Worlds Enough And Time by Dan Simmons
This is a collection of five novelettes / novellas:
1) Looking for Kelly Dahl
2) Orphans of the Helix
3) The Ninth of Av
4) On K2 With Kanakaredes
5) The End of Gravity
1) Looking For Kelly Dahl
The character narrating the story is in his Jeep in the wilds of Colorado - but he soon makes clear that it isn't our familiar Colorado. Somebody else - Kelly Dahl - has been recreating versions of Colorado based on historical and geological changes that have occurred during past epochs. The narrator isn't entirely happy with the accuracy with which Dahl has reproduced prehistoric geology.
Of more importance, at least in some sense, it isn't just him looking for Kelly Dahl - Kelly Dahl seems to be hunting him. The rationale behind this isn't very clear at first. He was a teacher and Dahl was one of his students, and there didn't seem to be a problem then. However, the narrator had some serious issues in his life and had decided to commit suicide in a way that would look like an accident, so as not to cause more hardship to people who knew him. It is after this attempt he finds himself in this altered world.
It’s an entertaining story, although I’d classify it more as “speculative fiction” than “science fiction”. It seems to me there is ambiguity in the interpretation, so different readers may assume different explanations of events.
2) Orphans of the Helix
This story takes place in the "Hyperion universe". It centers on a vast colony ship traveling through hyperspace in search of an isolated Earth-like planet for its culture. Along the way, the ship detects a distress call and stops to investigate. They find a binary star system in which one star has a ring of vegetation around it. A society of human / engineered from humans is living around this ring. However, every 50 years, a vast spacecraft comes to the ring, attacks parts of the population there, harvests part of the vegetation and leaves. The machine may belong to an extinct species from the other star in the binary system. The other star is now a red giant which could have destroyed any inhabited worlds. The machine is approaching again and is expected to cause death and destruction within a few days. They need a course of action that doesn't involve too much danger to the colony ship or those living in the ring or a possible world dependent on the machine's harvesting of vegetation.
Although the resolution struck me as coming a bit too easy, the story is good.
3) The Ninth Of Av
This is a story about the time around "the final fax" referred to in some of Simmons’ other works. On a future Earth, after much destruction and strange times, there are a small number of humans [of Jewish descent] as well as post-humans mostly living up in orbit. The post-humans are planning to send the humans' quanta in a waiting pattern while the Earth is restored to a "normal" condition. Or at least that’s what they’ve been told.
The story fills in some finer details not explicitly stated in Simmons’ other works, but I’m not sure how well it stand by itself for readers unfamiliar with his other writings.
4) On K2 With Kanakaredes
The premise of this story is that a generation ship of aliens arrived at Earth a while ago. They have a settlement in Antarctica. They're peaceful, but the government doesn't really understand their intentions. One of the aliens has asked the government about joining three human mountain climbers planning to scale K2.
The government finds a way to manipulate the climbers into letting the alien join them. During the climb up K2, the reader learns about K2, the Himalayas, mountain climbing and a bit about the alien(s). The aliens are somewhat inscrutable, but I suppose that's to be expected of aliens. There seems to be a bit of mumbo jumbo here, but it’s not in the foreground of most of the story. The story is told well.
5) The End Of Gravity
A writer is sent by his boss to learn more about today's Russian space program. We see some of the physical elements of the program, but the writer's aim and our story is more about the motivations of astronauts and human perspectives on going into space. That is entwined with the writer's heart condition, his relationship with his recently deceased father and the like.
While it's well written, it's only claim to being SF would be it is fiction and the Russian space program is related to science. We see a run-down, not especially high-tech Russian program. We hear reminiscences of the "good old days" of the USSR in space. The time is more or less the present, there's no new tech or science theories, no aliens... We don't even have a visit to today's "International Space Station".
On the whole, I wouldn’t recommend the book for a reader in the mood for “hard science fiction”. Orphans Of The Helix is certainly SF with some interesting SF perspectives. The Ninth Of Av is certainly about a future and includes some future tech. The alien is an ongoing thread in On K2 With Kanakaredes. However, the majority of the story is mountain climbing that is similar enough to what would happen today that it won’t always feel like an SF story. The other two stories don’t venture into the future, high-tech, or similar material that would put them further into the realm of SF.