Many of their greatest accomplishments were possible thanks to the discovery of null space. In null space the laws of physics no longer applied; nothing consumed energy, took up space, and time did not pass. Everything simply was. At first it was thought null space was useless for anything but a form of cold storage, but then a discovery was made that a bubble of real space could be created inside null space. The bubble itself followed the same rules that everything else in null space did, but anything inside the bubble followed the rules of normal space. They also discovered that null space could be layered to hide things. A great many things were possible thanks to these discoveries.
Time travel became possible but was generally agreed to be too complex for casual use, as such a group was set up in null space to watch time. They were instructed not to interfere with time or any changes in it unless it was to avert a cataclysmic event. The group was hidden behinds numerous layers of null space so that no one could find them unless they came out themselves.
Maybe more later?