PRIDE CHEKERAslows down within the vicinity of a relativistically accelerating
spaceship in outer space. This led Einstein to a paradox
famously known as the twin paradox.
Twin paradox
Suppose you have an identical twin, both of you are aged 15.
Then you board a spaceship and relativistically accelerate it into
deep space. According to special relativity, time slows down
within your vicinity, and it 'sweeps' faster on Earth. After 5
years you come back to Earth; you will meet your twin now
aged 60 whilst you are 20 years old. This seems fictional, but
it’s a reality in a universe of Einstein.
Lorentz length contraction and time dilation
Time is not fixed, its dynamical and depends on the spatial
coordinate occupied by an observer.
The Lorentz time dilation equation conspicuously shows the
time dilation {slowing down) and length contraction at speeds
whose magnitudes are a fraction of the speed of light.