String theory is quite interesting; it makes the string one of the main objects of study. A string is an object with a one-dimensional spatial extent, unlike an elementary particle which is zero-dimensional, or point-like. By postulating this one-dimensional structure, many desirable features of a more fundamental theory of physics automatically emerge. Most notably, almost any theory of strings consistent with quantum mechanics must also contain quantum gravity, which had not been described consistently prior to string theory.
Strings can be either open or closed. A closed string is a string that has no end-points, and therefore is topologically equivalent to a circle. An open string, on the other hand, has two end-points and is topologically equivalent to a line interval. Not all string theories contain open strings, but every theory must contain closed strings, as interactions between open strings can always result in closed strings. The oldest superstring theory containing open strings was type I string theory.
Since its birth as the dual resonance model which described the strongly interacting hadrons as strings, the term string theory has changed to include any of a group of related superstring theories and larger frameworks such as M-theory, which unite them. A shared property of all these theories is the holographic principle. String theorists have not yet completely described these theories, nor have they determined if or how these theories relate to the physical universe. The elegance and flexibility of the approach, however, and a number of qualitative similarities with more traditional physical models, have led many physicists to suspect that such a connection is possible. In particular, string theory may be a way to "unify" the known natural forces (gravitational, electromagnetic, weak nuclear and strong nuclear) by describing them with the same set of equations, as described in the theory of everything. (BTW, Theory of everything (TOE) is a hypothetical theory of theoretical physics that fully explains and links together all known physical phenomena. Initially, the term was used with an ironic connotation to refer to various overgeneralized theories. For example, a great-grandfather of Ijon Tichy — a character from a cycle of Stanisław Lem's science fiction stories of 1960s — was known to work on the "General Theory of Everything". Over time, the term stuck in popularizations of quantum physics to describe a theory that would unify or explain through a single model the theories of all fundamental interactions of nature. There have been many theories of everything proposed by theoretical physicists over the last century, but none have been confirmed experimentally. The primary problem in producing a TOE is that the accepted theories of quantum mechanics and general relativity are hard to combine.)
String Theory predicts the existence of more than the 3 space dimensions and 1 time dimension we are all familiar with. According to string theory, there are additional dimensions that we are unfamiliar with because they are curled up into tiny complicated shapes that can only be seen on tiny scales. If we could shrink to this tiny, Planck-sized scale we could see that at every 3D point in space, we can also explore 6 additional dimensions. This animation shows a Calabi-Yau surface which is a projection of these higher dimensions into the more familiar dimensions we are aware of.
Time Is A Human Construct
"You've started believing in the future eternal life?"
"No, not future eternal, but here eternal. There are moments, you reach moments, and time suddenly stops, and will be eternal."
"You hope to reach such a moment?"
"It's hardly possible in our time," Nikolai Vsevolodovich responded, also without any irony, slowly and as if thoughtfully. "In the Apocalypse the angel swears that time will be no more."
"I know. It's quite correct there; clear and precise. When all mankind attains happiness, time will be no more, because there's no need. A very correct thought."
"And where are they going to hide it?"
"Nowhere. Time isn't an object, it's an idea. It will die out in the mind."
- Kirillov to Stavrogin