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.
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.
If it is unintentional we won't see it. Think of the power levels required to be detectable for any practical volume of space.