The time it takes to travel a distance of 4.2 light years depends on the speed at which you are traveling. Since the speed of light is the fastest known speed in the universe, it serves as an upper limit for how fast information or objects can travel.
If we consider traveling at the speed of light, it would take approximately 4.2 years to travel a distance of 4.2 light years. This is because light itself takes 4.2 years to traverse that distance.
However, it's important to note that currently, we do not have the technology or means to achieve speeds anywhere near the speed of light. As of now, our fastest spacecraft and probes can only achieve a fraction of a percent of the speed of light. So, in practical terms, it would take significantly longer than 4.2 years to travel that distance using existing technology.
It's also worth mentioning that as an observer traveling close to the speed of light, time dilation would occur due to the effects of special relativity. This means that from your perspective as the traveler, the subjective experience of time would be different compared to an observer at rest. However, from an external perspective, 4.2 years would pass for observers on Earth while you are traveling the distance of 4.2 light years.