In special relativity, time dilation refers to the phenomenon where the passage of time for a moving object, as observed by an observer in a different frame of reference, appears to run slower compared to the time experienced by a stationary object in its own frame of reference. This effect arises due to the constancy of the speed of light in all inertial frames.
The physical implications of time dilation are profound. They challenge our intuitive understanding of time as an absolute and universal quantity. Some key implications are:
Relative Nature of Time: Special relativity asserts that time is not absolute but is dependent on the observer's motion and frame of reference. Different observers moving at different velocities will measure time differently.
Time Asymmetry: Time dilation introduces an asymmetry between moving and stationary objects. An object in motion experiences time dilation, causing its internal processes to appear slower from the perspective of a stationary observer. This effect is reciprocal, meaning both observers see time dilation in each other's frame.
Limit on Velocity: Time dilation becomes significant as an object approaches speeds close to the speed of light. This implies that no object with mass can reach or exceed the speed of light because, as an object approaches that speed, time dilation would become infinite, which is not physically meaningful.
Regarding the incorrect notion of clocks running slower when moving fast (Galilean invariance), it stems from classical or Galilean relativity, which was the prevailing understanding of motion before the advent of special relativity. According to Galilean relativity, time was considered absolute and independent of an observer's motion.
However, special relativity showed that the Galilean notion of time is inadequate when considering the behavior of light and the consistent laws of physics across different inertial frames. In special relativity, the constancy of the speed of light requires adjustments to the concept of time, leading to time dilation.
In contrast to Galilean relativity, special relativity accounts for the relative motion of objects and the effects it has on the measurement of time. It demonstrates that time dilation is a real and observable phenomenon, backed by experimental evidence such as muon decay experiments and precision timekeeping in fast-moving systems like GPS satellites.
Therefore, in the context of special relativity, it is incorrect to say that clocks run slower when moving fast from an absolute perspective. Instead, it is more accurate to state that clocks appear to run slower when observed from a relatively stationary frame of reference compared to a moving frame.