Traveling at the speed of light is not possible for any object with mass, according to our current understanding of physics. As an object with mass approaches the speed of light, its relativistic mass increases, requiring an infinite amount of energy to reach the speed of light itself. Therefore, according to Einstein's theory of special relativity, any object with mass cannot attain or exceed the speed of light in a vacuum.
However, we can still explore the concept of time dilation, which is a consequence of special relativity when objects approach relativistic speeds (i.e., speeds close to the speed of light). Time dilation states that time passes more slowly for objects in motion relative to an observer at rest.
Suppose you were to travel at a significant fraction of the speed of light (but not equal to it) and then return to Earth. In that case, you would experience time differently than your friends on Earth. From your perspective inside the spacecraft, time would appear to pass normally, just as it does for you on Earth.
However, from the perspective of your friends on Earth, who are at rest relative to the spacecraft, they would observe that time appears to be passing more slowly for you. This phenomenon is known as time dilation.
The formula for time dilation in special relativity is given by:
t' = t / √(1 - v^2/c^2),
where: t' is the time experienced by the moving observer (you in the spacecraft), t is the time experienced by the observer at rest (your friends on Earth), v is the velocity of the moving observer relative to the observer at rest (your velocity), c is the speed of light in a vacuum.
As you approach the speed of light (v → c), the denominator of the equation approaches zero, and time dilation becomes more significant. The faster you travel, the greater the time dilation effect.
So, if you were to travel at a significant fraction of the speed of light and then return to Earth, your friends on Earth would have aged more than you. The exact age difference would depend on your velocity during the journey, and it could potentially be significant for extremely high velocities close to the speed of light. However, it's essential to reiterate that achieving or exceeding the speed of light is currently considered impossible for objects with mass based on our current understanding of physics.