4 ms·
> For instance, we already understand tidal forces - that bodies can become tidally locked, that there is an inertial frame shear that drags bodies along around
by kmm 10y ago
> For instance, we already understand tidal forces - that bodies can become tidally locked, that there is an inertial frame shear that drags bodies along around a rotating centre of mass, and exchanges energy between an orbiting body and the centre.... So why is it infeasible that galaxies are tidally locked, and the lack of fall-off in radial velocity is down to the gravitational shear from the galactic core being far more intense than we anticipate, causing the behaviour we see. It doesn't require a rewrite of relativity, "just" of galactic evolution.
Because someone has indubitably already ran the numbers. The tidal force only has a non central, orbit changing influence on spatially extended bodies, and its effects even on objects as large as our solar system are completely negligible, as it doesn't seem to have a measurable effect on the orbits of the planets. The rotation curves are way off, which is a huge chunk of excess angular momentum that no tidal force can conjure. Where would it even come from, the rotational angular momentum of component stars?
- madaxe_again 10y agoYou're aware that mercury is tidally locked, as is our moon, mars' moons, and others? I would call those real, physical effects, not negligible. As to running the numbers - agreed - but one can get an answer which is correct but incorrect if your premises are incorrect. At a galactic scale the perturbations are likely tiny, but a tiny force applied over enough time adds up. Anyway. It's a poor example that's almost certainly wrong but my point was more about how a single incorrect assumption can wreck a model.