In I Ching wing dealing with Trigrams says that a long time past, the sages created the Book of Changes, using 3 for heads and 2 for tails and these combine to make all of the lines of the hexagrams.
The sages assigned 3 to Heaven, the spiritual realms, and 2 to Earth, the material realms. Heaven the spirit and Earth the matter come together to make life. In our physics, energy and matter are substance of the changing Universe. The I Ching like a planetarium holding the cycle of change within its pages.