Posted on 10/25/2001 9:13:53 AM PDT by RightWhale
Is there obvious proof that we could be alone in the Galaxy? Enrico Fermi thought so -- and he was a pretty smart guy. Might he have been right?
It's been a hundred years since Fermi, an icon of physics, was born (and nearly a half-century since he died). He's best remembered for building a working atomic reactor in a squash court. But in 1950, Fermi made a seemingly innocuous lunchtime remark that has caught and held the attention of every SETI researcher since. (How many luncheon quips have you made with similar consequence?)
The remark came while Fermi was discussing with his mealtime mates the possibility that many sophisticated societies populate the Galaxy. They thought it reasonable to assume that we have a lot of cosmic company. But somewhere between one sentence and the next, Fermi's supple brain realized that if this was true, it implied something profound. If there are really a lot of alien societies, then some of them might have spread out.
Fermi realized that any civilization with a modest amount of rocket technology and an immodest amount of imperial incentive could rapidly colonize the entire Galaxy. Within ten million years, every star system could be brought under the wing of empire. Ten million years may sound long, but in fact it's quite short compared with the age of the Galaxy, which is roughly ten thousand million years. Colonization of the Milky Way should be a quick exercise.
So what Fermi immediately realized was that the aliens have had more than enough time to pepper the Galaxy with their presence. But looking around, he didn't see any clear indication that they're out and about. This prompted Fermi to ask what was (to him) an obvious question: "where is everybody?"
This sounds a bit silly at first. The fact that aliens don't seem to be walking our planet apparently implies that there are no extraterrestrials anywhere among the vast tracts of the Galaxy. Many researchers consider this to be a radical conclusion to draw from such a simple observation. Surely there is a straightforward explanation for what has become known as the Fermi Paradox. There must be some way to account for our apparent loneliness in a galaxy that we assume is filled with other clever beings.
A lot of folks have given this thought. The first thing they note is that the Fermi Paradox is a remarkably strong argument. You can quibble about the speed of alien spacecraft, and whether they can move at 1 percent of the speed of light or 10 percent of the speed of light. It doesn't matter. You can argue about how long it would take for a new star colony to spawn colonies of its own. It still doesn't matter. Any halfway reasonable assumption about how fast colonization could take place still ends up with time scales that are profoundly shorter than the age of the Galaxy. It's like having a heated discussion about whether Spanish ships of the 16th century could heave along at two knots or twenty. Either way they could speedily colonize the Americas.
Consequently, scientists in and out of the SETI community have conjured up other arguments to deal with the conflict between the idea that aliens should be everywhere and our failure (so far) to find them. In the 1980s, dozens of papers were published to address the Fermi Paradox. They considered technical and sociological arguments for why the aliens weren't hanging out nearby. Some even insisted that there was no paradox at all: the reason we don't see evidence of extraterrestrials is because there aren't any.
In our next column, we'll delve into some of the more ingenious musings of those who have tried to understand whether, apart from science fiction, galactic empires could really exist, and what implications this may have for SETI.
Yep, right now we can move a few man-month's worth of environment at about 10 miles per sec.
That's an amazingly long, long way from moving several man-years worth of environment at 180,000+ miles per second- which is what is assumed by Pauli.
It's a question of something called "specific impulse". Essentially, it's a measure of how good a fuel is at carrying itself. If the specific impulse is too low, then in order to achieve any reasonable velocity, the starting fuel fraction (that is, the fraction of the starting mass of the ship that is composed of fuel) comes unacceptably close to 1. For any interstellar journey, even nuclear propulsion systems end up with a starting fuel fraction that is exquisitely close to 1, meaning that very little stuff can come along for the ride. The more stuff you want to take, the slower you must go.
(For the record, nuclear rockets have an excellent specific impulse for zipping around the solar system. This WILL happen.)
The only way to do it is to have an externally powered ship. A solar sail with a big driver laser in the home system can do it, although the economics are staggering and the range is limited to a few light years, max. A Bussard ramjet may be the only way to effect long-distance interstellar travel.
It could have happened many times. But just not recently or while SETI is being operated. They may have passed through the solar system itself just before we got radio, and won't be back until after earth is destroyed in a mysterious bright flash.
-- Sorry, we're not in right now. Leave a message, we'll return your call later.
YOWZA
One of the advantages of the center of the bell curve view is it's ability to handle the small sample set (1 in this case). If it turns out we're cranked over to one side or the other we'll find out, but until we have a statistically useful sample set we can assume other even out to be like us. That evening out is important. Technically speaking you could have a race that's actually slower to advance than us (or one that started more recently, pick you "disadvantage") still be even with us if they navigated certain things differently. You point out the 100 years gap. Remember that European civilization (the root of most technological progress on earth) effectively stalled for close to 300 years (the Dark Ages), actually it went a lit backwards during that time. What happens if a race starts 200 years AFTER us, but avoids there own dark ages? Well they're about 200 years ahead then.
Actually I lean towards your conclusions 1, 3 and 4. We could actually be on the far right (the A student side) of the bell curve, it's more likely we're right of center than left; as you point out if we were the failing students we'd probably have been run over by now. Given that from what we've seen war is the best way to advance technology (again cosmological center of the bell curve, there are probably better ways but if we're typical then war is the inspiration most civilizations use), you have the serious potential side effect of self destruction. Also, as I partly pointed out to RW, we're waving a very narrow beamed flash light (I like that analogy) around the galaxy, one narrow enough that we could shine it right on an alien race and still not notice. The only one I can't wrap my head around, because there are so many planets out there, is that we're alone. It just seems like a pathetic waste to have that big a galaxy and only one intelligent race to play with it.
Well gang. Gotta go. Been fun hanging on this thread. See you tomorrow.
And what powers these probes. Can we build a complex gadget that works for a 100 years much less 10,000. And who would fund such an endeavor.
Consider that the earth is about 4.5 billion years old, and the galaxy itself over ten billion years old. If, in fact, the conditions for the development of technical civilizations in our galaxy really are favorable enough for there to be some E.T.'s around sending radio broadcasts then why hasn't at least one flying saucer made its way to earth by now? Why isn't there at least one robot probe in our vicinity which has detected us?
Its a really long way out there. We haven't even really let ourselves be known yet. What would even bring a "flying saucer" this way.
I am skeptical of the premise of radio SETI, in other words. It's hard to understand the view that there are several advanced E.T. societies around transmitting messages of peace and good will but none have yet managed to show up in our neck of the woods in person or through their robot surrogates. I'm more willing to believe that we are the only technical civilization ever to exist in our galaxy than I am in that hypothesis.
The search I am involved in does not look for any radio signals purposely beamed at us. I am looking for another race that has developed far enough down the technological road to have developed radio like we have. There appears to be only 4 fundamental forces in all of nature; Strong Force, Weak Force, Gravity, and Electromagnetism EM. Both the strong force and Weak force are confined to the nucleus of the atom. Gravity requires prodigious amounts of energy to manipulate, so the only one that is practical for long distance communication is EM. In an extremely short period of time, we are using EM across the entire spectrum from basically DC to light. We are now radiating that same spectrum into outer space. In fact at certain frequencies, we are the brightest object in the known heavens. So what we are looking for, is a race that is doing the same thing we are, unintentional radiation of radio wave into outer space in all directions.
I can picture in my mind a world without war, a world without hate. And I can picture us attacking that world, because they'd never expect it.
Very interesting. That sounds like an effective way to spot a planet inhabited by intelligent beings from the vastness of space. I can see where our earth on the radio scale would shine like a bright beacon.
Von Neuman-type self replicating machines would make short work of the problem of technological lifespan.
Why are we alone ?? I have my own theories on it.
The fact that we're in a 500 LY wide vaccuum bubble from an old supernova could also convince other life forms that looking for civilizations here would be about the equivalent of us looking for a fully functional, working 7-11 in downtown Hiroshima around September 1945.
Because radio signals are extremely cheap and interstellar travel is extremely expensive, no matter how you figure it. So the fact that radio signals are scarce, at some level, means that interstellar travellers are extremely scarce. If the aliens were here already, chances are that the sky would emit a cacophony of radio signals, which apparently it does not.
Once a species develops nanotechnology, the speed of civilization begins to increase, and the scale of action relevant to the civilization begins to decrease. Radio communication simply becomes irrelevant as the scale of civilization goes down towards the quantum scale, and beyond that, who can tell? Who needs to communicate with the other side of the world, or even the next block, when there's a subjectively expanding universe in a grain of sand?
The information processing nexus called the industrial economy has become merged, at a cellular level, with the information processing nexus we call nature. Storm fronts of meshed intelligence ripple through the living fabric of the world...
Physicist writes: The only way to do it is to have an externally powered ship. A solar sail with a big driver laser in the home system can do it, although the economics are staggering and the range is limited to a few light years, max. A Bussard ramjet may be the only way to effect long-distance interstellar travel.
Building self-repairing, nuclear-powered robots or even peopled craft to travel hundreds of light-years would be difficult. It would not be impossible. There certainly is no principled reason we have now to think it cannot be done. There isn't any reason to believe that even we ourselves couldn't do these things within, say, five hundred years. We are likely to have advanced AI in robots by then, along with some actual examples of drawing board propulsion technology. I wouldn't be a lot of money against these things happening, at least.
I could be wrong, of course. There might be unforeseen difficulties which make instellar travel, or advanced AI, or other necessary technologies an impossibility. But if there are such principled difficulties we don't know about them at present.
Travel through space would not be cheap, as both of you have pointed out. It would never be cheaper than just broadcasting, or doing nothing at all and just letting one's domestic radio traffic travel out to the stars.
Notice, though, that if we're to explain the absence of E.T.'s here on earth through technical difficulties or expense we have to suppose that no E.T. civilization can solve these problems. Or we have to suppose that there isn't a single society which can solve these problems and is also interested in sending out probes or manned craft. There's no way we can be confident in these things. It's unreasonable to believe, and act on the belief that, there are E.T. civilizations, and advanced ones at that, and at the same time not one of them has the ability or inclination to expand into the galaxy.
Instead, it seems to me reasonable to suppose that as a society becomes more technologically sophisticated it will accumulate significant material and intellectual capital. So a society which has technology of the sort we imagine will sooner or later find the deployment of that technology affordable. In the case of sophisticated self-replicating robots, for example, the initial expense of sending one into space wouldn't be that large at all for a society which already has the AI technology.
As I've said, we can assume that it takes 100,000 years for a new bunch of explorers to set up flying saucer factories on the new world before a new crew heads out to the stars. Or, if you like, we can imagine self-replicating robots which take 100,000 years to make space-faring copies of themselves. Even if we imagine the number of space colonies doubling only every 100,000 years it's not long until the whole galaxy is filled up. There wouldn't have to be any special reason for E.T.'s to come to earth. If they started more than ten million years ago they should have visited our solar system just based on the properties of our sun. So, it seems unlikely that technological civilizations have arisen several times in the past but that no one has arrived here yet.
Of course, we still have to provide a motive for E.T.'s actually sending flying saucers or robot probes out into space. But as the cost to the original world of doing these things first moves from prohibitive to merely extravagant there's no reason to think they wouldn't do it. Even we, with our relatively new grasp of industrial technology, are willing to spend huge amounts of money on silly, gee-whiz stuff like the manned space station and shuttle missions. What would we say about the possibility of self-replicating robot probes?
There is also the fact that all it would take is one other civilization to get going to colonize everything. So, a civilization that starts thinking about it might well conclude that it should start colonizing the galaxy around itself to get there first.
So, it's still hard for me to believe that there are E.T. civilizations beaming out radio messages but that there is not direct evidence of their existence nearby. Let me clear, though, in saying that this could be the way things are. Who knows? SETI doesn't seem like a bad gamble, in any event, given the relatively low cost of doing it. I'm just skeptical it will work out.
I appreciate your remarks. Thanks. And good luck Radio Astronomer.
Thanks very much for the "good luck" :) It's highly appreciated!
Unless chocolate-covered indigenous population lips are considered a very cherished and tasty delicacy.....
METAPHOR MELTDOWN!!
Abandon Ship!!!
Pretty perfervid for Mr. Slide Rule. ;^)
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