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Originally Posted by xelasnave
Yes I understand this...... a pythagoras therom with a "fourth" ..side or arm... time....which time "changes" as space bends from an influence of local mass...
What I do not grasp is why mass needs to seek a "straight" path which is in point a line of the least resistence (of space) conecting to the most local "bent" space.... or what is it that tells the Sun to follow its "straight" line to where ever it seems to be headed...
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Hi Alex,
It is important to understand that in GR space and time do not have an independant existance. It is the "spacetime" that is warped by the presence of matter/energy as per the Einstein equation.
What one observer perceives at space, another in a different frame of reference may perceive as time. It is only be considering the spacetime (often written space-time but never space/time - they are not separate in any physically meaningful way) that the physical nature of the situation can be understood.
The notion of time being a "fourth" side or arm is Netwonian theory. I cannot stress enough that it is not the "space" that is warped by matter/energy in GR: it is the "spacetime".
In this way a body in an inertial reference frame (in free-fall like the Earth in orbit around the Sun) moves in a straight path through the spacetime which from the frame of reference of the Sun appears to be an ellipitical path though the space over time (to a good approximation anyway).
I seem to recall first reading something like the "push" concept of gravity in Richard Feynmann's little book "The Character of Physical Law" as effort to show the reader a possible physical explanation of Newtonian gravitation. As I recall, it was a concept he held up as a straw man in order to shoot it down. Unfortuantely I cannot find an online copy of this great little book
Take care,
Doug