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#No material object of nonzero mass can travel at or greater than the speed of light.  (Objects of zero mass, such as photons, travel at exactly the speed of light.)

#No material object of nonzero mass can travel at or greater than the speed of light.  (Objects of zero mass, such as photons, travel at exactly the speed of light.)

#Information can not travel faster than the speed of light.<ref>This assumption is commonly restated in this manner.  For example, a discussion of hypothetical [[tachyons]] talks "about using tachyons to transmit information faster than the speed of light, '''in violation of Special Relativity'''."[http://www.math.ucr.edu/home/baez/physics/ParticleAndNuclear/tachyons.html]</ref>  This is sometimes stated as:

#Information can not travel faster than the speed of light.<ref>This assumption is commonly restated in this manner.  For example, a discussion of hypothetical [[tachyons]] talks "about using tachyons to transmit information faster than the speed of light, '''in violation of Special Relativity'''."[http://www.math.ucr.edu/home/baez/physics/ParticleAndNuclear/tachyons.html]</ref>  This is sometimes stated as:

#There is no "action at a distance," because that would make observations dependent on the frame of reference.  See [[Action at a distance]] for a discussion of this point.

#There is no "action at a distance", because that would make observations dependent on the frame of reference.  See [[Action at a distance]] for a discussion of this point.

When the assumptions are stated clearly as above, the weaknesses in the theory are more apparent.  There “is” action at a distance in [[quantum entanglement]] and apparently also in gravity, as no gravitons can be found. However, no information has yet been transmitted via quantum entanglement, so while non-locality violates the spirit of relativity it is consistent with it if relativity is limited to the transmission of information. [[Quantum field theory]], an attempt to partially reconcile [[quantum mechanics]] with relativity, is incomplete at best.  As to the second assumption, it is contrary to the [[arrow of time]], which illustrates the lack of symmetry in time.  Logical defects include the incoherence of relativistic mass (see discussion below) and the lack of relativistic constraints near the beginning the universe (see above).

When the assumptions are stated clearly as above, the weaknesses in the theory are more apparent.  There “is” action at a distance in [[quantum entanglement]] and apparently also in gravity, as no gravitons can be found. However, no information has yet been transmitted via quantum entanglement, so while non-locality violates the spirit of relativity it is consistent with it if relativity is limited to the transmission of information. [[Quantum field theory]], an attempt to partially reconcile [[quantum mechanics]] with relativity, is incomplete at best.  As to the second assumption, it is contrary to the [[arrow of time]], which illustrates the lack of symmetry in time.  Logical defects include the incoherence of relativistic mass (see discussion below) and the lack of relativistic constraints near the beginning the universe (see above).

There's also the matter of simply "accepting" something, when a phenomenon is consistent with a theory that is already known to be valid.  The recoil from a gun is an example of this.  Everyone knows that there is a backward recoil when a gun is fired.  This is explained to people when they are first being taught how to use a gun, and they get used to it with practice.  The reason for the recoil is that it is an obvious consequence of Newtons' laws of motion.  But people don't specifically think about Newton's laws, or consider this to be a "proof", when they are firing a gun.  They just accept that the recoil is a known consequence of those laws.  Newton's laws of motion have been validated through thousands of experiments much more focused than the firing of a gun.

There's also the matter of simply "accepting" something, when a phenomenon is consistent with a theory that is already known to be valid.  The recoil from a gun is an example of this.  Everyone knows that there is a backward recoil when a gun is fired.  This is explained to people when they are first being taught how to use a gun, and they get used to it with practice.  The reason for the recoil is that it is an obvious consequence of Newtons' laws of motion.  But people don't specifically think about Newton's laws, or consider this to be a "proof", when they are firing a gun.  They just accept that the recoil is a known consequence of those laws.  Newton's laws of motion have been validated through thousands of experiments much more focused than the firing of a gun.

The [[Cockcroft and Walton Experiment|Cockcroft/Walton experiment]] is an example of this kind of acceptance.  The results are consistent (to within 5% when analyzed carefully) with Special Relativity, and many people consider it to be a validation of SR.  But there were too many other things going on, such as the use of the newly-invented particle accelerator, to make it a definitive test.  Assumptions have to be made about what is happening in the experiment in order to assert anything about [[E=mc2]].  See [[Cockcroft and Walton Experiment]].

The [[Cockcroft and Walton Experiment|Cockcroft/Walton experiment]] is an example of this kind of acceptance.  The results are consistent (to within 5% when analyzed carefully) with Special Relativity, and many people consider it to be a validation of SR.  But there were too many other things going on, such as the use of the newly-invented particle accelerator, to make it a definitive test.  In any case, Special Relativity had already been validated through more focused and definitive tests.  It is important to note that there are no known alternative theories explaining this result.

The anomalous behavior of the timing signals from [[GPS]] satellites is another example.  The phenomenon is well known&mdash;the system compensates for this; otherwise it wouldn't work&mdash;and the phenomenon is known to be a consequence of both special and general relativity.  But the GPS system should not be considered and experiment to test relativity.  No sensible person would build the GPS system as a test of relativity, if only because it exhibits two phenomena (time dilation of special relativity, 7 milliseconds per day, and time compression of general relativity, 45 milliseconds per day) that work against each other.  No one would design and experiment that tests two phenomena working against each other.  Newtonian physics also predicts the bending of light and might be fit to the observed GPS data as relativists do.

The anomalous behavior of the timing signals from [[GPS]] satellites is another example.  The phenomenon is well known&mdash;the system compensates for this; otherwise it wouldn't work&mdash;and the phenomenon is known to be a consequence of both special and general relativity.  But the GPS system should not be considered and experiment to test relativity.  No sensible person would build the GPS system as a test of relativity, if only because it exhibits two phenomena (time dilation of special relativity, 7 milliseconds per day, and time compression of general relativity, 45 milliseconds per day) that work against each other.  No one would design and experiment that tests two phenomena working against each other.  But the effect of both, 38 milliseconds per day, is well known, as is the reason for this.  It is important to note that there are no known alternative theories explaining this result.

While the experimental tests for General Relativity are rather esoteric, those for Special Relativity are fairly straightforward.  So much so that the Michelson-Morley experiment could be said to have single-handedly established the case for SR&mdash;the logical syllogism leading from Michelson-Morley to SR and the Lorentz transform was fairly clear once people saw it.

While the experimental tests for General Relativity are rather esoteric, those for Special Relativity are fairly straightforward.  So much so that the Michelson-Morley experiment could be said to have single-handedly established the case for SR&mdash;the logical syllogism leading from Michelson-Morley to SR and the Lorentz transform was fairly clear once people saw it.