A relatively modern theory, the idea is that particles are not dots in space-time but rather waves of infinitely long, one-dimensional lengths, like strings. These strings can join together and separate but require the existence of 10 or 26 dimensions for the theory to work.
String theory Term Timeline in A Brief History of Time
The timeline below shows where the term String theory appears in A Brief History of Time. The colored dots and icons indicate which themes are associated with that appearance.
...garnered attention. Soon, a new version of the theory, called the heterotic string, arose. These strings could eliminate all infinities, although this is not yet proven. But the biggest problem with... (full context)
...one-dimensional—just a line. Closer up you can identify many more points on the straw. In string theory , looking on a very small scale reveals ten dimensions. No room for space ships,... (full context)
...p-branes, which take up two or more dimensions in space, while particles are 0-brane and strings are 1-brane. Supergravity, string, and p-brane theories could all be estimations of one overarching theory,... (full context)
...it is an infinite tower of tortoises with the flat earth on their back, or string theory . Although the latter is more precise mathematically, it lacks observational evidence just as much... (full context)