The distance to cosmic objects like stars, galaxies, and quasars is often measured in light-years. This is because all forms of matter, no matter how much energy they have, can only approach but never reach the speed of light. Even massless entities like photons, gluons, and gravitational waves are the only ones that can achieve this maximum speed through space, while everything else is bound to travel more slowly, never reaching that speed while obeying the laws of physics.
The question is whether advanced alien species will always be unable to travel through space in a faster fashion, due to the cosmic speed limit. Despite the conservative expectation that the speed of light is an insurmountable limit, there are reasons to believe that there may be a way around it. One of these reasons is conventional motion, as described by special relativity. This theory states that motion, times, and distances are relative between observers, and the speed of light is an absolute constant.
According to these rules, if you were traveling at a constantly accelerated rate toward a distant astronomical object, you would find that you could never quite reach the speed of light but only approach it from below. Your experience of time and distance would be observed to change significantly during such a journey due to length contraction and time dilation.
Another possibility is the existence of particles with imaginary mass, known as tachyons, where the more energy you put into a tachyon, the closer it gets to the speed of light from above. While tachyons have not been proven to exist, their existence would enable faster-than-light travel.
In general relativity, the very fabric of spacetime is distorted by the distribution of matter and energy throughout space, leading to the possibility of wormholes or Einstein-Rosen bridges, allowing for shortcuts through space. Another mechanism is the creation of a warp drive using negative energy to distort space in a way that allows faster-than-light travel.
Finally, the possibility of closed time-like loops in general relativity could allow for journeys through space and time that surpass the limitations imposed by the speed of light. While these ideas may currently seem like science fiction, the future may hold new discoveries that overturn our current understanding of the universe and allow for faster-than-light travel.
