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What's the best way to explain why tidal forces for an observer free-falling through an event horizon are finite?
My first thought was to say that "gravity isn't a force, it's a curved space-time". On further thought, however, it seems to me that consideration of the Rindler horizon shows that the essential features of the issue don't really require curvature to resolve, and that it wouldn't really be a good idea to claim otherwise.
My best take on using the Rindler horizon approach so far is to consider a rigid rod, with absolutely no forces on it of any kind, it's just floating in free space.
Then we switch to an accelerating frame (the Rindler frame), and consider what happens to said rigid rod. It still has no forces on it, even when it passes through the Rindler horizon. It may not even "know" that it passed through the horizon, as the horizon is a property of the accelerating observer, and there could be several different observers with different horizon. As far as the rod is concerned, though, it's happily floating in empty space and doesn't care at all that someone else thinks it is at, near, passing through, or already past a horizon.
Perhaps we can mention a few other things at the same time about how things appear in the Rindler frame, such as the Rindler frame assigning an infinite time coordinate to the rod's penetration, and the Rindler frames notion of "gravity", i.e. the proper acceleration required to hold oneself stationary in the Rindler frame, increasing towards infinity as one approaches the horizon.
This is the best approach I can think of, but I suspect it's still too advanced if one is not already familiar with the ins and outs of the Rindler horizon :(.
This was inspired by a recent thread, I thought my question was sufficiently different in focus, narrowness, and tone that I'd start a new thread rather than derail the existing one.
My first thought was to say that "gravity isn't a force, it's a curved space-time". On further thought, however, it seems to me that consideration of the Rindler horizon shows that the essential features of the issue don't really require curvature to resolve, and that it wouldn't really be a good idea to claim otherwise.
My best take on using the Rindler horizon approach so far is to consider a rigid rod, with absolutely no forces on it of any kind, it's just floating in free space.
Then we switch to an accelerating frame (the Rindler frame), and consider what happens to said rigid rod. It still has no forces on it, even when it passes through the Rindler horizon. It may not even "know" that it passed through the horizon, as the horizon is a property of the accelerating observer, and there could be several different observers with different horizon. As far as the rod is concerned, though, it's happily floating in empty space and doesn't care at all that someone else thinks it is at, near, passing through, or already past a horizon.
Perhaps we can mention a few other things at the same time about how things appear in the Rindler frame, such as the Rindler frame assigning an infinite time coordinate to the rod's penetration, and the Rindler frames notion of "gravity", i.e. the proper acceleration required to hold oneself stationary in the Rindler frame, increasing towards infinity as one approaches the horizon.
This is the best approach I can think of, but I suspect it's still too advanced if one is not already familiar with the ins and outs of the Rindler horizon :(.
This was inspired by a recent thread, I thought my question was sufficiently different in focus, narrowness, and tone that I'd start a new thread rather than derail the existing one.