SkipCaptcha, Automoderated users, edit
3,266
edits
Changes
Jump to navigation
Jump to search
mLine 223:
Line 223: + + Line 236:
Line 238: − + + + − +
→Experimental and Observational Evidence Confirming Relativity
#''The laws of physics are identical in all reference frames.''
#''The laws of physics are identical in all reference frames.''
(The second is just a restatement of Galilean relativity, that is, the "common sense" that had been accepted for centuries.)
(The second is just a restatement of Galilean relativity, that is, the "common sense" that had been accepted for centuries.)
A naive "common sense" interpretation of Galilean relativity would require that measurements of the speed of light (or anything else) by different observers would get results that differ by the observers' relative speeds, and hence that principle #1 can't be true. Special relativity fixes this apparent paradox.
All of special relativity derives for these two principles, plus assumptions of exact conservation of momentum and energy in all cases.
All of special relativity derives for these two principles, plus assumptions of exact conservation of momentum and energy in all cases.
*Another is ''gravitational time dilation''. This is an effect separate from the time dilation of special relativity. It was tested by the Pound-Rebka experiment in 1959.
*Another is ''gravitational time dilation''. This is an effect separate from the time dilation of special relativity. It was tested by the Pound-Rebka experiment in 1959.
*Later in the 20th 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, if assumptions are made, could make the energy loss appear consistent with the predicted radiation. Those observations have not been followed up with more recent, precise data, raising questions about whether the pulsar data is consistent with the theory today.
*Later in the 20th century, even more subtle phenomena were tested. One was the phenomenon of ''gravitational radiation'', or "gravitational waves". These waves are incredibly difficult to observe, and had never been observed until 2015. 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, if assumptions are made<ref>Similar to the way Kepler chose orbital parameters to fit observed planetary motion to his theory</ref>, could make the energy loss appear consistent with the predicted radiation. The rotating pulsars have moved such that Earth is now out of the beams, so those observations have been discontinued.
*In late 2015 (and announced in 2016), the LIGO instruments directly detected gravitational waves. See [[Gravitational waves]].
An additional test of general relativity was performed with radio signals to the Cassini spacecraft.<ref>http://www.nature.com/nature/journal/v425/n6956/full/nature01997.html</ref>
*An additional test of general relativity was performed with radio signals to the Cassini spacecraft.<ref>http://www.nature.com/nature/journal/v425/n6956/full/nature01997.html</ref>
*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 21st 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.
*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 21st 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.