Read this science fiction book a couple of years (written in the 90s I think). It starts off with an interesting premise - if there are other intelligent beings in the universe, then where are they? Why haven't they visited or contacted us? And then goes off into an epic scale with grand mysteries, from structures on mars, hollow moons, existence of machine life, etc etc

Unfortuntately like many books where the mystery is critical to the story, the ultimate resolution is a bit of a let down. The reason for no other intelligent life out there, but plenty of evidence around that it did once exist is ...... this is a major spoiler, so don't read on if have plans to read the book ....... that every few thousand or million years two pulsars collide creating such a massive explosion that the ripples span out across the galaxy disrupting all the successful creations of intelligent species (space stations, cities, buildings, etc). Meaning that life has to go back to a simplier form, and hence no single species gets enough time to conquer the galaxy before the next pulsar explosion.

I always thought this seemed rather silly. Aren't scientists now trying to find gravitional waves from colliding black holes and pulsars, but that these are difficult to detect because the effects are so incredily weak by the time they get to us?

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PS: Please excuse me if this is in the wrong forum. First time here, and wasn't sure if this forum is for books generally or just the BA book.

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Yes; this should be in the Bad Movies! Bad TV! forum, which also covers literary works.
Manifold : Space is one of my absolute favorites; the GRB solution to the Fermi Paradox was reasonably popular at the time when Baxter wrote it, but is less popular now. I think that is because most GRB's are thought to be directional hypernovae nowadays (I might be wrong about that, however.)

The collision of two black holes would certainly give off a remarkable pulse of energy, however, and may well sterilise a large portion of a galaxy; this may happen occasionally, especially n the centres of galaxies, and probably wipes the centre of most galaxies clean of life periodically. Neutron stars colliding are also not nice to be near; but as for sterilising whole galaxies- I doubt that very much.

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