The twin paradox is a famous thought experiment in special relativity that illustrates how time dilation causes differential aging between two twins when one travels at relativistic speeds and the other remains on Earth.
In the scenario:
- One twin boards a spaceship and travels at speeds close to the speed of light on a long journey into space,
- The other twin stays on Earth.
According to special relativity, the traveling twin experiences time more slowly relative to the Earth-bound twin due to time dilation—a direct consequence of moving at high velocity. When the traveling twin returns, they are younger than their sibling who stayed behind.
This outcome seems paradoxical because, from the traveling twin’s perspective, the Earth is moving, so one might expect the Earth twin to age less. The paradox is resolved by recognizing that:
- The traveling twin undergoes acceleration and deceleration during the journey, breaking the symmetry between the twins’ frames of reference,
- The Earth twin remains in an inertial frame, while the traveling twin switches frames when turning around.
Key points about the twin paradox:
- It confirms that time is relative and depends on the observer’s motion,
- It has been experimentally confirmed with precise clocks on fast-moving aircraft and satellites,
- It highlights the non-intuitive nature of spacetime in Einstein’s theory.
The twin paradox reveals how relativity reshapes our understanding of time, proving that moving at speeds close to light fundamentally alters the passage of time for observers.