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Later in the 20^th century, even more subtle phenomena were tested.  One was the phenomenon of ''gravitational radiation'', or "gravity waves".  These waves are incredibly difficult to observe, and have never been observed.  But extremely dense binary pulsars radiate gravitational waves with sufficient energy loss that, even though we can't detect the waves from Earth, we can see the effect of the energy loss from the radiation.  The extreme precision of the timing of pulses from pulsars makes it possible to observe their energy loss with great accuracy.  Observations by Hulse and Taylor of the pulsar pair known as B1913+16 confirmed the energy loss consistent with the predicted radiation.

Later in the 20^th century, even more subtle phenomena were tested.  One was the phenomenon of ''gravitational radiation'', or "gravity waves".  These waves are incredibly difficult to observe, and have never been observed.  But extremely dense binary pulsars radiate gravitational waves with sufficient energy loss that, even though we can't detect the waves from Earth, we can see the effect of the energy loss from the radiation.  The extreme precision of the timing of pulses from pulsars makes it possible to observe their energy loss with great accuracy.  Observations by Hulse and Taylor of the pulsar pair known as B1913+16 confirmed the energy loss consistent with the predicted radiation.

Two other effects, ''geodetic precession'' (also known as "de Sitter precession"), and ''frame dragging'' (also known as the "Lense-Thirring effect") were tested by the "Gravity Probe B" satellite early in the 21^st century<ref>http://www.digitaljournal.com/article/306430</ref><ref>http://www.nap.edu/html/gpb/summary.html</ref><ref>http://www.sciencenews.org/view/generic/id/73870/title/Gravity_Probe_B_finally_pays_off_</ref><ref>http://www.nasa.gov/mission_pages/gpb/</ref><ref>http://einstein.stanford.edu/</ref><ref>http://spectrum.ieee.org/aerospace/space-flight/the-gravity-probe-b-bailout</ref><ref>http://www.engadget.com/2011/05/06/nasa-concludes-gravity-probe-b-space-time-experiment-proves-e/</ref>.  The precision required to observe this was phenomenal.  The results were announced on May 4, 2011.

Two other effects, ''geodetic precession'' (also known as "de Sitter precession"), and ''frame dragging'' (also known as the "Lense-Thirring effect") were tested by the "Gravity Probe B" satellite early in the 21^st century<ref>http://prl.aps.org/accepted/L/ea070Y8dQ491d22a28828c95f660a57ac82e7d8c0</ref><ref>http://www.digitaljournal.com/article/306430</ref><ref>http://www.nap.edu/html/gpb/summary.html</ref><ref>http://www.sciencenews.org/view/generic/id/73870/title/Gravity_Probe_B_finally_pays_off_</ref><ref>http://www.nasa.gov/mission_pages/gpb/</ref><ref>http://einstein.stanford.edu/</ref><ref>http://spectrum.ieee.org/aerospace/space-flight/the-gravity-probe-b-bailout</ref><ref>http://www.engadget.com/2011/05/06/nasa-concludes-gravity-probe-b-space-time-experiment-proves-e/</ref>.  The precision required to observe this was phenomenal.  The results were announced on May 4, 2011.

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