I just finished reading the Three-Body Problem and its sequels. I am a little confused about the nature of the Dual Vector Foil and why it's such a terrifying weapon.

In The Three-Body Problem, the Trisolarians create the sophons, which are explained as unfolded matter. They demonstrate that they can fold them up and then refold them fairly easily.

But later in Death's End, The Dual Vector Foil is used on the Solar System and then is described by Guan Yifan that they will never stop expanding. The book seemed to insinuate that it was an unstoppable weapon.

However, as noted, the Trisolarans have no problem folding and unfolding matter through different dimensions. Wouldn't this weapon just not be very threatening to super-advanced civilizations? So it seems like a weapon like Dual Vector Foil would have no use on them as they could potentially disarm a weapon like this. The chapter from Singer's perspective makes it seem like it's a super deadly and effective weapon.

Did I misunderstand the two technologies, and are they not really similar or relevant to each other?


3 Answers 3


The Trisolarans are, with some considerable difficulty, able to fold a single proton down from its usual number of dimensions, firstly into one dimension, then into three dimensions and finally into the desired two dimensional shape.

While this, theoretically, allows a modicum of defence against something being made two-dimensional by a Dual Vector Foil, the question is one of degree. It would, I would assume, be possible to take a three-dimensional object that has been folded into a two-dimensional object and, within a reasonable amount of time, refold the now two-dimensional matter back into its original configuration, but since this can only occur one proton or neutron at a time this makes it basically useless as a defence against a weapon that is unfolding quadrillions of atoms per second.


The main difference between the Trisolaras' use of dimensions and a Dual Vector Foil is that a Sophon is made of particulate matter and has mass that can be directly manipulated by those who have the technology, whereas a DVF is simply a pocket of two-dimensional space contained in a decaying force field. The DVF is significantly more dangerous because instead of acting within the bounds of the laws of local spacetime, it rewrites them entirely. For this reason, the Foil's effects on the universe are irreversible, and all that higher-dimensional beings can do to survive a Foil strike is to somehow adapt ahead of time to lower-dimensional conditions.

  • 3
    Hi, welcome to SF&F. This sounds like an interesting answer; can you provide any quotes to support this?
    – DavidW
    Apr 12, 2023 at 23:38

It's entirely speculative, but one could assume the state-change of the proton is a transient, whereas the state-change of the dual vector foil is not only self-sustaining but uncontrolled and irreversible. Compare to fission: you can split elements heavier than lead by hammering it with deuterium and it will release some energy, but hit a sizeable mass of enriched uranium and it will cause a chain reaction that will consume all the matter.

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