The amount of time dilation a human can experience depends on the relative velocities involved and the duration of the journey. However, for any realistic velocities achievable by humans with current technology, the time dilation effects would be extremely small and negligible.
To give you an idea, let's consider an example. Suppose we have a spacecraft traveling at a constant velocity of 90% of the speed of light (0.9c) relative to an observer on Earth. According to the theory of relativity, time dilation occurs as the relative velocity increases.
The time dilation factor, also known as the Lorentz factor, can be calculated using the formula:
γ = 1 / √(1 - (v^2 / c^2))
where v is the velocity of the spacecraft and c is the speed of light.
For our example with v = 0.9c, the Lorentz factor would be:
γ = 1 / √(1 - (0.9^2 / 1^2)) ≈ 2.294
This means that for every second experienced by the traveler on the spacecraft, approximately 2.294 seconds would pass for an observer on Earth. So, in a year of subjective time for the traveler, about 2.294 years would pass on Earth.
However, it's important to note that achieving velocities close to the speed of light is currently beyond our technological capabilities. Even if we could reach such velocities, the practical challenges, energy requirements, and physical limitations on humans would make it extremely difficult to realize significant time dilation effects.
In our everyday experiences and within the context of current technology, the time dilation effects we would encounter are negligible and would not have a significant impact on our lives.