According to our current understanding of physics, it is highly unlikely that someone could reach the other side of the universe, even if they were able to travel at close to the speed of light for millions of years. There are several reasons for this:
The Observable Universe: The observable universe is the portion of the universe from which light has had enough time to reach us since the Big Bang. It is estimated to have a radius of about 46 billion light-years. This means that even if someone traveled at the speed of light, they could only reach a maximum distance of 46 billion light-years from their starting point. The size of the entire universe beyond the observable universe is still unknown, and it could be much larger. So, reaching the "other side" of the universe is currently beyond our reach.
Expansion of the Universe: The universe is expanding, and the rate of expansion is increasing. As a result, distant galaxies are moving away from us at speeds greater than the speed of light. This phenomenon is known as the cosmic expansion or the metric expansion of space. It means that even if someone could travel at the speed of light, they would not be able to catch up with galaxies that are receding faster than the speed of light.
Time Dilation: As an object approaches the speed of light, time dilation occurs, which means that time passes more slowly for the moving object relative to a stationary observer. However, this time dilation effect would not allow someone to travel millions of years into the future or reach distant parts of the universe. It would only affect their own experience of time, not enable them to travel across vast cosmic distances.
Energy Requirements: Approaching the speed of light requires enormous amounts of energy. As an object accelerates, its mass increases, and it would require an infinite amount of energy to reach the exact speed of light. Even if we ignore the practical challenges of obtaining such energy, it would still be insufficient to overcome the vast distances and cosmic expansion to reach the other side of the universe.
It's important to note that our understanding of the universe is continually evolving, and future discoveries could reshape our understanding of these concepts. However, based on our current knowledge, traveling to the other side of the universe, even at speeds close to the speed of light, is highly improbable.