Light.
A wondrous thing.
Its rest mass was zero, and that was precisely what made it so wondrous.
For the number zero itself contained infinite mysteries.
The speed of light was the speed of light—an apparently tautological statement, yet one that in truth carried a far stricter explanation within it.
First, the transmission speed of "causal relationships" permitted by the spacetime of the universe had a maximum value.
And because light had zero rest mass, its speed remained fixed at that maximum value.
Thus, the speed of light was equivalent to the universe's limit.
Yet wondrously, light with zero mass was not without impact.
It sounded bizarre—
How could something with zero mass possess kinetic energy or impact force, no matter how fast it moved?
But in truth, the reason was simple.
Light could carry energy.
Light possessing sufficient energy could even form "radiation pressure," force so immense that it could sustain the structure of gigantic celestial bodies.
Energy, and mass.
They sounded as though they were not the same thing.
Yet they were one and the same.
The specific explanations were taught in Immortal Dao, Martial Dao, science, magic, and all manner of great disciplines used to explain the world and make use of its laws.
But simply put, it was only a single sentence.
—Mass was energy at rest.
Matter and mass were themselves energy; all things were one. Neutrons and protons contained inconceivable energy, yet they were bound and held still by the Mystic Convergence of Myriad Sources Force—or, in other words, the strong nuclear force—manifesting into forms observable by ordinary humans, becoming matter and mass.
But if this force were artificially controlled, released, and fully utilized by some being—
Then that being, with merely a gaze, would be enough to destroy everything.
Just like—
Right now.