In mathematics, a chord is a straight line connecting two ends of an arc. Although the arc is related to the central angle, the chord is naturally related to the central angle. However, the string obviously does not correspond to the arc.

There are superstring theory and m-theory in string theory, but we won't talk about that. Rather, it mainly discusses some superficial issues in depth, so as to achieve the purpose of learning from things. String theory is naturally inseparable from strings, so what are strings like? Are strings straight or curved? Because strings can fluctuate, and because space-time is bent. And the string theory says that strings are the most basic and ubiquitous. So, it seems to be curvilinear ones. However, it is true. We know that a curve can be thought of as a polyline with many folded corners, sometimes large and sometimes small. A polyline is made up of many line segments, and a line segment is a part of a straight line. In this case, the strings should be straight. And why is the fluctuation of the string not a global fluctuation, but a local fluctuation? So, that's a problem.

We know that strings are one-dimensional, so are closed strings two-dimensional or three-dimensional? It's a question of looking, where exactly are the boundaries of the dimension? It's easy to think that a closed string is two-dimensional, or that you think it's one-dimensional. Of course, it may also be considered three-dimensional. And I think a closed word, saying yin, it is one more dimension than a one-dimensional string. Although there is a negative dimension in mathematics, this is not the case in the world. I feel like the strings are three-dimensional. Because if the closed string is two-dimensional, then won't the string never form something three-dimensional? So, I think it's three-dimensional.

The electron is a point particle, but why can it split into three quasi-particles? Is it because there is no volume, or because quasiparticles are not considered particles? Not being able to decompose only refers to the particle aspect, not the quasi-particle aspect. We know that point particles have a limiting radius, but what about not having volume? Since it has a radius, it must occupy a certain space, how can it be without volume? If the volume is three-dimensional, then the point particles are likely to be two-dimensional. Because if this is not the case, then how can there be a radius? What does limit mean? The position of an electron is difficult to measure, and we can only know its probability cloud. The area covered by this limit radius is likely to be the entire probabilistic cloud.

Because the string has an imaginary mass, it can exceed the speed of light? Why? The rest mass of the photon is zero, so the velocity is the speed of light. If the string is superluminal, then the rest mass must be less than zero. We have no size for imaginary numbers, but here the implication requires the chords to be so. The answer is that imaginary numbers do have sizes, but we don't know how to compare them.

There was open-string confinement before the decay of the unstable D membrane, so is open-chord confinement related to quark confinement? Although there is not necessarily a direct relationship, there is definitely a connection. After all, it's all confinement.

The superpartner of the boson is the fermion, so is there one boson with two superpartners? That is, are the numbers of bosons and fermions the same, or is there a mapping between them? I guess neither. Of course, there is no evidence for this. We know that many particles have antiparticles, and the antiparticle of the Majorana fermions is itself. Therefore, fermions are a bit special. Besides, from the point of view of spin, it is impossible for fermions and bosons to correspond one-to-one.