[ Freelance Traveller Home Page | Search Freelance Traveller | Site Index ]

*Freelance Traveller

The Electronic Fan-Supported Traveller® Resource

Jump Theory

This article originally appeared in Cepheus Journal #005 and is reprinted here and in the January/February 2022 issue with permission.


It is foundational in most Cepheus Engine settings that it takes a week to travel between the stars. By having the speed of communication equal to the speed of travel, an “age of sail”-type culture follows which has very broad impacts on any game. But how do we look at that, relatively arbitrary, game mechanic from within the setting? This article examines that question. It does not attempt to introduce any new rules or changes that would perturb this fundamental constant, but rather to add internal nuance to it, as an aid in storytelling.

The Theory

Jump Theory itself is an insanely complicated branch of mathematics. Many cultures take several researchers’ lifetimes to reach a Grand Unified Field Theory of physics, or even longer for a Theory of Everything. Those are just attempts to describe the universe as we perceive it. Jump Theory goes beyond that by using them as building blocks to create a practical framework that allows for the totality of the universe to be characterized and manipulated.

It encapsulates cascading events from the sub­quantum level to the macro level covering all dimensions of space­time. In order to do this, it creates many more quasi­dimensions and spatial tensors to interpolate the calculations through. They all fall away at the final result, just leaving concrete reality, but understanding just some of them adds considerable difficulty to comprehending the entire work.

The classical work, if printed, would occupy several bookshelves. With commentaries, the digital form takes up notable space on any storage system. It has been around for centuries and is in the public domain. It is available in a considerable number of languages, as the bulk of the work itself is language-light and mathematics-heavy. Many aspiring mathematical graduates (and even more cranks) have a willingness to devote their life to understanding it. And, yet, despite this, the number of people who can genuinely claim to understand the totality of the work is very few, often estimated as single digits for the whole galaxy, at any point in time.

The Practice

The theory, at a pure level, describes a method for transporting any amount of mass from any position in the universe to any other position in the universe, taking any amount of time. However, to do so perfectly, every position, orientation, magnitude and motion of every point of matter and energy in the universe needs to be exactly known, and the computation based on that data would take any theoretical computer longer than the lifetime of the universe to calculate.

At a less pure level, and where the bulk of the work of modern research is conducted, there are many approximations of the theory. Each of these reduce the quantity of information needed, and the complexity of the calculations. They make certain assumptions, add certain boundaries, and produce results tinged with a certain amount of probabilistic uncertainty.

The most widespread of approximations that have been approved for commercial use follow the rule of thumb that jumps must take place beyond 100 diameters of the nearest high-mass object and will take about a week to traverse one to six parsecs. Within these restrictions the algorithms work well, and rarely result in anomalous behavior. When such occurs, it is generally categorized as a “misjump” and can run the range of simple temporal displacement to rapid unplanned disassembly.

Edge Conditions

Considerable research has been devoted to improving upon established approximations, but coming up with revolutionary new algorithms has not been fruitful. There have been a number of specialty algorithms that have been useful in narrow or unique circumstances.

Most of these optimizations rely on trading one element off for another. Flat space makes for easier calculations. So the further one is away from gravity masses, the better. Low velocity for the pertinent frame of reference helps. The better understood the masses are in the departure and arrival systems the better. On the other side of things, accepting a higher approximate travel time is one area where things can be made less restrictive. Similarly the resulting position, orientation, or even velocity can be less guaranteed. And there is just always the chance that either nothing or extremely bad things will happen.

Most notably the military have their own approximations that have optimized arrival time at the expense of time of calculation, characterization of initial conditions, and added a slightly elevated risk. Using this allows fleets of ships to assemble, arrange themselves very precisely, process the calculations in parallel across all of their ship’s computers, and then jump simultaneously, all arriving in the target system within a narrow timeframe. There are obvious benefits to this for military maneuvers, but such risk is held less tolerable commercially.

Many megacorporations specializing in personnel and cargo transport go a different route. They boast of customized algorithms that are optimized for reducing risk, allowing those using them for transshipping to decrease their insurance premiums. Captains are given approximations tailored to specific models of ships, must maintain those ships within precise regulations, and must depart from specific travel lanes at low nominal velocities. Their ship’s logs are inspected for adherence to these requirements and deviations are fined.

There are any number of services on the dockside offering to optimize a ship’s jump algorithm. The more honest of these are just specialists who understand the standard official software well, and can dive into various options that better tailor it to an individual ship. This is wise to do especially after a refit or major work. The less honest promise greatly improved performance, or lower risk, and only tinker with fairly meaningless settings. The outright criminal have cracked versions of official software that allows for parameters beyond what is considered safe, or that their own mathematical geniuses have ‘optimized’ to put the users ahead of the rest. It is often hard to tell the difference between these outlets.

Plot Hooks

The above interpretation of Jump Theory does not fundamentally alter how travel between the stars works at a game mechanic level. The intrepid referee might allow for DM ±1 for exceptional circumstances, but the fundamentals should not be different. That does not mean that the implications of this can’t be relevant to the game in other ways.

Knowing the Territory

The Scout service will generally always pay for high quality scans of planetary objects and systems. Part of the reasons for this is to keep the galactic almanacs up to date. Every ship has one, and updates to them filter across known space as people travel. Only the Scouting service can approve updates to them. Unknown to many is that the jump approximations on ships use these almanacs for their calculations. So keeping them up to date is vital for interstellar commerce.

If the players have travelled in less common regions, or in the outer reaches of more commonly travelled systems, they can usually pick up an extra Cr100 to Cr1000 by selling copies of their scans to a Scout representative at an official scout base. High bounties will be posted at actual Scout Bases for going to especially obscure locations. (Especially for exScouts.) A referee can use this as a convenient way to get the players to a specific location, or going in a certain direction.

The military are also interested in optimizing their travel options. Their priorities frequently differ from commercial priorities. Consequently it is possible to pick up scan bounties at Naval bases. These often pay more (especially for ex-Navy), but come with the requirement for disguising their activity as something else, and the contracts prevent them from taking other scans or selling the scans to others.

Dr. Doorling Duiters The All Knowing

During a moment of tension on the ship, trying to run away from an antagonist, escape a natural calamity, avoid a pitched naval battle, one of their passengers reveals themselves as Dr. Doorling Duiters, PhD from the Department of Mathematics in Noogeng der Aarede University, affectionately referred to as “The All Knowing” by their grad students and the local popular media. They are an expert in Jump Theory and, if given access to their computer and navigation software, can craft a jump solution to extract them from the situation they find themselves in.

No one else on the ship can vouch for them, nor does the situation give them the time to check references. They must choose to believe or not believe based on how well the good Doctor argues.

If they refuse the help, the Doctor will be seriously offended, and will not speak to them until they depart the ship. If the help is taken, the Doctor will root through the software, access many of the deeper menus labeled “qualified engineers only” and make myriad changes to settings before finishing with a great flourish saying the solution to all their problems lies in pressing the big red “initiate jump” button.

When they press it, jump is initiated. Their controls flash in colors not seen before (what exactly is mauve alert?) and any number of warning alerts go off. Once they are in jumpspace, a readout of the proceedings is hard to interpret. They were clearly able to leave whatever dire straits they were in, but the system recorded any number of other anomalies. Doorling will put these off as “ill-written software” unable to appreciate their genius.

The rest of the jump can be as tense as the referee wishes to make it. Waves of nausea may inflect the players at times. They might notice their watches are out of sync depending on how they travel across the ship. Sensors may register other objects appearing in jump space where there should be nothing. Or the jump may continue right up to the high end of the normal period of variability.

Dr. Duiters, similarly, can either turn out to be a nutcase, or just an eccentric. Their story may slowly fall apart over the course of the voyage, with the only reference of Aarede University found in the records being of their outstanding Agriculture School. Or they can genuinely be a mathematical genius, but with a Cassandra-like flaw of never being believed because of their over-the-top mannerisms.

Either way the players emerge rattled, but not overly harmed by the experience. One just hopes they took a recent backup of their jump software settings!

Guinea Pig

The players are approached by representatives from a small research firm at a class B starport that is conducting experiments with improved jump algorithms. They have a new algorithm that has been approved for experimental use that is perfectly suited for the size and mass distribution of the player’s ship. They are willing to pay them a 1000Cr to 10,000Cr honorarium for any jump they take with the new algorithm, for which complete records are maintained and sent back to the institute.

It is up to the referee about how legitimate they want to make this. They may have the backing of a local megacorporation, who see it as a long shot, but worth investing in just in case. Or, unbeknownst to the institute, there may be criminal backing, and it really is just an elaborate money laundering scheme to funnel illegitimate money to guild ships.

Similarly the algorithm may be imperceptibly different. The referee can make entertaining dice rolls after ominously asking which algorithm they are using. With no actual real change.

Additional psychosomatic symptoms may be felt during jump. Or the referee can use it as an excuse for strategic misjumps to occur that get the players to places they are required to be for story purposes.

Either way, it can help plays on a low-margin ship make their monthly payments by taking on a bit of extra risk.


In areas of high commerce raiding, or along critical supply routes, patrolling Navy ships sometimes offer to provide escort to groups of merchants. The Navy has specialized jump software that allows them to jump fleets in tandem. It is flexible enough so that they can assemble a civilian convey at jump range, get the specifics of each ship that is part of it, use their software to compute a jump solution, and pass it on to the ships for a synchronous jump.

It can take eight hours to a day for their computers to compute the solution. Any ship that signs up and changes their mind will cause the whole solution to be recomputed, delaying the rest of the convoy and pissing off the Navy. Any ship lying about its mass distribution also risks perturbing the calculations and throwing off the jump for the whole convoy (pissing off 10­20 merchants, in addition to the Navy). So it’s something that free­wheeling players might avoid. But it is also the sort of thing that an antagonist, seeking to avoid said free-wheeling players, might join in to put them “under the Navy’s wing” for at least a jump.

During a time of conflict, players might be hired specifically to spoof such a convoy and disrupt shipping. This could be as simple as a false manifest, or as complicated as having a last minute failure of their jump drive. Other ideas along this line would be antagonists who have booked passage on their ship specifically to sabotage their jump drive at the last minute and disrupt the convoy. Or, it might be an adventure hook that the players are told to book passage and sabotage the jump drive of a ship that is known to be going on a naval convoy.

The Tattoo

The players may have been enjoined by the local nobility on a relatively primitive world. Business (and politics) are all personal there and official duties are mixed with social ones. The young of the clan may be particularly interested in them for their off­world stories and tales of the larger universe. One of the more impressionable, who also happens to be politically important, is sufficiently star struck that they decide to get a tattoo of the fundamental essence binding the universe together: the Jump Theory Equation.

The problem is that there isn’t really one equation that summarizes Jump Theory. And even a minimalist representation would require more skin than his whole clan possesses. This will not deter them and they will insist. On the surface this appears as willful ignorance. Through conversation, or possibly guidance by other elders, the true reasons for the tattoo are for proclaiming aspirations and connectivity between this young noble’s ambitions and where the clan is going. It is not so much the substance of the tattoo, but what it represents.

So it is up to the players to decide the shape and form of the tattoo. The Jump Theory texts are easily acquired. They often adorn the bookshelves of people who are trying to look smart. If they don’t have a copy easily accessible, they might be able to find one in the foyer of a local legal firm or even as set dressing. Hand the players a leftover book on college Physics or the equivalent web page and let them choose what they want, or make something up.

Ultimately they will be judged by how they present their result. The youth will have questions on the philosophical meaning and representation of each element of the design and as long as the players have satisfying answers, and don’t appear to be trying to make fun of the youth, the culture, or their ambitions, they will be happy, and the characters will find their business on the planet will prosper.