Where does the material for the infinite replication of these probes come from?
Missed it by THAT much!
Just a slight hijack:
Would you consider a valid signal from an alien species to be the most significant discovery of the (pick one): week?, year?, decade?, century?, millennium?, history of mankind?, other?
Let’s say that we could decipher the signal and it was a generic text message, no more than one paragraph in length, meant for the benefit of any alien life form lucky enough to intercept it. How would you like the message to read?
Or, in lieu of text, would you rather receive a series of digital photographs? Alien porn? Other?
These in combination provide a possible scenario. Civilizations that develop the technology for your “hello” probe typically develop FTL drive shortly afterwards. With FTL drive, they typically catch up to the hello probes before they spread farther than 10^2 ly or so. We also must accept that once they develop FTL drive, they don’t have any desire to communicate with us, and also have a desire to suppress the spread of their own probes, and that their expansion is limited by something other than distance.
That just leaves the civilizations that launched the probe but were destroyed before they developed FTL, AND had millions of years head start. That could be pretty small numbers!
Personally, I don’t buy the idea that civilizations destroy themselves. They don’t want to do that, and I think we’d notice unnatural side effects of civilizations destroying themselves.
But I also don’t buy FTL drive, or the desire to suppress communication.
That leaves me with the hypothesis that for some reason, it’s unlikely for a space-faring civilization to have developed before ours in our galaxy. There may be many out there, but in our galaxy, they are young like us. Maybe the density of supernova remnants has to reach a critical threshold before you get rocky planets with shallow oceans and plenty of metal.
Its exponential replicas, and perhaps ramjet technology is all you need (use magnetic fields to trap interstellar hydrogen, fusion it and expell it. Once you arrive at the next star system, you land on whatever is there, set up a fusion plant, build a factory, and generate and launch probes. This is slower than c, but even .5 c only slows the expansion by half. So its 4 million years instead of 2 million. It’s still a blink.
On re-reading my original post I realized that I hadn’t actually specified as to this issue, and that a more literal-minded person might believe that I was suggesting a magical probe that could reproduce itself in space using nothing other than itself. As this is obviously theoretically impossible, so such a probe would have to be capable of finding and reprocessing raw materials on its own. Asteroids, rock moons, kuiper debris belts, and so forth.
My use of the hyper technical phrase “some sort of replicating hardware” was evidently ill-defined. I’d thought it was obvious.
And with the sole exception of maintenance power, propulsion, and deceleration, what would you need energy for in interstellar space? The solar systems are the objective, not the void between them. Once a desired speed was achieved, a probe would go cold until it began its re-entry into the target system.
All of this is, of course, rather off-topic. The OP is about why SETI hasn’t found anything, not why Grossbottom Can’t Build A Self-Replicating Space Probe. No on Earth can do that, to my knowledge. On the other hand, if you assert that no advanced civilization could build one, then that’s your opinion and you’re welcome to it. We have one intelligent species to study, and that’s ourselves. We’re a heck of alot closer to being able to build these than we are to building FTL drives.
Looking at Earth as the standard - we’ve got evidence of life on this planet for over a billion years. Multicellular life for hundreds of millions of years. Recognizable cooperative organisms for at least 100 million years. Intelligence, in the most restrictive definition - Homo sapiens, only - for about 20,000 years. And the ability to send signals that could be detected by a sufficiently sensitive instrument for about 200 years. So, compared to recognizable life, we’re talking about looking for a signal representing less than 0.001% of the time for recognizable chordate life on this planet. And we’re hoping that it will show up, here, at the same time as we have the ability to look for it - which is only since about 1950, or a quarter of the time that we’ve been able to put forth the signal we’d be looking for.
So, this signal, based on the only sample we have, represents an incredibly finite blip of a very long development of life.
Add to that, even limiting the search to stars within 100 light years of the earth leaves a huge sample size. At the Smithsonian’s Air and Space Museum they’ve got an exhibit that shows in detail just how many stars are within that distance, it’s a staggering amount. Assuming that Alpha Centauri as a standard distance (5 Light Years separation between solar systems) a sphere 100 light years in radius contains (4/3 pi r^3) over four million cubic light years which is room for 8000 solar systems within that sphere.
As someone else as pointed out, even assuming that the Milky Way is over populated with technological races, the odds that we’re able to contact them via light speed signals is infinitessimal.
Then there are all the “bad” SF ideas out there. Fred Saberhagen’s Beserkers are not something we can discount. An automated, Von Neumann probe that destroys life as it detects it is very easy to postulate.
Getting away from that, let’s consider this: AIUI there is exactly one species on the earth that can deal with jet lag. With technological travel capabilities, this is not a small concern. As a counter-example, without supporting the idea that an agrarian society is the ideal (I have trouble believing that any successful species won’t try to reproduce to take advantage of all available resources, to be honest.) and stable intelligent society, how many species on earth cannot colonize into new ecological niches? Our current example of life in the universe shows us that relatively mobile species, like the rabbit, rat, human, coyote, and cockroach are the exception. Many species are so tied to a local environment that they can be made extinct by changing the habitat of 100 hectacres. It may be that the human drive to see what’s behind the next hill is relatively unique among tool-using intelligences.
There are a lot of reasons that SETI may end up with nothing. Even if it runs for millenia.
Having said that, we can’t even say that SETI has analyzed all the signals it has recorded. It’s got a huge backlog of content to consider, still. I’d be thrilled if we find out that the Flexianads have been telling us to bring The Honeymooners back to the airwaves, or else, for the past twenty years. I don’t believe it will happen, though.
Realistically, if the human race gets off Earth to spread - it’s likely the galaxy is going to be human-descended. Unless there’s a way to cheat relativity.
I’m with Tibbycat here. Getting a message like the one we sent on the Vovager would have an 'ooh-ahh factor at first, but the novelty would soon wear off for the general public, IMO.
Do you think that if we did in fact receive such a signal from other life in space- that perhaps the government (or some other entity) would try to suppress (or debunk) it? I mean, aren’t there a huge number of people that believe, because their religion teaches them so, that we are the only ones in the Universe? I could just imagine some kind of utter pandemonium- the "I told you so"s would start fighting with the "we’re alone"rs, and burning and looting would ensue. Of course that’s exaggerated, but beliefs are a strong thing, and I could imagine a “message” would be a pretty big blow to some…
Yeah, I dropped an order of magnitude, here or there.
Still, we couldn’t detect ourselves from 5000 light years, even knowing where to look, unless the background was perfect.
Tris
The day, I guess. Right alongside a story about unrest in the Middle East. I do understand the fascination with this topic, but at the very basis of all the other unknowns is the fact that life itself is tenuously defined. There is no guarantee that we would recognized a living thing if we stepped right on its head, or that we would recognize a message as information of any kind.
We tend to think in terms of rhythm and periodicity because of our heartbeats. If there were some other mechanism for supplying oxygen to the brain besides blood circulation, we might think in terms of something else. From what I’ve heard — and I certainly could be wrong — SETI concentrates on patterns of periodicity. But consider how vastly different earth civilizations have been from each other. Look at the difference between Western and Eastern applications of, say, gun powder. The Eastern mindset was so very different from the Western one that, had the West had gunpowder first, the East might long ago have been subjugated by force.
So much more so for alien life forms, whatever that means and whatever they are. It seems to me that for them even to desire to contact us, they would have to be so like us that they might as well be considered just a separate species of humanity, along the lines of Neanderthals. I’m no more interested in whether there was “life” around some star that burned out a hundred million years ago than I am in whether there was ever a dung beetle on a particular mountain in Cambodia.
I think this kind of “we wouldn’t recognise it” argument is vastly overplayed, actually. If we found something on Earth which was characterised by some kind of metabolism, growth or directed motion, we would immediately recognise it as something interesting regardless of whether or not we have yet shaped a linguistic set capable of holding everything which is “alive” and barring everything “not alive” (which I think Varela’s does nicely, incidentally). Further study would yield evidence suggesting that its “living thing” status ought at least to be considered.
Similarly with signals, anything which deviates from simple Gaussian noise is worth looking at further, and statistical analysis yielding results which cannot be explained by known natural sources (eg. quasars) would again indicate that there was something interesting. We might not understand what whalesong, bee dances or bat chirps mean, but it is certainly not the case that the whale, bee or bat must desire to talk to us before we break out of our solipsistic stupor to even notice that there is a signal which deviates from Gaussian noise in our vicinity.
In short, if there was anything which deviated from noise incident upon us, we would almost certainly detect it, record it, and analyse it as being a possible communication. Heck, that’s how quasars were discovered in the first place.
I’ve been meaning to jump into this one for a while now. Apologies for the mound of this that is repeating what others have said.
SETI, for one, is only looking for signs of life within our galaxy. Yes, the Arecibo signal was sent to the M13 nebula, but that was more of a publicity stunt just to show we could do that sort of thing. Learning how to maintain a single consistent civilization for the minimum 50,000 years it would take to get an answer from there is a much neater trick than figuring out how to send the signal in the first place.
So it doesn’t really matter how much life there might be in the universe, since current technology is unable to allow us to communicate effectively with it even if it was there.
Radio Astronomy came into its own just as our world was bathing itself in radio-frequency transmissons. It made sense, in the 1960s, to assume you could find other civilizations by somehow detecting and identifying their radio broadcast signatures. That’s all SETI is looking for. Radio signals. They’ve always been flying more or less blind, and more or less destitute. For the record, they do not receive government funding and haven’t for many many years. It’s mostly privately funded through the Planetary Society these days.
When Frank Drake started it off with Project Ozma in the 1960s, he had no way of knowing whether or not the two sunlike stars (Tau Ceti and Epsilon Eridani) he chose to observe even had planets, never mind the facts that the first now seems to only have a protoplanetary asteroid belt far too prone to collisions to harbor long-term life, and the second has such an unexpected planetary system structure that it takes everything we thought we knew about planetary formation and turns it on its head. We still don’t even know for sure, and won’t for at least a few more years, whether ANY star SETI has looked at has Earthlike planets or moons that might offer us hope of a hit.
So for starters, we may simply be looking where the little green men aren’t (which may include everywhere if they don’t exist at all).
Another issue is that once SETI manages to get some telescope time to scan the skies, its gets a mountain of data that must be analyzed. Theis takes a lot of computer power that they don’t always have access to, which is why distributed projects like SETI@Home were started. They now have, based on the results of the SERENDIP IV project, what they think are some promising candidates, but they need a lot more processing done to weed out the red herrings.
So in addition, we may already have a hit but not know about it yet.
There are a lot of radio sources out there that are very “loud”, compared with what we’d expect from a source hundreds of light years away. We are dealing with the inverse-square law, after all. Plus, the Drake equation, even though it yields a number of possible civilizations in our galaxy, says absolutely nothing about when in galactic history these civilizations exist. Add to that the fact that in just a few short decades, we have already started making a transition from uncoded broadcast signals to encrypted, directional signals, and we realize the possibility that other civilizations may have made the same transition, meaning that what SETI was designed to look for may be quite short-lived, and did not necessarily happen in a time frame that would allow the weak, possibly intelligible signals to pass by us at exactly the moment (the few decades past) we were listening. And that’s assuming that we’d even understand what to look for
So furthermore, when ET phoned home, we may have missed it completely or had no idea we were looking it right in the face.
Rome had some very advanced technology - plumbing and water for instance, that was ahead of the world for the next 1700 years and more. Perhaps European science was the second attempt, which would make science much more likely.
i think Malthus and natural selection ensures that a stable agrarian society with enough to eat is the sign of a very advanced civilization, that has gone through science already, not a primitive one that has never discovered science.
Don’t confuse technology with science. Ancient Rome and premodern India and China provide excellent examples of “stable agrarian societies.” And for most of the history of each, scientific progress was virtually nil. (And technological progress not much better.)
Can you not imagine alien encoding too sophisticated for us to even notice?
There can be Gaussian noise without any randomness other than amplitude. Suppose the pattern were one of changing frequencies. Or suppose the pattern were one of hundred-year periods. What seems like Gaussian noise and thus is abandoned quickly may be merely the comma in a message that takes twelve-hundred years to compose. As elephants are to humingbirds, so might an alien “life form” be to us, with metabolisms so slow that we don’t even notice they are moving, let alone have the patience to detect their messages. Alien means that our tiny recognition spectra are iffy at best.
Well, I said explicitly earlier that perfectly compressed coding is indistinguishable from Gaussian noise. I’m just commenting on anything which isn’t.
Like this?
But again, there must be some basic astrobiological reason why such long-lived complex lifeforms didn’t evolve on Earth, and if not, how different could another environment realistically be? Surely they would have been outcompeted by busy little mortals before they attained enough intelligence to send a message? I’m not saying it’s impossible, but it really does sound vastly improbable.
No