General Relativity Experiments
Classical Mechanics
Level
2
Which of the following experimental signals of general relativity has not been observed as of early 2016?
Gravitational lensing of light
Gravitational time dilation
B-mode polarization in the CMB
Gravitational waves
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1 solution
Gravitational lensing was one of the first observed signals of GR, by Eddington's 1919 expedition.
Gravitational time dilation was tested in the Hafele-Keating experiment, where atomic clocks were flown around the world repeatedly. Its effects are also visible in GPS calibration.
A gravitational wave signal was observed for the first time by the LIGO collaboration in late 2015.
The only remaining answer is B-mode polarization in the CMB. This was reported to have been observed by the BICEP2 collaboration in 2015, but the report was later revised that summer to note that the apparent signal was due to interstellar dust, not primordial gravitational waves. As of early 2016 these are as yet unobserved.