  How the two theories connect

  ┌───────────┬────────────────────────────────┬───────────────────────────────────────────────┐
  │           │       Special relativity       │              General relativity               │
  ├───────────┼────────────────────────────────┼───────────────────────────────────────────────┤
  │ Scope     │ Inertial frames, flat          │ All frames, curved spacetime                  │
  │           │ spacetime                      │                                               │
  ├───────────┼────────────────────────────────┼───────────────────────────────────────────────┤
  │ Gravity   │ Not included                   │ Described as spacetime curvature              │
  ├───────────┼────────────────────────────────┼───────────────────────────────────────────────┤
  │ Geometry  │ Minkowski (flat)               │ Riemannian/pseudo-Riemannian (curved)         │
  ├───────────┼────────────────────────────────┼───────────────────────────────────────────────┤
  │ Reduces   │ Newtonian mechanics at v ≪ c   │ Newtonian gravity in weak fields at low       │
  │ to        │                                │ speeds                                        │
  └───────────┴────────────────────────────────┴───────────────────────────────────────────────┘

  Special relativity is the limiting case of general relativity in the absence of gravity (flat
  spacetime).

  ---
  Open frontiers

  Quantum gravity: General relativity is a classical theory. It is incompatible with quantum
  mechanics at extreme scales (singularities inside black holes, the Big Bang). Unifying the two is
  one of the great unsolved problems in physics. Approaches include string theory, loop quantum
  gravity, and others, but none are experimentally confirmed.

  Dark matter and dark energy: General relativity, combined with observations, implies that ~95% of
  the universe's mass-energy content is in forms we don't yet understand. Whether this requires
  modifying general relativity itself or discovering new particles/fields remains an open question.

✻ Cooked for 1m 11s

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