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If the outer spaceship B speeds up it will move out, but moving out puts it into a slower orbit. If spaceship B wants to speed up, it must first slow down, which will drop it into a smaller orbit, which is faster.

A body in orbit is travelling along a straight line in curved space sophie. I don't think potential energy due to gravity comes into it - that is, it doesn't have any potential energy until it's stopped. And the energy needed to stop it then becomes...

Isn't this similar to the situation on Mars where the spring is replaced by gravity?

GR isn't hard stuff - not even thinking of gravitational 'force' as time gradients - GR is one of the most simple and elegant things ever conceived.

The Newtonian concept of gravitation was an immense achievement and serves as a good approximation, as does the concept that atoms are indivisible, which I believe is still taught to young children.GR isn't hard stuff - not even thinking of gravitational 'force' as time gradients - GR is one of the most simple and elegant things ever conceived.

What would be the point of me giving you a demo? What would that achieve?

lightarrow: Time, space (spacetime) and energy appear to be fundimentals whichever model you use.

sophiecentaur: I took a graduate seminar on GR a few years back, and we did derive the elliptical orbits from GR. The way we did it was to show that in the small-mass, large-distance limit, GR reduces to Newton's equations, and you can solve it from there. [] GR ends up not having simple, closed-form solutions in most cases.

The way we did it was to show that in the small-mass, large-distance limit, GR reduces to Newton's equations, and you can solve it from there.

Quote from: jpetruccelli on 21/06/2008 23:03:21The way we did it was to show that in the small-mass, large-distance limit, GR reduces to Newton's equations, and you can solve it from there. Even for light's deflection near the mass?

A lot of really frightening bouncing, jumping contortion, pogo stick madness. wink