Scientists continue to debate faster-than-light speeds, and to search for the subatomic particles known as Tachyons. These particles would theoretically travel faster than light in air, water, space, or any other medium, and would have real energy but imaginary mass (based on the square root of -1). Their existence is controversial, though, and as far as I know, they haven’t yet been detected.
Still super-C travel remains intriguing. A simple space-time diagram can be used to see that an object traveling faster than the speed of light toward an observer would appear to them to move in the opposite direction from its true flight…and to grow younger as it streaks “away.” That’s because the object is closing in on the observer faster than the “light” that leaves it at every instant…the same light that tells our instruments where the object “is” along its flight. And that would mess up the relationship between when the object actually arrives at our destination and when we (or our instruments) think it arrives. This poses all kinds of problems for our ideas about cause and effect…and might (if only in a sci-fi novel) permit observers in the past to learn about future events.
Physicists would like to catch Tachyons among the high-energy particles that strike Earth every day. But this too presents difficulties…because any Tachyons moving toward our detectors would reach them before the “normal” particles that resulted from their collisions with our atmosphere. We’d only see these normal “secondary” particles after the Tachyons had come and gone. And again, if we were able to actually see the Tachyons’ approach, they’d appear to grow younger as they flew FROM our detectors toward space in one direction…and then after they passed our detectors, would appear to grow older as they continued to fly away from our detectors toward space in the opposite direction. You might say that they’d exhibit a kind of “Time Doppler Shift”…where they’d appear to grow younger as they approach…and then older after they pass.
I remember reading a long time ago that Relativity doesn’t actually disallow super-C speeds. It just forbids objects that normally travel slower than C from accelerating to light speed…and those that “normally” travel faster than light from slowing down to C. It would take an infinite amount of energy to force either object to reach C. And Tachyons (if they exist) would come from a realm “beyond the relativistic light-cone,” where things can only travel faster than light.
