The theory of relativity is a fundamental framework in physics developed by Albert Einstein in the early 20th century. It actually consists of two interrelated theories:
1. Special Relativity (1905)
- Special relativity applies to objects moving at constant speeds, especially those moving close to the speed of light, in the absence of gravity.
Key ideas:
- The laws of physics are the same in all inertial (non-accelerating) frames of reference.
- The speed of light (c) is the same for all observers, regardless of their motion or the light source's motion.
Consequences:
- Time dilation: Time passes slower for objects moving close to the speed of light (as observed from another frame).
- Length contraction: Objects appear shorter in the direction of motion at high speeds.
- which means mass and energy are interchangeable.
2. General Relativity (1915)
General relativity expands the theory to include gravity and accelerated motion.
Key idea:
- Gravity is not a force (like Newton thought), but the effect of curved spacetime caused by mass and energy.
Consequences:
- Massive objects (like planets, stars, black holes) warp the fabric of space and time, and this curvature affects how objects move.
- Predicts phenomena like:
- Gravitational time dilation (time runs slower near strong gravitational fields),
- Gravitational lensing (light bending around massive objects),
- Black holes and
- The expansion of the universe.
In Summary:
- Special Relativity General Relativity
- No gravity involved Includes gravity
- Constant velocity (non-accelerating frames) Accelerated frames (includes free-fall)
- Time dilation, length contraction, E=mc² Spacetime curvature, black holes, gravitational time dilation
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