Compute the Planck length \(\ell_p\), the unique distance scale determined by combinations of powers of only \(G\), \(c\), and \(\hbar \). Where \(L\) refers to length, \(M\) to mass, and \(T\) to time. These constants are fundamental to general relativity and quantum mechanics, and have units: Researchers in high-energy physics typically use a system of units called Planck units in which \(G=c=\hbar=1\), where \(G\) is Newton's gravitational constant, \(c\) is the speed of light, and \(\hbar\) is the reduced Planck constant. In order to understand the distance, time, and energy scales at which string theory should be a good description of nature, it is useful to describe the theory in the appropriate system of units. Although the theory is not yet complete, modern research efforts in string theory have greatly advanced the current state of understanding in major related fields of study including algebraic geometry, black hole physics, cosmology, and condensed matter physics. Eventually, it was realized that the modes of oscillation of these strings could describe a great many more particles within a quantum framework, including the graviton, photon, and potentially the rest of the particles of the Standard Model. String theory began as an effective theory to describe the interactions of the strong force, because the gluons that bind together quarks seemed to function a lot like rubber bands or strings holding together the quarks with some tension. Lastly, in string theory one vibrational mode of closed strings must correspond to a graviton, so quantum gravity is an inescapable consequence of the theory.
Furthermore, the dimension of spacetime is uniquely fixed to be ten in order for the theory to be internally consistent mathematically.
#GRAVITY STRINGS THEORY FREE#
In contrast, the Standard Model of particle physics relies on nineteen dimensionless free parameters that set the particle masses and force strengths. It is only dependent on one dimensionless parameter, the string length \(\ell_s\). One reason many physicists find string theory attractive is that it is highly constrained. String theory is a quantum theory in that the mass spectrum of strings is discrete, so string theory is an example of a quantum theory of gravity. Particles in string theory are identified with particular patterns of vibration of a one-dimensional elementary object called a string. String theory is a candidate for a unified theory of the four fundamental forces of nature: electromagnetism, the weak force, the strong force, and gravity.
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