3 ms·

You’re moving in the time direction — and when spacetime is curved, you end up moving in the space direction as well, to follow the geodesic.

AlexandrB 2y ago
Not arguing for or against this explanation, but it's hard enough (impossible for me) to visualize a curved 3d space, once you try to think of what curved 4d space might be like any intuitive sense of what should happen goes out the window. Classic diagrams of curved spacetime portray space as a 2d sheet with divots in it. I wonder what a similar visualization of curved 1d time + 1d space would look like. Long valleys for gravitational wells and everything moving along the sheet in the direction of positive time?
ars 2y ago
> and when spacetime is curved, you end up moving You did the same as everyone else: You hard waved right past "end up moving". Why do I end up moving instead of just sitting there? And if I "end up moving" that means I exchange momentum, if it's just bent space that magically makes me move, what did I exchange momentum with, if not via a force toward another particle? Gravity is a force that acts on energy. If you disagree please give me a counter example.
- Filligree 2y ago
  You do just sit there. In the GR-realism view, the only thing particles _ever_ do is self-propagate forwards in time. The problem is, this means the particle’s definition of “time”. Spacetime is 4D, and this can be any timelike direction. That’s what causes it to appear to move, from the perspective of someone whose time vector is pointed differently. Then time can be curved, which reorients said vector as the particle propagates through it. That’s gravity.
jumping_frog 2y ago
The river model of general relativity. https://www.youtube.com/watch?v=hFlzQvAyH7g&list=PL__fY7tXwodn7_NGVJxnX1joL_eQJCR-4&index=3 https://www.youtube.com/watch?v=hFlzQvAyH7g&list=PL__fY7tXwo...

AlexandrB 2y ago

Not arguing for or against this explanation, but it's hard enough (impossible for me) to visualize a curved 3d space, once you try to think of what curved 4d space might be like any intuitive sense of what should happen goes out the window. Classic diagrams of curved spacetime portray space as a 2d sheet with divots in it. I wonder what a similar visualization of curved 1d time + 1d space would look like. Long valleys for gravitational wells and everything moving along the sheet in the direction of positive time?

ars 2y ago

> and when spacetime is curved, you end up moving You did the same as everyone else: You hard waved right past "end up moving". Why do I end up moving instead of just sitting there? And if I "end up moving" that means I exchange momentum, if it's just bent space that magically makes me move, what did I exchange momentum with, if not via a force toward another particle? Gravity is a force that acts on energy. If you disagree please give me a counter example.

Filligree 2y ago
You do just sit there. In the GR-realism view, the only thing particles _ever_ do is self-propagate forwards in time. The problem is, this means the particle’s definition of “time”. Spacetime is 4D, and this can be any timelike direction. That’s what causes it to appear to move, from the perspective of someone whose time vector is pointed differently. Then time can be curved, which reorients said vector as the particle propagates through it. That’s gravity.

jumping_frog 2y ago

The river model of general relativity. https://www.youtube.com/watch?v=hFlzQvAyH7g&list=PL__fY7tXwodn7_NGVJxnX1joL_eQJCR-4&index=3 https://www.youtube.com/watch?v=hFlzQvAyH7g&list=PL__fY7tXwo...