According to the uncertainty principle of quantum physics, quantum states themselves existed in an ambiguous state. Like light's wave-particle duality, only when an observer was present would they collapse in reality and return to a definite state.
The renowned quantum physicist Schrödinger once proposed a hypothesis involving a cat: suppose there was a cat inside a box containing a small amount of radium and highly toxic cyanide, while the decay of the radium was probabilistic.
If the radium decayed, it would trigger a mechanism that shattered the vial of cyanide and poisoned the cat to death. If the radium did not decay, the cat would remain alive.
According to quantum mechanics, since the radioactive radium existed in a superposition of decayed and undecayed states, the cat should likewise exist in a superposition of a dead cat and a living cat. In other words, the cat was both dead and alive.
But when an observer opened the box and observed the cat's state of survival, the cat's quantum superposition immediately collapsed into either death or survival.
When no observer existed, the cat was a "ghost" that was both dead and alive.
The famous Huaguo writer Liu Cixin once proposed a conjecture in one of his novels: if weapons using quantum states were used to eliminate an army with exceptionally strong willpower, one could obtain a quantum army like a host of ghosts.
When no observer existed, this force could pass through any obstacle, be harmed by nothing, and even enter the enemy's heart directly to deliver a fatal blow.
Shen Feng had previously studied the feasibility of quantum weapons with Jingwei, but because they simply had not had enough time for dedicated research, they had only scratched the surface.
Everything happening before them now was precisely the quantum ghosts described in