Changes

==Fallacious Claims of Experimental Verification of Relativity==

==Fallacious Claims of Experimental Verification of Relativity==

Generally speaking, the effects of relativity, that is, the differences in physical observations between a formulation under relativity and a purely classical formulation, are extremely tiny.  This is related to the extremely high speed of light, <math>3 \times 10^8 m/s</math> relative to ordinary phenomena observed by humans.  (However, it's worth noting that ordinary magnetism can be considered a relativistic effect, dictated by the need for electrostatic theory to be correct under relativity.  The speed of light in fact appears in the formulas ([[Maxwell's Equations]]) governing electricity and magnetism -- but these equations were developed long before relativity was proposed.)

Generally speaking, the effects of relativity, that is, the differences in physical observations between a formulation under relativity and a purely classical formulation, are extremely tiny.  This is related to the extremely high speed of light, <math>3 \times 10^8 m/s</math> relative to ordinary phenomena observed by humans.  (However, it's worth noting that ordinary magnetism can be considered a relativistic effect, dictated by the need for electrostatic theory to be correct under relativity.  The speed of light in fact appears in the formulas ([[Maxwell's Equations]]) governing electricity and magnetism, though these equations were developed long before relativity was proposed.)

Because the effects of relativity are so tiny, scientists have been devising sophisticated and sensitive tests ever since the theory was formulated in 1905.  In fact, at the end of Einstein's original 1905 paper [http://www.fourmilab.ch/etexts/einstein/E_mc2/www/ "Does the Inertia of a Body Depend its Energy Content?"], he speculates on the possibility that the equation <math>E = m c^2</math>, which would normally be very hard to verify, could be verified with the extremely high energies of the newly-discovered phenomenon of radioactivity.  The significance of that equation, however, remains debatable as nothing in [[quantum mechanics]] depends on it.

Because the effects of relativity are so tiny, scientists have been devising sophisticated and sensitive tests ever since the theory was formulated in 1905.  In fact, at the end of Einstein's original 1905 paper [http://www.fourmilab.ch/etexts/einstein/E_mc2/www/ "Does the Inertia of a Body Depend its Energy Content?"], he speculates on the possibility that the equation <math>E = m c^2</math>, which would normally be very hard to verify, could be verified with the extremely high energies of the newly-discovered phenomenon of radioactivity.  The significance of that equation, however, remains debatable as nothing in [[quantum mechanics]] depends on it.

General relativity predicts this extra precession, in the amount of <math>3 v^2/c^2</math> revolutions per planet's "year", where <math>v</math> is the planet's average orbital speed.  There is some controversy over whether general relativity's results are really accurate in terms of modern observations.

General relativity predicts this extra precession, in the amount of <math>3 v^2/c^2</math> revolutions per planet's "year", where <math>v</math> is the planet's average orbital speed.  There is some controversy over whether general relativity's results are really accurate in terms of modern observations.

[[Image:Cassini-science-289.jpg|right|thumb|The Shapiro effect: A signal dipping into a gravity well around the [[sun]] is delayed slightly]]

[[Image:Cassini-science-289.jpg|right|thumb|The Shapiro effect: A spacecraft signal dipping into a gravity well around the [[sun]] is delayed slightly.]]

As the 20^th century progressed, more tests of general relativity were proposed.  One was the ''Shapiro effect'', involving time delay in radio signals passing through the gravity well of a planet.  Various spacecraft have confirmed this.

As the 20^th century progressed, more tests of general relativity were proposed.  One was the ''Shapiro effect'', involving time delay in radio signals passing through the gravity well of a planet.  Various spacecraft have confirmed this.

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'' and the ''Lense-Thirring effect'' (also known as "frame dragging") were tested by the "Gravity Probe B" satellite early in the 21^st century.  The precision required to observe this was phenomenal.  The results were announced on May 4, 2011.

Two other effects, ''geodetic precession'' and the ''Lense-Thirring effect'' (also known as "frame dragging") 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.

{{clear}}<!-- make the Shapiro picture not obliterate the next section heading -->

{{clear}}<!-- make the Shapiro picture not obliterate the next section heading -->