The Xeelee Sequence, by Stephen Baxter, is a sprawling series of novels and short stories all set within the same universe.In the far future, mankind expands out into a hostile universe, filled with intelligent species as weirdly varied as they are ruthless. Above them all, however, are the top dogs of the universe: the Xeelee, the god-like de-facto rulers of the universe. The novels of the "sequence" follow various threads, such as Earth being invaded and occupied by bizarre aliens, or a hopeless war between mankind and the Xeelee, along with various other stories concerning humanity's place in a relatively bleak universe.Overall, the Sequence is a loosely connected series, covering literally billions of years of history, with later stories expanding the scope to include literally the entire history of the universe, from beginning to end. The main connecting thread throughout all the novels are the Xeelee's enduring presence and influence on the history of the universe and mankind. The series has a definite chronology, but the novels and short stories were published in Anachronic Order. However, all of them can be read as individual stand-alone stories.
Novels in the Xeelee Sequence:
Raft: A group of humans are stranded in an alternate universe where the force of gravity is much stronger.
Timelike Infinity: Set during a time where Earth has been conquered by aliens. A group of cultists Time Travel 1,500 years into the past but, rather than warning anyone about the invasion, they follow their own inscrutable agenda.
Flux: Follows a group of highly-modified humans who live inside a neutron star. A particular severe magnetic field instability, worse than any on record, threatens to destroy their home. To survive, a young woman must travel to a far off city, and eventually outside of the star itself.
Ring: A generation ship is launched on a thousand-year mission, cruising near the speed of light. Five million years pass in the outside world due to time dilation. The ship arrives back in our Solar System only to find that the sun (and every other star in the observable universe) has aged prematurely into a red giant...something that shouldn't happen for another five billion years.
Vacuum Diagrams (short story collection)
The Destiny's Children sub-series
Coalescent: In contrast to the other novels, this is set on modern-day Earth, with flashbacks to the age of the Roman Empire. George Poole (father of Michael Poole, a prominent character in the other novels) discovers he has a long-lost sister with ties to an ancient conspiracy.
Exultant: Set during one of mankind's hopeless wars against the Xeelee, this novel follows a young soldier who pulls off an exotic maneuver in battle which results in him time-traveling into the past and encountering his younger self. The bold tactic pays off and they capture a Xeelee ship. But when they return to Earth, he and his younger self are not welcomed as heroes for their breakthrough but rather tried as deserting criminals (true From a Certain Point of View) and learn about the dark side of their government.
Transcendent: Follows Michael Poole's early life, as well as a posthuman woman named Alia who's observing Michael's life half a million years in the future. Michael tries to save the near-future Earth's ecosystem from failing, all the while dealing with mysterious visions of his dead wife. A direct sequel to Coalescent, as George and several other characters show up.
Future humans make it to Type III and try to attack the Xeelee by shooting a whole neutron star at them like a bullet. The Xeelee brush this off as though it were insignificant.
There's also the Photino Birds, creatures of dark matter against whom the Xeelee fight a multi-billion year existential war and lose, who have absolute mastery over all the dark matter in the universe (which outmasses regular baryonic matter by about 9 to 1).
Aliens Are Bastards: Played straight with some species. Averted (more or less) with the Xeelee, who go out of their way to prevent extinction of other sentient lifeforms, even humanity, which repeatedly attacked them.
Also averted with the Silver Ghosts, who are much less aggressive than humanity (except the Black Ghost) but unfortunately end up in the path of the Third Expansion.
Big Damn Villains: The Qax are tricked into fulfilling this role at the end of the final story in Vacuum Diagrams, distracting the photino birds long enough for the last of humanity to escape through the Ring.
Big Dumb Object: The novels feature an object called "Bolder's Ring", built by the titular aliens; it's constructed out of the remains of galaxies (and is revealed to be the cause of the Real Life "Great Attactor") and is essentially a black hole that has been stretched into a one-dimensional loop millions of light years in length. It's eventually revealed to be an escape route for the Xeelee from the Universe, by means of tearing a hole in spacetime through the middle of the ring via the unimaginably strong gravitational forces created through its rotation.
Also, the "Sugar Lump" - a perfect cube the size of a small moon, which appears to serve no purpose whatsoever. Later is revealed to be one of many identical devices which sent the Xeelee back in time to essentially create themselves using a Stable Time Loop.
Bittersweet Ending: The Xeelee ultimately lose against the Photino Birds and the universe as we know it ends. However in one last act, the Xeelee give the remnants of humanity and others a vessel to escape to a new universe where they can hopefully build civilization anew.
Colony Drop: There's the extreme colony drop option where a Neutron Star is accelerated to high fraction of light speed and smashed into Bolder's Ring (see Big Dumb Object above).
Cool Ship: Xeelee nightfighters, which can travel at near-lightspeed even before they fire up their hyperdrive, by flapping wings made of folded space-time.
Crapsack World: Millions of years of humanity in a massive Hopeless War of attrition against the Xeelee who are also fighting a race of dark matter beings who want to render the universe unfit for baryonic life (like humanity). They lose. First the humans, than the Xeelee.
Well, at least the Xeelee not only managed to get the hell out of the doomed Universe, but also provided means for at least the remnants of humanity to escape. While some refugees from our Universe ended up in one that was practically unfit for human life, this wasn't any of the known evacuation groups, so there is at least some hope for the humanity...
Forever War: The Xeelee are nearly immortal, and humanity quickly proves itself a race of consummate survivors. They don't like each other. Do the math. But even that pales before the Xeelee-Photino war.
Genius Bruiser: The tribelike mannerisms of the Boneys from Raft hide minds well-versed in orbital mechanics to rival trained scientists.
Higher-Tech Species: The Xeelee are an extreme example. Despite being "only" this trope (because their universe-shattering technology is recognizable as such), they could absolutely run rings around quite a few examples of Sufficiently Advanced Aliens from other works.
Intangible Man: Michael Poole after the encounter with the "Anti-Xeelee".
Lensman Arms Race: The Xeelee use cosmic strings to build a wormhole (dubbed by humans as "Bolder's Ring") in order to escape into another universe. The Ring is so massive that it's gravity well is pulling in galaxies from all directions towards it at high speed. The Xeelee's antagonists one up on this by meticulously arranging galaxies around the Ring in just the right pattern to form a gravitational resonance that will shake the Ring apart.
Mile-Long Ship: The Xeelee Nightfighter has "wings" that stretch out for kilometers, though the cabin is rather small.
No Dead Body Poops: Implied aversion in Raft. One character sees "a shape hanging from rope" and "a pool of something brown and thick" beneath it.
Non-Indicative Name: The "Interim Coalition of Governance" actually rules humanity for an "interim" period over 20,000 years long.
Poor Communication Kills: Humans start a massive war with Xeelee because they believe that the Ring is intended to wreck the Universe. Unforunately, they discover too late that it's actually a wormhole created by the Xeelee as the only way for baryonic life to escape extinction at the hands of the unstoppable Photino Birds. Similarly, the Photino Birds are so alien that they most likely do not even realise that they are wiping out untold numbers of species in the process of making the Universe more comfortable for themselves.
Reality Warper: The "Snowmen" technology used to protect Earth in the short story "The Siege of Earth" (from Resplendent) seems to at least border on this.
Rule of Cool: Celestial bodies up to and including entire galaxies used as projectiles? Megastructures millions of light years across? Handguns that can destroy stars? Aliens altering the value of Planck's constant simply in order to build a faster computer? Stephen Baxter was rocking this trope before it was mainstream.
Science Marches On: Virtually inevitable given Baxter's heavy reliance on speculative physics. For example, recent results from the Large Hadron Collider appear to have refuted at least the simplest variants of supersymmetry, rendering the science behind the Susy drive depicted in 'The Quagma Datum' far more dubious.
Scry vs. Scry: Humanity fights a War against the Xeelee over the Milky Way Galaxy where both sides can send information backwards in time using FTL. In practice, neither side can ever get an advantage. This goes on for tens of thousands of years.
Shadow Archetype: Averted with the "Anti-Xeelee", since it's name actually refers to the fact it travels backwards in time, like some anti-particles are theorized to do. The antagonists of the Xeelee, the Photino Birds, fit.
Son of an Ape: By the time of Exultant humanity has converted almost the entirety of the Milky Way into an industrial war machine with which they are engaging in a multi-millenial pan-galactic campaign against the Xeelee. Still, the Xeelee view this as roughly the equivalent of an especially persistent cockroach infestation, and think of humanity as little more than pond life.
Space Whale: The Spline are giant living armored spaceships that evolved from alien whales. They live off interstellar gas and other species use them as transports and warships. In one case, the entire Qax race, which consist of cell-like vortices in any fluid (ocean, air, gas giant, star, space-time...), is transported off its homeworld when the sun goes nova.
Stable Time Loop: It's eventually revealed that the Xeelee sent themselves back in time to supercharge their own development.
Starfish Aliens: Pretty much every single race in the series. There's almost nothing remotely human-like, aside from humanity's descendants— if then.
Sufficiently Advanced Aliens: The Xeelee are really not this trope, even though their actual power far exceeds many other examples that are. This is simply because their godlike technology is still recognizable as such and uses comprehensible interfaces, if not comprehensible principles; they're a hyper-extreme example of Higher-Tech Species instead. However, the Anti-Xeelee definitely is sufficiently advanced, in a Deus Est Machina sort of way.
Time Abyss: The traitorous humans who collaboratorated with the alien who conquered Earth were given eternal life as a reward. They eventually begin to regret this.
My name is Luru Parz. I was born in the year AD 5279, as humans once counted time. Now I have lived so long that such dates have no meaning. We have lost the years, lost them in orders of magnitude.
Unperson: The alien Qax attempt to do this to the entire history of humankind, in a project know as the "Extirpation", in order to make humans more docile slaves.
Wave Motion Gun: The Xeelee starbreakers, which shoot focused gravity waves that can tear apart stars or cause them to go nova, certainly qualify. By the time of Exultant, humanity also uses guns which fire magnetic monopoles and later black holes.