In a weak field, the electric terms correspond to Newtonian gravitation. The new magnetic terms will come into evidence when both source and test body are in relative motion. The magnetic interaction between the spinning Earth and a spinning gyro is measurable and is the basis of a new test of general relativity to be attempted in the space program within the next 10 years. Magnetic gravitation is expected to be a large effect in the field of a spinning black hole. It may play a role in astrophysical phenomena, in particular in the explanation of the jets in extragalactic double radio sources.
Gravitational radiation is predicted in all relativistic theories of gravitation.
The sources of the radiation are accelerating masses. The direct detection of the radiation could serve to test general relativity by confirming the propagation speed and polarization states of the waves. Gravitational wave astronomy could well open a new view of the universe as it will expose phenomena that involve the.coherent motions of large masses at relativistic speeds. A particularly exciting although highly speculative prospect is the possible detection of gravitation radiation noise from the very earliest epoch of the universe that is completely obscured in the electromagnetic and even neutrino astronomies. The first observational evidence for relativistic gravitation was the small discrepancy in the orbital motion of the planet Mercury discovered in the nineteenth century.