Q: If black holes have so much gravitational force that light cannot escape doesn't that mean faster than light is possible in reverse?
A: The fact that black holes trap light doesn't imply—or allow—a kind of "reverse" faster-than-light (FTL) travel. Instead, it reflects how gravity warps spacetime to funnel every possible path inward once you're inside the event horizon.
To elaborate, in general relativity the speed of light is a locally measured constant. This means that no matter where you are—even near a black hole—if you measure the speed of light in your immediate vicinity, you'll always get the same value, \(c\). What happens near a black hole is that the curvature of spacetime becomes so extreme that within the event horizon the very structure of the "future" (as defined by the light cones) points inward toward the singularity. In other words, any attempt to move away from the black hole—even by light—is doomed because the paths available in that warped spacetime do not lead outwards.
The term "escape velocity" is sometimes used to describe the speed needed to escape a gravitational field; for a black hole, this exceeds \(c\) at the event horizon. However, this doesn't mean something is physically accelerating to speeds greater than the speed of light. Rather, it's a coordinate-dependent way of describing how spacetime is curved. Locally, nothing ever exceeds the speed of light—the barrier is built into the geometry of spacetime itself.
So, while it might seem that if gravity can so powerfully trap even light then it might somehow allow "reverse" superluminal speeds, that isn't what's happening. Instead, the structure of spacetime near a black hole prevents any object from escaping once the event horizon is crossed, but it does so without violating the fundamental cosmic speed limit. Every observer, regardless of their position, will always measure the local speed of light as \(c\). This means there is no loophole allowing faster-than-light travel, whether "forward" or "in reverse."
Now that you've got a clearer picture of how spacetime curvature works around black holes, it raises additional interesting questions: How do gravitational time dilation and redshift affect observations of objects near event horizons? Or, how do physicists reconcile these extreme conditions with the otherwise smooth behavior of spacetime predicted by general relativity? These topics offer a fascinating glimpse into the deeper nature of our universe.
