Both faster-than-light (FTL) travel and time travel are currently speculative concepts that lie beyond our current understanding of physics. However, based on our current knowledge, it is generally considered that achieving FTL travel is more challenging than achieving time travel. Here's why:
FTL travel: According to our current understanding of physics, specifically Albert Einstein's theory of relativity, the speed of light (denoted as 'c') is an absolute cosmic speed limit. Objects with mass cannot reach or exceed the speed of light without violating the known laws of physics. As an object approaches the speed of light, its relativistic mass increases, requiring an infinite amount of energy to reach the speed of light itself. This makes it incredibly challenging to conceive of a mechanism to achieve FTL travel while remaining consistent with our current understanding of physics.
Time travel: The concept of time travel involves the ability to move backward or forward in time, which is still purely speculative and subject to scientific investigation. While time travel also poses significant challenges, there are theoretical frameworks within physics that allow for the possibility of time travel under certain conditions. For instance, some solutions of Einstein's field equations in general relativity, such as rotating black holes or the theoretical concept of wormholes, have been explored as potential avenues for time travel. However, significant technological and theoretical hurdles remain to be overcome to make time travel a reality.
It's important to note that both FTL travel and time travel are still subjects of active scientific research, and our understanding may evolve over time. Currently, they are primarily explored in the realms of science fiction and speculative physics. Achieving either of these concepts would likely require breakthroughs that revolutionize our understanding of fundamental physics and energy sources beyond our current capabilities.