Unification of theories in physics

<h2 id="unification-of-gravity-and-astronomy">Unification of gravity and astronomy</h2>
The "first great unification" was <a href="/facts/Isaac_Newton/4L7gTncN">Isaac Newton</a>'s 17th century <a href="/facts/Newton%2527s_law_of_universal_gravitation/F6qH2XC3">unification of gravity</a>, which brought together the understandings of the observable phenomena of gravity on Earth with the observable behaviour of <a href="/facts/Celestial_bodies/BCHLa0Q2">celestial bodies</a> in space.<a class="footnote-ref" id="fnref:4" href="#fn:4">4</a><a class="footnote-ref" id="fnref:5" href="#fn:5">5</a><a class="footnote-ref" id="fnref:6" href="#fn:6">6</a>
His work is credited with laying the foundations of future endeavors for a grand unified theory. For example, it has been stated that "If we have to take any single individual as the originator of the quest for a unified theory of physics, and, by implication, the whole of knowledge, it has to be Newton."<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a> Physicist <a href="/facts/Steven_Weinberg/G61D6kJw">Steven Weinberg</a> stated that "It is with Isaac Newton that the modern dream of a final theory really begins".<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a> 

<h2 id="unification-of-magnetism-electricity-light-and-related-radiation">Unification of magnetism, electricity, light and related radiation</h2>
The <a href="/facts/History_of_China/TNqRSvQ4">ancient Chinese</a> people observed that certain rocks such as <a href="/facts/Lodestone/8bqkYHbR">lodestone</a> and <a href="/facts/Magnetite/SVxoGUs2">magnetite</a> were attracted to one another by an invisible force. This effect was later called <a href="/facts/Magnetism/eo75vApl">magnetism</a>, which was first rigorously studied in the 17th century. However, prior to ancient Chinese observations of magnetism, the <a href="/facts/Ancient_Greece/PTVBrWXq">ancient Greeks</a> knew of other objects such as <a href="/facts/Amber/GHP6h5gx">amber</a>, that when rubbed with fur would cause a similar invisible attraction between the two.<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> This was also studied rigorously in the 17th century and came to be called <a href="/facts/Electricity/hNC8D65W">electricity</a>. Thus, physics had come to understand two observations of nature in terms of some root cause (electricity and magnetism). However, work in the 19th century revealed that these two forces were just two different aspects of one force – <a href="/facts/Electromagnetism/oAkmALHT">electromagnetism</a>. 
The "second great unification" was <a href="/facts/James_Clerk_Maxwell/jtYyze61">James Clerk Maxwell</a>'s 19th century <a href="/facts/Maxwell%2527s_equations/LfJ1drHS">unification of electromagnetism</a>. It brought together the understandings of the observable phenomena of <a href="/facts/Magnetism/eo75vApl">magnetism</a>, <a href="/facts/Electricity/hNC8D65W">electricity</a> and <a href="/facts/Light/jeofpMn4">light</a> (and more broadly, the spectrum of <a href="/facts/Electromagnetic_radiation/Ynx7ujCW">electromagnetic radiation</a>).<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a> This was followed in the 20th century by <a href="/facts/Albert_Einstein/CNTet8qu">Albert Einstein</a>'s unification of space and time, and of <a href="/facts/Mass%25E2%2580%2593energy_equivalence/ExXawGcc">mass and energy</a> through his theory of <a href="/facts/Special_relativity/vsFFc63E">special relativity</a>.<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a> Later, <a href="/facts/Paul_Dirac/6bt5yRdk">Paul Dirac</a> developed <a href="/facts/Quantum_field_theory/VoewsNJV">quantum field theory</a>, unifying <a href="/facts/Quantum_mechanics/BRc3Mzgr">quantum mechanics</a> and special relativity.<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a> 
A relatively recent unification of electromagnetism and the <a href="/facts/Weak_nuclear_force/f6upmKMs">weak nuclear force</a> now consider them to be two aspects of the <a href="/facts/Electroweak_interaction/QATz4dYF">electroweak interaction</a>.

<h2 id="unification-of-the-remaining-fundamental-forces-theory-of-everything">Unification of the remaining fundamental forces: theory of everything</h2>
This process of "unifying" forces continues today, with the ultimate goal of finding a <a href="/facts/Theory_of_everything/rpossh4t">theory of everything</a> – it remains perhaps the most prominent of the <a href="/facts/List_of_unsolved_problems_in_physics/vJ3d1A83">unsolved problems in physics</a>. There remain <a href="/facts/Fundamental_interaction/WrFEJaFl">four fundamental forces which have not been decisively unified</a>: the <a href="/facts/Gravity/bqAN7DdQ">gravitational</a> and <a href="/facts/Electromagnetism/oAkmALHT">electromagnetic</a> interactions, which produce significant long-range forces whose effects can be seen directly in everyday life, and the <a href="/facts/Strong_interaction/JjRsKcLg">strong</a> and <a href="/facts/Weak_interaction/f6upmKMs">weak interactions</a>, which produce forces at <a href="/facts/Subatomic_scale/Y3JPd4ru">minuscule, subatomic distances</a> and govern nuclear interactions. Electromagnetism and the weak interactions are widely considered to be two aspects of the <a href="/facts/Electroweak_interaction/QATz4dYF">electroweak interaction</a>. Attempts to unify <a href="/facts/Quantum_mechanics/BRc3Mzgr">quantum mechanics</a> and <a href="/facts/General_relativity/jVsoIg8X">general relativity</a> into a single theory of <a href="/facts/Quantum_gravity/t7whBMNE">quantum gravity</a>, a program ongoing for over half a century, have not yet been decisively resolved; current leading candidates are <a href="/facts/M-theory/5KJgrr9P">M-theory</a>, <a href="/facts/Superstring_theory/1gY26F0D">superstring theory</a> and <a href="/facts/Loop_quantum_gravity/6Xueeoux">loop quantum gravity</a>.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Weinberg, S. (1993). Dreams of a Final Theory: The Search for the Fundamental Laws of Nature. Hutchinson Radius. ISBN 978-0-09-177395-3. <a href="978-0-09-177395-3" target="_blank">978-0-09-177395-3</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">"Unification theories and a theory of everything". AccessScience. 2014. doi:10.1036/1097-8542.BR0814141. Retrieved 2024-07-27. <a href="https://www.accessscience.com/content/unification-theories-and-a-theory-of-everything/BR0814141" target="_blank">https://www.accessscience.com/content/unification-theories-and-a-theory-of-everything/BR0814141</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">Nitesh Soni (2013), Unification of forces, Symmetry Magazine <a href="https://www.symmetrymagazine.org/article/june-2013/unification-of-forces" target="_blank">https://www.symmetrymagazine.org/article/june-2013/unification-of-forces</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">"Unification theories and a theory of everything". AccessScience. 2014. doi:10.1036/1097-8542.BR0814141. Retrieved 2024-07-27. <a href="https://www.accessscience.com/content/unification-theories-and-a-theory-of-everything/BR0814141" target="_blank">https://www.accessscience.com/content/unification-theories-and-a-theory-of-everything/BR0814141</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">Fritz Rohrlich (25 August 1989). From Paradox to Reality: Our Basic Concepts of the Physical World. Cambridge University Press. pp. 28–. ISBN 978-0-521-37605-1. <a href="978-0-521-37605-1" target="_blank">978-0-521-37605-1</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Klaus Mainzer (2 December 2013). Symmetries of Nature: A Handbook for Philosophy of Nature and Science. Walter de Gruyter. pp. 8–. ISBN 978-3-11-088693-1. <a href="978-3-11-088693-1" target="_blank">978-3-11-088693-1</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">Rowlands, Peter (2017). Newton and Modern Physics. World Scientific Publishing. p. 21. ISBN 978-1-78634-332-1. <a href="978-1-78634-332-1" target="_blank">978-1-78634-332-1</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">Weinberg, Steven (1994). Dreams of a Final Theory: The Scientist's Search for the Ultimate Laws of Nature. New York: Vintage Books. p. 11. ISBN 978-0-679-74408-5. <a href="978-0-679-74408-5" target="_blank">978-0-679-74408-5</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">Stewart, J. (2001). Intermediate Electromagnetic Theory. World Scientific. p. 50. ISBN 978-981-02-4471-2. <a href="978-981-02-4471-2" target="_blank">978-981-02-4471-2</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Unification theories and a theory of everything (Report). McGraw-Hill Education. 2014. doi:10.1036/1097-8542.br0814141. <a href="https://www.accessscience.com/content/briefing/aBR0814141" target="_blank">https://www.accessscience.com/content/briefing/aBR0814141</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">Unification theories and a theory of everything (Report). McGraw-Hill Education. 2014. doi:10.1036/1097-8542.br0814141. <a href="https://www.accessscience.com/content/briefing/aBR0814141" target="_blank">https://www.accessscience.com/content/briefing/aBR0814141</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">Bhaumik, Mani L. (2022). "How Dirac's Seminal Contributions Pave the Way for Comprehending Nature's Deeper Designs". Quanta. 8 (1): 88–100. arXiv:2209.03937. doi:10.12743/quanta.v8i1.96. S2CID 212835814. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">"Unification theories and a theory of everything". AccessScience. 2014. doi:10.1036/1097-8542.BR0814141. Retrieved 2024-07-27. <a href="https://www.accessscience.com/content/unification-theories-and-a-theory-of-everything/BR0814141" target="_blank">https://www.accessscience.com/content/unification-theories-and-a-theory-of-everything/BR0814141</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
</ol>

Unification of theories in physics open-in-new

Unification of theories in physics