Re:Gravitational waves provide dose of reality about extra d...
by Sharlin on Monday September 17, 2018 @11:45AM
(#18006982)
Remember that Newtonian concepts of gravity such as the equation g = Gm1m2/r^2 are only strictly valid within the Newtonian framework which, among other things, does assume that the effect of gravity is instantaneous. To derive accurate equations of motion under finite propagation speed of gravity, you need the machinery of general relativity. Of course, in mundane situations like the Earth-Sun system the two models give nigh identical results.
[ Parent
| on HN ]
Re:Gravitational waves provide dose of reality about extra d...
by BurnGpuBurn on Tuesday September 18, 2018 @03:29AM
(#18013257)
Thank you for your answer. True, Newton basically uses "instant gravity", and his equations really do work. I don't know enough about general relativity I must say, I've just never been able to really get it.
Re:Gravitational waves provide dose of reality about extra d...
by Sharlin on Tuesday September 18, 2018 @08:55AM
(#18014828)
His equations work in the limit of slow speeds and low masses; GR keeps giving valid predictions in cases Newtonian mechanics breaks down. Famously, Newton cannot explain the slight observed precession of Mercury’s orbit which is something GR predicts precisely. But the effect is tiny and in almost all cases you don’t need a full relativistic treatment to predict the motions of Solar System bodies sufficiently accurately.
One quite mundane situation where one does need GR is compensating for the clock drift of GPS satellites caused by their height and speed relative to a ground-based observer (time is relative, not absolute as Newton thought!) Because positioning critically relies on very precise clocks, a non-adjusted satellite positioning system would very quickly start giving completely inaccurate results.