A combined research team of a number of species of the galaxy invents a device that is capable of accelerating any object to significant portions of C, the human member of the team proceeds to be a human. -- Anon Guest
The breakthrough came, as breakthroughs often do, by accident. One person noticed that the interference on their experimental quantum computer was too regular to be just interference. The paired electrons weren't merely paired. They were grouped. They were grouped with other electrons somewhere far, far away, and someone was using them as a communications method.
With that realisation, the herculean effort to understand what they were saying and how they encoded it began. Decoding an unknown language is never easy, just ask the people attempting to decipher Mayan hieroglyphs. With no rosetta stone, with no common ground, with only basic mathematical concepts, they did it inside of fifty years. Crowd-sourcing really cut down on the problem solving.
Communication began, soon after that. The other side simply assumed that these distant people with a rudimentary understanding of GalStand Simple were new members in the Alliance. Assumption has wrecked more than one life. It would wreck many more after this one. Understanding grew. Concepts were exchanged. Invention... followed.