Interstellar Travel is a term used to describe all methods used to move between star systems within a time frame that permits interstellar interaction. All require what are called "Advanced Physics" as standard Physical laws would nominally prevent the breaking of the speed of light. Enormous power is required for these systems, usually large banks of high-power fusion reactors or utilization of energy released from matter/anti-matter annihilation.
The Heim Drive, named for 20th Century theoretical physicist Dr. Burkhard Heim, uses gravito-magnetic field manipulations to permit a vessel to travel at faster than light speeds without actually exceeding the speed of light in real terms. These drives have a solid feasible speed cap of 53c - 53 times the speed of light - and while they were vital for early space exploration and colonization, the slowness of the drive means any workable interstellar state would be small in size. In the modern era Heim drives are most often found on vessels that are limited to intra-system travel or specialized drives to assist in crossing shoal regions.
Inevitably a race that has discovered the use of Heim Drives tends to come across the necessary mechanics to effect a ship shifting into hyperspace. The utilization of gravito-magnetic fields of higher intensity than those employed in a Heim Drive allows such a bending of space-time that an object, even a transmission, can be projected into hyperspace. Hyperspace exists as a "foundation membrane" of space-time, according to hyperspace physicists, and within the confines of hyperspace a vessel traveling at an ordinary speed will, in interaction with real-space, be traveling at faster-than-light velocities.
Hyperspace is not uniform, however. They have close interactions with real-space gravity wells, such that a hyperspace transit must be performed a minimum distance from a star and astronavigation requires calculating for the presence of stars along one's route. As a result, regions in which stars are few or rare or regions in which gravitational fields are of particular form create "Shoal" space, areas where Hyperspace becomes energized and stretched. Vessels have a harder time moving through hyperspace in Shoals; a worn down drive can even fail to successfully transition between hyperspace and realspace, while the energy resistance inside hyperspace creates wear on the spaceframe of a vessel. Though there are lanes through the Shoals, most scientists believe them to be the result of an ancient star-faring race that refined hyperspace dredging to the point that they could place limited lanes through Shoals.
Along the other side of the spectrum, particular gravitational fields of local stars can create "lanes" in hyperspace, cylinders of light-year-scale space where hyperspace is quiet and far easier to traverse. These lanes increase the speed of standard hyperdrives by several factors, enabling trips that would ordinarily take a week to happen in the space of a couple days. In some places, these gravitational effects can lead to a great many lanes clumping in the vicinity of a single star system, creating a "Hyperspace Junction" and also usually signifying that many neighboring star systems are within the confines of a lane, thus meaning interstellar travel within the sector is vastly easier.
Any section of hyperspace that is not considered "Shoal" hyperspace but is not in a lane is considered "off-network". This hyperspace is energetic and resistant to travel, but nowhere near as dangerous as shoal space. Experiments since the 31st Century have since shown that it is possible to "dredge" hyperspace through the generation of intense Heim fields within it; the result is a process that over many years can permit a state to "dredge" lanes within a sector that is primarily off-network, permitting easier colonization of local systems and planets.
Most interstellar states now rely on standard hyperdrive, but the mysterious Collectors of the Wild Space shoal region are an exception that proves the rule. Expanding in a region that is entirely Shoals, the Collectors developed hyperdrive technology that accesses a higher plane of hyperspace, requiring more energy but being less effected by wide-scale gravitational fields. As a result Collector hyperdrives are not held back by Shoal space, but by the same token they gain no benefit from being outside Shoals or in a hyperspace lane.
A Hyperdrive works by generating a gravito-magnetic "submersion" field that "slips" a vessel into hyperspace. Departing hyperspace is the result of this field being de-energized, permitting a ship to "slow" in relation with real-space until it reaches "transition velocity" and can shift back into real-space.at a safe subluminal velocity that causes minimal, if any, time dilation. For emergencies, there are also systems that force a ship to actively shift itself back into real-space through a sudden, powerful stop and an active field shift instead of a field shut-down; these are highly dangerous maneuvers and can cause the destruction of not only the vessel attempting the maneuver but of any vessels nearby, in both hyperspace or real-space, as a result of the violent energy shift.
Hyperspace "interdiction" is possible in two ways. One is the favored method of commerce raiders and pirates; an in-hyperspace intercept and a forced grappling onto a ship, permitting the attacker, if they are powerful enough, to overwhelm a ship's submersion field into their own and thus letting them dictate the exit from hyperspace. Such can be dangerous - if the submersion field of the intercepted ship fails before the attacker's field can be asserted the result will trigger the safeties built into all hyperdrives, with the emergency active shift coupled with a slowdown, both ships being vulnerable to destruction. Secondly, a method used by most star nations is an "interdiction field" at points where hyperlanes intersect solar systems, forcing the ship to drop out of hyperspace if it does not want to risk being forced out and potentially crippled or destroyed in the process. The downside to the interdiction field is that the generating station is somewhat fragile, hard to protect, and easily destroyed by a combat fleet conducting an invasion.
Developed in the 32nd Century by a UN team from CERN, Crimson Commune-1, and FermiLab, Warp Gates are an entirely new approach to interstellar travel. They ignore the issues of standard hyperspace entirely by creating a pocket of "warp space" that directly connects two points across vast interstellar distances, in the fashion of a wormhole. Though they require vast amounts of energy, a Warp Gate permits near-instantaneous travel between two points, the Sending Point and Receiving Point, ignoring Shoals along the route.
Currently the limitation of the technology is found in its mass/energy limits over distance. The more mass you attempt to transit through a Warp Gate, the more energy it requires. Over relatively short distances - 2 standard sectors - the energy demand of shifting even the largest warships is sustainable by modern technology. But beyond this "fleet transit distance", as it is called, the power demand goes up logarithmically, such to the point that to go from one side of the known galaxy to another - from, say, Chamarra in the Chamarran Hierarchy to Guangdong in Tianguo - requires every available joule from the best modern power source for a Gate to transit just one vessel of Light size and tonnage, when the same amount of energy can transfer roughly 20 times that amount of mass in vessels within the fleet transit distance. Just as much, moving the equivalent of a Heavy hull just one extra sector by itself beyond the fleet transit distance requires more energy than any modern power source can provide (as in there are no means for any power source currently available to transfer the necessary energy to the Warp Gate).
Due to these limitations and the expense of construction and maintenance, most states only maintain one Warp Gate for their home system. The UN, at five divided among thirteen sectors, has the most of any state in the cosmos. Warp Gates are primarily used for rapid transit of government officials and VIPs for interstellar diplomatic summits and negotiations, as well as for high-cost luxury liner passage between major systems and for the transfer of high-value, short-life items that cannot be shipped to their purchaser in time if done via normal hyperspace route. Only in cases where a state has two or more Warp Gates, within two sectors of each other, are they capable of use for more, such as larger-scale ships and for military fleet deployments that move faster than standard lane-utilizing hyperspace.