According to our current understanding of physics, it is not possible for an object with mass to travel at the speed of light. As an object with mass accelerates towards the speed of light, its energy and momentum increase, approaching infinity as it gets closer to the speed of light. This would require an infinite amount of energy, which is not achievable.
However, let's consider a hypothetical scenario where you could travel at the speed of light and then come back. In this thought experiment, we encounter a paradox known as the "twin paradox."
Suppose you have a twin sibling and you embark on a journey in a spaceship that can travel at the speed of light. Your twin remains on Earth. As you approach the speed of light and travel away from Earth, time dilation effects would occur. Time dilation means that time appears to pass slower for the moving observer relative to a stationary observer.
From your perspective, time on Earth would appear to be passing much faster while you travel at the speed of light. If you were to turn back and return to Earth, you would find that your twin has aged significantly more than you. From your perspective, it might seem as though only a short time has passed, while your twin has aged considerably.
In this scenario, when you return, it would be your twin's future relative to your own experience. From your twin's perspective, you would be the one who has experienced time dilation, and it would be your past that they observe.
The twin paradox highlights the asymmetry of time dilation effects between the traveling twin and the stationary twin. It demonstrates the consequences of relativity and the fact that time is not absolute but depends on the relative motion between observers.
It's important to note that this scenario is purely hypothetical, as objects with mass cannot reach or exceed the speed of light. The twin paradox is a thought experiment that helps us understand the implications of relativity but does not reflect a practical possibility.