The apparent change in size, distance, and time of objects in motion relative to an observer is due to the effects of special relativity, a theory proposed by Albert Einstein in 1905. Special relativity introduces the concept that space and time are not absolute but are interconnected in what is known as spacetime.
According to special relativity, as an object's velocity approaches the speed of light, several effects come into play:
Length Contraction: When an object moves at a significant fraction of the speed of light relative to an observer, its length appears contracted or shortened along the direction of motion as observed by the observer. This phenomenon is known as length contraction or Lorentz contraction.
Time Dilation: Time dilation refers to the slowing down of time for a moving object relative to an observer at rest. An observer in motion relative to the object perceives time to be passing more slowly for the moving object compared to their own time. This effect becomes more pronounced as the velocity of the object approaches the speed of light.
Relativistic Doppler Effect: The relativistic Doppler effect occurs when there is a change in the observed frequency (and therefore color) of light emitted by a moving object. The observed frequency appears shifted towards the red end of the spectrum (redshift) as the object moves away and towards the blue end of the spectrum (blueshift) as the object moves closer.
These effects arise from the fundamental postulate of the constancy of the speed of light in all inertial reference frames. As an object's velocity increases, these relativistic effects become more pronounced and can result in the apparent changes in size, distance, and time as observed by an observer in relative motion.
It's important to note that these effects are only significant at speeds approaching the speed of light, and in everyday life, their impact is negligible. However, they become crucial to consider when dealing with high-speed objects or situations involving extreme velocities or strong gravitational fields.