What is "time dilation" in the context of special relativity?

Time dilation is a concept from Einstein's theory of special relativity, which states that time measured in a moving reference frame will appear to pass more slowly compared to time measured in a stationary reference frame. This means that an observer in a stationary frame will perceive less time passing for a clock that is moving relative to them, compared to their own clock.

This effect becomes significant at speeds approaching the speed of light, illustrating that space and time are intertwined in such a way that the relative motion affects the passage of time itself. As a result, if two observers are moving relative to each other, each will measure time in the other's system as dilated, hence confirming a central tenet of relativity.

The other options do not accurately represent the principle of time dilation. For example, saying time passes more quickly in a moving reference frame contradicts the essential concept of time dilation. Similarly, claiming that time is the same in all reference frames ignores the effects of relative motion. Finally, stating that time cannot be measured in a moving reference frame misrepresents our ability to measure time; it can still be measured, but the measurements will differ depending on the relative velocity of the observers.