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Like other scientific theories, relativity progressed gradually from the status of a "wild surmise," to a theory backed by imperfect experiments whose validity was debated, to a theory whose truth is now almost taken for granted. No particle accelerator built since the 1950s would work unless the mass increase predicted by special relativity not only occurred, but occurred to the precise degree predicted by the theory. In 1972, scientists flew extremely accurate clocks around the world in both directions on commercial airlines, and were directly able to observe the relativistic "twin paradox;" the eastbound clock gained 273 ns and the westbound clock lost 59 ns, matching the predictions of general relativity to within experimental accuracy.<ref>as described in [http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html What is the experimental basis of Special Relativity?], a personal web page, which cites Haefele and Keating (1972), ''Science'' Vol. 177 pp 166-170 as its source</ref><ref><ref>Sullivan, Walter (1972), "Relativity Theory Awaits Affirmation",  September 23, 1972, p. 61. Note: Article refers to a different experiment, which Sullivan discusses, saying that if successful it would be "the second time within a year" that relativity had been confirmed, then proceeds to discuss Hafele[sic] and Keating's experiment as the first.</ref>

Like other scientific theories, relativity progressed gradually from the status of a "wild surmise," to a theory backed by imperfect experiments whose validity was debated, to a theory whose truth is now almost taken for granted. No particle accelerator built since the 1950s would work unless the mass increase predicted by special relativity not only occurred, but occurred to the precise degree predicted by the theory. In 1972, scientists flew extremely accurate clocks around the world in both directions on commercial airlines, and were directly able to observe the relativistic "twin paradox;" the eastbound clock gained 273 ns and the westbound clock lost 59 ns, matching the predictions of general relativity to within experimental accuracy.<ref>as described in [http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html What is the experimental basis of Special Relativity?], a personal web page, which cites Haefele and Keating (1972), ''Science'' Vol. 177 pp 166-170 as its source</ref><ref><ref>Sullivan, Walter (1972), "Relativity Theory Awaits Affirmation",  September 23, 1972, p. 61. Note: Article refers to a different experiment, which Sullivan discusses, saying that if successful it would be "the second time within a year" that relativity had been confirmed, then proceeds to discuss Hafele[sic] and Keating's experiment as the first.</ref>

Relativity has generated a huge following by advocates of moral relativism{{fact}}. The idea of moral relativity may exist independent of (and substantially predates) the theory of relativity, but invocations of the theory are used in attempts to lend legitimacy to this version of morality.

Relativity has generated a huge following by advocates of moral relativism{{fact}}. The idea of moral relativity may exist independent of (and substantially predates) the theory of relativity, but invocations of the theory are used in attempts to lend legitimacy to this version of morality.

Today some physicists are working on a [[quantum theory of gravity]] (the "theory of everything"), including [[string theory]].  Critics increasingly point out that [[string theory]] is largely untestable and unfalsifiable, and thus potentially unscientific under the principles of science advanced by [[Karl Popper]].

Today some physicists are working on a [[quantum theory of gravity]] (the "theory of everything"), including [[string theory]].  Critics increasingly point out that [[string theory]] is largely untestable and unfalsifiable, and thus potentially unscientific under the principles of science advanced by [[Karl Popper]].