String theory — the concept that all particles can be represented as strings or string-loops of incredibly minute length, oscillating at various frequencies — was initially developed to help explain why quarks, the tiny fundamental particles that make up protons and neutrons, are always confined within larger composite particles. However, string theory has evolved to allow scientists to deal with some wider issues. For example, they can use string theory to devise explanations for some grand problems in cosmology, such as the state of the universe — its shape, size, etc. — just after the Big Bang, when quarks roamed freely.
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