Thread: "The Great Silence"

Originally Posted by sailor jack

My main problem with any message though is understanding.You could phone a guy in Brazil and say all you wanted, but he isnt going to get any information out of you or reach a conclusion of where the message is from (unless he speaks english, but its a needle in a haystack)

Hmm, I don't mean to sound nit-picky, but this is a somewhat flawed analogy. The "language barrier" problem is a pretty obvious one, and so, as you might guess, it's been considered at length by scientists involved with this question. The Arecibo message, though it wasn't a serious communications effort in terms of target or transmitting time, does provide a pretty good illustration of how the "language barrier" issue can be addressed, and how the likelihood that the recipient will make sense of the message can be maximized . The best solution has to do with mathematical and numerical patterns, based on the assumption that any species which can build a high-sensitivity radio receiver (and all the other technological gizmos that go along with that level of sophistication) will have to understand math in some way, and that mathematics is universal. For instance, they will probably know about prime numbers too. So the Arecibo message, which in it's "natural" form is just a squirt of radio waves with the frequency hopping slightly up and back down several times per second, will hopefully have a certain significance to anyone who understands mathematics (i.e., presumably, anyone who builds radio equipment). The number of bits (frequency shifts) in the Arecibo message is the multiple of two prime numbers. Arrangement of these bits as visual elements on a plane, with the number of elements (pixels) along each edge corresponding to one of these two prime numbers, produces an image. There are two possible ways to do this but one of them has noticeable symmetry and other traits that mean it may well stand out and lead an alien observer to recognize that it's the correct way, while the other is gibberish. From there, at least some of the parts of the image probably have a fighting chance of being interpreted correctly by any organism that relies on visual sensing.

Obviously this still rests on some assumptions that may not hold true. The aliens MAY not understand prime numbers, but if they can receive the message in the first place, they probably will. It may never occur to them to arrange the bits as visual elements on a two-dimensional plane, but on the other hand, we can imagine how we would respond if we received a recognizably artificial radio signal from space: Great numbers of scientists, with access to a huge budget and all sorts of equipment and resources, would probably spend night and day for months subjecting the signal to every sort of analysis and processing imaginable, looking for any patterns or meaningful properties whatsoever. Another species that would construct devices to listen for signals from space is probably reasonably likely to have a similar response. For various reasons, there's a decent chance that arrangement of the bits as visual elements on a plane would be one of the basic things they'd try. From there, they may not recognize the significance of structured symmetry vs. random noise, but that frankly seems nearly as unlikely as their being able to build radio receivers without understanding mathematics. They may not rely on visual sensing, but there is good reason to believe that there's at least a decent chance they do. And they may not be able to make sense of all of the image's components even if they do use vision, but at least some of them will probably suggest certain things to them for various reasons (I'm talking specifically about the contents of the Arecibo message here, but the same would presumably hold true of the messages sent in more realistic attempts at communication). At the end of the day, there's no guarantee that whoever detects the message can make sense of it, but there is at least a fighting chance they can extract some meaning from it even if not all of it's meaning. Probably more of a chance than your "needle in a haystack" comment might suggest, since that would seem to suggest that the chance would be vanishingly minuscule. There are probably better-than-minuscule chances that radio-receiver-building aliens understand math, would at some point arrange the message's bits as a two-dimensional grid, would recognize the significance of symmetry, and would understand the concept of visual information and thus an image.

Also, while two people on a telephone babbling at each other in different languages may not be able to reach a conclusion about where the other is calling from, the same rules don't quite hold true for radio transmissions. Even if we (or an alien civilization) couldn't make any sense whatsoever of a received radio signal, even if it was pure and total gibberish to us/them, one thing we/they could still tell would be the direction from which the signal came and thus, probably, it's origin. That's not all that the signal reveals even if its actual meaning/contents are totally mysterious to the recipient. At a bare minimum, such a signal tells the recipient not only where it came from, but that it was sent by a tool-using civilization which possesses the technical capability and understanding of physics/math/etc. to construct radio transmitters of the type needed to send that signal, and, presumably, the inclination to use that technology to attempt contact with other such civilizations (which reveals a mindset that is at least somewhat outward-looking and inquisitive, disposed to dream up and consider hypotheticals like the existence of life elsewhere in the universe, and attempt to discover whether they are correct). Furthermore the receipt of a message may tell the receiver something about what the sender considers likely places to find other intelligent life, and thus perhaps something about the sender's own planetary environment, star system, and so forth.

That may not be a huge quantity of information but it is some very significant basic knowledge about the sender of the signal, which can be gleaned without even beginning to understand the signal itself. Such a signal also implies several things about the evolution of intelligence, the incidence of life in the universe, the frequency of life-bearing planets and technological civilizations, etc., based on how far away the signal's source is, and what is known about that source in astronomical terms. So even a message that goes totally "untranslated" tells it's recipient a lot and will probably stimulate a great deal of research, speculation, and other activity in the recipient civilization. Certainly I think that would be the case if such a message was received here on Earth. A message from another species would carry a lot of significance totally apart from it's actual content (and again, understanding that content may actually be a good bit easier than "finding a needle in a haystack", if the message is properly designed).

Originally Posted by Atmoscheer

If we received some type of vague alien communication whose validity, meaning, and purpose we would struggle immensely to discern, I'm certain we would hardly bat an eye, much less make any dedicated, meaningful effort to establish any type of contact.

Well sure, if even the communication's "validity" was very difficult to discern (i.e. if it was hard to determine whether the signal was really of artificial and alien origin), then it might not be a big deal. That's not saying much, though; it's essentially saying "there wouldn't be huge excitement over an alien message if we didn't know it was alien", which is an obvious and also kind of pointless observation. Assuming the message could be recognized as having a clearly artificial, extraterrestrial origin, I think it would be a pretty huge deal even if it's meaning and purpose were totally unknown. You might not bat an eye but a lot of scientists and a lot of people in general would flip their shit. Whether we would/could make a serious effort to send a reply message of our own would of course depend on how far away the message came from.

Originally Posted by Syme

Lasers would be ideal because they aren't subject to the inverse-square law.

Our best lasers don't stay collimated for an infinite amount of distance, and they certainly wouldn't stay collimated for astronomical distances.

At essentially infinite distance you'd have the same result as a dipolar emitter: something that looks basically like a plane wave (i.e. extremely large radius of curvature) with very low intensity.

Also, I have never heard of a "RASER." You, however, must be familiar with one of them, so please, tell us about it and its operation.

Originally Posted by Syme

Sure you have heard of them, they just aren't usually called "rasers". They are usually just called "RF masers". Many masers emit on radio wavelengths.

Uh-huh. You might want to check the wavelength range of rf lasers and masers. And yeah, a true "Radio Amplification by Stimulated Emission of Radiation" device would be called a "RASER."

Sure, masers might emit what are technically radio waves, but they are just on the border between radio waves and microwaves. They aren't the sort of radio waves we're talking about here. It's not like radio waves are as narrow a band of wavelengths as visible light.

Okay, I just saw an experimental 128 km "laser" that's been made, but if that is really a radio-aser, then it is hardly ready for practical use.

Although I have read (can't recall where) that lasers for interstellar communication might actually be visible-light.

Well that's fine. The fact is that no laser, maser, or blank-aser can stay collimated for interstellar distances. If you can find one that can, I think you'd be a candidate for a Nobel Prize.



But since you're obviously expert on all this, I'll just leave this thread.

Did I say something to piss you off? I'd be happy to have your input here, you almost certainly know more about some of this stuff than I do. I explained my understanding of collimation, but also freely admitted that it's a layman's understanding and I could easily be wrong. It sounds like you are telling me that laser beams do in fact de-collimate over distances. Is this correct? I did not know that but certainly don't pretend that means it isn't true.

And yes, I know that "raser" would indeed be the proper name for an RF maser. Along with grasers and irasers and all that. But in practice you are much more likely to see an RF maser called just that, an RF maser, rather than a "raser" (as far as I can tell it's rare for anyone to actually use those frequency-range-specific laser terms). I don't know anything about the wavelength range of RF masers; if you do, please tell me. I said what I said because I do know that there are RF masers, distinguished from 'normal' masers because they emit in what's normally considered the true radio spectrum rather than microwaves, HF radio though it may be. You asked about rasers, I told you that. If you had meant "rasers operating below a certain frequency", you should have said so.

EDIT: Also, if you poke around on google a bit, you will find plenty of serious discussions about the advantages of using lasers for interstellar communication.
http://adsabs.harvard.edu/full/1992lbsa.conf..637S
http://www.coseti.org/ross_02.htm
http://oreilly.com/catalog/alien/chapter/ch07.html

In fact apparently there is a whole parallel SETI effort, called OSETI, focused on looking for optical communications from other star systems instead of radio signals. Again, the lasers considered are usually actually visible-light lasers, so the problems of making a raser that operates on long wavelengths is probably irrelevant.