The notion that 95 percent of the stars that will ever shine have already shone reminded me that I had once read that 6 percent of all the humans that have ever lived are alive today. The latter statistic is a consequence of the exponential growth of the human race (and, if it keeps growing, could eventually create problems for the idea of reincarnation).

You might not think it has anything to do with the stars. But philosophers and cosmologists have wondered if there is an answer to the question of why we live where and when we do.

The cartoon history that they would like to tell goes like this: Coming out of the Big Bang 13.7 billion years ago, the universe consisted of hydrogen and helium and a little lithium. Our bodies are made of oxygen, carbon, nitrogen and iron that had to be synthesized in thermonuclear reactions in successive generations of stars that went bang and seeded space and future stars with heavier elements.

That took time. The Milky Way was born near the height of the star baby boom, about 10 billion years ago. The Sun and solar system, with its heady mix of life-ready elements, came into being 4.5 billion years ago. It took evolution another 3.8 billion years to make us, the putative princelings of the cosmos. Could it all have happened faster to someone else some place else? Nobody knows.

Nobody knows for sure, either, why cosmic star production has slowed down, the astronomers say.

In recent years, they have found evidence that some of the more violent denizens of the modern cosmos, like giant black holes and supernova explosions, can create powerful winds that blow the gas out of galaxies, preventing it from condensing into stars. One black hole in the galaxy NGC 1275 was found to be “singing,” or belching pressure waves, to the tune of a B flat 57 octaves below middle C, thus squelching star formation over much of the entire Perseus cluster — hundreds of galaxies.

Some theorists, notably Freeman Dyson of the Institute for Advanced Study in Princeton, have suggested ways that life could go on past the twilight of the stars, by extracting energy from black holes, for example. But that was before astronomers discovered that dark energy — what appears to be a sort of cosmic antigravity — is speeding up the expansion of the universe.