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→Experimental and Observational Evidence Confirming Relativity: another one
===Local Position Invariance===
===Local Position Invariance===
The ''equivalence principle'', which is the underpinning of gravity under general relativity, states that there is absolutely no perceived effect of gravity on an object in free fall, that is, in a gravitational field. This has been tested many times, and is the basis of all space-time calculations in relativity. But in 2019, it was reported to have been successfully tested in a gravitational field very much stronger than ever before. The phenomenon is called ''local position invariance'', or LPI. It was measured on the light emitted from a star called "S2", closely orbiting the "Sagittarius A*" black hole at the center of the galaxy. The gravitational field that S2 is subject to is vastly more powerful than any other gravitational field that has been measured.<ref>https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.122.101102</ref>
The ''equivalence principle'', which is the underpinning of gravity under general relativity, states that there is absolutely no perceived effect of gravity on an object in free fall, that is, in a gravitational field. This has been tested many times, and is the basis of all space-time calculations in relativity. But in March 2019, it was reported to have been successfully tested in a gravitational field very much stronger than ever before. The phenomenon is called ''local position invariance'', or LPI. It was measured on the light emitted from a star called "S0-2", closely orbiting the "Sagittarius A*" black hole at the center of the galaxy. The gravitational field that S0-2 is subject to is vastly more powerful than any other gravitational field that has been measured.<ref>https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.122.101102</ref>
===Further Measurements near Sagittarius A*===
In July 2019, another star, S0-102, was characterized accurately by Andrea Ghez and her team.<ref>https://science.sciencemag.org/content/early/2019/07/24/science.aav8137</ref> It is even closer to the Sagittarius A* black hole than S0-2. Together, the two stars made it possible to map the gravity well in 3 dimensions, providing an even more accurate test of General Relativity. "Making a measurement of such fundamental importance has required years of patient observing, enabled by state-of-the-art technology. Through their rigorous efforts, Ghez and her collaborators have produced a high-significance validation of Einstein's idea about strong gravity." The statistical significance of these measurements is 5-sigma (5σ).
===Geodetic Precession===
===Geodetic Precession===