A time paradox, also known as a temporal paradox, refers to a situation in which the normal flow of cause and effect is disrupted, leading to inconsistencies or contradictions in the timeline of events. Time paradoxes are often discussed in the context of time travel scenarios.
One common example of a time paradox is the grandfather paradox. Imagine a person travels back in time and kills their own grandfather before their parent is conceived. This would create a contradiction because if the person's grandfather was killed before their parent was born, then the person would not exist to travel back in time and carry out the act. This paradox raises questions about the possibility and consequences of changing the past.
Regarding your second question, if an object were to travel at or near the speed of light, it would experience certain effects described by the theory of special relativity, such as time dilation and length contraction. These effects arise from the fundamental postulate that the speed of light in a vacuum is constant for all observers.
Time dilation refers to the phenomenon where time appears to pass more slowly for a moving object relative to a stationary observer. As an object approaches the speed of light, time dilation becomes more pronounced. From the perspective of a traveler moving close to the speed of light, time would appear to pass more slowly compared to an observer at rest.
For example, if a hypothetical spacecraft were to travel near the speed of light and return to Earth, the travelers on board might experience only a few years passing, while a much longer time could have passed on Earth. This is often referred to as the "twin paradox," where one twin stays on Earth while the other twin travels at near light speed and returns younger than the stationary twin.
It's important to note that these effects are based on our current understanding of physics and have been experimentally verified to a high degree of accuracy. However, traveling at near light speed is currently beyond our technological capabilities, and we have not yet observed these effects directly with human travelers.