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'''Relativity''' is a mathematical system built on untestable hypotheses.  By relying on ''assumptions'' about nature rather than ''observations'', the theories of relativity violate [[Isaac Newton]]'s rule against the use of hypotheses:  "Hypotheses non fingo" ("I feign no hypotheses)".<ref>http://plato.stanford.edu/entries/newton-philosophy/</ref>  Relativity also rejects -- without any experimental evidence -- Newton's [[action at a distance]], which is basic to Newtonian gravity and [[quantum mechanics]].

'''Relativity''' is a mathematical system built on untestable hypotheses.  By relying on ''assumptions'' about nature rather than ''observations'', the theories of relativity violate [[Isaac Newton]]'s rule against the use of hypotheses:  "Hypotheses non fingo" ("I feign no hypotheses)".<ref>http://plato.stanford.edu/entries/newton-philosophy/</ref>  Relativity also rejects -- without any experimental evidence -- Newton's [[action at a distance]], which is basic to Newtonian gravity and [[quantum mechanics]].

Unlike [[Newton]]ian physics, in which space and time intervals are each invariant as seen by all observers, in SR the only invariant quantity is a quadratic combination of space and time intervals (x² - c t²). The (assumed) instantaneous transmission of [[Newton]]ian gravitational effects also contradicts special relativity.

Unlike [[Newton]]ian physics, in which space and time intervals are each invariant as seen by all observers, in SR the only invariant quantity is a quadratic combination of space and time intervals (x² - c² t²). The (assumed) instantaneous transmission of [[Newton]]ian gravitational effects also contradicts special relativity.

In quantum mechanics, the [[uncertainty principle]] suggests that virtual particles can sometimes travel faster than the speed of light which would violate causality, but "[t]he only known way to resolve this tension involves introducing the idea of antiparticles."<ref>http://nobelprize.org/nobel_prizes/physics/laureates/2004/wilczek-lecture.pdf (p. 102)</ref>  Consequently, in 1928 Paul Dirac derived the Dirac equation, one of the first quantum mechanical equations compatible with special relativity, by which Dirac predicted the existence of antimatter. Four years later, antimatter (the positron) was discovered by Carl Anderson, as successfully predicted by relativistic quantum mechanics.  [[Quantum field theory]], a generalization of quantum mechanics, is fully compatible with special relativity but not with general relativity.

In quantum mechanics, the [[uncertainty principle]] suggests that virtual particles can sometimes travel faster than the speed of light which would violate causality, but "[t]he only known way to resolve this tension involves introducing the idea of antiparticles."<ref>http://nobelprize.org/nobel_prizes/physics/laureates/2004/wilczek-lecture.pdf (p. 102)</ref>  Consequently, in 1928 Paul Dirac derived the Dirac equation, one of the first quantum mechanical equations compatible with special relativity, by which Dirac predicted the existence of antimatter. Four years later, antimatter (the positron) was discovered by Carl Anderson, as successfully predicted by relativistic quantum mechanics.  [[Quantum field theory]], a generalization of quantum mechanics, is fully compatible with special relativity but not with general relativity.