There’s another factor to take into account. Even with all the very generous assumptions you make in your article (the most generous being the guess about Eukaryotic life developing) we still need to factor in the stochastic nature of things. Humans evolved because grass reduced the forests, but we became tool-making apes only after multiple genetic mutations enabled us to develop what we call imagination. How likely, therefore, even on a planet with Eukaryotic life, such another tool-making creature would emerge and go on to build complex technologies? If we look at our own moment of fleeting existence it appears a highly unlikely event indeed.

But even if we assume that against all odds some other technological species develops and exists at the same time we do, there’s the problem of distance. The odds of this unlikely phenomenon occurring near us in this vast galaxy of ours are very remote indeed. There’s a far greater probability it would be so distant that communication of any kind would be impossible and therefore we’d never even be aware of each other’s existence — even if one or both species were still around thousands of years from now by the time signals had traveled across the void.

To all intents and purposes we’re alone in the universe.