Hyperion Cantos is an epic series of four novels by Dan Simmons. It has it all: a marvelous ensemble cast of characters, a multi-layered story unfolding over narration from multiple points of view, and like a cherry on the top: one of the most fearsome, badass, and bizarre antagonists in all literature. I’m not here to talk about the story or review the books, but rather to look at the universe and its laws from the point of view of a physics graduate.

The universe of Hyperion is one of the more fascinating ones in science fiction. In terms of realism, it’s on the soft side of science fiction. The universe has metaphysics and fantasy elements, but the story also explores constraints from relativity (time dilation, speed of light, etc.) and how they influence the politics and economy of the Galactic Hegemony. There is also time travel in various forms, with quite a unique take.

I won’t discuss the story in detail, but don’t avoid spoilers either. If you haven’t read the books, then read them already and come back here afterward!

Basic concepts

Four centuries after a black hole released in the Big Mistake caused Earth to be destroyed, the Hegemony of Man is a young interstellar civilization that has colonized few hundred planets. The story of the Hyperion saga starts near a war between the Hegemony and the Ousters, a deeply untrusted civilization with common ancestry to the Hegemony humans. The Hegemony has chosen seven travelers for a mission to take a pilgrimage to the Time Tombs on planet Hyperion. The Time Tombs is a site contsisting of several structures moving backward in time.

The Time Tombs are the dwelling of the Shrike: a semi-organic, semi-mechanical killing machine with ambiguous purpose and motive. Like its namesake family of birds, the Shrike incites fear by impaling its victims either to the numerous blades and thorns covering its body – or worse – to its Tree of Pain where its victims spend eternity in agony, unable to die. According to the legend, the Shrike will grant one wish to a party consisting of a prime number of pilgrimages, killing the ones it denies. The Hegemony wishes the pilgrimage to flip the odds in their favor, but the travelers also have motives of their own.

The Time Tombs and the Shrike originate from the far future, where humans and AI are waging war. The Tombs, Shrike, and ultimately the pilgrims play their part in the wars waged in the present and the future.

The Hyperion saga consists of two duologies. The first duology, Hyperion and The Fall of Hyperion, explores the pilgrim and its aftermath. The second duology, consisting of Endymion and The Rise of Endymion, continues the story with a new cast two centuries later. It explains some concepts left unclear in Hyperion and is an enjoyable read and fine supplemental material. Unfortunately, it’s a considerably weaker pair of novels than the first duology and retcons some events in a way that makes consistent analysis difficult. I will only consider Endymion when it doesn’t conflict with Hyperion.

Faster-than-light travel and messaging

The humanity in Hyperion Cantos only started colonizing other star systems less than a thousand years ago. The original colonists populated the universe in “regular” slower-than-light spaceships, set to wake them up from cryogenic sleep after reaching their target. In the following centuries, several faster-than-light technologies emerged.

In our universe following the laws of general relativity, the most ”realistic” hypothetical faster-than-light travel technology is based on Alcubierre drive, a solution to the equations of general relativity describing a bubble contracting space front, and expanding it behind. A spaceship in the bubble could travel faster than light.

The faster-than-light spaceships in the Hyperion universe utilize the Hawking drive, which comes with two main caveats. The passengers suffer from time dilatation: more time passes for distant observers than the passengers. The in-universe term for the difference is time debt. The passengers also need to stay in a cryogenic fugue to avoid psychological damage from the sensory input of the faster-than-light travel. These caveats are seemingly inconsistent with the Alcubierre drive. In Alcubierre’s geometry, the spaceship crew would remain inside a bubble of flat spacetime, supposedly having a similar experience as ”regular” space travelers. In addition, the proper time of passengers inside the bubble equals the coordinate time of a distant observer, meaning no time dilatation. That seems to rule out that the Hawking drive follows Alcubierre’s solution. Instead, it appears a hybrid solution: the drive warps spacetime around the spaceship, and the spaceship experiences velocity relative to the faster-than-light bubble and a distant observer.

For even more convenient space travel, there is farcasting. It is a technology allowing instant displacement between two farcaster portals. During farcasting, no time passes in the coordinate time of the portals. That is reminiscent of the Einstein-Rosen bridge, more colloquially known as wormholes. However, the farcaster portals are not just mouths of a traversable wormhole. Instead, there is just one farcaster, and any portal is reachable from any other portal, with access controlled by the portal technology rather than physical limits. This suggests an extremely complicated spacetime geometry, with multiple entry points coalesced.

The Hegemony heavily depends on the fatline, a medium for instant message passing. Unlike farcasters, the fatline system cannot transfer matter. On the other hand, it allows communication between arbitrary points. That is evident since many characters in the Hyperion universe wear implants allowing fatline mediated access to datumplane, a highly sophisticated (and fast!) wireless internet. Since the fatline system doesn’t distort spacetime like the farcaster network or the Hawking drive supposedly does, it appears to provide instant communication between two spacelike points in a Minkowski space. That poses a morbid threat to causality.

Let me elaborate for those not yet familiar with the fundamentals of special relativity. In our usual three-dimensional space, different observers all agree on the squared distance \( x^2 \) between two points in space. Time \( t \) doesn’t enter this equation. This is called Galilean invariance. In the theory of relativity, space and time are mixed, and the quantity every observer agrees on is the interval \( s^2 = x^2 - (ct)^2 \) between two events. Events are labeled both by the place and time they took place. If an observer moving at or slower than the speed of light can travel between two events, we have \( s^2 \leq 0 \), and the events are lightlike or timelike, respectively. If the opposite holds, we have \( s^2 > 0 \), and the events are spacelike. Spacelike events are never causally connected, and it can be proven that different observers moving relative to each other may observe them in a different order.

From this theory, it is understood how instant communication between distant planets dozens of light-years apart violates causality. Between them, observers cannot agree on the order of events over dozens of years. Given a suitable observer, it appears possible to use a fatline message to order the assassination of one’s grandfather before he has fathered an offspring.

Later in the novel series, it is explained that faster-than-light travel and messaging are possible because of an unknown quantum field called Void Which Binds. Even if this quantum field could enable technologies like Alcubierre drive and wormholes, I have a hard time believing any consistent theory of quantum gravity – even with Void Which Binds included – could violate causality at the galactic scale.

On the other hand, assuming that causality-breaking technologies exist, it’s not a massive leap to imagine that time travel exists too.

Time travel

The stories of the pilgrimages in Hyperion all deal with time in one way or another. A common theme is the effect of time dilatation on one’s life and relationships. There is a bittersweet love story of a couple, aging at different paces and experiencing vastly different periods between their reunions. One of the main characters is an Earth-born poet living through centuries thanks to an extreme amount of space travel and cryogenic sleep.

There is also time travel. Time travel doesn’t exist in our universe, and will almost certainly never exist, meaning that authors have great freedom to invent rules that serve their stories. The time travel mechanics in Hyperion are distinctive. As explained in the Fall of Hyperion and the Endymion novels, the future is not set in stone. What happens in the future (and hence is reflected in now via time travel) is partially determined by the events unfolding in the story. Some things are constant, but for instance, the mission and motivation of the Shrike appear to differ based on whoever controls it in the distant future.

The main site of the story, the Time Tombs moving backward in time, is wrapped in an anti-entropic field. It remains unexplained if this is a separate quantum field or an emergent phenomenon of Void Which Binds. The Hegemony era civilization can observe and study the anti-entropic field, although it knows next to nothing about the Void Which Binds. Given that the Shrike – a being closely connected to the Time Tombs – utilizes Void Which Binds in its time jumps, there is no reason to believe there are two fundamentally separate quantum fields facilitating time travel. That is analogous to how the force binding atomic nuclei together was only later discovered to be a manifestation of the more fundamental strong force. The lengths scale of Void Which Binds is implied to be the Planck scale, meaning that it will likely remain inaccessible to normal scientific instruments.

The term anti-entropic field is an obvious reference to the second law of thermodynamics, which allows us to define that forward is the direction of time in which entropy increases. The presence of the anti-entropic field suggests that the entropy of the Time Tombs decreases. It makes sense: since the laws of physics on a microscopic scale are reversible, one cannot conclude that the Time Tombs travel backward in time by observing individual particles. Only by observing a macroscopic system, like the Time Tombs as a whole, is it possible to deduce the direction of time by observing how the entropy within that region evolves.

The analysis of the entropy within the Time Tombs is complicated because they are an open system, meaning that they exchange energy and particles across their boundary. Technically speaking the entropy of an open system doesn’t need to increase, as long as the system can dispose of some of its entropy to its surrounding. However, it is expected that an observer would see the entropy within the Time Tombs decrease spontaneously without increasing the entropy of the planet Hyperion as a whole.

The Time Tombs originate from the future, but the concept of the anti-entropic field helps explain how they emerge in our forward running time. As the tombs slowly erode in their frame of reference, they reduce to dust. An observer in the distant past would see the reverse process: dust particles coalescing just the right way to form the tombs. It’s also suggested that the Shrike can freely move in spacetime, without such anti-entropic processes. Given that matter cannot be spontaneously created or annihilated, it’s harder to imagine how the sudden appearance and disappearance of the Shrike works. No doubt it’s due to the interaction between Void Which Binds and the familiar fermionic and bosonic quantum fields.

I especially like that time travel as technology is beyond explanation in-universe. Just like space travel would have been inexplicable for our ancestors, the Hegemony era civilization has no understanding of time travel. The characters in the story play a part in the far future civil war between humanity and the ultimate AI, but how and why is deliberately left ambiguous.