the first message we get will be interstellar spam:

[ April 11, 2002: Message edited by: fando ]</p>

Wyrdsmyth

LOL! That's hysterical. Junk e-mail from a 2 million old wireless Internet in the Andromeda Galaxy... Now that's a great premise for a First Contact story.

I am a fish

And then shortly afterwards we receive another message saying, "Molog is a false god. Worship none save Kraalnoth. Zarglon is his prophet."