Changes

=== Classical mechanics ===

=== Classical mechanics ===

When <tt>v</tt>, the speed of the object in question, is low relative to <tt>c</tt>, γ approaches <math>\frac{1}{\sqrt{1-0}} = 1</math>, causing the Einstein-Lorentz relativity equations to be equivalent to Newton's equations.  This is why [[classical mechanics, governed by [[Isaac Newton]]'s laws of motion, works for particles at low mass and low speed.  However, at higher velocities, γ diverges, causing relativity to be essential.

When <math>v</math>, the speed of the object in question, is low relative to <math>c</math>, γ approaches <math>\frac{1}{\sqrt{1-0}} = 1</math>, causing the ''Einstein-Lorentz relativity'' equations to be equivalent to Newton's equations.  This is why [[classical mechanics]], governed by [[Isaac Newton]]'s laws of motion, works for [[Subatomic particle|particles]] at low mass and low speed.  However, at higher velocities, γ diverges, causing relativity to be essential.

Electromagnetism, including for light and gamma radiation, where the quanta (photons) travel at light speed have no rest mass, is always relativistic.

Electromagnetism, including for [[light]] and gamma radiation, where the quanta ([[photon]]s) travel at [[Speed of light|light speed]] have no rest mass, is always relativistic.

===Universal speed limit ===

===Universal speed limit ===

At the other extreme, when <tt>v</tt> approaches <tt>c</tt>, γ approaches <math>\frac{1}{\sqrt{1-1}} = \frac{1}{0} = \infty</math>.  Since infinite γ means infinite mass, no object can ever reach the speed of light.  (Some theorists have postulated hypothetical [[tachyon]]s, 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 [[tachyon]]s, 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 ==