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SETI Results By Scientific American
Paul Cobbaut writes "This http://www.sciam.com/2000/070 0issue/0700crawford.html is a link to an article on SA about Seti results so far. It discusses about why we found no ET yet, and provides more links." Very lucid and informative. Compare and contrast with a previous story.
See: Misconceptions Regarding SETI, Dyson Spheres and the Fermi Paradox
The bottom line is this -- nanotechnology enables the transition from pre-Kardashev-Type-I civilizations (us) to post-KT-II civilizations in decades. Such civilizations are resistant to almost all hazards on galactic scales and will thus be the dominant form of life in galaxies. If we are typical, it only takes a few hundred years to evolve from the discovery of the laws of physics to reach KT-II levels. KT-II civilizations survive for trillions of years. Unless the evolution of intelligent life is very, very difficult our galaxy should be dominiated by KT-II civilizations (Dyson shell supercomputers, a.k.a. Matrioshka Brains) with thought capacities in excess of a trillion trillion times the human mind.
Intentional communications generally occurs between entitites of approximately the same capacity. As we are at the sub-worm level in comparison to KT-II civilizations, they will not be directing communications at us. Non-intended leakage communications could be detected by SETI out to a few dozen light years, but we should be looking in the MHz frequences, not in the GHz frequencies. Therefore SETI@home is a waste of CPU cycles.
Interstellar travel is possible (the British Interplanetary Society Project Daedalus Study showed that). It is however pointless. The speed-of-light delays and communications costs for large volumes of data, mean you get little benefit from colonization. You do not want to become larger, you want to become smaller (or at least work very hard to minimize propagation delays)! The fact that KT-II civilizations can each build billions of lunar diameter telescopes makes rationalizations for interstellar travel difficult (why go "there" when you can "watch" there?). You also don't go very far, because "there", by the time you arrive, may not be there anymore (a closer civilization may have occupied the location). Arguments that we should colonize the galaxy in a few million years fail to understand that the rate of expansion is not limited by the speed-of-light but by the time it takes to dismantle planets, gas giants, brown dwarfs, etc. and turn them into something useful. It isn't the stars that are desirable to KT-II civilizations, it is planets with heavy metal abundances that "happen" to be on courses around the galaxy that these civilizations find attractive.
It is worth noting that the gravitational microlensing results, suggest that our galaxy is surrounded by ~200 billion "objects" of masses around 0.3-0.5 Msun. Astronomers are currently unable to provide an good explanation for what these might be. The best current guess is primordial black holes. (Of course most of the astronomers involved assume the universe is "dead".)
Comments by Verteiron, regarding the use of radio are absolutely correct. Given the capacities of KT-II civilizations, they are going to be able to build very large telescopes that can detect any other KT-II civilizations. If they want to communicate, they will do it using tightly focused lasers, probably in the blue or UV regions. This minimizes photon (energy) loss due to beam spreading and allows the highest data rates.
Note that the majority of cell phones in use today use digital CDMA spread-spectrum encoding. There are several benefits to this technology, which was originally developed for military use. CDMA transmissions are highly resistant to noise interference; are hard to snoop; and are very easy to hide in background noise. If you don't know what to look for, you won't see it. There's no intensity spike at any frequency.
This has been known for decades. It's entirely possible to foresee that all of our radio communications may use this technology in a few more decades' time, due to its benefits. This considerably increases the difficulty of anyone randomly discovering our existence by scanning our spectrum.
Giving ETI's credit for as much cleverness as we have, we are trying to find a ET civilization radiating within a few decades of its technological awakening.
It appears that is the way we are heading, in a matter of decades. It could be that detectable signals are only sent for a very very short period in the time of a civilization.
Everything that is being done in SETI assumes modulated RF. What if after a while using radio, other civilisations simply move to something else like quantum coupled whatevers?
If the time that a civilisation uses RF signals is limited then so is it's exposure. This could even be a feature if there are other unfriendly civilisations out there.
Nah, SETI@home is interesting and I have about 430 workunits. There is still a time where a cvilisation is visible in the RF spectrum, even if it isn't the whole time.
seti@home won't find alien life because it is just a distributed MP3 compression job on the Aricebo astronomers CD collection.
Bob.
One of the major reasons that ET will prove so elusive is the fact that we're not only looking at narrow slices of space, on narrow frequencies... but we're also looking for a signal that may encompass a very narrow slice of time for a civilization.
Putting aside the argument that intelligent life is not the "goal" of evolution (which is also a very good thing to remember), let's assume that an intelligent civilization DOES evolve out there. How long are they going to use radio for communication?
I don't claim to know tons about the area of the EM spectrum we're currently searching, but don't you think there will be better ways to communicate?
Analogy: Two tribes in two valleys separated by hills communicate via smoke signals. This is, to them, not only the best, but one of the only ways to communicate. Yet, all around them, even passing through them, are our radio waves, from our civilization, carrying speech and music, microwaves carrying our voices... Is it really so hard to adapt this analogy to our situation?
For all we know, there could be civilizations all around us, communicating; we just don't have the technology to detect the transmissions.
End of lesson. You may press the button.
Thus, we don't need every civilization to decide not to interfere. We only need the first to decide on a Prime Directive and decide to enforce it.
It gets even more likely as we go farther back: if we assume a few million years between civs, civ A is now so overwhelming that it could do anything it wanted without effort. (To paraphrase a line from Gardner, "(They) had a billion years of evolution on humans. To call them godlike would be demeaning.")
Eric
"Seven Deadly Sins? I thought it was a to-do list!"
It's a good thing, since we'd probably try to destroy any extraterrestrial culture we bumped into.
Or they'd destroy us.
********* sig: If you don't like the law, get filthy stinking rich, and buy a better one.
- are as rare as Crawford maintains, based on the unlikelihood that simple life forms evolve into more complex ones
- are in all probability very, very far away from our galaxy and therefore more difficult to detect by conventional means
- have been broadcasting (purposely or inadvertantly) in a different medium than the ones we consider likely.
For example, a truly advanced civilization may have learned how to propogate messages through "gravity waves" or the extra dimensions (six, IIRC) that superstring theorists postulate must exist, or using the "spooky action at a distance"property of quantum particles. And these are only the examples we know enough to guess at.Obviously we have good reasons to be searching the radio frequencies for signs of intelligence - after all, such frequencies are commonly emitted by all sorts of cosmic objects and can be used fairly easily to transmit messages over long distances. But perhaps the very fact that these frequencies are clogged already would lead other (more?) advanced civilizations to avoid them and look for other, clearer means of transmission.
Coupled with Crawford's theory that intelligent life has a low probability of evolving out of simpler life forms (i.e. bacteria or protozoa), and the follow-on assumption that such civilizations would thus be spread very thinly around the universe, this hypothesis could be a plausible explanation for why we haven't found anything yet. After all, we've only just started looking.
Was that out loud?
Here's some thoughts I've had about SETI:
Something I've never seen is any information about how powerful the extraterrestrial signals have to be for us to hear them- to do that, we need to know how much gain the receiving antenna has, what the sensitivity of the receiver is, and the intensity of the background noise. From that information we can get an idea of what sort of transmitters (at what distance) we're looking for. For example, a big radio station in the US is about 100KW, with antennas that point the signal more or less to the horizon. We make it a point not to send too much energy up- the intensity pointing straight up at the sky is many dB down from the main lobe. Just how far away could the Aricibo antenna hear a station that had an effective 1KW (isotropic) pointed in their direction?
Of course the Aricibo antenna doesn't listen at the frequencies of FM radio, it listens to signals in the microwave region (for SETI work, from what I understand). At these frequencies, it is even easier to point the signal from an antenna. Unless someone is broadcasting to us intentionally, I have a feeling we're never going to hear them.
There has been much talk about how we've been broadcasting to the universe- but at stellar distances, all those signals are going to look like they're coming from the same point, albeit diverse in frequency. But everything at the same frequency gets added together- and if you add enough non-correlated signals together- guess what: it looks like noise! Can our signals compete with the EM noise put out by the Sun?
Another thing: as our technology improves, our signals look more and more like noise, and we use less effective power- consider any sort of spread spectrum- the energy has been spread out over a wide area to combat interference, lowering the peak power at any one frequency. At the same time we're making improvements with our receivers so that we don't need to transmit as much power. It all ends up as more efficient use of what we have (more bandwidth for the same power) I can't think of any expanding intelligence that couldn't see the utility of that- so as an intelligent race expands, the overall amount of unintended radiation may not go up proportinately.
On the other hand, I support SETI- I've got it running on 4 machines, and I've completed over 350 SETI@Home work units. If we don't look, we won't find anything until they land on the White House lawn. These are just some things I've been thinking about.
One of the assumptions of those who believe that SETI will yield a positive result (signal from extra-terestial civilization) make some assumptions about the probability of life springing up on other planets that may be incorrect.
We have all learned in elementary school that if you put some hydrogen, amonia, methane and other gases in a chamber and apply some electricty, that simple amino acids are formed. And the hypothesis goes, once you get amino acids, simple organisms are certain to appear. However, this may be an over simplicity of what really needs to happen.
One of the characteristics of life (as we understand it), is that a means for self replication of the genetic code is required. This requires two 'matching pieces' of genetic material, DNA and RNA. DNA on its own cannot self replicate - it needs RNA to complete this process, and the RNA must exactly match the requirements of the DNA to cause the self replication.
Considering that in the primordial soup, the random arraingement of amino acids join together (defying entropy since the universe in general tends towards disorder)to form an ordered chain of DNA,
AND
that an arraingement of amino acids join together (again defying entropy) to form an ordered chain that makes the complimentary RNA chain
AND
that they just happen to be floating in the primordial soup with sufficient proximity that they 'hook up' ( a significant statistical improbability)
THEN
you may or may not have a DNA chain that is capable of self replication, let alone one that is yields to a single celled organism, something that we would recogize as life, from which all other live could eventually evolve from mutations in its cellular division.
I am not implying that we are alone, just that the universe may not be "teeming with life" as we might like to believe.
The next probe will probably carry a DVD instead. Now how do we explain to the aliens why these "lawyers" are coming to "sue" them simply because they really managed to decode our discs.
All opinions are my own - until criticized
(One sq. km will allow you to detect an Earth-size planet, at a distance of 1 AU from it's sun, at a resolution of 1 pixel.)
You also want to place the dish(es) in space, to reduce noise pollution from unintelligent life-forms, such as humans.
(A reasonable starting configuration would be two dishes 500 miles in diameter, shielded by the moon from Terrestrial interference, and placed far enough apart to use interferrometry, etc, to guague distance and motion.)
Then, you have to use a practical time-base. Most modern radio telescopes use as long a time-base as they can get away with, to maximise signal gain. For SETI work, you really need the =SHORTEST= possible time-base your equiptment will allow, so that signals aren't smudged into the background.
Third, it's easier to detect complex, unstable atmospheres than it is to detect a signal, so using the absorbtion lines as a filter would help. This would avoid false positives, such as reflected signals, because ALL the signals you're looking for would need to be reflected in just the right way to appear to come from exactly the same distance and direction.
Lastly, assumptions about the nature of the signal should be avoided at all costs. Checking a few thousand, a few million or even a few billion channels in a very narrow band is really not going to have much chance of success. To carry out a SETI search, you must check several septillion channels, over a wide band, with checks for all usable rates at all frequencies scanned, with and without allowance for doplar on one (or both) ends, without excluding "random noise". (What may be "random", when examined over one interval, may stand out as "WOW! II, the Real Signal" over another. By recording the raw data, and examining it using a variety of methods, you stand a much better chance of locating a signal.)
Oh, and don't forget aliens with CB's, who only use the side-bands.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
- the existence of moon of sufficient size to help create tides and provide a just the right amount of long term stability to the earth to allow life to evolve. . . That is a rare event
- the extinction of the dinosaurs by an asteroid impact
- birth and procreation of mutated ape of sufficient intelligence to create civilization
- The existence of a very few brilliant individuals
- A long period of time without a life killing catastrophe of natural origin.
I think that if the probability of intelligent life arising naturally is nonzero (i.e. there is no divine intervention or the like required), then it must have happened many times throughout the universe; the universe is simply too unimaginably huge for it not to have. However, intelligent life in a galaxy a gigaparsec from us is not terribly interesting; if that's our closest neighbor, then we might as well be alone. The interesting question is whether there is intelligent life close enough that we might be able to interact with it someday, and on that question we are basically ignorant. We have no idea how typical our own planet and solar system really are. We have begun to see signs that planets, at least, are not all that uncommon, and this is progress, but we have no idea how likely the coincidences that allowed technological civilization to evolve really are. Any attempt to generalize from the one example we have to the galaxy as a whole is mere speculation. Not that there is anything wrong with speculation, mind you, but we should take care not to confuse our speculation with fact.Granted, but is this the only stable configuration? What about moons around gas giants? What about configurations that don't occur at all in our solar system?
Why is this necessary? Who is to say that the dinosaurs wouldn't have spawned an intelligent race on their own, had they survived. Or maybe they would have died off for other reasons; the late Cretaceous is not the only mass extinction in earth history, after all.
We have no data on how rare this really is, nor can we be sure that something resembling a primate is the only sort of life that can develop civilization.
This is a very distorted view of scientific and technological progress. Closer examination of history shows that when the time for an idea is right, there are usually many people working on it independently. We remember the one who got there first, and we forget the also-rans, but that doesn't mean they weren't there. If Newton had died of the plague, others would have picked up the torch. Maybe we would have had to wait another decade or two, but physics would have developed, just the same.
Sure, but how rare is that, really? With only our own planet's history to draw from, it's hard to say, exactly.
Since we are too ignorant to predict from theory what we might find out there, our only recourse is to look and see what we can turn up. SETI is a crude tool; there are too many ways for it to fail to detect something that really is out there. For the moment, however, it is the only tool we have. Someday we will have space-based interferometers that are capable of resolving nearby planets directly, and that will tell us a lot more about how typical or atypical our own planet really is. And after that, who knows? We may never find out whether or not we are alone, but if we don't look, then we'll definitely never know.
``Sure the game is rigged, but don't let that stop you. If you don't bet, then you can't win.'' --Robert A. Heinlein
-rpl