According to the theory of special relativity, as described by Albert Einstein, an object with mass cannot travel at the speed of light, and it would require an infinite amount of energy to accelerate an object with mass to the speed of light. Therefore, in reality, nothing with mass can reach or exceed the speed of light.
However, let's explore the concept theoretically to understand the implications of traveling at the speed of light or faster.
Speed of Light Limit: As an object with mass approaches the speed of light, its relativistic mass increases, and its length contracts in the direction of motion. This means that the energy required to accelerate it further also increases exponentially, making it impossible to reach or exceed the speed of light. Hence, an object with mass cannot travel at the speed of light.
Gravitational Pull: As long as an object has mass, it will experience the gravitational pull of other masses, such as the Earth. Even if an object could hypothetically travel at a significant fraction of the speed of light, it would still experience gravitational forces. These forces would not prevent the object from being affected by gravity.
Time Dilation: Time dilation is a fundamental consequence of special relativity. As an object approaches the speed of light, time for that object appears to slow down relative to a stationary observer. If you were to travel at a substantial fraction of the speed of light away from Earth and then return, you would age less compared to people who remained on Earth. This effect has been experimentally verified and is crucial for the functioning of GPS satellites, for example.
Time Travel and Light Speed: One of the most intriguing implications of time dilation is the concept of "twin paradox." It suggests that if one twin stays on Earth while the other twin travels at near-light speed and returns, the traveling twin will age less, effectively "time-traveling" into the future relative to the Earthbound twin. However, this is not time travel in the conventional sense where one can move freely backward and forward in time at will.
Time travel to the past, as commonly depicted in science fiction, faces significant challenges and paradoxes, such as the famous "grandfather paradox." If time travel to the past were possible, it could lead to logical contradictions, like going back in time and preventing one's own existence.
In summary, objects with mass cannot travel at or faster than the speed of light, but they will still experience gravitational forces. Time dilation, a consequence of special relativity, could allow for "time travel" into the future under certain conditions, but time travel to the past as portrayed in many sci-fi scenarios remains a topic of speculation and is subject to various theoretical challenges.