Lucien had only just learnt the matrix mechanics. Also, he intentionally did not refer to the files in his spirit library but inferred it with his memories and understanding. Therefore, it was not as fluent and natural as the papers he wrote before, when he could write more than ten pages without any stop under the assistance of magic. It was quite troublesome this time.
Lucien could've picked Dirac's version of quantum mechanics that was more concise, beautiful and easier for the arcanists to understand, and he could've handled it with the mathematical tools in the previous arcana system. However, the matrix could be applied to a variety of fields in the future. This was the best opportunity to come up with it. After all, he would throw out Dirac's paper in two months and free the arcanists from the maze of matrix.