Einstein hypothesized that the similar experiences of weightless observers and inertial observers in special relativity represented a fundamental property of gravity, and he made this the cornerstone of his theory of general relativity, formalized in his equivalence principle.
This function determines the dynamics of the scalar (Phi), and only the property of gravity constrains its concrete form, as far as we do not assume any symmetry argument.
David Spergel, a theoretical astrophysicist at Princeton University, says the consistency between results from the two techniques "is a triumph for [Einstein's theory of] general relativity," which describes gravity as a property of the geometry of space and time.
The conceptual difficulties basically follow from the nature of the gravitational interaction, in particular the equivalence of gravitational and inertial mass, which allows one to represent gravity as a property of spacetime itself, rather than as a field propagating in a (passive) spacetime background.
Explaining these properties of gravity remains an active area of research in theoretical physics (Randall 2005).
I have not been able to discover the cause of those properties of gravity from phenomena, and I frame no hypotheses; for whatever is not deduced from the phenomena is to be called an hypothesis; and hypotheses, whether metaphysical or physical, whether of occult qualities or mechanical, have no place in experimental philosophy.
Newton is here appealing to the well-known property of terrestrial gravity that weight is compositional: the weight of a compound body is equal to the sum of the weights of its constituent parts.
General relativity generalizes special relativity and Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or spacetime.
The requirements imposed on the design of the lander are: (1) Provide a lightweight lander structure to minimize the launch costs and maximize the payload carrying capability, (2) Minimize the lander launch envelope to allow for launching multiple landers on a single launch vehicle, (3) Given specific approach velocities, design a lander with geometric properties (low center-of-gravity, etc).
AFTER years of dizzying ascents, a big dose of gravity has hit residential-property markets around the world.
