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Although it has never been experimentally proven, its predictions are astonishing.
The universe appears to have four fundamental forces that determine the interactions of everything within it. Three of them have been well explained by the Standard model of quantum mechanics.
But the fourth force, gravity, remains an outlier. Compared to the other forces it is exceptionally weak, which has made it impossible to detect in a particle collider, the main instrument used to examine the world of quantum mechanics.
But unlike the other forces, it has a long range, meaning that it becomes by far the dominant force on the large scales of moons, planets, stars, and galaxies.
So far we have been able to split our models of the universe in two: The Standard Model explains the small, and Einstein’s general relativity explains the large. Both models are exceptionally accurate.
General relativity has been the theoretical base with which we have landed men on the moon, put robots on Mars, Jupiter, Venus, and Titan, and flown probes past Pluto and into interstellar space.
Physicist Richard Feynman compared the accuracy of the predictions from quantum mechanics as akin to specifying the width of North America to within one hair’s breadth of accuracy.
But the two theories are mathematically incompatible. In areas where the two overlap, such as in black holes or in the early seconds of the universe following the big bang, applying the two theories at once produce illegible and mathematically impossible outcomes. Part of the reason for this is that, at the Planck length, general relativity assumes that the universe is smooth and uniform, while quantum mechanics assumes it to be chaotic and warped. Using the two together produces strange results like lengths that somehow have less than one dimension.
This means that the world of the Planck length and the secret that lies there is a new frontier of science. String Theory is the leading theory that attempts to unify all four fundamental forces of the universe into a single framework. A theory of everything that explains the basis of all known phenomena in the universe.
What is String Theory?
Instead of a smooth or warped surface at the planck length, string theory speculates that every particle contains planck length-sized string-like structures that vibrate in different ways. The vibrations of these strings create the particles described in the Standard Model, like plucking a guitar string can create the musical notes G, A, B, C, etc.
It is through these different vibrations that properties like mass, and force charge is created. So an up quark is created by one set of vibrations, an electron is created by another, and the explanation for how gravity comes about at the quantum level is that there is another set of vibrations that create a particle called a graviton.
These strings are really weird. They don’t just move in four dimensions (three for space, one for time) like a tiny piece of regular string, they move in up to eleven dimensions. This concept is absolutely wild.
An artist’s conception of a vibrating string. The diameter of the string is equal to the Planck Length.