5. Tests of the "Twin Paradox"
Haefele and Keating, Nature 227 (1970), pg 270 (Proposal); Science Vol. 177 pg 166--170 (1972) (Experiment).
They flew atomic clocks on commercial airliners around the world in both directions, and compared the time elapsed on the airborne clocks with the time elapsed on an earthbound clock (USNO). Their eastbound clock lost 59 ns on the USNO clock; their westbound clock gained 273 ns; these agree with GR predictions to well within their experimental resolution and uncertainties (which total about 25 ns).
Vessot et al, "A Test of the Equivalence Principle Using a Space-borne Clock", Gel. Rel. Grav., 10, (1979) 181-204; "Test of Relativistic Gravitation with a Space borne Hydrogen Maser", Phys. Rev. Lett. 45 2081-2084.
They flew a hydrogen maser in a Scout rocket up into space and back (not recovered). Gravitational effects are important, as are the velocity effects of SR.
C. Alley, "Proper Time Experiments in Gravitational Fields with Atomic Clocks, Aircraft, and Laser Light Pulses," in Quantum Optics, Experimental Gravity, and Measurement Theory, eds. Pierre Meystre and Marlan O. Scully, Proceedings Conf. Bad Windsheim 1981, 1983 Plenum Press New York, ISBN 0-306-41354-X, p363-427.
They flew atomic clocks in airplanes which remained localized over Chesapeake Bay, and also which flew to Greenland and back.
Bailey et al., "Measurements of relativistic time dilatation for positive and negative muons in a circular orbit," Nature 268 (July 28, 1977) pg 301;
Nuclear Physics B 150 pg 1-79 (1979).
They stored muons in a storage ring and measured their lifetime. When combined with measurements of the muon lifetime at rest this becomes a highly-relativistic twin scenario (v ~ 0.9994 c), for which the stored muons are the traveling twin and return to a given point in the lab every few microseconds. Muon lifetime at rest:Meyer et al., Physical Review 132, pg 2693; Balandin et al. JETP 40, pg 811 (1974); Bardin et al. Physics Letters 137B, pg 135 (1984). Also a test of the clock hypotheses (below).