Star Travel

There are three known ways of travelling between stars.

Direct Drive

All known spacefaring civilizations have discovered the simple method of travelling directly from one point to another at high acceleration. As technology improves this works first for interplanetary travel and finally for interstellar travel. The main weakness in this method is the relativistic effect of time dilation; although travel over long distances is quite possible in short subjective times, time on the host planets passes much more slowly. Stasis and suspended animation make it possible for people to travel for subjective times of years in confined quarters, and thus star colonization is possible using direct drive. However, traffic between worlds is difficult due to the long time lags. This is the chief reason why the Great War endured for thousands of years; the long delays between battles made it impossible to end quickly.

If a starship travels at an acceleration of one standard gravity, the relation between distance travelled, subjective time of the travellers and elapsed time on the home planet is roughly as charted below. As the table shows, sending a ship on a return voyage to a star system 10 light years away will require the people on the home planet to wait well over 20 years for its return although the star travellers themselves will see only about 10 years go by and may have spent that in suspended animation without aging.

Historically, direct drive travel was only found practical for distances on the order of 10 ly, and the Terran Sphere was thought to be only about 50 ly in radius, limited chiefly by the political difficulties inherent in managing such widespread territories.

Wormhole Drive

Black holes have been known since ancient times, and the theory of wormholes (tunnels connecting black holes to other points in space) dates back millenia. To this date their fine structure is little understood and they are seen much the same way they have always been; large holes which catch and destroy anything that passes too close to them. When humans first discovered advanced gravitational theory, though, they saw that black holes might be somewhat more complex than that, and advances in gravitational engineering made it possible to probe and investigate. Most probes were simply destroyed but a few appeared at distant points in space. The wormhole drive had been discovered.

Soon after, manned starships followed the probes. In the early days of wormhole travel the losses were horrific and starship colonization attempts were little better than suicide. With time the method was improved and the risks cut, until at the peak of wormhole technology the death rate per wormhole transit was less than of a tenth of one percent. Exact statistics are hard to estimate since this period coincided with the Great War. The gravitational technology used to build wormhole-drive ships was probably as big a factor in faster travel as the wormholes themselves, since it protected passengers on starships from the effects of acceleration and made direct-drive travel possible at accelerations greatly in excess of one standard gravity.

Wormholes are still used for travel, in areas not connected by any charted spacefold. Although in theory wormholes could connect any point in the universe (or possibly another universe) in practice there are few known wormholes which extend in distance beyond a few hundred light years. Wormholes are known to often be \u201cbundled\u201d together so that a black hole with a connecting wormhole is often close to another black hole with a wormhole that connects in the reverse direction. A common misunderstanding is that black holes connect to other black holes or to some sort of \u201cwhite hole\u201d. This is not generally true, although it is possible that many apparently-unconnected black holes in fact simply connect in ways which ordinary matter cannot escape.

Spacefold theory provides plausible explanations for many of the features of wormhole travel. Black holes are inherently, as classical theory suggested, destructive objects in which all travel is one-way and no escape is possible. However, in some cases the areas of warped space near the black hole overlaps with a space fold and thus an object that passes near the event horizon within the right range of velocities will traverse the spacefold instead of being destroyed - the black hole provides an alternative way of accessing the spacefold. This explains why wormholes in opposite directions do not meet (the warping effect of the black holes adds a random element to the trajectory of the object traversing the spacefold). It also explains the long-known lore of starship captains that wormhole traversal is only possible by \u201cspinning\u201d the black hole - hitting its edge at a near-tangent with just the right velocity. The relatively short distance traversed by wormholes compared to spacefolds is thought to be explained by some impossibility of long-distance wormholes existing in warped space, perhaps being \u201cpinched off.\u201d

Spacefold Drive

Like wormholes, theories have existed since ancient times of how our space could be folded or crumpled in a space of higher dimensions. Thus, two points which seem far distant to us can actually be quite close if seen from the perspective of more dimensions. Early philosophers postulated that the degree of folding might be related to the amount of mass, and more advanced theories speculated on all manner of possible relations between the structure of what we see and the structure of what we cannot see. By the time of the wormhole drive these theories had become quite sophisticated, yet a great many possibilities were still plausible because they required experimental evidence beyond our comprehension. For millenia, no progress was made until finally one of many random experiments testing various theories stumbled on the correct answer.

Although our knowledge of superspace is still limited, significant progress has been made in understanding it and we have discovered several practical rules. Spacefolds are points where space intersects with itself in higher dimensions. They seem never to be found in areas of space with significant mass (with the exception of black holes). They are regions of space rather than exact points. The potential existence of a spacefold can be predicted but there remains a random element and there may or may not be an actual usable spacefold at the point predicted.

To traverse a spacefold, a starship must be travelling within a narrow cone of velocities. Spacefolds can in theory connect any two points in the universe, and it has been observed in practice that the longer-reaching spacefolds require a narrower range of velocities closer to the speed of light. Thus it is possible that all spacefolds connect somewhere but we have not yet found the correct velocity to unlock them. No spacefold has ever been found to link to more than one other spacefold but there are many examples of two different spacefolds found close to each other. Starhub is the best-known example of a star system with more than one spacefold, hosting 17 known folds. The maximum recorded number of folds, however, occurs in the system 3E2:178:0D-2039, which has 28 known folds. The longest known distance connected by a space fold is the traversal from Starhub to Springboard, a distance of some thirty-one thousand light years. It is often theorized that the Imperial Army knows of longer folds but keeps them secret, and occasional leaks have forced them to admit to the previously-disclaimed existence of spacefolds with particular strategic value.

Disappearance

Although the mechanism of the disappearance is unknown, the most popular theory is that the disappeared travelled somewhere else by unknown means. If true, this would be the most efficient form of star travel ever discovered.