According to string theory, fundamental particles such as electrons, quarks, and photons are not considered to be made of strings but are rather interpreted as different vibrational modes of the fundamental strings. In this framework, particles are excitations or vibrations of the underlying strings.
In string theory, the strings are one-dimensional objects, similar to tiny, infinitely thin filaments, and they have a characteristic length scale known as the string length. These strings can vibrate in different ways, just like the different modes of vibration of a guitar string. Each mode of vibration corresponds to a different particle with specific properties, such as mass, charge, and spin.
For example, the lowest vibrational mode of a string corresponds to the particle with the least energy, which is interpreted as a massless particle called a graviton, associated with the gravitational force. Higher energy excitations correspond to particles with mass and other properties.
Therefore, in string theory, the elementary particles are not considered to be composed of smaller entities like atoms are composed of protons, neutrons, and electrons. Instead, they are identified as different vibrational patterns of the fundamental strings.
It's important to note that string theory is a highly complex and mathematically intricate framework, and our understanding of it is still evolving. The precise nature of how the vibrational modes of strings give rise to the diverse properties of particles is an active area of research.