Star Venom

Why are the heavens silent? Are we alone in the universe? Where is ET? Here's one possibility:

At some point around 5-10 billion years ago our galaxy was full of civilizations that traveled between the stars.

Each civilization would eventually disappear, perhaps driven to extinction by competition or perhaps evolved into something different. But they were always replaced by another civilization.

This pattern ended gradually. Over a period of 1-10 billion years, the number of new interstellar civilizations fell to zero. Intelligent life would evolve over and over again, and then disappear before spreading beyond the planet where the intelligence evolved.

It takes a very very long time to establish permanent colonies in space using chemical rockets or space elevators, but this was the only practical way to do it. Nuclear energy was not viable for most civilizations because early population II stars were metal poor.

When metal-rich planets orbiting younger population I stars began to evolve intelligent life, nuclear energy was more readily available, but the most (perhaps only) cost-effective way to use nuclear energy to establish interstellar space colonies is external combustion nuclear pulse propulsion. And that means making lots of small cheap hydrogen bombs.

Those civilizations which were not burnt to a cinder by global thermonuclear war were poisoned to death by cumulative terrorist attacks thanks to the proliferation of cheap nuclear pulse units. Even slow poisoning was too fast for these civilizations to establish a long-term presence in space. Whatever colonies they left behind eventually collapsed.

We could blame the end of galactic civilization on violence and greed, but is that fair when the younger civilizations were never faced with a similar challenge? Ultimately the stars themselves must bear the blame, having fattened themselves on the heavy elements produced by the death throes of older stars in a cannibalistic cycle which makes civilization-killing heavy elements ubiquitous.