In string theory, all particles are simply different vibrating modes of an underlying, more fundamental structure: strings. their string theory analogues (bottom) gives rise to surfaces which can have non-trivial curvature. By viewing each of the elementary particles as either an open or closed string that vibrated at specific, unique frequencies, and the fundamental constants of nature as various states of the vacuum in string theory, physicists could finally hope to unify all the fundamental forces together.įeynman diagrams (top) are based off of point particles and their interactions. For one, string theory suddenly made it plausible that the Standard Model of particles and interactions could be reconciled with General Relativity. That spin-1 particle could be the photon, and other excited states could be associated with the known Standard Model particles.Īll of a sudden, a long sought dreamed seemed within reach in this new framework. Instead of working at the energy scales where nuclear interactions are important, the idea was put forth to take the energy scale all the way up to the Planck energy, where the spin-2 particle that made no sense could now play the role of the graviton: the theoretical force-carrying particle responsible for a quantum theory of gravity.
Bethke .58:351-386,2007īut a decade or so later, this idea was reborn into what's now known as modern string theory. This idea is known as 'asymptotic freedom,' which has been experimentally confirmed to great precision. At large distances, it increases rapidly. The Standard Model, now complete, didn't need this new, esoteric, and simultaneously ineffective framework.Īt high energies (corresponding to small distances), the strong force's interaction strength drops. QCD described the strong nuclear force and interactions extraordinarily well without these pathologies, and the idea was abandoned. Then the idea of asymptotic freedom was discovered and the theory of quantum chromodynamics (QCD) came to be, and the string model fell out of favor. The string model was interesting for this reason, but predicted a number of strange things that didn't appear to match reality, such as a spin-2 boson (which wasn't observed), the fact that the spin-1 state doesn't become massive during symmetry breaking (i.e., there's no Higgs mechanism), and the need for either 10 or 26 dimensions. If you envision a meson as a string, then pulling it apart increases the tension in the string until you reach a critical moment, resulting in two new mesons. This was initially where string theory began: as the string model of the strong nuclear interactions.
If you 'snap' a bar magnet in two, it won't create an isolated north and south pole, but rather two new magnets, each with their own north and south poles. These permanent magnets remain magnetized even after any external magnetic fields are taken away. Magnetic field lines, as illustrated by a bar magnet: a magnetic dipole, with a north and south pole.
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