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"Even Phil Klass thinks Earth has probably been visited by at least an alien probe, or so I have read."

I am unaware of this. Seems dubious.

There is an argument--along the lines of the Fermi Paradox. It goes like this:

The Sun is a 3rd-generation star. If there are lots of intelligent ETs, they've been around for thousands or millions of years, and their technology would appear godlike to us. Even at 5% of the speed of light, there has been ample time for every star to be visited.

One strategy would be to build 'von Neumann' robots. Programmed to select a star at random, gather all data, and build a copy of themselves from local materials. Dump the entire database into the copy; then both vehicles randomly go to two more stars. You get an exponential explosion of probes, each knowing everything its ancestors did. The payoff: every once in a while, one of the probes wanders home and dumps its data. A huge payoff for a modest investment.

The problem is that there ought to be a traffic jam of probes right here, right now. We do not observe them. Hence either there are no intelligent ETs or the difficulty of achieving even 5% of "c" are insurmountable.

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Incidentally, the book "Rare Earth" makes distressingly-persuasive arguments which lead to the conclusion that we are the only intelligent species in the Universe--or maybe only the Milky Way Galaxy. Recommended reading.

--Boris

I don't begin to remember where I read that about Klass, I will try to find it, though.

The "Fermi Paradox" argument is compelling.

Have never heard of "Rare Earth," so looked it up on Google. Found a discussion in which the authors stated that the operative word is "rare" rather than nonexistent. Drake was included in the discussion, along with others. Interesting stuff, theories on the requirements for "complex animal" life which I had not been aware of.

I am wondering whether or not you think that there is intelligent alien life.

My gut feeling is that there is, though I don't at all feel competent to speculate on whether it could be common or rare. Nor am I convinced that it has visited Earth, though I think it may well have.

I have always spent alot of time outdoors, both at sea, which requires alot of time looking at the sky (because of the need to be constantly aware of the weather) and in the woods. I have yet to see any suggestion of a ufo. I figure most reports of them have to be mistakes...but perhaps not all, some accounts remain too difficult to explain away.

I tend to think that those who would be too positive either in believing or disbelieving are assuming too much. Surely we have established the truth of certain laws of physics, from which we can draw conclusions. Yet I persist in believing that there likely remains much still undiscovered that may well, as the future unfolds, change drastically what we think we understand of the universe.

I also am thinking that if there are races advanced as far beyond us as we are beyond, say, a frog, then their capabilities will never be within our understanding.