Rant about Aliens...

its about statistics. Most , almost all are uninhabitable. But their number is huge. I mean if 1 in 100.000 is habitable, but their are trillions of them.
For me we are not alone. But they are SO FAR. That communication is not possible. Even at speed of light. Add to it ever increasing expansions of universe, not only increasing but also increasing speed. For me we go into a dark night.
 
Phishfry said:
That sounds exaggerated. I see catalogues with 500,000,000+ stars
So billions might not be out of the question.
Click to expand...
The dimension that is so often ignored in making these kinds of estimates of the number of habital planets is time. Consider the 4.5 billion year old age of the earth. For most of that time, the planet has not had an ecosystem that could support a human agricultural system as we know it, which is the foundation of our modern civilisation. If you landed your spaceship on the earth any time before the last 5 million years, would humans have been able to settle it? Perhaps one could argue we would be able to establish agriculture in the cenozoic, but is it realistic to think we could do so earlier than that? If we limit it to the cenozoic, that's 100 million out of the 4.5 billion year age of the earth when humans could conceivably settle here, which is only the last 2% of the earth's lifespan. If we take a more realistic estimate and say that we might conceivably be able to establish agriculture if we landed on earth some time within the last 10 million years, that is a window that is just 0.2% of the earth's lifespan.

This means that if we did develop a technology that made it possible for us to travel to other star systems, we would have to arrive there at just the right small period of time in those planets lifetimes, to be able to settle them to establish a viable human culture. Landing on earth as it was, 1 billion or more years ago, ie during 3/4 of it's history, likely wouldn't have helped you very much.
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The Drake equation states:- https://en.wikipedia.org/wiki/Drake_equation

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Each of the terms in the equation become progressively smaller as we read towards the right. While fp and ne may be relatively large numbers, and perhaps even fi, if we then consider the appearance of Homo Sapiens, perhaps 300000 years ago, as the fraction of the lifespan of the earth that has sustained intelligent life, we are talking about a time window that is 0.006% of the earth's 4.5 billion year lifespan. So I think at any one point in time, the value of fi is likely to be small. Similarly if we consider the time since the development of radio astronomy, which is less than the last 100 years, then we are talking about a truly tiny time window as a proportion of the age of the earth. Of course we don't know if a technological civilisation elsewhere might survive for 1000 or 100000 or 10 million years, but the evidence we have from earth is that a mass extinction is currently underway and hence the lifespan of technological civilisations may be rather small before they self-destruct, if our experience here on earth is representative of other planets. So the solution value of N may turn out to be a rather small number, at any given point in time.

There may well have been hundreds or even thousands of technological civilisations in existence in the milky way galaxy during the last 14 billlion years of its existence, but the numbers of them co-existing at any one point in time may be a very small number.
 
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