请解释相对论，要求回答用json格式输出，且包含3个要点。
user
```json
{
  "theory_of_relativity": {
    "definition": "A theory developed by Albert Einstein that revolutionizes our understanding of space, time, and gravity.",
    "special_relativity": {
      "explanation": "Describes the relationship between space and time in the absence of gravitational influence, introducing concepts like time dilation and length contraction.",
      "key_equation": "E=mc²"
    },
    "general_relativity": {
      "explanation": "Expands special relativity to include gravitation, describing gravity as the curvature of spacetime caused by mass and energy.",
      "impact": "Fundamental to our understanding of the universe's structure and evolution."
    }
  }
}
```
assistant