Item from remembrance-of-earths-past by
Sentient supercomputers fashioned by Trisolaran engineers from single protons unfolded across multiple dimensions and refolded — sent to Earth at light speed to corrupt particle accelerators, surveil every transmission, and write death-threats on the retinas of physicists.
The sophons are the most elegant weapon in the trilogy. They cannot kill anyone directly, and they do not need to — by sabotaging particle physics and reading every electromagnetic signal on Earth, they freeze human science at its 21st-century level for four hundred years. They are quantum-entangled with their counterparts on Trisolaris, providing real-time communication between worlds. The fact that they cannot read human thoughts is the fragile margin in which the Wallfacer Project survives.
Invisible. A sophon in its base form is a single proton. Its presence is detectable only by its effects: a flickering countdown on the inside of someone's eyelids, an inexplicable pattern in the cosmic microwave background, a particle accelerator whose results have stopped converging.