Both faster-than-light (FTL) travel and time travel are highly speculative concepts that go beyond our current understanding of physics. However, based on our current scientific knowledge, FTL travel is considered to be more difficult to achieve than time travel.
According to the theory of relativity, as formulated by Albert Einstein, the speed of light in a vacuum (approximately 299,792,458 meters per second) is an absolute speed limit. This means that no object with mass can accelerate to or exceed the speed of light. The theory of relativity has been extensively tested and confirmed through experiments, and it is a fundamental framework in modern physics.
On the other hand, while time travel is also a challenging concept, it is not explicitly forbidden by the laws of physics. Time dilation, a phenomenon predicted by the theory of relativity, suggests that time can pass at different rates for objects in relative motion or under the influence of strong gravitational fields. This means that, in certain scenarios, it could be possible to experience time at a different rate compared to an external observer.
However, achieving practical time travel, especially to the past, remains purely speculative and involves numerous theoretical and technological hurdles. Concepts such as traversable wormholes, exotic matter with negative energy density, or cosmic strings have been proposed as potential mechanisms for time travel, but these ideas are purely hypothetical at this point.
In summary, while both FTL travel and time travel are currently beyond our technological capabilities, FTL travel is considered to be more challenging based on our current understanding of physics.