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Theory of relativity
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<p>The theory of relativity usually encompasses two interrelated <a href="/facts/Physics/a7aH2y08">physics</a> theories by <a href="/facts/Albert_Einstein/CNTet8qu">Albert Einstein</a>: <a href="/facts/Special_relativity/vsFFc63E">special relativity</a> and <a href="/facts/General_relativity/jVsoIg8X">general relativity</a>, proposed and published in 1905 and 1915, respectively. Special relativity applies to all physical phenomena in the absence of <a href="/facts/Gravity/bqAN7DdQ">gravity</a>. General relativity explains the law of gravitation and its relation to the forces of nature. It applies to the <a href="/facts/Cosmological/yM19zM7Y">cosmological</a> and astrophysical realm, including astronomy. </p><p>The theory transformed <a href="/facts/Theoretical_physics/Cs2Y12rQ">theoretical physics</a> and <a href="/facts/Astronomy/0ArJVM1p">astronomy</a> during the 20th century, superseding a 200-year-old <a href="/facts/Classical_mechanics/ykG8upsN">theory of mechanics</a> created primarily by <a href="/facts/Isaac_Newton/4L7gTncN">Isaac Newton</a>. It introduced concepts including 4-<a href="/facts/Dimension/0ktmUyac">dimensional</a> <a href="/facts/Spacetime/uRIN1x4b">spacetime</a> as a unified entity of <a href="/facts/Space/tq6LUM3C">space</a> and <a href="/facts/Time_in_physics/5s0grGmk">time</a>, <a href="/facts/Relativity_of_simultaneity/xphdsCxC">relativity of simultaneity</a>, <a href="/facts/Kinematics/o7mSyeJA">kinematic</a> and <a href="/facts/Gravity/bqAN7DdQ">gravitational</a> <a href="/facts/Time_dilation/fYj7FYbK">time dilation</a>, and <a href="/facts/Length_contraction/4of503Dg">length contraction</a>. In the field of physics, relativity improved the science of <a href="/facts/Elementary_particle/CTFDM97U">elementary particles</a> and their fundamental interactions, along with ushering in the <a href="/facts/Atomic_age/33vIXnMt">nuclear age</a>. With relativity, <a href="/facts/Physical_cosmology/ww4ChbEq">cosmology</a> and <a href="/facts/Astrophysics/krFPRWLA">astrophysics</a> predicted extraordinary <a href="/facts/Astronomy/0ArJVM1p">astronomical phenomena</a> such as <a href="/facts/Neutron_star/4enfoxBA">neutron stars</a>, <a href="/facts/Black_hole/1r2lmkcF">black holes</a>, and <a href="/facts/Gravitational_wave/4XWN3NtG">gravitational waves</a>. </p>