The phenomenon you are referring to is known as time dilation, which is a fundamental concept in the theory of relativity. It may seem counterintuitive at first, but time dilation is a well-established and experimentally verified aspect of our understanding of physics.
In the scenario you described, where a photon clock on a train ticks faster for a passenger compared to a stationary observer, it's essential to consider the relative motion between the observer and the moving clock. According to the theory of special relativity, time dilation occurs when two observers are moving relative to each other at significant speeds.
When an observer is in motion relative to another observer, they will perceive time to be passing differently. Specifically, the moving observer will perceive time to be passing more slowly compared to the stationary observer. This effect becomes more pronounced as the relative velocity between the observers increases.
In the case of the photon clock on a train, the observer inside the train (the passenger) is moving along with the clock, while the stationary observer is outside the train. Due to their relative motion, the passenger experiences time passing slower (clock ticking faster) compared to the stationary observer.
It's important to note that time dilation is a relative effect. Each observer will observe the other's clock to be ticking slower from their own perspective. The key insight is that the experience of time is relative to the observer's frame of reference and their relative motion.
So, in summary, time dilation is a phenomenon where time appears to slow down or speed up depending on the relative motion between observers. It is not time itself that is changing but rather the perception of time from different frames of reference.