请尽量详细且全面地阐述相对论的主要内容及相关理论，回答中不能使用“相对论”这个词，并且必须指出主要应用领域，回答需要用json格式表示。
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{
  "main_content": [
    {
      "theory": "Special Theory of Relativity",
      "description": "Introduced by Albert Einstein in 1905, this theory deals with the relationship between space and time in a flat spacetime. It is based on two postulates: the laws of physics are invariant in all inertial frames of reference, and the speed of light in vacuum is constant for all observers, regardless of the motion of the light source or observer.",
      "implications": [
        "Time dilation: time moves slower for objects moving at near-light speeds relative to an observer at rest.",
        "Length contraction: objects moving at high speeds will appear length contracted in the direction of motion.",
        "Mass-energy equivalence: the famous equation E=mc², which states that energy and mass are interchangeable."
      ],
      "applications": [
        "Global Positioning System (GPS): requires relativistic corrections to provide accurate positioning.",
        "Particles physics: understanding the behavior of particles at high energies."
      ]
    },
    {
      "theory": "General Theory of Relativity",
      "description": "Published in 1915, this theory generalizes the special theory to include gravity and curved spacetime. It posits that massive objects cause a distortion in spacetime, which is felt as gravity.",
      "implications": [
        "Curved spacetime: matter and energy cause spacetime to curve, and this curvature affects the motion of objects.",
        "Gravitational time dilation: time moves slower in stronger gravitational fields.",
        "Gravitational lensing: light bends around massive objects due to the curvature of spacetime."
      ],
      "applications": [
        "Astronomy: understanding black holes and the expansion of the universe.",
        "Cosmology: studying the origins and evolution of the universe."
      ]
    }
  ]
}
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