Consider the 3-D interior and 2-D surface of the metaphoric pond. For the correspondence to work, the interior must be mathematically described by string theory, in which electrons, photons, gravitons and the rest of nature’s building blocks are invisibly small, one-dimensional lines, or “strings.” Mass and other macroscopic properties correspond to the strings’ vibrations, and interactions between different kinds of matter and forces come from the way strings split and connect. These strings live inside the pond.
Now, imagine that the 2-D surface of the pond is described by quantum mechanics. Particles are the splashes on the surface, and waves are the cascade of ripples from those splashes. On the surface of this imaginary pond, there is no force of gravity. https://www.quantamagazine.org/string-theory-black-holes-and-a-strange-superconducting-material-20130701/