Changes

== Mathematics ==

== Mathematics ==

The central equation of special relativity is<ref>http://www2.slac.stanford.edu/vvc/theory/relativity.html</ref>:

The central equation of special relativity is:<ref>http://www2.slac.stanford.edu/vvc/theory/relativity.html</ref>

:γ=<math>\frac{1}{\sqrt{1-\frac{v^2}{c^2}}}</math>, where:

:γ=<math>\frac{1}{\sqrt{1-\frac{v^2}{c^2}}}</math>, where:

* γ is the factor relating relativistic time, mass, and momentum to non-relativistic time, mass, and momentum.

* γ is the factor relating relativistic time, mass, and momentum to non-relativistic time, mass, and momentum.

===Universal speed limit ===

===Universal speed limit ===

At the other extreme, when <math>v</math> approaches <math>c</math>, γ approaches <math>\frac{1}{\sqrt{1-1}} = \frac{1}{0} = \infty</math>.  Since infinite γ means infinite mass, no object can ever reach [[Speed of light|the speed of light]].  (Some theorists have postulated hypothetical [[tachyons]], which would always travel faster than the speed of light<ref>http://www.math.ucr.edu/home/baez/physics/ParticleAndNuclear/tachyons.html</ref>. No evidence has been found for them.  If they existed, special relativity would mean that they cannot ever travel slower than the speed of light.)

At the other extreme, when <math>v</math> approaches <math>c</math>, γ approaches <math>\frac{1}{\sqrt{1-1}} = \frac{1}{0} = \infty</math>.  Since infinite γ means infinite mass, no object can ever reach [[Speed of light|the speed of light]].  (Some theorists have postulated hypothetical [[tachyons]], which would always travel faster than the speed of light.<ref>http://www.math.ucr.edu/home/baez/physics/ParticleAndNuclear/tachyons.html</ref>  No evidence has been found for them.  If they existed, special relativity would mean that they cannot ever travel slower than the speed of light.)

== Experimental Proofs ==

== Experimental Proofs ==