14

That's basically the Fermi paradox. It seems likely that there are numerous civilizations in the galaxy, and yet we see no trace of them anywhere. The Drake equation is often invoked to calculate the probability of existence of other civilizations, by compounding several other, more simple probabilities: the probability that a star has planets, that the ...


10

The real reasoning has nothing to do with some civilization "deliberately" hiding its radio emissions. Rather, the problem is that we can not expect some other civilization to do something we would not do ourselves. It makes no sense whatsoever to radiate large amounts of energy into space when there exist other, more economical alternatives. Radio ...


6

In our paper we just used Mercury because it was convenient (close, airless, low binding energy). But we did not try to optimize the Dyson sphere design at all. It turns out that one can likely construct a far more efficient sphere out of very thin aluminium foil reflectors balancing light pressure and solar gravity to stay in place. That only takes the mass ...


5

The true explanation to the Fermi paradox is not known. There is a very long list of proposed explanations, some of which are listed here: https://en.wikipedia.org/wiki/Fermi_paradox#Hypothetical_explanations_for_the_paradox What you're saying is literally the first one on the list, also known as the Rare Earth hypothesis. https://en.wikipedia.org/wiki/...


5

I think this too broad, but I'll offer the following: The star Kepler 444 is orbited by several small, assumed to be rocky, exoplanets. Kepler 444 is estimated to be a very old star, perhaps 11 billion years old, with a metal content of about one third that of the Sun. Whilst the planets around Kepler 444 are small, they are too hot to be "earth like", but ...


3

I think you're question is incorrect, and what you should be asking is "Which of these is plausible", in which case, all of them are. I think you are also missing other options: There is alien life, who have already visited, but have not made formal contact with us, for any one of a number of reasons. We are the alien life, who has forgotten how we arrived ...


1

Already 15 million years after Big Bang! That is 13,783 million years ago. Well, that is according to the "habitable zone" criteria which is the temperature where water can exist as a liquid. The entire universe had a temperature which allowed for liquid water on all rocky planets, though rocky planets themselves were quite rare back then in the old days. ...


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