In non-technical terms, M-theory presents an idea about how matter is constructed. String theory, superstring theory, and quantum mechanics explain things we cannot see, yet their existence can be inferred. Gravity is an invisible measurable force that we can sense.
In school we may have learned about the atom having proton(s) and neutron(s) in the center, called the nucleus, with electron(s) spinning about the nucleus. This is much like our solar system where the Sun is the nucleus and the Planets revolve around it at different distances. There are also smaller particles in and around the atomic nucleus called subatomic particles. These may exist for an extremely small moment in time, and then transmute into another subatomic particle, or other energy form. Examples are quarks, baryons, tachyons, neutrinos, and many others.
One-dimensional strings, which are smaller than any subatomic particle, are believed to exist inside atoms. Strings are lines that can be straight, curled and circular. Note well that these strings do not extend beyond their 1st dimension, and using advanced physics mathematics equations to explain all matter seen and unseen scientists have given arguments for existence of the 4th dimension and upwards to 26! Three dimensions explain mass or objects. But now we must step outside our world when we study Einstein's theories of special relativity and general relativity and go to other dimensions - to 12 dimensions or even more.
The speed of light in vacuum, c, is assumed to be a constant in the Einsteinian equations. Equations for the higher dimensions involve imaginary numbers, and include the folding of space at sublight and normal light speeds through time itself, known as space-time.
Electrons and subatomic particles travel at close to c -- the speed of light. If we were to think smaller and travel inside the atom we could imagine a dot, a point containing these invisible imaginary strings. They vibrate, in one sense of the word, to form all the other particles, subatomic particles and co-exist with energies which make up atoms, which comprise matter. M-theory sews the five superstring theory threads into one fabric.
To read more in-depth see M-theory.
