The Nature of Light | Physics

<!DOCTYPE html> <html lang="en" dir="ltr"> <head>  <meta http-equiv="X-UA-Compatible" content="ie=edge"> <meta charset="utf-8"> <base href="https://www.visionlearning.com"> <title>The Nature of Light | Physics | Visionlearning</title> <link rel="canonical" href="https://www.visionlearning.com/en/library/physics/24/the-nature-of-light/132"> <meta name="description" content="Learn about early theories on light. Provides information on Newton and Young's theories, including the <i>double slit</i> experiment."> <meta name="keywords" content="particles or waves, what is light made of, how does light travel"> <meta name="viewport" content="width=device-width, initial-scale=1.0, shrink-to-fit=no"> <meta name="msvalidate.01" content="D8E20F39AD48052260032E56DE409970"> <script type="application/ld+json"> { "@context": "http://schema.org/", "@type": "Article", "mainEntityOfPage": { "@type": "WebPage", "@id": "https://visionlearning.com/en/library/physics/24/the-nature-of-light/132" }, "name": "The Nature of Light", "headline": "The Nature of Light: Particle and wave theories", "author": { "@type": "Person", "name": "Nathaniel Page Stites, M.A./M.S." }, "datePublished": "2005-07-05 16:30:48", "dateModified": "2017-02-12T08:30:00+05:00", "image": { "@type": "ImageObject", "url": "/img/library/moduleImages/featured_image_132-23061210060855.jpeg", "width": 696, "height": 464 }, "publisher": { "@type": "Organization", "name": "Visionlearning, Inc.", "logo": { "@type": "ImageObject", "url": "http://visionlearning.com/images/logo.png", "width": 278, "height": 60 } }, "description": "For centuries, controversy over whether light is made of particles or waves abounded. This module traces the controversy over time, from Isaac Newton's corpuscle (particle) theory, which prevailed for centuries, to Thomas Young's groundbreaking <i>double slit</i> experiment, which provided evidence that light traveled in waves.", "keywords": "particles or waves, what is light made of, how does light travel", "inLanguage": { "@type": "Language", "name": "English", "alternateName": "en" }, "copyrightHolder": { "@type": "Organization", "name": "Visionlearning, Inc." }, "copyrightYear": "2005"} </script> <meta property="og:url" content="https://visionlearning.com/en/library/physics/24/the-nature-of-light/132"> <meta property="og:title" content="The Nature of Light | Physics | Visionlearning" /> <meta property="og:type" content="website"> <meta property="og:site_name" content="Visionlearning"> <meta property="og:description" content="Learn about early theories on light. 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aria-labelledby="acc-button-measurement" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/general-science/3/the-metric-system/47">The Metric System</a></li> </ul> </div> <button class="accordion__button" id="acc-button-physical-properties" data-accordion="button" aria-controls="acc-panel-physical-properties" aria-expanded="false"> <span class="accordion__button__label"> Physical Properties </span> </button> <div class="accordion__panel" id="acc-panel-physical-properties" data-accordion="panel" aria-labelledby="acc-button-physical-properties" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/general-science/3/temperature/48">Temperature</a></li> <li><a href="/en/library/general-science/3/density-and-buoyancy/37">Density and Buoyancy</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-math-in-science" data-accordion="button" aria-controls="acc-panel-math-in-science" aria-expanded="false"> <span 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href="/en/library/math-in-science/62/exponential-equations-ii/210">Exponential Equations II</a></li> <li><a href="/en/library/math-in-science/62/scientific-notation/250">Scientific Notation</a></li> <li><a href="/en/library/math-in-science/62/measurement/257">Measurement</a></li> </ul> </div> <button class="accordion__button" id="acc-button-statistics" data-accordion="button" aria-controls="acc-panel-statistics" aria-expanded="false"> <span class="accordion__button__label"> Statistics </span> </button> <div class="accordion__panel" id="acc-panel-statistics" data-accordion="panel" aria-labelledby="acc-button-statistics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/math-in-science/62/introduction-to-descriptive-statistics/218">Introduction to Descriptive Statistics</a></li> <li><a href="/en/library/math-in-science/62/introduction-to-inferential-statistics/224">Introduction to Inferential Statistics</a></li> <li><a href="/en/library/math-in-science/62/statistical-techniques/239">Statistical Techniques</a></li> </ul> </div> <button class="accordion__button" id="acc-button-trigonometric-functions" data-accordion="button" aria-controls="acc-panel-trigonometric-functions" aria-expanded="false"> <span class="accordion__button__label"> Trigonometric Functions </span> </button> <div class="accordion__panel" id="acc-panel-trigonometric-functions" data-accordion="panel" aria-labelledby="acc-button-trigonometric-functions" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/math-in-science/62/wave-mathematics/131">Wave Mathematics</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-physics" data-accordion="button" aria-controls="acc-panel-physics" aria-expanded="false"> <span class="accordion__button__label"> Physics </span> </button> <div class="accordion__panel" id="acc-panel-physics" data-accordion="panel" aria-labelledby="acc-button-physics" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-light-and-optics" data-accordion="button" aria-controls="acc-panel-light-and-optics" aria-expanded="false"> <span class="accordion__button__label"> Light and Optics </span> </button> <div class="accordion__panel" id="acc-panel-light-and-optics" data-accordion="panel" aria-labelledby="acc-button-light-and-optics" role="region"> <ul class="nav text-color-link"> <li class="current">The Nature of Light</li> <li><a href="/en/library/physics/24/electromagnetism-and-light/138">Electromagnetism and Light</a></li> </ul> </div> <button class="accordion__button" id="acc-button-mechanics" data-accordion="button" aria-controls="acc-panel-mechanics" aria-expanded="false"> <span class="accordion__button__label"> Mechanics </span> </button> <div class="accordion__panel" id="acc-panel-mechanics" data-accordion="panel" aria-labelledby="acc-button-mechanics" role="region"> <ul class="nav 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the Scientific Community</a></li> <li><a href="/en/library/process-of-science/49/scientific-ethics/161">Scientific Ethics</a></li> <li><a href="/en/library/process-of-science/49/scientific-institutions-and-societies/162">Scientific Institutions and Societies</a></li> </ul> </div> <button class="accordion__button" id="acc-button-ideas-in-science" data-accordion="button" aria-controls="acc-panel-ideas-in-science" aria-expanded="false"> <span class="accordion__button__label"> Ideas in Science </span> </button> <div class="accordion__panel" id="acc-panel-ideas-in-science" data-accordion="panel" aria-labelledby="acc-button-ideas-in-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177">Theories, Hypotheses, and Laws</a></li> <li><a href="/en/library/process-of-science/49/scientific-controversy/181">Scientific Controversy</a></li> <li><a href="/en/library/process-of-science/49/creativity-in-science/182">Creativity in Science</a></li> </ul> </div> <button class="accordion__button" id="acc-button-research-methods" data-accordion="button" aria-controls="acc-panel-research-methods" aria-expanded="false"> <span class="accordion__button__label"> Research Methods </span> </button> <div class="accordion__panel" id="acc-panel-research-methods" data-accordion="panel" aria-labelledby="acc-button-research-methods" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-practice-of-science/148">The Practice of Science</a></li> <li><a href="/en/library/process-of-science/49/experimentation-in-scientific-research/150">Experimentation in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/description-in-scientific-research/151">Description in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/comparison-in-scientific-research/152">Comparison in 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href="/en/library/process-of-science/49/the-how-and-why-of-scientific-meetings/186">The How and Why of Scientific Meetings</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-scientists-and-research" data-accordion="button" aria-controls="acc-panel-scientists-and-research" aria-expanded="false"> <span class="accordion__button__label"> Scientists and Research </span> </button> <div class="accordion__panel" id="acc-panel-scientists-and-research" data-accordion="panel" aria-labelledby="acc-button-scientists-and-research" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-scientific-research" data-accordion="button" aria-controls="acc-panel-scientific-research" aria-expanded="false"> <span class="accordion__button__label"> Scientific Research </span> </button> <div class="accordion__panel" id="acc-panel-scientific-research" data-accordion="panel" aria-labelledby="acc-button-scientific-research" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/scientists-and-research/58/collaborative-research-in-the-arctic-towards-understanding-climate-change/183">Collaborative Research in the Arctic Towards Understanding Climate Change</a></li> <li><a href="/en/library/scientists-and-research/58/from-stable-chromosomes-to-jumping-genes/184">From Stable Chromosomes to Jumping Genes</a></li> <li><a href="/en/library/scientists-and-research/58/an-elegant-experiment-to-test-the-process-of-dna-replication/187">An Elegant Experiment to Test the Process of DNA Replication</a></li> <li><a href="/en/library/scientists-and-research/58/the-founding-of-neuroscience/233">The Founding of Neuroscience</a></li> <li><a href="/en/library/scientists-and-research/58/tracking-endangered-jaguars-across-the-border/189">Tracking Endangered Jaguars across the Border</a></li> <li><a href="/en/library/scientists-and-research/58/atmospheric-chemistry-research-that-changed-global-policy/211">Atmospheric Chemistry Research that Changed Global Policy</a></li> <li><a href="/en/library/scientists-and-research/58/revolutionizing-medicine-with-monoclonal-antibodies/220">Revolutionizing Medicine with Monoclonal Antibodies</a></li> <li><a href="/en/library/scientists-and-research/58/uncovering-the-mysteries-of-chronic-mountain-sickness/238">Uncovering the Mysteries of Chronic Mountain Sickness</a></li> </ul> </div> <button class="accordion__button" id="acc-button-profiles-in-science" data-accordion="button" aria-controls="acc-panel-profiles-in-science" aria-expanded="false"> <span class="accordion__button__label"> Profiles in Science </span> </button> <div class="accordion__panel" id="acc-panel-profiles-in-science" data-accordion="panel" aria-labelledby="acc-button-profiles-in-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/scientists-and-research/58/luis-e.-miramontes/232">Luis E. Miramontes</a></li> <li><a href="/en/library/scientists-and-research/58/bernardo-houssay/237">Bernardo Houssay</a></li> <li><a href="/en/library/scientists-and-research/58/craig-lee/256">Craig Lee</a></li> <li><a href="/en/library/scientists-and-research/58/david-ho/241">David Ho</a></li> <li><a href="/en/library/scientists-and-research/58/louis-tompkins-wright/244">Louis Tompkins Wright</a></li> <li><a href="/en/library/scientists-and-research/58/carlos-j.-finlay/217">Carlos J. Finlay</a></li> <li><a href="/en/library/scientists-and-research/58/cecilia-payne/290">Cecilia Payne</a></li> <li><a href="/en/library/scientists-and-research/58/jazmin-scarlett/291">Jazmin Scarlett</a></li> <li><a href="/en/library/scientists-and-research/58/ramari-stewart/292">Ramari Stewart</a></li> <li><a href="/en/library/scientists-and-research/58/johnson-cerda/300">Johnson Cerda</a></li> <li><a href="/en/library/scientists-and-research/58/ellen-ochoa/201">Ellen Ochoa</a></li> <li><a href="/en/library/scientists-and-research/58/ruth-benerito/205">Ruth Benerito</a></li> <li><a href="/en/library/scientists-and-research/58/franklin-chang-díaz/219">Franklin Chang Díaz</a></li> <li><a href="/en/library/scientists-and-research/58/percy-lavon-julian/221">Percy Lavon Julian</a></li> <li><a href="/en/library/scientists-and-research/58/luis-walter-alvarez/229">Luis Walter Alvarez</a></li> <li><a href="/en/library/scientists-and-research/58/france-anne-dominic-córdova/230">France Anne-Dominic Córdova</a></li> </ul> </div> </div> </div> </div> </div> </li> <li>  <button class="button" data-toggle="dropdown">Physics </button> <div class="nav__dropdown box-shadow-1 padding-1"> <div class="accordion accordion--secondary font-size-sm"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-sub-button-light-and-optics" data-accordion="button" aria-controls="acc-sub-panel-light-and-optics" aria-expanded="false"> <span class="accordion__button__label"> Light and Optics </span> </button> <div class="accordion__panel" id="acc-sub-panel-light-and-optics" data-accordion="panel" aria-labelledby="acc-sub-button-light-and-optics" role="region"> <ul class="nav text-color-link"> <li class="current">The Nature of Light</li> <li><a href="/en/library/physics/24/electromagnetism-and-light/138">Electromagnetism and Light</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-mechanics" data-accordion="button" aria-controls="acc-sub-panel-mechanics" aria-expanded="false"> <span class="accordion__button__label"> Mechanics </span> </button> <div class="accordion__panel" id="acc-sub-panel-mechanics" data-accordion="panel" aria-labelledby="acc-sub-button-mechanics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/physics/24/defining-energy/199">Defining Energy</a></li> <li><a href="/en/library/physics/24/waves-and-wave-motion/102">Waves and Wave Motion</a></li> <li><a href="/en/library/physics/24/gravity/118">Gravity</a></li> <li><a href="/en/library/physics/24/thermodynamics-i/200">Thermodynamics I</a></li> </ul> </div> </div> </div> </div> </li> </ul> </nav>  <div id="theTop"></div> <main id="skip-header-content"> <div class="margin-bottom-5"> <article class="container wide module"> <header class="grid grid--sidebar-right module__header"> <div class="module__header__title"> <span class="subcategory"> <strong><em>Light and Optics</em></strong> </span> <h1>The Nature of Light: <sub><em>Particle and wave theories</em></sub></h1> <p class="byline">by Nathaniel Page Stites, M.A./M.S.</p> <nav class="module__header__tabs"> <ul class="tabs-nav tabs-nav--horizontal library"> <li> <a href="/en/library/physics/24/the-nature-of-light/132/reading" aria-current="page" >Reading</a> </li> <li> <a href="/en/library/physics/24/the-nature-of-light/132/quiz">Quiz</a> </li> <li> <a href="/en/library/physics/24/the-nature-of-light/132/resources">Teach with this</a> </li> </ul> </nav> </div> <script type="application/ld+json"> { "@context": "http://schema.org", "@type": "AudioObject", "contentUrl": "https://www.visionlearning.com/img/library/moduleAudio/module_132.mp3", "description": "Recording of The Nature of Light : For centuries, controversy over whether light is made of particles or waves abounded. This module traces the controversy over time, from Isaac Newton's "corpuscle" (particle) theory, which prevailed for centuries, to Thomas Young's groundbreaking <i>double slit</i> experiment, which provided evidence that light traveled in waves.", "encodingFormat": "mp3", "name": "module_132.mp3" } </script> <div class="module_header_audio"> <div class="audio-player border border-radius"> <audio id="audio"> <source src="https://www.visionlearning.com/img/library/moduleAudio/module_132.mp3" type="audio/mpeg"> Your browser does not support the audio element. </audio> <div class="audio-player__title"> <p>Listen to this reading</p> <span class="audio-player__timestamp" id="timestamp"> 00:00 </span> </div> <div class="audio-player__controls" id="controls"> <button class="button button--icon-only" id="play-pause-button"> <span class="icon icon-play" aria-hidden="true"></span> </button> <div class="audio-player__progress" id="progress-bar" tabindex="0" aria-valuemin="0" aria-valuemax="100" aria-valuenow="0" aria-label="Use arrow keys to forward or rewind the audio" role="slider"> <div class="audio-player__progress__fill"> <span class="audio-player__thumb"></span> </div> </div> <div class="audio-player__volume-container"> <button id="mute-button"> <span class="icon icon-volume"></span> </button> <div class="audio-player__volume" tabindex="0" aria-valuemin="0" aria-valuemax="100" aria-valuenow="100" aria-label="Use arrow keys to adjust volume" role="slider"> <div class="audio-player__volume__fill"> <span class="audio-player__thumb"></span> </div> </div> </div> </div> </div> </div> </header> <hr class="divider"/>   <div class="grid grid--sidebar-right grid--divider"> <div class="order-2 order-1--lg module__main"> <div class="narrow margin-x-auto margin-y-5"> <div class="accordion margin-bottom-5">  <button class="accordion__button" id="acc-button-key-concepts" data-accordion="button" aria-controls="acc-panel-key-concepts" aria-expanded="true" tabindex="0"> Did you know? </button> <div class="accordion__panel shown show" id="acc-panel-key-concepts" data-accordion="panel" aria-labelledby="acc-button-key-concepts" role="region"> <div class="accordion__panel__content"> <p>Did you know that scientists and philosophers debated for centuries about whether light traveled in waves or particles? Finally in the 20th century, one of science's "most beautiful experiments" seemed to confirm the wave-like nature of light, until it was further refined some 100 years later.</p> </div> </div>  <button class="accordion__button" id="acc-button-table-of-contents" data-accordion="button" aria-controls="acc-panel-table-of-contents" aria-expanded="false" tabindex="0"> Key concepts </button> <div class="accordion__panel" id="acc-panel-table-of-contents" data-accordion="panel" aria-labelledby="acc-button-table-of-contents" role="region" aria-hidden="true"> <div class="accordion__panel__content"> <ul class="bulleted"> <li><p>A long-running controversy in science, debated by many prominent scientists, was over whether light consists of particles or waves.</p></li> <li><p>In the early 1800s, Thomas Young provided clear evidence that showed that light exhibits properties consistent with wave behavior; specifically showing that it exhibits patterns of constructive and destructive interference.</p></li> <p><li>Our modern understanding of light has built on the work of Young and others.</p></li> </ul> </div> </div>  <button class="accordion__button" id="acc-button-terms-you-should-know" data-accordion="button" aria-controls="acc-panel-terms-you-should-know" aria-expanded="false" tabindex="0"> Terms you should know </button> <div class="accordion__panel" id="acc-panel-terms-you-should-know" data-accordion="panel" aria-labelledby="acc-button-terms-you-should-know" role="region" aria-hidden="true"> <div class="accordion__panel__content"> <dl> <dt><a href="/en/glossary/view/beam">beam </a></dt> <dd> a ray or shaft of light from a source </dd> <dt><a href="/en/glossary/view/particle">particle </a></dt> <dd> a tiny piece of matter </dd> <dt>phenomenon </dt> <dd> a fact or event that can be observed</dd> </dl> </div> </div> </div> <hr class="border-color-dark" /> <section> <div class="container narrow"> <p><section id="toc_1" class=""> <h2>Early theories</h2></p> <p>For as long as the human imagination has sought to make meaning of the world, we have recognized <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark> as essential to our existence. Whether to a prehistoric child warming herself by the light of a fire in a cave, or to a modern child afraid to go to sleep without the lights on, light has always given comfort and reassurance.</p><p>The earliest documented <mark class="term" data-term="theory" data-term-url="/en/glossary/view/theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;">theories</mark> of <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark> came from the ancient Greeks. <mark class="term" data-term="Aristotle" data-term-def="A Greek philosopher born in Stagira (384-322 BCE). He joined Plato's Academy in Athens (then being run by Eudoxus) at the&hellip;" data-term-url="/en/glossary/view/Aristotle/4466">Aristotle</mark> believed that light was some kind of disturbance in the air, one of his four "elements" that composed <mark class="term" data-term="matter" data-term-def="The substance that makes up physical objects." data-term-url="/en/glossary/view/matter/8264">matter</mark>. Centuries later, Lucretius, who, like <mark class="term" data-term="Democritus" data-term-def="Greek natural philosopher born in Thrace (ca. 460-370 BCE). With his teacher, Leucippus, Democritus developed the atomist concept of the cosmos,&hellip;" data-term-url="/en/glossary/view/Democritus/4513">Democritus</mark> before him, believed that matter consisted of indivisible "atoms," thought that light must be a <mark class="term" data-term="particle" data-term-def="A tiny piece of matter." data-term-url="/en/glossary/view/particle/8259">particle</mark> given off by the sun. In the tenth century <mark class="term" data-term="CE" data-term-def="An abbreviation for Common Era, which is a designation for the time beginning with year 1 of the Gregorian calendar. CE&hellip;" data-term-url="/en/glossary/view/CE/3721">CE</mark>, the Middle Eastern mathematician <mark class="term" data-term="Alhazen" data-term-def="The Latinized name for the Muslim scientist Ab&#363;-Al&#299; al-Hasan ibn al-Hasan ibn al-Haytham who was born in Basra, Mesopotamia (Iraq) (965-1039&hellip;" data-term-url="/en/glossary/view/Alhazen/3718">Alhazen</mark> developed a <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> that all objects radiate their own light. Alhazen's theory was contrary to earlier theories proposing that we could see because our eyes emitted light to illuminate the objects around us.</p><p>In the seventeenth century, two distinct <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">models</mark> emerged from France to explain the phenomenon of <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark>. The French philosopher and mathematician <mark class="term" data-term="Rene Descartes" data-term-def="Mathematician and philosopher born in Indre-et-Loire, France (1596-1650). Descartes invented analytical geometry and developed what is now called the Cartesian coordinate&hellip;" data-term-url="/en/glossary/view/Descartes%2C+Rene/4501">Rene Descartes</mark> believed that an invisible substance, which he called the <em>plenum</em>, permeated the <mark class="term" data-term="universe" data-term-def="The cosmos and everything that exists in it." data-term-url="/en/glossary/view/universe/5288">universe</mark>. Much like <mark class="term" data-term="Aristotle" data-term-def="A Greek philosopher born in Stagira (384-322 BCE). He joined Plato's Academy in Athens (then being run by Eudoxus) at the&hellip;" data-term-url="/en/glossary/view/Aristotle/4466">Aristotle</mark>, he believed that light was a disturbance that traveled through the plenum, like a wave that travels through water. Pierre Gassendi, a contemporary of Descartes, challenged this <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark>, asserting that light was made up of discrete <mark class="term" data-term="particle" data-term-def="A tiny piece of matter." data-term-url="/en/glossary/view/particle/8259">particles</mark>.</p></section> <section id="toc_2"> <h2>Particles vs. waves</h2><p>While this <mark class="term" data-term="controversy" data-term-def="An argument, disagreement, or difference of opinion that involves many people. A true scientific controversy involves a sustained debate within the&hellip;" data-term-url="/en/glossary/view/controversy/8241">controversy</mark> developed between rival French philosophers, two of the leading English scientists of the seventeenth century took up the particles-versus-waves battle. <mark class="term" data-term="Isaac Newton" data-term-def="English alchemist, physicist, astronomer and mathematician born in Woolsthorpe-by-Colsterworth, Lincolnshire (1643-1727). In 1672, Newton offered an experimental proof that light is&hellip;" data-term-url="/en/glossary/view/Isaac+Newton/3725">Isaac Newton</mark>, after seriously considering both <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">models</mark>, ultimately decided that <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark> was made up of <mark class="term" data-term="particle" data-term-def="A tiny piece of matter." data-term-url="/en/glossary/view/particle/8259">particles</mark> (though he called them corpuscles). <mark class="term" data-term="Robert Hooke" data-term-def="An English physicist, born on the Isle of Wight (1635-1703). Hooke's studies were extremely diverse, encompassing biology, geology, physics, chemistry, and&hellip;" data-term-url="/en/glossary/view/Hooke%2C+Robert/4460">Robert Hooke</mark>, already a rival of <mark class="term" data-term="Isaac Newton" data-term-url="/en/glossary/view/Isaac+Newton" data-term-def="English alchemist, physicist, astronomer and mathematician born in Woolsthorpe-by-Colsterworth, Lincolnshire (1643-1727). In 1672, Newton offered an experimental proof that light is&hellip;">Newton</mark>'s and the scientist who would identify and name the <mark class="term" data-term="cell" data-term-def="The basic structural unit of all living things." data-term-url="/en/glossary/view/cell/8286">cell</mark> in 1655, was a proponent of the wave <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> (see our <a href="/library/module_viewer.php?mid=64">Discovery and Structure of Cells</a> module). Unlike many before them, these two scientists based their <mark class="term" data-term="theory" data-term-url="/en/glossary/view/theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;">theories</mark> on <mark class="term" data-term="observation" data-term-def="1. The act of noticing something. 2. A record of that which has been noticed." data-term-url="/en/glossary/view/observation/8255">observations</mark> of light's behaviors: reflection and <mark class="term" data-term="refraction" data-term-def="The change in direction and usually speed of a wave as it crosses a boundary between two different media, for example,&hellip;" data-term-url="/en/glossary/view/refraction/1673">refraction</mark>. Reflection, as from a mirror, was a well-known occurrence, but refraction, the now familiar phenomenon by which an object partially submerged in water appears to be "broken," was not well understood at the time (Figure 1).</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_6670.jpg"> <img src="/img/library/modules/mid132/Image/VLObject-6670-140516020521.jpg" alt="Figure 1: These seemingly "broken" straws in a glass of water result from the refraction of light." /> </button> <figcaption> <p><strong>Figure 1:</strong> These seemingly "broken" straws in a glass of water result from the refraction of light.</p> <span class="credit">image ©Pat_Hastings/Shutterstock</span> </figcaption> </figure> </div> <p>Proponents of the <mark class="term" data-term="particle" data-term-def="A tiny piece of matter." data-term-url="/en/glossary/view/particle/8259">particle</mark> <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> of <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark> pointed to reflection as <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> that light consists of individual particles that bounce off of objects, much like billiard balls. <mark class="term" data-term="Isaac Newton" data-term-url="/en/glossary/view/Isaac+Newton" data-term-def="English alchemist, physicist, astronomer and mathematician born in Woolsthorpe-by-Colsterworth, Lincolnshire (1643-1727). In 1672, Newton offered an experimental proof that light is&hellip;">Newton</mark> believed that <mark class="term" data-term="refraction" data-term-def="The change in direction and usually speed of a wave as it crosses a boundary between two different media, for example,&hellip;" data-term-url="/en/glossary/view/refraction/1673">refraction</mark> could be explained by his <mark class="term" data-term="law" data-term-def="In science, a principle that describes a phenomenon, often mathematically." data-term-url="/en/glossary/view/law/8686">laws</mark> of motion, with particles of light as the objects in motion. As light particles approached the <mark class="term" data-term="boundary" data-term-def="A line or limit that divides one area from another." data-term-url="/en/glossary/view/boundary/8272">boundary</mark> between two materials of different densities, such as air and water, the increased gravitational <mark class="term" data-term="force" data-term-def="An influence (a "push or pull") that changes the motion of a moving object (e.g., slows it down, speeds it up,&hellip;" data-term-url="/en/glossary/view/force/883">force</mark> of the denser material would cause the particles to change direction, <mark class="term" data-term="newton" data-term-def="A metric (or SI) unit measuring force and named for English physicist Isaac Newton. One newton (N) represents the force needed&hellip;" data-term-url="/en/glossary/view/newton/5596">Newton</mark> believed (see our <a href="/library/module_viewer.php?mid=37">Density</a> module).</p><p>Newton's <mark class="term" data-term="particle" data-term-def="A tiny piece of matter." data-term-url="/en/glossary/view/particle/8259">particle</mark> <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> was also based partly on his <mark class="term" data-term="observation" data-term-def="1. The act of noticing something. 2. A record of that which has been noticed." data-term-url="/en/glossary/view/observation/8255">observations</mark> of how the wave phenomenon <mark class="term" data-term="diffraction" data-term-def="The bending or spreading of waves when they meet an obstruction." data-term-url="/en/glossary/view/diffraction/3606">diffraction</mark> related to sound. He understood that sound traveled through the air in <mark class="term" data-term="waves" data-term-def="The motion of rising and falling in curves; undulation." data-term-url="/en/glossary/view/waves/8274">waves</mark>, meaning sound could travel around corners and obstacles; thus, a person in another room can be heard through a doorway. Since <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark> was unable to bend around corners or obstacles, <mark class="term" data-term="Isaac Newton" data-term-url="/en/glossary/view/Isaac+Newton" data-term-def="English alchemist, physicist, astronomer and mathematician born in Woolsthorpe-by-Colsterworth, Lincolnshire (1643-1727). In 1672, Newton offered an experimental proof that light is&hellip;">Newton</mark> believed that light could not <mark class="term" data-term="diffract" data-term-def="To undergo the process of diffraction." data-term-url="/en/glossary/view/diffract/3607">diffract</mark>. He therefore supposed light was not a wave.</p><p>Hooke and others – most notably the Dutch scientist <mark class="term" data-term="Christian Huygens" data-term-def="Dutch mathematician born in The Hague (1629-1695). Huygens ground and polished his own telescope lenses, and in 1655, he detected the&hellip;" data-term-url="/en/glossary/view/Huygens%2C+Christian/4473">Christian Huygens</mark> – believed that <mark class="term" data-term="refraction" data-term-def="The change in direction and usually speed of a wave as it crosses a boundary between two different media, for example,&hellip;" data-term-url="/en/glossary/view/refraction/1673">refraction</mark> occurred because <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark> <mark class="term" data-term="waves" data-term-def="The motion of rising and falling in curves; undulation." data-term-url="/en/glossary/view/waves/8274">waves</mark> slowed down as they entered a denser medium such as water and changed their direction as a result. These wave theorists believed, like Descartes, that light must travel through some material that permeates space. Huygens dubbed this medium the <em>aether</em>.</p><p>Because of <mark class="term" data-term="Isaac Newton" data-term-url="/en/glossary/view/Isaac+Newton" data-term-def="English alchemist, physicist, astronomer and mathematician born in Woolsthorpe-by-Colsterworth, Lincolnshire (1643-1727). In 1672, Newton offered an experimental proof that light is&hellip;">Newton</mark>'s fame and reputation, many scientists of the seventeenth and eighteenth centuries subscribed to the view that <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark> was a <mark class="term" data-term="particle" data-term-def="A tiny piece of matter." data-term-url="/en/glossary/view/particle/8259">particle</mark>. The wave <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> of light, however, would receive a major boost at the beginning of the nineteenth century from an English scientist named <mark class="term" data-term="Thomas Young" data-term-def="English physicist and physician, born in Milverton, Somerset (1773-1829). Young's experiments with deflecting light showed interference patterns, proving that light is&hellip;" data-term-url="/en/glossary/view/Young%2C+Thomas/4514">Thomas Young</mark>.</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form class="" name="cc6058"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Scientists who believed that light was made of particles pointed to __________ as evidence to support their ideas.</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-6058-0-option-a" name="quiz-option-6058" type="radio" value="reflection" > <span class="option__label"> <span class="screen-reader-only">a.</span> reflection </span> </label> <span class="quiz__response" id="response-6058-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-6058-1-option-b" name="quiz-option-6058" type="radio" value="wave theory" > <span class="option__label"> <span class="screen-reader-only">b.</span> wave theory </span> </label> <span class="quiz__response" id="response-6058-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_3"> <h2>The waves have it</h2><p>On November 24, 1803, <mark class="term" data-term="Thomas Young" data-term-def="English physicist and physician, born in Milverton, Somerset (1773-1829). Young's experiments with deflecting light showed interference patterns, proving that light is&hellip;" data-term-url="/en/glossary/view/Young%2C+Thomas/4514">Thomas Young</mark> stood before the Royal Society of London to present the results of a groundbreaking <mark class="term" data-term="experiment" data-term-def="A test or trial carried out under controlled conditions so that specific actions can be performed and the results can be observed." data-term-url="/en/glossary/view/experiment/8292">experiment</mark>. Young had devised a simple scheme to see if <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark> demonstrated a behavior particular to <mark class="term" data-term="waves" data-term-url="/en/glossary/view/waves" data-term-def="The motion of rising and falling in curves; undulation.">waves:</mark> interference. To understand this concept, imagine two <mark class="term" data-term="waves" data-term-def="The motion of rising and falling in curves; undulation." data-term-url="/en/glossary/view/waves/8274">waves</mark> traveling toward each other on a string, as shown in Figure 2:</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid132/Image/VLObject-3385-050617090638.jpg" alt="Figure 2: Traveling wave pulses interfering constructively." /> </button> <figcaption> <p><b>Figure 2:</b> Traveling wave pulses interfering constructively.</p> </figcaption> </figure> </div> <p>When the <mark class="term" data-term="waves" data-term-def="The motion of rising and falling in curves; undulation." data-term-url="/en/glossary/view/waves/8274">waves</mark> reach the same part of the string at the same time, as shown in the middle diagram, they will add together and create one wave with double the <mark class="term" data-term="amplitude" data-term-def="Magnitude; a measure of height from the highest to lowest point on a vertical axis; a measure of the size of&hellip;" data-term-url="/en/glossary/view/amplitude/8762">amplitude</mark> (height) of the original <mark class="term" data-term="waves" data-term-url="/en/glossary/view/waves" data-term-def="The motion of rising and falling in curves; undulation.">waves</mark>. This adding together of waves is known as <em>constructive interference</em> because the waves combine to construct a new, bigger wave.</p><p>Another possible scenario is shown in Figure 3:</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid132/Image/VLObject-3388-050617090643.jpg" alt="Figure 3: Traveling wave pulses interfering destructively." /> </button> <figcaption> <p><b>Figure 3:</b> Traveling wave pulses interfering destructively.</p> </figcaption> </figure> </div> <p>Here, the two <mark class="term" data-term="waves" data-term-def="The motion of rising and falling in curves; undulation." data-term-url="/en/glossary/view/waves/8274">waves</mark> approaching each other have equal and opposite <mark class="term" data-term="amplitude" data-term-def="Magnitude; a measure of height from the highest to lowest point on a vertical axis; a measure of the size of&hellip;" data-term-url="/en/glossary/view/amplitude/8762">amplitudes</mark>. When they pass each other (middle diagram), they completely cancel each other out. This canceling effect is known as <em>destructive interference</em> because the <mark class="term" data-term="waves" data-term-url="/en/glossary/view/waves" data-term-def="The motion of rising and falling in curves; undulation.">waves</mark> temporarily disappear as they pass.</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form class="" name="cc6059"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">When waves cancel each other out, this is called</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-6059-0-option-a" name="quiz-option-6059" type="radio" value="constructive interference" > <span class="option__label"> <span class="screen-reader-only">a.</span> constructive interference </span> </label> <span class="quiz__response" id="response-6059-0"> <strong>Incorrect.</strong> </span> </div> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-6059-1-option-b" name="quiz-option-6059" type="radio" value="destructive interference" > <span class="option__label"> <span class="screen-reader-only">b.</span> destructive interference </span> </label> <span class="quiz__response" id="response-6059-1"> <strong>Correct!</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_4"> <h2>Beam splitting: Young's "Double Slit" experiment</h2><p>Thomas Young recognized that if <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark> behaved like a wave, it would be possible to create patterns of constructive and destructive interference using light. In 1801 he devised an <mark class="term" data-term="experiment" data-term-def="A test or trial carried out under controlled conditions so that specific actions can be performed and the results can be observed." data-term-url="/en/glossary/view/experiment/8292">experiment</mark> that would force two <mark class="term" data-term="beam" data-term-def="A ray or shaft of light from a source." data-term-url="/en/glossary/view/beam/8277">beams</mark> of light to travel different distances before interfering with each other when they reached a screen. To accomplish this, Young set up a mirror to direct a thin beam of sunlight into a darkened room (and an assistant to make sure the mirror aimed the sun's light properly!). Young split the beam in two by placing a very thin card edgewise in the beam.</p> <p>When the two beams of light shone on a screen, Young observed a very interesting pattern of light and dark "fringes" where the two beams interfered with each other constructively and destructively (Figure 4). Bright fringes appeared where the intensity of the light hitting the screen was highest, and dark fringes appeared where the intensity was zero. Where the two beams of light were exactly "in phase" (see Figure 5), they interfered constructively and created light that was brighter than either beam by itself. Where the beams of light were exactly "out of phase," they interfered destructively to produce a dark spot where the total light intensity was zero.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_13675.jpg"> <img src="/img/library/modules/mid132/Image/VLObject13675-24101504100339.jpeg" alt=" NatureofLight4 " /> </button> <figcaption> <span class="credit">image ©Public Domain</span> </figcaption> </figure> </div> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid132/Image/VLObject-3392-050617090650.jpg" alt="Figure 4: Top, Young's depiction of the results of his experiment (Young, 1845). The dark spot represents the card held in front of a window slit, producing two parallel beams of light. The light and dark bands represent the brighter and darker bands he observed. Bottom, schematic diagram that shows how Young's observation can be explained by constructive and destructive interference. " /> </button> <figcaption> <p><strong>Figure 4:</strong> Top, Young's depiction of the results of his experiment (Young, 1845). The dark spot represents the card held in front of a window slit, producing two parallel beams of light. The light and dark bands represent the brighter and darker bands he observed. Bottom, schematic diagram that shows how Young's observation can be explained by constructive and destructive interference. </p> </figcaption> </figure> </div> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid132/Image/VLObject-3394-050617090654.jpg" alt=" Waves: In Phase " /> </button> </figure> </div> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid132/Image/VLObject-3395-050617090657.jpg" alt="Figure 5: In-phase and out-of-phase waves. Top: The red and orange waves are "in phase," and the combination of these two waves (shown in blue) is a wave with double the amplitude of the each original wave. Bottom: The red and orange waves are "out of phase," and the result (shown in blue) is a wave of zero amplitude." /> </button> <figcaption> <p><b>Figure 5:</b> In-phase and out-of-phase waves. Top: The red and orange waves are "in phase," and the combination of these two waves (shown in blue) is a wave with double the amplitude of the each original wave. Bottom: The red and orange waves are "out of phase," and the result (shown in blue) is a wave of zero amplitude.</p> </figcaption> </figure> </div> <p>To understand the pattern of fringes in Young's <mark class="term" data-term="experiment" data-term-def="A test or trial carried out under controlled conditions so that specific actions can be performed and the results can be observed." data-term-url="/en/glossary/view/experiment/8292">experiment</mark>, let's examine the movement of two <mark class="term" data-term="waves" data-term-def="The motion of rising and falling in curves; undulation." data-term-url="/en/glossary/view/waves/8274">waves</mark> in more detail. Imagine starting with two <mark class="term" data-term="waves" data-term-url="/en/glossary/view/waves" data-term-def="The motion of rising and falling in curves; undulation.">waves</mark> that are perfectly in phase, as shown in Figure 6:</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid132/Image/VLObject-3397-050617100601.jpg" alt="Figure 6: Two waves that are in phase upon reaching the screen at the right side of the figure." /> </button> <figcaption> <p><b>Figure 6:</b> Two waves that are in phase upon reaching the screen at the right side of the figure.</p> </figcaption> </figure> </div> <p>If one wave travels a greater distance than the other, the peaks and troughs of the <mark class="term" data-term="waves" data-term-def="The motion of rising and falling in curves; undulation." data-term-url="/en/glossary/view/waves/8274">waves</mark> will become offset from one another and they may be out of phase when they reach their destination, as shown in Figure 7.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid132/Image/VLObject-3399-050617100605.jpg" alt="Figure 7: Two waves that have traveled different distances and are out of phase upon reaching the screen at the right side of the figure." /> </button> <figcaption> <p><b>Figure 7:</b> Two waves that have traveled different distances and are out of phase upon reaching the screen at the right side of the figure.</p> </figcaption> </figure> </div> <p>If the difference in distance traveled by the two <mark class="term" data-term="waves" data-term-def="The motion of rising and falling in curves; undulation." data-term-url="/en/glossary/view/waves/8274">waves</mark> is even greater, they will reach a point where the peak of one wave aligns with the trough of the other. Finally, if the wave that travels farther follows a path that is exactly one <mark class="term" data-term="wavelength" data-term-def="The distance between corresponding points on two successive waves, generally measured from crest to crest." data-term-url="/en/glossary/view/wavelength/1500">wavelength</mark> longer than the path the other wave follows (or two or three or any integer multiple longer), then their peaks will again align and they will arrive at their destination in phase, as shown in Figure 8.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid132/Image/VLObject-3401-050617100618.jpg" alt="Figure 8: Two waves that have traveled different distances yet are in phase when they reach the screen at the right side of the figure. The additional distance traveled by the red wave (indicated by the vertical green lines) is exactly equal to one wavelength, so the waves arrive at their destination in phase with each other even though they have traveled different distances." /> </button> <figcaption> <p><b>Figure 8:</b> Two waves that have traveled different distances yet are in phase when they reach the screen at the right side of the figure. The additional distance traveled by the red wave (indicated by the vertical green lines) is exactly equal to one wavelength, so the waves arrive at their destination in phase with each other even though they have traveled different distances.</p> </figcaption> </figure> </div> <p>Young realized that the bright spots on his screen occurred where the difference in the length of the path traveled by the <mark class="term" data-term="beam" data-term-def="A ray or shaft of light from a source." data-term-url="/en/glossary/view/beam/8277">beams</mark> of <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark> was an integer multiple of the <mark class="term" data-term="wavelength" data-term-def="The distance between corresponding points on two successive waves, generally measured from crest to crest." data-term-url="/en/glossary/view/wavelength/1500">wavelength</mark> of the light. The <mark class="term" data-term="waves" data-term-def="The motion of rising and falling in curves; undulation." data-term-url="/en/glossary/view/waves/8274">waves</mark> that met at this spot were perfectly in phase and had formed a bright spot because the peaks and troughs aligned with each other.</p><p>At the spots where there was no <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark> at all, the difference in path lengths was a multiple of exactly one half-wavelength, so the two <mark class="term" data-term="waves" data-term-def="The motion of rising and falling in curves; undulation." data-term-url="/en/glossary/view/waves/8274">waves</mark> were completely out of phase and interfered destructively, as seen in Figure 9.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox=""> <img src="/img/library/modules/mid132/Image/VLObject-3404-050617100621.jpg" alt="Figure 9: Two waves that have traveled different distances and are perfectly out of phase when they reach the screen at right. The additional distance traveled by the red wave (indicated by the vertical green lines) is exactly equal to one half-wavelength, so the waves arrive at their destination out of phase and interfere destructively." /> </button> <figcaption> <p><b>Figure 9:</b> Two waves that have traveled different distances and are perfectly out of phase when they reach the screen at right. The additional distance traveled by the red wave (indicated by the vertical green lines) is exactly equal to one half-wavelength, so the waves arrive at their destination out of phase and interfere destructively.</p> </figcaption> </figure> </div> <p>Through this <mark class="term" data-term="experiment" data-term-def="A test or trial carried out under controlled conditions so that specific actions can be performed and the results can be observed." data-term-url="/en/glossary/view/experiment/8292">experiment</mark> (often called Young's "Double Slit" experiment, and voted by <em>The New York Times</em> in 2002 as science's fifth most beautiful experiment), Young demonstrated with certainty the wave-like nature of <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark>. His experiment answered <mark class="term" data-term="Isaac Newton" data-term-url="/en/glossary/view/Isaac+Newton" data-term-def="English alchemist, physicist, astronomer and mathematician born in Woolsthorpe-by-Colsterworth, Lincolnshire (1643-1727). In 1672, Newton offered an experimental proof that light is&hellip;">Newton</mark>'s charge that light could not bend around corners or obstacles because, when it bent around the edge of the card, it had. </p><p>Physicists now know that <mark class="term" data-term="waves" data-term-def="The motion of rising and falling in curves; undulation." data-term-url="/en/glossary/view/waves/8274">waves</mark> will go around obstacles – a <mark class="term" data-term="process" data-term-def="Method, procedure; series of actions or steps." data-term-url="/en/glossary/view/process/8256">process</mark> referred to as <em>diffraction</em> – but only if the size of the obstacle is comparable to the size, or <mark class="term" data-term="wavelength" data-term-def="The distance between corresponding points on two successive waves, generally measured from crest to crest." data-term-url="/en/glossary/view/wavelength/1500">wavelength</mark>, of the wave. The card that Young used in his apparatus was very thin – only about as thick as the wavelength of the <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark> he was using it to divide, so the light did, indeed, bend around the card.</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form class="" name="cc6062"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">In Young's experiment with two beams of light traveling toward each other, bright spots appeared on the screen when</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-6062-0-option-a" name="quiz-option-6062" type="radio" value="the peaks and troughs of the wavelengths aligned with each other." > <span class="option__label"> <span class="screen-reader-only">a.</span> the peaks and troughs of the wavelengths aligned with each other. </span> </label> <span class="quiz__response" id="response-6062-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-6062-1-option-b" name="quiz-option-6062" type="radio" value="the peaks and troughs of the wavelengths offset each other." > <span class="option__label"> <span class="screen-reader-only">b.</span> the peaks and troughs of the wavelengths offset each other. </span> </label> <span class="quiz__response" id="response-6062-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_5"> <h2>Light theory in the 19th century and beyond</h2><p>In the face of this compelling <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark>, nineteenth-century scientists had to concede that <mark class="term" data-term="light" data-term-def="A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human&hellip;" data-term-url="/en/glossary/view/light/1498">light</mark> was a wave. This happened slowly, though, hampered by <mark class="term" data-term="Isaac Newton" data-term-url="/en/glossary/view/Isaac+Newton" data-term-def="English alchemist, physicist, astronomer and mathematician born in Woolsthorpe-by-Colsterworth, Lincolnshire (1643-1727). In 1672, Newton offered an experimental proof that light is&hellip;">Newton</mark>'s reputation and the legacy of his corpuscular <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark>. Yet, once it did take root, the idea of light as a wave paved the way for the nineteenth-century Scottish physicist <mark class="term" data-term="James Clerk Maxwell" data-term-def="Scottish theoretical physicist and mathematician born in Edinburgh (1831-1879). Maxwell developed the classical electromagnetic theory, which synthesized previously unrelated observations, experiments,&hellip;" data-term-url="/en/glossary/view/Maxwell%2C+James+Clerk/4558">James Clerk Maxwell</mark> to devise an elegant description of light as a wave, which unified two rapidly developing concepts of physics into one complete theory. It was this description that set the stage for a discovery that would arise 100 years later, when a young German-born <mark class="term" data-term="patent" data-term-def="A document issued by the government that grants an inventor the sole right to his or her invention for a set&hellip;" data-term-url="/en/glossary/view/patent/8750">patent</mark> clerk by the name of <mark class="term" data-term="Albert Einstein" data-term-def="Theoretical physicist, born in Württemberg, Germany (1879–1955), who became an American citizen in 1940. While working as a patent clerk in&hellip;" data-term-url="/en/glossary/view/Einstein%2C+Albert/4458">Albert Einstein</mark> would show that the conception of light as a wave was not entirely correct and thereby revolutionize scientific thinking of the twentieth century.</p> </div> </section> <hr class="border-color-dark" /> <footer class="module__footer"> <p class="citation"> <em> Nathaniel Page Stites, M.A./M.S. “The Nature of Light” Visionlearning Vol. PHY-1 (3), 2005. </em> </p>  <div class="title-list" id="refs" name="refs"> <p class="h6 title-list__title"> References </p> <ul class="title-list__list"> <li><p>Young, T. (1845). <em>A course of lectures on natural philosophy and the mechanical arts</em> (Vol. 1). Taylor and Walton.</p></li> </ul> </div>  <div class="title-list" name="further"> <p class="h6 title-list__title"> Further Reading </p> <ul class="grid grid--column-2--md grid--column-3--md gap-1"> <li> <a class="no-hover-focus height-100" href="/en/library/Physics/24/Light-and-Electromagnetism/138"> <article class="flex-row align-items-center flex-column--md align-items-start--md height-100 theme-light padding-2 gap-2"> <div class="width-30 width-auto--md"> <img class="border-radius box-shadow-1" src="/img/library/moduleImages/featured_image_138-23061210060920.jpeg" alt="Electromagnetism and Light"> </div> <div class="flex-grow-shrink"> <h2 class="h6 font-weight-normal"> Electromagnetism and Light: <em>Introduction to the electromagnetic spectrum</em> </h2> </div> </article> </a> </li> <li> <a class="no-hover-focus height-100" href="/en/library/Physics/24/Waves-and-Wave-Motion/102"> <article class="flex-row align-items-center flex-column--md align-items-start--md height-100 theme-light padding-2 gap-2"> <div class="width-30 width-auto--md"> <img class="border-radius box-shadow-1" src="/img/library/moduleImages/featured_image_102-23061210060944.jpg" alt="Waves and Wave Motion"> </div> <div class="flex-grow-shrink"> <h2 class="h6 font-weight-normal"> Waves and Wave Motion: <em>Describing waves</em> </h2> </div> </article> </a> </li> </ul> </div> </footer> </div>   </div>  <div class="order-1 order-2--lg module__tools"> <div class="narrow margin-x-auto position-sticky-top font-size-md"> <div class="padding-2 border-radius box-shadow-1--lg"> <div class="tabs" role="tablist"> <nav> <button class="button button--icon-label" id="tab-button-in-this-module" aria-label="Table of Contents" aria-controls="tab-panel-module__tools" aria-selected="true" role="tab"> <span class="icon icon-list" aria-hidden="true"></span> <span class="button__text">Contents</span> </button> <button class="button button--icon-label" id="tab-button-toggle-terms" aria-controls="tab-panel-toggle-terms" aria-selected="false" role="tab"> <span class="icon icon-glossary-highlight"></span> <span class="button__text">Glossary Terms</span> </button> </nav> <hr class="divider" /> <div class="tabs__panel shown" id="tab-panel-module__tools" aria-labelledby="tab-button-module__tools" role="tabpanel"> <p class="font-weight-bold margin-bottom-1"> Table of Contents </p> <div class="table-of-contents" id="module-toc"> <ul> <li><a href="/en/library/physics/24/the-nature-of-light/132#toc_1">Early theories</a> </li> <li><a href="/en/library/physics/24/the-nature-of-light/132#toc_2">Particles vs. waves</a> </li> <li><a href="/en/library/physics/24/the-nature-of-light/132#toc_3">The waves have it</a> </li> <li><a href="/en/library/physics/24/the-nature-of-light/132#toc_4">Beam splitting: Young's "Double Slit" experiment</a> </li> <li><a href="/en/library/physics/24/the-nature-of-light/132#toc_5">Light theory in the 19th century and beyond</a> </li> </ul> </div> </div>   <div class="tabs__panel" id="tab-panel-toggle-terms" aria-labelledby="tab-button-toggle-terms" role="tabpanel"> <div class="reading-toggle"> <div class="reading-toggle__switch"> <div class="form-entry__option__switch"> <label> <input type="checkbox" name="termsToggleSwitch" id="terms-toggle-switch" /> <span class="switch__slider"></span> <span class="option__label text-decoration-none font-size-md"> Highlight Glossary Terms </span> </label> </div> </div> <div class="reading-toggle__help"> <p> <em> Activate glossary term highlighting to easily identify key terms within the module. Once highlighted, you can click on these terms to view their definitions. </em> </p> </div> </div> </div> <div class="tabs__panel" id="tab-panel-toggle-ngss" aria-labelledby="tab-button-toggle-ngss" role="tabpanel"> <div class="reading-toggle"> <div class="reading-toggle__switch"> <div class="form-entry__option__switch"> <label> <input type="checkbox" name="ngssToggleSwitch" id="ngss-toggle-switch" /> <span class="switch__slider"></span> <span class="option__label text-decoration-none font-size-md"> Show NGSS Annotations </span> </label> </div> </div> <div class="reading-toggle__help"> <p> <em> Activate NGSS annotations to easily identify NGSS standards within the module. 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The Nature of Light | Physics | Visionlearning