3 ms·

This is about relativity. We're going straight in space-time, but space-time itself is curved because of the heavy mass nearby (the Earth). This is visualized b

This is about relativity. We're going straight in space-time, but space-time itself is curved because of the heavy mass nearby (the Earth). This is visualized by the rocket curving towards the planet in the video, and the bent sheet experiment where the balls spiral towards the center. So we're curving in towards the center of the mass of the Earth, but the reason we don't end up in the core of the Earth is because the surface stops us. The Earth is "pushing" us away from the center, and that's the acceleration. It's accelerating you off your straight line path, and this is the deviation from the geodesic.

strken 6y ago
I thought that the Earth curved spacetime, and since an inertial observer approaching the earth would follow a straight line through curved spacetime, they'd appear to be following a curved line through space towards the earth. What's confusing me here is the notion that when two objects collide, they accelerate into each other. Why and how is force constantly applied after the collision? My intuition is falling down here, and none of the resources I've looked at so far have explained why the acceleration happens.
- manigandham 6y ago
  1st sentence is correct and is the same as what I said, sorry if I wasn't clear. Remember that spacetime = space + time dimensions. The object is always travelling through time, and the curvature of spacetime is converting some of that speed through time into speed through space. That's what you perceive as motion (caused by gravity). Time and space are linked together. The faster you go through space, the "slower" you go through time (as in you experience it slower). This is very measurable and even used to alter timings for satellites GPS readings. You can take an atomic clock on a plane and age slower than someone who just stayed on the ground. So the spacetime curvature is continuously converting some of your temporal motion into spatial motion, until that's stopped by the surface of the Earth which is constantly "accelerating" to stop you from going further. As to why we always move through time, that's beyond my understanding at this point but it's a fundamental axiom of physics.
  - strken 6y ago
    Yeah, sorry, I was restating what I understood you had said, in case I'd misunderstood any part of it, and then explaining where I was lost. Your explanation makes sense, and it sounds like I'd need to understand the maths behind relativity to be able to really understand how objects behave in spacetime.

strken 6y ago

I thought that the Earth curved spacetime, and since an inertial observer approaching the earth would follow a straight line through curved spacetime, they'd appear to be following a curved line through space towards the earth. What's confusing me here is the notion that when two objects collide, they accelerate into each other. Why and how is force constantly applied after the collision? My intuition is falling down here, and none of the resources I've looked at so far have explained why the acceleration happens.

manigandham 6y ago
1st sentence is correct and is the same as what I said, sorry if I wasn't clear. Remember that spacetime = space + time dimensions. The object is always travelling through time, and the curvature of spacetime is converting some of that speed through time into speed through space. That's what you perceive as motion (caused by gravity). Time and space are linked together. The faster you go through space, the "slower" you go through time (as in you experience it slower). This is very measurable and even used to alter timings for satellites GPS readings. You can take an atomic clock on a plane and age slower than someone who just stayed on the ground. So the spacetime curvature is continuously converting some of your temporal motion into spatial motion, until that's stopped by the surface of the Earth which is constantly "accelerating" to stop you from going further. As to why we always move through time, that's beyond my understanding at this point but it's a fundamental axiom of physics.
- strken 6y ago
  Yeah, sorry, I was restating what I understood you had said, in case I'd misunderstood any part of it, and then explaining where I was lost. Your explanation makes sense, and it sounds like I'd need to understand the maths behind relativity to be able to really understand how objects behave in spacetime.