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Special relativity
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<p>In <a href="/facts/Physics/a7aH2y08">physics</a>, the special theory of relativity, or special relativity for short, is a scientific theory of the relationship between <a href="/facts/Spacetime/uRIN1x4b">space and time</a>. In <a href="/facts/Albert_Einstein/CNTet8qu">Albert Einstein</a>'s 1905 paper, <a href="/facts/Annus_Mirabilis_papers/8LhL5hm7"> "On the Electrodynamics of Moving Bodies"</a>, the theory is presented as being based on just <a href="/facts/Postulates_of_special_relativity/HEQuAUGp">two postulates</a>: </p> <ol><li>The <a href="/facts/Laws_of_physics/aVtc4wpk">laws of physics</a> are <a href="/facts/Invariant_(physics)/UfHcehYs">invariant</a> (identical) in all <a href="/facts/Inertial_frame_of_reference/1U6TrdG3">inertial frames of reference</a> (that is, <a href="/facts/Frame_of_reference/15yYfB9M">frames of reference</a> with no <a href="/facts/Acceleration/UVDmjYvR">acceleration</a>). This is known as the <a href="/facts/Principle_of_relativity/8I2xlmoP">principle of relativity</a>.</li> <li>The <a href="/facts/Speed_of_light/sKSQwdNx">speed of light</a> in <a href="/facts/Vacuum/BTk3goyV">vacuum</a> is the same for all observers, regardless of the motion of light source or observer. This is known as the principle of light constancy, or the principle of light speed invariance.</li></ol> <p>The first postulate was first formulated by <a href="/facts/Galileo_Galilei/98VT2z3v">Galileo Galilei</a> (see <i><a href="/facts/Galilean_invariance/fFhMN2yv">Galilean invariance</a></i>). </p>