There is one rule of physics that all the advanced technology in the galaxy hasn’t been able to break: you can’t travel faster than the speed of light. Thankfully, it was discovered that while you can’t break through that obstacle, you can go around it! The invention of the Tangent Drive allowed the spacefaring races to circumvent the universal speed limit and travel between the stars. Before I can explain how, I first have to describe the nature of space-time in the Tangent Space universe.
The dimensional levels of space-time in Tangent Space form a sphere of infinite size. Normal space that we exist within resides in the layer evenly between the exterior and core of the sphere. It is a point of equilibrium where the total amount of energy cannot be changed. It is also the only dimension where physical matter naturally exists. Everything core-ward of normal space is considered to be subspace, and everything exterior-ward of normal space is considered to be hyperspace.
Hyperspace is infinitely large and gets larger the higher you ascend towards the exterior of the sphere. Hyperspace is in a state of spontaneous energy generation. This chaotic dimension is so energetic that it appears to be opaque white. Few things can survive long in hyperspace due to the intense conditions that threaten to rip it apart. Energy from hyperspace naturally shifts into normal space to maintain the equilibrium there.
Subspace is infinitely small and gets smaller the deeper you descend into the sphere towards the core. Subspace is in a state of constant energy elimination. Subspace is a pitch black void where energy cannot exist for more than a split second. Energy from normal space naturally shifts into subspace to maintain the equilibrium.
The groundbreaking discovery about space-time is that movement in one dimension directly corresponds to movement in all others. Therefore, by diving into the smaller subspace dimension, a ship can travel a few inches, and then surface to discover they had actually traveled a few miles in normal space! The Tangent Drive was created to allow a ship to do exactly that. Exceeding the speed of light is no longer a concern as the rate of travel is now determined by how deeply a ship can dive into subspace. Cheaper T-Drives are good for travel through the local areas of space, while more advanced drives can be used to travel across the entire galaxy. Many attempt to create a drive capable of sending a ship to another galaxy, but none have succeeded.
T-Drives have come with their own set of complications. For one, the dive into subspace is very energy intensive to initiate. Ships guzzle helium-3 for their fusion generators to open a small rift into hyperspace. The energy from hyperspace is collected inside a shielded chamber, which disrupts the equilibrium of normal space. The excess energy is pulled into subspace along with the T-Drive and the ship it is attached to. A thin bubble of normal space must be maintained around the ship to isolate it from the unique physics of that dimension. If the bubble is disrupted at any time, the ship is violently thrown back into normal space as matter can only exist there. The isolation bubble of ships in subspace causes a tachyon echo in normal space that can be used to estimate their location.
Another technology based around the nature of space-time is the Dimensional Flow Generator. DFGs open small rifts into both hyperspace and subspace, allowing the intense energy from hyperspace to surge directly into subspace. Power is generated by the passage of energy through the area of normal space between the two rifts. Once the rifts are created, the DFG is able to provide limitless energy. However, DFGs are extremely dangerous and are prone to instability due to having two dimensional rifts in such close proximity to one another. A loss of containment on a DFG would result in a hyperspace breach strong enough to leave a crater in the side of a planet that could be seen from orbit. This resulted in the need for Artificial Intelligence to meticulously manage and maintain DFGs. Only wealthy cities and military capital ships use DFGs for power due to the high cost and expertise they demand. During combat, a capital ship will normally shut down its DFG and rely on fusion generators to minimize the risk of a devastating containment malfunction. There is an agreement in League space to never develop a weaponized version of a DFG, though it is suspected that the Hegemony is actively working to produce one themselves.