Are we (humans) alone in the universe?

You mean: are there other intelligent beings somewhere in the universe, beyond the earth?

It is possible, but so far there is no scientifically confirmed observation in this sense. The question is taken seriously by scientists. Just look at the announcement by the VRT a few weeks ago, or at the activities of the SETI (www.seti.org).

Science fiction writer Isaac Asimov pointed out that within the event horizon(1) no extraterrestrial intelligence has been observed so far, and assuming that the earth (a priori(3)) does not occupy a privileged place in space-time (we are neither in the center nor at the edge of the universe, and we are not at the origin nor at the end of the universe today), this means that our event horizon already covers quite a large part of the universe-about-being- life span. From this we must conclude that, even if other civilizations exist, they are not many.

The important nuance here is that Asimov considers intelligences or civilizations that are expansive(4), using electromagnetic radiation (radio waves) for communication. Such a civilization will become a bright “electromagnetic star”(2) in a few hundred years, and will not escape the attention of our radio telescopes. Other types of sentient life / civilizations may therefore escape our notice.

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(1) event horizon: compare it to the “ordinary” horizon, the dividing line between earth and sky. You can see just to the horizon, but not what lies beyond. However, the horizon does not prevent you from seeing the entire sky/heaven. The event horizon is the dividing line between past and future. We can see the past (like archaeologists…) but not the future. The event horizon shifts to the past as we look further. Eg. if we look at a star 10 light years away, that’s where the event horizon is 10 years in the past. So we can see the local “present” of much of the universe, and local history as well, to the extent that local events from the past remain visible.

(2) electromagnetic star: a planet from which enough radio waves are transmitted is a bright dot in the sky, seen with “radio receiver eyes”. So the Earth itself is also an electromagnetic star. But we don’t see any other…

(3) a priori: say something about the chance of something happening without (before) you can do an experiment.

(4) expansive: who populate their own planet, and subsequently other planets.