General relativity shows how curved spacetime affects the motion of objects in the neighborhood of a large mass such as a planet or a star. Planetary orbits are described as the path of a planet moving in a straight line on a curved surface.
I have had no problem comprehending how curved spacetime would cause a moving object to move in a circular orbit without the application of an arbitrary force, but I’ve always had trouble understanding why a stationary object would move under the influence of gravity. It is not taking a straight line path anywhere regardless of the spacetime curvature it lies in. Why do we experience gravitational force if we are not on an inertial path? The answer I’ve been given is in that case, the object falls down the gravitational well–to which I respond, that’s no answer, you are using gravity to explain gravity! A more rigorous answer will show a path that seeks the lowest energy using something like a Lagrangian equation solution. But I still ask, why would potential energy be higher the further you move away from the gravitational well? It’s still using gravity to explain gravity.
In the last few posts, I have postulated the existence of an Activation Layer, a 3 dimensional slice of 4 dimensional spacetime. This activation layer shows why we only observe objects and interactions at one point in time at any point in time. I worked out some basic principles and properties of this activation layer, and then demonstrated the resulting futility of doing time travel. I showed that the activation layer would have to curve along with spacetime near large masses such as a planet or star, and that the activation layer has to continuously move forward in the time dimension, even if that dimension has been curved due to nearby masses.
I found that the activation layer provides an elegant solution to the gravity problem I describe above. I suddenly realized that even if an object is perfectly still, it will still be residing in the activation layer, which is constantly moving forward along the time dimension. There’s the path we needed! Look at the diagram to see how the activation layer will always tilt toward the gravitational well no matter where the object is. Since the activation layer is always moving forward in time, the tilt of this motion will always take the path of the object forward toward the gravitational well. Even with no initial motion in 3D space, the object will experience a force in that direction. (It’s important not to get confused by the apparent time direction of the activation layer out of the gravitational well–this is an artifact of drawing a 4D image on a 2D surface).
What’s so neat about this is how the activation layer concept shows why gravitational forces emerge from nothing more than curved space time plus the basic axiom that the activation layer always moves forward along the time dimension, even if that time dimension is curved.
Agemoz
Tags: general-relativity, gravity, physics, special-relativity
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