Maggie's Farm

It may be possible to provide broad estimates. Of course, that will leave the Fermi Number (N) with wide margins of uncertainty.


That is quickly becoming something humans can determine with reasonable accuracy.


Almost all scientists believe that a planet suitable for the origin of life is one with liquid water. But habitability by humanoid colonizers may not. (See below.)


Assuming the alien civilization is as sophisticated as Earthlings, then they should be able to detect signals from the former Arecibo Observation as far as 12,000 light-years away. Signals from the Deep Space Network could be detected 60 light-years away. However, ordinary radio signals leaking into space could not be detected much beyond Earth's nearest stellar neighbors. Human technology is rapidly advancing, though, so those distances will almost certainly increase.


That is not correct. Sub-light speeds are more than sufficient to populate the galaxy.

Consider a humanoid civilization that reaches the Kuiper Belt, each plutino or dwarf planet being hollowed out for humanoids to create self-sustaining colonies, using the ice for fusion power. Over time, given exponential growth*, the descendants of humans would populate the Kuiper Belt. These objects, being self-sustaining, could easily travel interstellar space for hundreds of generations, looking for and finding new plutinos or planets to colonize. Think spores of civilization. They don't have to be habitable planets either, just icy. Now, given a spread in all directions of just 0.1% of the speed of light, the humanoids would have reached all corners of the galaxy in just 100 million years.

* If the human population could grow just 0.85% per year without limit (the current rate), ceteris paribus, the mass of humans would exceed that of the Sun in 5,000 years. Their energy production, assuming the same rate of growth would outshine the Sun.

The origin of life requires a habitable zone, but the spread of life does not. Of course, this just makes Fermi's Conundrum even more intriguing.

feeblemind: It would sure be interesting to know who cashed those checks totaling $130b, and where the money went.

Only about $15 billion has been spent, most from California state funds. The money has been used for land acquisition, utility relocation, viaducts and bridges preliminary to laying track.