The Masters of The Masters of LightLight

– – a history of the celebrities of light a history of the celebrities of light

from Euclid to Einsteinfrom Euclid to Einstein

The beginning and Big BangThe beginning and Big Bang

Euclid – the law of reflectionEuclid – the law of reflection

Alhazen – the origin of lightAlhazen – the origin of light

Snell & Descartes – the law of refractionSnell & Descartes – the law of refraction

Fermat´sFermat´s principle principle

Ole Ole RømerRømer – the hesitation of light – the hesitation of light

Newton – the spectrum of lightNewton – the spectrum of light

Huygens principleHuygens principle

Young´sYoung´s exp expeerimentriment

Maxwell – the electromagnetic wavesMaxwell – the electromagnetic waves

Bohr´s atomic modelBohr´s atomic model

Einstein and lightEinstein and light

The BeginningThe BeginningIn the beginning God created the heavens and In the beginning God created the heavens and the earth. the earth.

Now the earth was formless and empty, darkness Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit was over the surface of the deep, and the Spirit of God was hovering over the waters. of God was hovering over the waters.

And God said, "Let there be light," and there was And God said, "Let there be light," and there was light. God saw that the light was good, and He light. God saw that the light was good, and He separated the light from the darkness. God called separated the light from the darkness. God called the light "day," and the darkness he called the light "day," and the darkness he called "night." And there was evening, and there was "night." And there was evening, and there was morning — the first day.morning — the first day.

This is how Genesis begins.This is how Genesis begins.

Big BangBig Bang

Religion or scienceReligion or scienceGenesis tells the story of creation which takes place upon seven Genesis tells the story of creation which takes place upon seven days. But you cannot find the word “day” in the Hebrew manuscript.days. But you cannot find the word “day” in the Hebrew manuscript.

Instead of “day” the term “period” ought to be used. “Period” would Instead of “day” the term “period” ought to be used. “Period” would be a more correct translation. Thus there is no conflict between be a more correct translation. Thus there is no conflict between religion and science at this point.religion and science at this point.

The Big Bang took place about 14,000,000,000 years ago. It took The Big Bang took place about 14,000,000,000 years ago. It took about 300,000 years to cool the Universe sufficiently and to about 300,000 years to cool the Universe sufficiently and to weaken the gravitational forces enough to make light escapeweaken the gravitational forces enough to make light escape..

So from the beginning there was no light – only darkness, just as So from the beginning there was no light – only darkness, just as Genesis tells usGenesis tells us. .

Consequently we will never be able to see the beginning of Consequently we will never be able to see the beginning of everything – without the light we are blindeverything – without the light we are blind..

Euclid – the law of reflectionEuclid – the law of reflectionThe Greek philosophers made the first The Greek philosophers made the first thoughts about the nature of the light. In the thoughts about the nature of the light. In the year 280 B.C. Euclid discovered that the light year 280 B.C. Euclid discovered that the light is spreading in an upright way and thus he is spreading in an upright way and thus he formulated the law of reflectionformulated the law of reflection : :

The incident and the reflected ray of light are The incident and the reflected ray of light are equal to the normal of the mirror and the equal to the normal of the mirror and the angle of incidence is equal to the angle of angle of incidence is equal to the angle of reflectionreflection ..

But Euclid thought that light are rays which But Euclid thought that light are rays which come from the eye. It had to spread with an come from the eye. It had to spread with an infinite velocity as, when opening your eyes, infinite velocity as, when opening your eyes, you are immediately able to see distant you are immediately able to see distant objects.objects.

In the year 60 A. D. Heron of Alexandria advanced the general hypothesis In the year 60 A. D. Heron of Alexandria advanced the general hypothesis that light is spreading according to the shortest distance between two points. that light is spreading according to the shortest distance between two points. On this basis he was able to derive the results of EuclidOn this basis he was able to derive the results of Euclid..

Alhazen – the origin of lightAlhazen – the origin of lightAbout the year 1000 the focus of About the year 1000 the focus of science had moved to the Arabic science had moved to the Arabic world, where Alhazen in Baghdad world, where Alhazen in Baghdad wrote a series of books about optics.wrote a series of books about optics.

Alhazen was the first to understand Alhazen was the first to understand that light has its origin outside the that light has its origin outside the human being and that the rays of light human being and that the rays of light are reflected into the eyes from the are reflected into the eyes from the objects they strike.objects they strike.

Alhazen also advanced a hypothesis Alhazen also advanced a hypothesis about the final velocity of light and the about the final velocity of light and the reduced velocity of light when reduced velocity of light when passing through dense materials .passing through dense materials .

Alhazen = Abu Ali Hasan Ibn Al-HaithamAlhazen = Abu Ali Hasan Ibn Al-Haitham

Snell & Descartes – the law of refractionSnell & Descartes – the law of refractionIn 1621 the next major breakthrough In 1621 the next major breakthrough took place. The Dutchman Willebrord took place. The Dutchman Willebrord Snell discovered how light is refracted Snell discovered how light is refracted by various materials. This is the law by various materials. This is the law of refraction as demonstrated on the of refraction as demonstrated on the following page.following page.

René Descartes René Descartes also formulated the also formulated the Law of refraction, but he believed that Law of refraction, but he believed that light spreads with an infinite velocitylight spreads with an infinite velocity..

The law of refraction.The law of refraction.You can change the indices of refraction, view the rays of light You can change the indices of refraction, view the rays of light and move the fish.and move the fish.

Fermat´s principleFermat´s principleThe Frenchman Pierre de Fermat did The Frenchman Pierre de Fermat did not agree with the theories of not agree with the theories of DescartesDescartes..

He thought, just like Heron and He thought, just like Heron and Alhazen, that the light has a finite Alhazen, that the light has a finite velocityvelocity..

In 1657 he formulated the principle In 1657 he formulated the principle saying that light follows the shortest saying that light follows the shortest distance between 2 pointsdistance between 2 points..

On this basis Fermat was able to On this basis Fermat was able to formulate the law of the rectilinear formulate the law of the rectilinear spreading of light, the law of relection spreading of light, the law of relection and the law of refraction which and the law of refraction which together form the basis oftogether form the basis ofgeometrical optics.geometrical optics.

Ole Rømer – Ole Rømer – the hesitation of lightthe hesitation of lightIn 1676 Ole Roemer performed a series In 1676 Ole Roemer performed a series of measurements of the periods of of measurements of the periods of revolution for the moons of Jupiter. He revolution for the moons of Jupiter. He observed irregularities in the periods of observed irregularities in the periods of revolution. His explanation was the revolution. His explanation was the hesitation of light due to the variable hesitation of light due to the variable distance between the Earth and Jupiter.distance between the Earth and Jupiter.

Ole Roemer discovered that it takes the Ole Roemer discovered that it takes the light 8 to 11 minutes to reach the Earth light 8 to 11 minutes to reach the Earth from the Sun. Today we know that it from the Sun. Today we know that it takes 8 minutes and 20 seconds.takes 8 minutes and 20 seconds.

The velocity of light is 299.792.458 m/s The velocity of light is 299.792.458 m/s in vacuum, but normally we use the in vacuum, but normally we use the rounded figure 300.000 km/s.rounded figure 300.000 km/s.

Newton – Newton – the spectrum of lightthe spectrum of lightIn the sixteenth century Isaac Newton In the sixteenth century Isaac Newton was the great master of mechanical was the great master of mechanical physics. He also made important physics. He also made important works of optics.works of optics.

He invented the reflecting telescope He invented the reflecting telescope and discovered that the white light is and discovered that the white light is formed by blending light of all colours.formed by blending light of all colours.

In 1704 Newton published his workIn 1704 Newton published his work ”Opticks – or a treatise of the ”Opticks – or a treatise of the reflexions, refractions, inflexions and reflexions, refractions, inflexions and colours of light”.colours of light”.

Newton strongly advocated that light Newton strongly advocated that light is made of particlesis made of particles..

Huygens´ principleHuygens´ principleThe Dutch physicist Christiaan Huygens The Dutch physicist Christiaan Huygens was an opponent of the ideas of light was an opponent of the ideas of light particles of Newton.particles of Newton.

In 1678 he published ”In 1678 he published ”Traité de la LumièreTraité de la Lumière”, ”, where he described the nature of light as where he described the nature of light as waves.waves.

The principle of Huygens states that each The principle of Huygens states that each point of a ray of light can be explained by point of a ray of light can be explained by small waves coalesce to form a wave front.small waves coalesce to form a wave front.

The theory of Huygens gave a beautiful The theory of Huygens gave a beautiful explanation of refraction, diffraction, explanation of refraction, diffraction, interference and reflection – and prepared interference and reflection – and prepared the way for an interpretation of the the way for an interpretation of the polarization of the light and double polarization of the light and double refraction.refraction.

Young's experimentYoung's experimentIn 1801 the British doctor Thomas Young In 1801 the British doctor Thomas Young performed a conclusive experimentperformed a conclusive experiment..

He proved that light displays interference He proved that light displays interference which is a single-valued wave length which is a single-valued wave length phenomenon. He decided this wave phenomenon. He decided this wave length to be about 0, 0005 mmlength to be about 0, 0005 mm . .

It was now possible to prove that all It was now possible to prove that all geometrical optics is a consequence of geometrical optics is a consequence of the wave theorythe wave theory . .

Young´s experiment – interference between 2 sources of light (SYoung´s experiment – interference between 2 sources of light (S11 and S and S22))

Press ”Fringes” to view the screen. Move P to see the interference spectrum.Press ”Fringes” to view the screen. Move P to see the interference spectrum.

Maxwell – the electromagnetic wavesMaxwell – the electromagnetic wavesJames Clerk Maxwell James Clerk Maxwell became the first to became the first to investigate the relation between light and investigate the relation between light and electromagnetic waveselectromagnetic waves . .

The equations of Maxwell are an The equations of Maxwell are an outstanding theoretical work based on the outstanding theoretical work based on the works of Faraday, Reimann and Gaussworks of Faraday, Reimann and Gauss..

In 1862 Maxwell wrote “hardly can we not In 1862 Maxwell wrote “hardly can we not avoid the conclusion that the light is made avoid the conclusion that the light is made of transverse waves in the same medium of transverse waves in the same medium which cause electric and magnetic which cause electric and magnetic phenomena.”phenomena.”

Subsequently Hertz was the first to prove Subsequently Hertz was the first to prove the theories of Maxwell experimentally by the theories of Maxwell experimentally by means of an oscilloscope.means of an oscilloscope.

Maxwell – the electromagnetic waves (Maxwell – the electromagnetic waves (E=electric field, B=magnetic fieldE=electric field, B=magnetic field). ). You may change the frequency and the wave lengthYou may change the frequency and the wave length ..

Bohr´s atomic modelBohr´s atomic modelNiels Henrik David Bohr is the most famous Niels Henrik David Bohr is the most famous Dane next to H.C. Andersen.Dane next to H.C. Andersen.

In 1913 he advanced the theory of his In 1913 he advanced the theory of his atomic model which indicates, that the atomic model which indicates, that the electrons follow certain orbits around the electrons follow certain orbits around the nucleus. His theory implicates that there nucleus. His theory implicates that there are a certain number of energy states for a are a certain number of energy states for a an atom. Bohr´s theory explains a number an atom. Bohr´s theory explains a number of nuclear light phenomena.of nuclear light phenomena.

The complementary principle of Bohr The complementary principle of Bohr implies that you may view light as waves or implies that you may view light as waves or as particles – photons – depending on as particles – photons – depending on which phenomenon you consider .which phenomenon you consider .

The correspondence principle of Bohr The correspondence principle of Bohr bridged the classic physics and the bridged the classic physics and the quantum physics.quantum physics.

Einstein and lightEinstein and lightIn 1905 Albert Einstein described the In 1905 Albert Einstein described the light as packets of energy – photons.light as packets of energy – photons.

Different light have different photons Different light have different photons and some photons are able to loosen and some photons are able to loosen electrons from certain metals. If the electrons from certain metals. If the photons loosen a lot of electrons so photons loosen a lot of electrons so that they succeed one another the that they succeed one another the electrons produce electricity. Thus electrons produce electricity. Thus Einstein explained the photoelectric Einstein explained the photoelectric effect. effect.

In 1917 Einstein developed the theory In 1917 Einstein developed the theory which resulted in the development of which resulted in the development of laser light. laser light.

Watch the animation of photons. Watch the animation of photons.

The Moon reflects some of the light particles – photons – which come The Moon reflects some of the light particles – photons – which come from the Sun. Press mirrors and watch photons being reflectedfrom the Sun. Press mirrors and watch photons being reflected . .