How Does Light Actually Work?
How Does Light Actually Work?
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If you like this video, check out writer Geraint Lewis´ excellent book, co-written with Chris Ferrie:
Where Did the Universe Come From? And Other Cosmic Questions: Our Universe, from the Quantum to the Cosmos
https://www.amazon.com/Where-Universe…
AND check out his YouTube channel:
/ alaslewisandbarnes
Incredible thumbnail art by Ettore Mazza, the GOAT: https://www.instagram.com/ettore.mazz…
Animations by the superb Jero Squartini https://www.fiverr.com/share/0v7Kjv
Music from Silver Maple, Epidemic Sound and Artlist.
Stock footage from Storyblocks and Artgrid, images of galaxies from NASA and ESO/Hubble.
World line animation By Cyp - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index…
00:00 Introduction
05:18 What Is Light?
12:58 An Invisible World
21:11 An Impossible Particle
30:54 Both And Neither
46:52 The Life of a Photon
#quantum #relativity
Content
1.04 -> the newly born Universe buzzed and Frost
4.68 -> with Boundless Energy even after the
7.379 -> Raging furnace of the first few minutes
9.3 -> had died away temperatures Universe wide
12.12 -> were more than a hundred million degrees
14.36 -> for thousands of years this Primal heat
17.64 -> burned Cosmos of plasma a super hot mix
21.48 -> of particles and radiation
24.42 -> until one day it changed forever
29.76 -> that day arrived when the universe was
32.16 -> almost 400 000 years old and had cooled
35.1 -> to about 3 000 Kelvin in this now
37.8 -> comparatively tepid soup lone electrons
40.86 -> methylone protons and finally could
43.559 -> stick together forming the first atoms
47.219 -> but this was not all for each electron
50.7 -> and proton bound together a small amount
53.1 -> of energy was released a packet of
55.739 -> energy that raced away the cosmic speed
57.96 -> limit the speed of light a particle of
60.6 -> energy born in the formation of a
62.579 -> hydrogen atom a particle we call a
65.159 -> photon a particle of light itself
69.659 -> this Photon was far from the first but
72.42 -> as the universe began transitioning from
74.46 -> plasma into neutral gas light could then
77.22 -> for the first time stream freely through
79.979 -> its reaches and so how photons long long
84.299 -> journey
85.68 -> began
88.439 -> it headed out first into the universe's
91.259 -> Dark Ages a time before the first Stars
94.08 -> burned a time before the first galaxies
96.659 -> formed in the Eerie Darkness gravity
99.24 -> pulled on mass to mold the first seeds
101.88 -> of cosmic structure
103.799 -> the photon sped on and noticed nothing
107.18 -> eventually the first Stars burst into
109.68 -> life around it massive and Bloated these
112.14 -> ancient Suns burned themselves out in a
114.42 -> cosmic blink of an eye as the first
116.52 -> supergiant black holes grew rapidly
118.74 -> between them as they eagerly devoured
120.899 -> Mass
122.159 -> but the photon sped on
124.979 -> and notice nothing
127.079 -> the first galaxies began to assemble the
129.899 -> sky lit up with the fires of uncountable
132.36 -> young Stars across the cosmos as they
134.64 -> began to fuse the initial hydrogen and
136.62 -> helium atoms into heavier elements
139.92 -> but the photon sped on
142.62 -> and noticed
144.54 -> nothing
146.58 -> Millions steadily turned into billions
149.4 -> of years and as galaxies grew and
151.56 -> matured eventually the intense light of
153.959 -> young Stars began to settle the photon's
157.08 -> journey could have potentially lasted
158.94 -> forever into eternity but after almost
161.459 -> 14 billion light years of travel a large
164.58 -> spiral galaxy steadily came into view
167.36 -> its Destiny was set
170.7 -> near a small blue dot orbiting a small
174 -> white star after crossing the last few
176.819 -> thousand light years the photon collided
180 -> with a piece of metal part of a
182.459 -> telescope built by humans and orbiting
185.16 -> near the planet Earth
187.26 -> the photon's energy was completely
189.12 -> absorbed energizing electrons and
191.22 -> registering on detectors
195.06 -> but as the photon vanished from
197.159 -> existence its billions year-long Journey
200.28 -> complete
201.54 -> it's still simply did not notice
205.819 -> because to the photon itself
209.76 -> the journey never took place
213.26 -> 13.8 billion years of cosmic time
216.5 -> disappeared in an instant
219.72 -> yet how can this be light has existed in
223.62 -> the universe from its earliest moments
225.72 -> and will continue to exist long after
228.42 -> humanity and the stars are shred to dust
231.9 -> just how does it work and how can it
235.739 -> seemingly last forever
238.14 -> perhaps most importantly
240.319 -> what even is it
252.9 -> light is fast it only takes 0.13 seconds
256.739 -> for it to circulate the entire Globe
258.9 -> through fiber optic cables that slows
261.06 -> down by a third but that still means
262.919 -> that with surf shark changing your
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276.06 -> to stream whatever you want from
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282.3 -> seems to escape definition as it
283.86 -> exhibits properties of both the particle
285.54 -> and a wave and now you too can be
288.18 -> similarly inscrutable to Big tech
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298.38 -> personal information when using the
299.94 -> internet and even warns you of potential
302.1 -> data breaches so check out surfshark by
305.04 -> clicking on the link in the description
306.3 -> and get 83 off and three months for free
309.36 -> as well as a 30-day money-back guarantee
311.759 -> thanks to surf shark for supporting
314.22 -> educational content on YouTube
316.81 -> [Music]
320.94 -> light had played a pivotal role since
323.4 -> the cosmos's very beginning in these
326.28 -> earlier times it had only existed for
328.32 -> the very briefest of moments slamming
330.72 -> into speeding particles before it had a
332.82 -> chance to travel anywhere one piece of
335.16 -> light dying as another was born however
338.88 -> our parcel of light was born into a very
341.4 -> different very transparent Universe with
345.3 -> the cosmic Maelstrom of the Big Bang
347.28 -> finally abated our Photon could begin
350.039 -> its immense Journey unhindered as it
353.46 -> traveled many generations of stars led
355.919 -> to our sun and billions of years after
358.639 -> humans began to walk on the surface of
362.1 -> our small rocky planet and So eventually
365.58 -> as our Photon was a couple of thousand
367.979 -> light years distant from Earth
370.08 -> those humans began
372.96 -> to wander
376.139 -> all men by Nature desire to know an
379.32 -> indication of this is the Delight we
381.06 -> take in our senses and above all others
383.46 -> the sense of sight this most of all the
386.4 -> senses makes us know and brings to light
389.1 -> many differences between things
393.56 -> the ancient Greeks wondered if light
396 -> emanated from the eyes touching and
398.16 -> feeling the world around us but clearly
400.5 -> there are times when it is dark when we
402.539 -> can't see anything so they concluded
404.699 -> light must be something external
406.74 -> something captured by our eyes Islamic
410.34 -> scientists went on to unravel the
412.139 -> properties of light finding rules of
414.24 -> reflection and the magnification
415.74 -> properties of glass lenses light was
418.56 -> clearly a natural part of the universe
421.139 -> around us
423.36 -> but it took the coming of the Scientific
425.52 -> Revolution and a fight between two
427.979 -> giants of science the light's deepest
430.44 -> secrets to be finally uncovered
434.94 -> the year was 1652 and Dutch physicist
437.94 -> astronomer mathematician and all-round
440.16 -> genius Christian Huygens was exploring
443.22 -> Optical phenomena he had noted how light
446.759 -> traveled through lenses and bounced off
449.039 -> mirrored surfaces and was particularly
451.139 -> interested in the phenomenon of
452.88 -> refraction where the path of light is
455.039 -> bent when it passes from one medium to
457.259 -> another
458.16 -> Huygens noticed that light was often
460.319 -> split into the colors of the rainbow by
462.539 -> his instruments and sometimes strange
464.639 -> patterns of dark and light would be
466.259 -> produced clear evidence to him that
468.96 -> light was some sort of wave some sort of
472.8 -> traveling oscillating phenomenon
475.4 -> oscillations can be found throughout
477.599 -> nature from planetary orbits to
479.52 -> vibrating electrons but let's start with
482.34 -> a simple picture
483.919 -> think of a child on a swing
490.74 -> as they swing their position oscillates
492.96 -> from one position to the next and then
494.759 -> back again just like a pendulum that
496.62 -> drives the regular ticking and talking
498.12 -> of a grandfather clock when oscillations
500.819 -> act in unison but slightly out of Step
502.819 -> waves are formed a stone thrown in a
505.8 -> flat Pond pulls the water down with it
507.9 -> but the water bounces back this splash
510.78 -> of water pulls on its neighbors inducing
513.12 -> them to oscillate which in turn pulls on
515.7 -> their own neighbors these oscillations
518.219 -> fan out across the pond as a steadily
520.979 -> Rippling pattern of waves waves are
525.06 -> everywhere from sound waves Crossing in
527.279 -> the air to ocean water waves driven by
529.56 -> the wind and moon seismic shifts can
532.2 -> generate violent and destructive
533.82 -> earthquakes in our planetary crust
535.8 -> whilst similar waves Ripple in the
538.14 -> atmosphere of the Sun and other stars
541.62 -> and so light seemed also to be a wave
546.36 -> but this left an obvious question if
549.6 -> light is a wave
551.519 -> just what was doing the waving
556.62 -> in Britain Robert Hook also reached a
559.08 -> similar conclusion about the nature of
561 -> light and he realized that this picture
562.98 -> of wavy light could explain a lot of the
565.44 -> phenomenon he had seen this was
567.779 -> cutting-edge science at the time but
570.06 -> hook had a problem
572.399 -> and that problem
573.779 -> was a man
576.24 -> there are no surviving portraits of
578.459 -> Robert Hook and over the years a rumor
580.8 -> passed down the generations that this
582.779 -> powerful man was to blame having
584.76 -> conveniently lost the painting when
586.98 -> taking over his head of the Royal
588.42 -> Society in London for Robert Hook had a
591.66 -> powerful enemy and that enemy's name
594.959 -> was Isaac Newton
597.72 -> since cleared of any wrongdoing in the
599.82 -> absence of contemporary images of hook
601.38 -> there is still little question that the
603.72 -> two men were not friends for as well as
606.3 -> his far-reaching discoveries in
608.04 -> mathematics and gravity Newton also had
610.98 -> an interest in Optics and the nature of
613.74 -> light itself and he did not like what
617.399 -> hook or highgens had to say indeed it
621.42 -> was Newton who discovered that white
622.92 -> light could be split into a rainbow by
625.14 -> passing it through a prism and like hook
627.36 -> he had kept musing on this but unlike
630.18 -> hook Newton did not conclude that light
632.519 -> was some sort of wave to Newton light
635.7 -> consisted of corpuscles to Newton light
639.839 -> was made of tiny individual
643.14 -> particles
645.82 -> [Music]
647.459 -> Newton's Focus was the phenomenon of
649.62 -> diffraction the fact that waves bend
651.72 -> around a sharp edge he knew the sound a
654.24 -> wave in the air bent as it traveled past
656.339 -> sharp edges it was clear that you could
658.5 -> eavesdrop on a conversation from around
660.24 -> a corner without being able to see the
662.94 -> gossipers you could hear from behind an
665.519 -> object but you could not see so he
669.839 -> reasoned light simply could not be a
673.14 -> wave
674.04 -> and he didn't stop there Newton went
677.279 -> further much much further he reasoned
681.06 -> the light as a stream of particles would
683.82 -> even feel the pull of gravity in his
686.519 -> book Optics published in 1704 he wrote
689.279 -> do not bodies act upon light at a
692.16 -> distance and by their action Bend its
695.1 -> rays and though on this he was correct
697.86 -> he was not proved correct for centuries
701.76 -> so it was Newton's corpuscular theory of
704.459 -> light that reigned Supreme due more to
706.92 -> his weight of personality and scientific
708.839 -> standing as opposed to its ability to
711.18 -> explain the complex observations of
713.579 -> light
714.36 -> over the years however steadily the tide
717.12 -> began to turn away from Newton
719.82 -> in 1800 polymath Thomas Young Shawn
722.7 -> light threw a pair of narrow slits and
725.22 -> observed a pattern of interference on a
727.14 -> background screen this wasn't the first
729.12 -> demonstration of interference but it was
731.22 -> the clearest how could Newton's picture
733.8 -> of light as particles explain Young's
736.56 -> observation of interference how could
739.62 -> light as Tiny bullets passing through
741.66 -> either one slit or the other produce The
744.12 -> observed pattern simply throwing a
746.279 -> couple of Pebbles into a Still Pond
747.959 -> reveals that interference is naturally
749.94 -> produced by waves either in water or in
754.5 -> light other observations of light
756.48 -> supported its wave-like nature including
758.82 -> light's polarization through a material
760.86 -> called calcite but for centuries the big
764.16 -> secondary question remained unanswered
767.399 -> if light was a wave
770.04 -> just what was doing
772.92 -> the waving
776.16 -> foreign
779.15 -> [Music]
781.519 -> parcel of light was born when a proton
784.32 -> captured an electron It sped out into
786.959 -> the universe powerful and energetic but
789.839 -> as it traveled and the universe expanded
791.88 -> it started to lose some of that energy
794.16 -> the light originally blew to our eyes
796.86 -> steadily morphed through the colors of
799.079 -> the rainbow and into the red soon it was
802.92 -> joined by other energetic light shining
805.079 -> from countless billions of newly formed
807.3 -> stars there were different types of
809.519 -> light as well light of exceptionally
811.8 -> high energy and light with barely any
814.38 -> energy at all
816.12 -> the universe was Awash
819.839 -> of course our light did not know that
821.76 -> these would be invisible to human eyes
823.56 -> for it would be many billions of years
825.54 -> until eyes existed and indeed these
829.079 -> X-rays and radio waves as we call them
832.079 -> were unknown to us until the very end of
835.86 -> the 19th century
837.32 -> [Music]
840.72 -> in this new era thought itself will be
844.44 -> transmitted by radio
848 -> gulielmo Marconi was at his father's
850.74 -> estate near bologna in Italy he was
853.5 -> still a young man aged only 20 but his
856.139 -> education had opened his eyes to an
858.24 -> invisible world in the decades before
860.76 -> the nature of light had steadily been
862.8 -> unraveled and Marconi was ready to use
865.5 -> this newfound knowledge to change
868.139 -> everything staring at his equipment
870.54 -> Marconi was waiting to see a faint spark
873.06 -> in the darkness with the bundle of wires
875.459 -> and coils of his Workshop such a spark
877.68 -> could not be surprising but the impetus
880.139 -> for this spark was not in the equipment
882.36 -> before him it was in similar equipment
885.06 -> located several miles away of course the
888.959 -> 19th century had seen the arrival of the
891.06 -> telegraph where electronic pulses were
893.04 -> sent along wires that crossed entire
894.899 -> countries and continents but this needed
897.72 -> wires to be strung through the air and
899.88 -> under the oceans Marconi had no need for
903.779 -> such wires he would be sending messages
906.3 -> not along bits of copper his messages
909.3 -> would simply fly completely unseen
912.019 -> through the air
914.699 -> but how
916.92 -> the answer lies with one of science's
919.079 -> greatest Geniuses the answer lies with
922.38 -> James Clark Maxwell
925.29 -> [Music]
927.48 -> when a young James Clark Maxwell arrived
929.579 -> at the University of Cambridge in 1850
931.38 -> he was told that attendance at the 6 a.m
933.899 -> church service was compulsory for all
936 -> students
937.079 -> The scottish-born Prodigy had long been
938.82 -> a night owl and simply responded I I
942.18 -> suppose I could stay up that late his
944.519 -> name is writ large across the modern
946.32 -> world with his crowning achievement was
948.48 -> uniting two seemingly disparate
950.639 -> phenomena and creating something
952.56 -> remarkable
954.5 -> electricity and magnetism had been known
956.82 -> about since ancient times seen in the
959.279 -> strange attraction of robbed materials
960.899 -> and mysterious stones that knew how to
963.24 -> find North but by the 19th century it
965.88 -> was becoming clear that these two were
967.98 -> not truly distinct a flow of an electric
970.74 -> current could generate a magnetic field
972.899 -> and a changing magnetic field could
975.66 -> generate a current in a wire but as
978.66 -> Maxwell stared at these equations he
981.24 -> began to see a deeper picture instead of
985.079 -> separate relationships he saw that
987.6 -> electricity and magnetism could be
990.12 -> united into a single hole a United set
994.26 -> of mathematics that encompassed all
996.839 -> electric and all magnetic phenomena
1001.82 -> but Maxwell's great Insight was not only
1004.1 -> concerned with electromagnetic
1005.899 -> complexity for he wondered about the
1008.48 -> simplest situation of all
1011.259 -> electromagnetism in the nothingness of a
1015.079 -> vacuum
1017.3 -> how does light travel through the
1020.48 -> emptiness of space
1023 -> Maxwell knew that electromagnetic fields
1025.339 -> filled all of space even in vacuums but
1028.22 -> it was imagined that in empty space
1029.66 -> these fields would be null effectively
1032.419 -> not there but what if you plucked one of
1035.12 -> these fields either electric or magnetic
1037.28 -> so that these fields were not at zero at
1039.74 -> some location Maxwell pondered this
1042.26 -> question using his equations to explore
1044.24 -> how the situation would evolve and the
1047.12 -> answer was astounding think about
1050.059 -> pinching the skin on the back of your
1052.22 -> hand what happens when you let go of
1054.38 -> your pinch your skin sinks back to its
1057.02 -> unpinched self quickly if you are young
1059.12 -> and somewhat slower if you are older
1060.98 -> Maxwell's equations told him that the
1063.14 -> electromagnetic pinch would evolve away
1065.419 -> back to zero but that this was not the
1068.84 -> end of the story pinching the electric
1071.539 -> field would generate a similar pinch in
1073.58 -> the magnetic field and the pinch in the
1075.799 -> magnetic field would generate a pinch in
1077.78 -> the electric field and these pinches did
1080.48 -> not simply fade back to zero instead
1083.84 -> they oscillated regenerating each other
1086.66 -> from one moment to the next and just
1089.9 -> like ripples on a pond these
1091.7 -> oscillations traveled away as waves
1095.6 -> and so Maxwell realized these
1097.82 -> oscillations had the property of a light
1101.08 -> light he realized is a self-propagating
1105.7 -> electromagnetic wave but what was
1109.22 -> causing the ripples what was the
1111.2 -> electromagnetic equivalent of the stone
1113.179 -> thrown in the pond he saw that it was
1116 -> electric charges something we now know
1118.22 -> as electrons as these charges jiggle and
1121.64 -> oscillate they disturb nearby electric
1123.679 -> and magnetic fields and these
1125.78 -> disturbances Ripple away as
1127.6 -> electromagnetic radiation what we call
1130.88 -> light he also realized that the inverse
1133.94 -> must be true as light entered the eye
1136.039 -> and fell on the retina the oscillations
1138.14 -> of the light must cause electrons in
1140.179 -> atoms in the eye to jiggle and it is
1143.059 -> this jiggling of electrons in the eye
1144.919 -> center signals to the brain that we
1147.74 -> perceive as vision
1149.53 -> [Music]
1152.419 -> finally Maxwell understood what it was
1154.94 -> that was waving and what caused the
1157.94 -> waves
1158.9 -> and one more thing
1161.299 -> he knew that light had waves with a
1163.7 -> length of about a millionth of a meter
1165.38 -> but his equations showed no limitation
1167.78 -> on the wavelength of his electromagnetic
1170.179 -> waves and so he concluded that there
1173.299 -> must be light with both long and short
1175.7 -> wavelengths that is invisible to the eye
1178.94 -> it would take two more decades for the
1181.4 -> answer to this puzzle to present itself
1183.1 -> decades in which Maxwell died of cancer
1185.66 -> at the age of only 48.
1188.24 -> in 1886 Heinrich Hertz working at the
1191.12 -> University of karlsruhe was the first to
1193.16 -> find these invisible waves
1195.679 -> named herzian waves after their
1197.72 -> Discoverer a new Revolution had been
1200.059 -> born we now refer to these herzian waves
1203.9 -> as radio Hertz was understandably very
1207.2 -> pleased with his Discovery but when
1209 -> asked about the Practical use these
1210.74 -> radio waves have he apparently responded
1213.4 -> nothing I guess
1217.039 -> and yet it was these radio waves that
1219.5 -> only a few years later Marconi was using
1222.32 -> to send messages across miles and then
1225.679 -> across counties oceans and all across
1229.34 -> the immensity of the globe
1231.3 -> [Music]
1235.46 -> in 1909 Marconi received the Nobel Prize
1238.7 -> for his work on wireless telegraphy
1240.64 -> Hertz however died in 1894 at the
1243.98 -> youthful age of 36 never seeing the true
1247.22 -> promise of his discovery
1250.58 -> the world was set to become full of
1252.62 -> invisible light as the 20th century
1254.48 -> began and the Mystery of light's
1256.58 -> properties seemed settled
1259.82 -> that was until 1905.
1263.12 -> and a remarkable year for one German
1266.12 -> patent Clerk
1267.44 -> [Music]
1274.039 -> the universe continued to change and
1276.559 -> evolve as our particle of light traveled
1278.72 -> the mixture of light joining it on its
1281.059 -> Journey reflected that change bursts of
1283.76 -> radio waves and high energy gamma rays
1286.34 -> becoming more and more frequent this
1289.34 -> energy surged through space much of it
1292.159 -> flowing between the stars and into the
1294.74 -> darkness but some encountered lone atoms
1298.46 -> in The Emptiness of the Void the low
1301.88 -> energy radio waves very gently Shook and
1304.82 -> energized these atoms like a calm ocean
1307.64 -> wave lapping at a Sandy Shore just as we
1310.58 -> would expect from Maxwell's picture of
1313.1 -> electromagnetic waves but the behavior
1315.98 -> of the high energy gamma rays was
1318.919 -> different they delivered their energy to
1321.38 -> the atoms with a violent punch that
1323.78 -> ripped electrons clean away not a
1326.539 -> lapping Ripple but an isolated smash
1330.559 -> the gamma rays hit the atoms not like
1333.38 -> waves but like hard little energetic
1337.039 -> particles
1339.02 -> but how could Maxwell be wrong could on
1344.12 -> some occasions light be more like
1345.86 -> Newton's vision and act like a particle
1349.1 -> and if so just what would those
1352.58 -> occasions be
1354.45 -> [Music]
1360.08 -> for the present we have to work on both
1361.94 -> theories on Mondays Wednesdays and
1364.039 -> Fridays we use the wave theory on
1366.2 -> Tuesdays Thursdays and Saturdays we
1368.24 -> think in streams of flying energy quanta
1370.88 -> or corpuscles
1373.41 -> [Music]
1376.94 -> Alfred Nobel had made his fortune
1379.039 -> through his inventions and his
1380.539 -> businesses especially in the field of
1382.64 -> explosives and weapons and so perhaps
1385.58 -> not unfairly in an 1888 obituary in a
1388.76 -> French newspaper he was called The
1391.46 -> Merchant of death
1393.62 -> this surprised Nobel firstly as he was
1396.86 -> still very much alive but secondly and
1399.62 -> more distressingly because he realized
1401.96 -> what his historical Legacy was to be so
1406.28 -> in his will he decided to leave most of
1408.62 -> his fortune to a series of prizes prizes
1411.62 -> that would honor those that have
1412.88 -> conferred the greatest benefit to
1414.919 -> humankind across science the Nobel
1417.5 -> prizes are perhaps the most prestigious
1419.36 -> the list of winners replete with the
1421.52 -> Giants of science over more than a
1423.62 -> century and in 1901 the inaugural Nobel
1427.34 -> Prize in physics was awarded to the
1429.679 -> German Wilhelm rundgan for his
1432.2 -> discoveries about the nature of light
1436.4 -> for it was he who discovered the X-ray
1442.94 -> ronkin's experiments with various
1444.919 -> materials found that only the densest
1446.9 -> could halt x-rays he even managed to
1449.84 -> convince his wife Bertha to place her
1452.179 -> hand in the beam after realizing his
1454.52 -> x-rays should stream through her flesh
1456.62 -> but be partly blocked by her denser
1458.96 -> bones thus producing the first x-ray
1462.2 -> photograph
1463.76 -> whilst it was suspected that X-rays were
1466.159 -> electromagnetic radiation with a
1467.78 -> wavelength much smaller than visible
1469.58 -> light as opposed to radar which was much
1471.919 -> longer it took several decades to
1474.26 -> conclusively show that this was the case
1476.299 -> although in the meantime the medical
1478.039 -> application of x-rays to fix bones and
1480.32 -> save lives grew without bounds
1483.26 -> and so this meant that by the early
1484.88 -> 1900s Maxwell's vision of
1487.159 -> electromagnetic waves beyond the visible
1489.26 -> had been undoubtedly confirmed all of
1492.08 -> light's Secrets uncovered even the
1494.24 -> electron having been discovered all the
1496.88 -> remained was to find the rest of the
1498.5 -> light we could not see gamma rays
1501.02 -> microwaves and more to fill out the last
1503.36 -> gaps on the electromagnetic spectrum and
1506 -> wrap up the story
1508.97 -> [Music]
1511.22 -> but of course if physics feels that a
1513.799 -> job is done a rude shock is usually just
1517.7 -> around the corner
1519.38 -> in Maxwell's picture of light it could
1521.659 -> be thought of as a continuous wave
1523.64 -> scientists had found that when light
1525.62 -> crashed into most materials it
1527.84 -> continuously dumped energy that
1529.64 -> energized electrons causing them to be
1532.22 -> emitted this was called the
1534.08 -> photoelectric effect by lowering the
1536.6 -> intensity of light it took longer for
1538.34 -> energy to be deposited and it usually
1540.44 -> took longer for the electrons to begin
1542.299 -> to be spat out
1544.039 -> usually for that was not what was
1546.679 -> observed when light was shown on certain
1548.96 -> Metals electrons would seemingly be
1551.24 -> ejected instantaneously from the metal
1553.46 -> surface and the really confusing
1555.74 -> observation came from adjusting the
1557.659 -> color of the light being shown blue
1560.6 -> light would result in very energetic
1562.64 -> electrons being emitted green light
1564.62 -> resulted in less energetic electrons and
1567.559 -> red light produced no electrons at all
1571.9 -> this made no sense if all colors of
1575.84 -> light carry energy why did Red Light
1578.179 -> fail to energize the electrons
1583.7 -> this mystery was solved and new
1586.34 -> Mysteries were born in a very special
1589.1 -> year this was no ordinary year it was a
1593.72 -> miraculous year for it was the year that
1596.779 -> Albert Einstein changed physics
1600.2 -> forever
1601.82 -> most people are familiar with Einstein's
1604.1 -> Anna's mirabilis 1905 the year he wrote
1607.82 -> down the special theory of relativity
1610.1 -> but that was just the beginning Einstein
1613.4 -> was awarded the Nobel Prize in physics
1615.44 -> in 1921. the citation noted the award
1618.74 -> was for his services to theoretical
1620.6 -> physics yet one Topic in particular was
1624.14 -> singled out for recognition and it was
1626.84 -> not his work on relativity it was
1631.48 -> especially for his discovery of the law
1634.52 -> of the photoelectric effect
1637.34 -> when Einstein explored the photoelectric
1639.74 -> effect he had to radically revise
1641.659 -> Maxwell's vision of light he realized
1644.419 -> that when light interacted with
1646.039 -> electrons it could not do so as a
1648.5 -> continuous wave of energy instead the
1651.74 -> energy must be concentrated and dumped
1654.14 -> into an electron as an instantaneous
1656.6 -> packet light Einstein declared must be
1660.98 -> quantized it must be chunks of energy it
1665 -> must interact
1666.98 -> like a particle
1668.659 -> Einstein went on to explain that each
1670.88 -> packet of energy was proportional to the
1672.799 -> frequency of the light a packet of red
1675.02 -> light carries less energy than a packet
1676.88 -> of green light a packet of green light
1678.74 -> carries less energy than a packet of
1680.48 -> blue and so in experiments the red light
1683.36 -> simply didn't deliver enough energy for
1686.539 -> an electron to escape
1689.37 -> [Music]
1692 -> this enigmatic packet of energy didn't
1694.279 -> get its current name until 1926 when in
1697.159 -> an article in the journal Nature Gilbert
1699.559 -> Lewis coined the name Photon evidence
1703.34 -> for the particle nature of light swiftly
1705.38 -> grew and it was in 1923 Arthur Compton
1708.74 -> put together an important experiment but
1711.74 -> one that relied on a bizarre fact
1714.44 -> light
1715.94 -> can push
1720.02 -> this might seem like a strange thing to
1722.299 -> say how can light which has no Mass push
1725.48 -> but Maxwell's equations showed that in
1728.12 -> carrying energy light also carries
1730.58 -> momentum you can easily buy a Crooks
1733.279 -> radiometer today as an executive toy for
1735.5 -> your desk consisting of four veins in an
1738.26 -> evacuated glass tube one side black and
1741.14 -> the other side white when placed in
1743.48 -> bright sunlight the veins begin to spin
1746.32 -> pushed supposedly by the momentum of
1749.299 -> nothing more than sunlight as ever the
1752.36 -> physics of the Crux radiometer is more
1754.22 -> complex than this simple explanation but
1756.799 -> the force of sunlight pushing on the
1758.48 -> veins is real with some Visionaries
1761 -> imagining future Humanity coursing
1763.76 -> amongst the planet's solar sailing on
1767.059 -> sunlight
1768.32 -> in 1923 Arthur Compton's experiment
1771.32 -> however was a little different in his
1774.2 -> experiment Compton aimed a beam of high
1776.659 -> energy X-rays at an atomic Target thus
1779.779 -> ripping electrons from the outer part of
1781.76 -> the atoms but when examining the
1783.98 -> rebounding X-rays and recoiling
1785.899 -> electrons Compton found that Maxwell's
1788.48 -> picture of a wave of energy and momentum
1790.46 -> simply did not work instead Compton had
1794.179 -> to treat the x-rays and electrons like
1796.399 -> colliding billiard balls for when an
1798.919 -> x-ray hit an electron it delivered its
1801.26 -> energy and its momentum as a discrete
1803.779 -> packet when an x-ray hit an electron
1806.84 -> they definitively interacted
1809.899 -> like hard particles
1814.6 -> Newton's vision of particles of light
1817.279 -> was reborn but was this definitive proof
1821.059 -> that light was a particle
1823.46 -> not quite there was of course still a
1826.22 -> mountain of evidence for its wave-like
1828.02 -> nature if anything scientists were more
1831.02 -> confused than ever before despite
1833.6 -> Maxwell's picture of electromagnetic
1835.58 -> waves proving extremely powerful and
1837.86 -> successful these experiments in the
1840.08 -> early 1900s demanded that light must be
1843.32 -> a particle and so people began to wander
1847.46 -> was there even an answer to be found
1856.58 -> we began this story following a photon
1859.159 -> of light as it traveled across the
1861.14 -> universe Maxwell tells us that this
1863.48 -> Photon was formed by the changing energy
1865.52 -> of an electron and that it vanishes when
1867.919 -> finally absorbed by electrons at its
1870.26 -> Journey's End
1871.76 -> but what happens in between is this Epic
1875.659 -> Journey simply governed by Fate does the
1878.539 -> photon really fly off in a random
1880.58 -> Direction careening into an electron at
1882.98 -> some arbitrary point in its future this
1885.679 -> question is the next part of our story
1888.38 -> from the early 20th century it was
1891.14 -> realized that this simply could not be
1894.62 -> the case
1895.82 -> in the language of quantum mechanics the
1898.58 -> photons Journey has nothing to do with
1901.64 -> chance
1906.14 -> not only is the universe Stranger than
1908.299 -> we think it is Stranger than we can
1911.539 -> think
1914 -> we begin on a chilly morning in France
1916.279 -> in January 1793.
1920.299 -> with a swish of a guillotine Blade the
1922.58 -> King Louis XVI was no more throughout
1925.64 -> this upheaval chaos reigned across
1927.679 -> France Victor Francois the second Duke
1930.08 -> de broy battled for his King but
1932.299 -> eventually like many others of the
1933.919 -> aristocracy he fled France for safety
1936.559 -> abroad the de bruise eventually returned
1939.02 -> to their native France to shape the
1940.7 -> country after the upheaval of Revolution
1942.799 -> and after a series of Statesmen
1945.08 -> diplomats and writers in 1892 into the
1949.039 -> de bruy family was born the man who
1951.919 -> would change our understanding of
1954.38 -> everything
1955.34 -> his name was Louis Victor Pierre Ramon
1958.64 -> seventh Duke dubroy but in the annals of
1961.76 -> physics history he is simply known as
1964.82 -> the broy
1967.6 -> in the early 20th century he bore
1970.279 -> witness to the birth of quantum
1971.899 -> mechanics and the growing confusion
1973.64 -> about whether light was a particle or a
1976.52 -> wave to Deborah however there was one
1979.52 -> obvious solution though a
1981.26 -> counter-intuitive one light was neither
1984.2 -> and both at the same time it was clear
1988.64 -> that light when it traveled traveled as
1990.98 -> a wave producing the effects of
1992.779 -> interference and diffraction but when it
1995.059 -> interacted it interacted like a particle
1997.88 -> it seemed to exhibit properties of being
2000.1 -> both a particle and a wave but was never
2002.98 -> really either de broyer's remarkable
2005.679 -> Insight was to realize that this was
2008.44 -> true not only for light but for the
2011.44 -> entire Quantum world
2014.08 -> here he claimed there were no true
2016.299 -> particles and no true waves everything
2019.48 -> de broyer told us was some sort of
2023.62 -> quantum
2024.94 -> thing
2027.88 -> and so in his PhD in 1924 he claimed
2031.84 -> that electrons which were clearly
2033.7 -> particles should also exhibit wave-like
2036.88 -> properties and in 1929 he received the
2040.179 -> Nobel Prize when experiments or out his
2043.659 -> predictions there has been significant
2045.94 -> philosophical discussion about this wave
2048.28 -> particle duality in quantum mechanics
2050.5 -> but its observational consequences are
2053.379 -> incontrovertible a series of single
2055.599 -> photons or electrons sent through
2057.52 -> multiple slits still result in
2059.56 -> interference patterns and even large
2062.139 -> complex molecules have also been shown
2064.72 -> to have properties of both waves and
2067 -> particles the largest yet tested being 2
2070.78 -> 000 atoms in size and so with quantum
2074.5 -> mechanics in hand the quest was on to
2076.899 -> understand just how light and electrons
2080.139 -> interacted
2083.679 -> with classical physics the physics of
2085.839 -> Maxwell electrons jiggled as
2088.06 -> electromagnetic waves passed by just
2090.52 -> like seagulls bobbing on a choppy ocean
2092.5 -> and by their jiggling the electrons
2094.54 -> emitted their own electromagnetic waves
2096.82 -> adding to the mix but the quantum
2099.58 -> picture had to be different for the
2102.099 -> quantum world was one of quanta and
2105.339 -> particle reactions
2107.5 -> despite these opposing situations it
2109.72 -> didn't take long for a solution to be
2111.46 -> found and it was another scientific
2113.68 -> Titan Paul Adrian Maurice Dirac that
2117.099 -> began to crack the code in the late
2119.5 -> 1920s he was working to unite two of the
2122.74 -> greatest breakthroughs in modern physics
2124.96 -> The Strange World of quantum mechanics
2127.48 -> and Einstein's special theory of
2130.3 -> relativity dirac's story has been told
2132.76 -> many times about his famous
2134.76 -> absent-mindedness and lack of
2136.54 -> communication skills Quantum Pioneer
2139.119 -> Niels Bohr went as far as to call him
2141.04 -> the strangest man but there was
2143.74 -> absolutely no doubt that Iraq was a
2146.14 -> revolutionary genius and it was through
2148.599 -> his work on quantum mechanics the Dirac
2151.42 -> made his mark on scientific history
2158.26 -> to understand the modern view he helped
2160.599 -> to bring about we have to accept that
2163.599 -> everything is actually
2166.599 -> feels
2168.52 -> these fields are different to things
2170.44 -> like classical electric and magnetic
2172.72 -> fields in Quantum field Theory there are
2175.599 -> electron Fields Photon Fields fields for
2178.78 -> the various quarks and more a ripple for
2181.66 -> example in the electron field is an
2183.46 -> electron and a ripple in the photon
2185.68 -> field a photon
2188.26 -> think of an atom what do you see in our
2192.04 -> minds we often have the picture given to
2193.839 -> us by Niels Bohr of electrons orbiting a
2196.599 -> nucleus like a planet orbiting a star
2198.94 -> and when an electron jumps from a higher
2201.22 -> orbit to a lower orbit a photon of light
2203.56 -> is emitted but when considering the
2206.14 -> quantum world this is not quite correct
2209.16 -> in Quantum field Theory we think of an
2212.14 -> orbiting electron as a vibrational
2213.88 -> pattern in the electron field the higher
2217 -> energy orbit is one particular pattern
2218.92 -> and the lower energy orbit is another
2221.98 -> in the language of physics the electron
2224.56 -> field and the photon field are coupled
2227.8 -> together and jumping between the higher
2230.32 -> and lower orbits the electron field
2232.42 -> generates a vibration in the photon
2235.119 -> field
2239.56 -> Quantum field theory has grown to become
2241.9 -> arguably the most successful theory of
2244.18 -> our world to date describing almost
2246.52 -> everything in our universe across 24
2248.98 -> Quantum Fields corresponding to the
2251.98 -> various possible interactions of the
2254.02 -> standard model and so simple everything
2257.5 -> is fields and the fields interact
2261.46 -> but of course as they often do in the
2264.22 -> quantum World things are about to get a
2267.88 -> lot stranger many of the greatest minds
2271.42 -> of quantum mechanics were involved in
2273.339 -> this move towards strangeness but
2275.74 -> perhaps the most well-known is a man
2278.26 -> from Far Rockaway with a broad Brooklyn
2281.14 -> accent
2282.52 -> a man named Richard Feynman
2287.5 -> born in 1918 he started his career as
2290.859 -> part of the Manhattan Project and was
2293.079 -> recommended by Oppenheimer himself for
2295.42 -> Berkeley in a now famous letter sent in
2298 -> 1942 he is by all Lords the most
2301.18 -> brilliant young physicist here and
2303.339 -> everyone knows this I may give you two
2305.74 -> quotations from men with whom he has
2307.599 -> worked beta has said that he would
2310 -> rather lose any two other men than
2311.859 -> Feynman from this present job and vigna
2314.5 -> said he is a second Iraq only this time
2317.68 -> human though his 1985 autobiography
2321.579 -> surely you're joking Mr Feynman was an
2324.28 -> eye-opener for many not only regarding
2326.38 -> his numerous contributions to science
2328.24 -> but also his extroverted personality and
2331.06 -> complex private life including a ponchon
2334 -> for strip clubs these aspects did not
2336.64 -> fit the stereotypical vision of a
2339.04 -> professor indeed Murray girl man another
2341.619 -> giant of quantum mechanics once even
2344.079 -> quipped of Feynman feinman was a great
2346.54 -> scientist but he spent a great deal of
2349.06 -> his effort generating anecdotes about
2351.339 -> himself
2352.54 -> And yet when it came to thinking about
2354.46 -> the quantum world for many physicists
2357.16 -> Feynman changed everything
2359.53 -> [Music]
2361.859 -> whilst feynman's famous quip that no one
2364.54 -> truly understands quantum mechanics may
2366.579 -> have been true Feynman himself certainly
2369.22 -> understood the depth of the mathematics
2371.079 -> that underlies it
2373.119 -> this gave him the insights to think
2375.46 -> about the true nature of light and how
2378.4 -> it interacts
2380.26 -> it all starts with a solitary electron
2383.26 -> in the electromagnetics of Maxwell the
2385.96 -> charge of the electron results in an
2387.82 -> electric field surrounding it and a
2390.099 -> charge in an electric field feels the
2392.619 -> presence of the electric field in this
2395.619 -> situation there must be energy in the
2397.66 -> interaction but the question was how
2400.54 -> much the problem was every time Feynman
2403.48 -> tried to calculate the amount of energy
2405.16 -> the answer came out to be the same
2407.46 -> Infinity so Feynman did something quite
2411.579 -> radical he threw away the classical
2414.16 -> notion of the electric field as defined
2417.04 -> by Maxwell in the acceptance speech for
2419.92 -> the award of his Nobel Prize in 1965
2422.64 -> Feynman said I suggested to myself that
2426.46 -> electrons cannot act on themselves they
2429.52 -> can only act on other electrons
2433.839 -> and a new bizarre picture of the
2436.78 -> interaction of light and electrons
2438.7 -> emerged
2440.11 -> [Music]
2442.24 -> the best visual representation of this
2444.339 -> interaction is the diagram named after
2446.38 -> Feynman himself
2448.42 -> the Feynman diagram
2451.06 -> they are often a complicated mixture of
2453.28 -> lines Wiggles and Loops but at their
2456.28 -> heart Feynman diagrams describe all of
2459.52 -> the possible interactions in quantum
2461.98 -> mechanics to pick apart a Feynman
2464.26 -> diagram it is best to start with the
2466.3 -> simplest of interactions the interaction
2468.76 -> between electrons and Light
2472.06 -> Feynman diagrams represent an
2473.98 -> interaction over space and time lone
2476.859 -> electrons Trace out straight line paths
2479.32 -> through space-time a path known as its
2482.5 -> World line the electron is really just a
2485.02 -> vibration in the quantum electron field
2487.48 -> and with no interactions it happily
2490.06 -> traces a simple straight line path we
2493.24 -> also know however that the electron
2495.339 -> field can couple with the photon field
2497.98 -> and when this happens the vibrations in
2500.32 -> the electron field change in an atom the
2503.44 -> electron jumps from a high energy orbit
2505.48 -> to a low energy orbit but for a free
2508.3 -> electron conservation of momentum means
2511.3 -> that the electron changes direction if
2514.42 -> we imagine this over space time the
2517 -> world line of the electron possesses a
2519.16 -> distinct Kink and this occurs where and
2521.74 -> when the photon usually depicted as a
2524.079 -> wavy line is emitted this structure this
2527.44 -> Junction is known as a vertex and it is
2530.98 -> the basic Lego piece
2532.54 -> for building all Feynman diagrams of
2535.48 -> course full Feynman diagrams are more
2537.4 -> complex than a single vertex they
2539.5 -> usually combine several distinct pieces
2541.839 -> the emitted Photon from one electron is
2544.48 -> eventually received by another electron
2546.52 -> two vertices are joined together to give
2548.56 -> the complete interaction two kinked
2551.02 -> electron paths joined with the wiggly
2553.06 -> line representing the photon but what
2556 -> governs the coupling between the
2557.92 -> electron field and the photon field this
2561.099 -> is related to the charge on the electron
2563.079 -> and one of Nature's constants the fine
2565.3 -> structure constant this is
2568.079 -> electromagnetism and the exchange of the
2570.46 -> photon between two electrons is the
2572.32 -> electromagnetic force in action
2576.88 -> and so in feynman's view we wave goodbye
2580.599 -> to the electromagnetic field in its
2583.54 -> place we simply have two electrons
2585.46 -> interacting through the exchange of a
2588.28 -> photon and when huge numbers of these
2590.5 -> photons are exchanged it approximates
2592.54 -> the classical Force even though at its
2595.42 -> heart this electromagnetic force is a
2598.54 -> Quantum phenomenon
2601.23 -> [Music]
2603.16 -> and it's not just electromagnetism for
2606.16 -> it is also true for the fundamental weak
2609.04 -> and strong nuclear forces
2611.68 -> for the strong force it is gluons
2613.78 -> instead of photons that are exchanged
2615.579 -> between quarks and for the weak force it
2618.28 -> is via the exchange of massive particles
2620.619 -> known as the w and z and again all of
2624.339 -> these forces can be presented by a
2626.619 -> combination of Feynman vertices
2630.28 -> but this was not the end Feynman had one
2634.24 -> even stranger card yet to play when it
2637.42 -> came
2638.319 -> to light
2640 -> he had said that one electron acts upon
2642.52 -> another and this happens through the
2644.26 -> exchange of a photon producing the
2646.3 -> complete Feynman diagram of the
2647.92 -> interaction but did this mean that an
2650.38 -> electron fired out a photon at random
2653.079 -> did this Photon stream out into the
2655.3 -> universe with only a remote chance of
2657.16 -> being absorbed by another electron
2659.52 -> counter-intuitively the answer Feynman
2662.02 -> said was no he told us that the photon
2666.099 -> is only passed between two electrons
2668.44 -> that have agreed on the exchange
2672.16 -> but there is something odd happening
2673.839 -> here if we are in the middle of the
2675.7 -> photon's journey it's emission from one
2677.8 -> electron occurred in the past while the
2679.96 -> absorption of the photon by the other
2681.52 -> electron is going to occur in the future
2683.859 -> so when did the electrons communicate
2686.319 -> and agree to exchange the photon how did
2689.44 -> they even know of each other's presence
2691.26 -> it clearly cannot be via the
2693.4 -> electromagnetic force as this is
2695.14 -> precisely what the exchange of the
2696.64 -> photon actually is
2699.099 -> so what is the solution
2702.64 -> as with a lot of quantum mechanics
2704.68 -> what's the mathematics just works the
2707.44 -> interpretation the question of what is
2709.66 -> really happening is the biggest
2711.579 -> challenge and so Feynman with his
2714.52 -> supervisor John Wheeler put a
2716.619 -> mind-bending possibility on the table
2719.6 -> [Music]
2722.68 -> the suggestion is something we now call
2724.9 -> the transactional interpretation they
2727.96 -> said that the two electrons handshake
2730.3 -> their acceptance of exchanging the
2732.099 -> photon but that this handshake is taken
2736.119 -> Through Time one electron messages from
2739.78 -> the past
2740.92 -> and the other
2742.18 -> from the future this might sound
2744.7 -> ridiculous but it completely fits with
2747.52 -> the mathematics of quantum mechanics
2750.46 -> and so on a dark night when you gaze at
2753.4 -> a distant star an electron in your eye
2756.4 -> and an electron in the atmosphere of
2758.56 -> that star spoke to each other through
2761.079 -> time and agreed to exchange the photon
2764.04 -> you see
2766.119 -> and going even further for the lonely
2768.579 -> Photon we met at the beginning of our
2770.26 -> story two distant electrons shook hands
2773.92 -> over billions of years of time billions
2776.14 -> of light years of space and agreed that
2779.56 -> the photon should undertake it Cosmic
2782.859 -> Journey
2784 -> the bizarre world of quantum mechanics
2786.579 -> never disappoints
2789.819 -> and yet there is one final even stranger
2794.26 -> mystery to unfold about light and our
2796.78 -> lonely Photon in the Blackness of space
2799.72 -> as it travels over many billions of
2802.359 -> light years
2803.68 -> just what does the photon
2806.859 -> experience
2814.56 -> we've followed our Photon over many
2817.3 -> billions of years eventually a Journey's
2820.119 -> End the universe it inhabits is very
2822.4 -> different to the one of its birth
2824.8 -> yet there is a disconnect for once this
2828.22 -> Photon was almost as old as the universe
2830.8 -> itself
2831.76 -> it remained
2833.619 -> eternally useful
2837.88 -> galaxies formed in the void stars were
2840.88 -> born lived and died whole superclusters
2843.76 -> splintered and collapsed
2846.099 -> and the photon Misty doll because to the
2850.54 -> photon time itself
2853.3 -> meant nothing
2855.22 -> this might seem like a strange thing to
2857.319 -> say the photon clearly had an existence
2859.42 -> in time but with the coming of Einstein
2861.88 -> and his special theory of relativity it
2864.099 -> was realized that time was actually
2866.04 -> flexible it was relative dependent upon
2870.099 -> who or what was actually measuring it
2872.92 -> and light light takes this idea
2876.88 -> to the extreme
2878.71 -> [Music]
2882.28 -> what would the universe look like if I
2884.319 -> were riding on the end of a light beam
2886.18 -> at the speed of light
2888.43 -> [Music]
2889.72 -> in the middle of the 17th century only
2892.359 -> Roma was baffled working at the Paris
2895.42 -> Observatory Roma was peering at IO one
2898.54 -> of the bright moons of Jupiter like
2900.46 -> clockwork of the Moon orbited the giant
2902.56 -> planet in just over 42 hours Vanishing
2905.8 -> from view as it dugged in and out of
2907.72 -> Jupiter's Shadow except there seemed to
2910.06 -> be something odd about this Cosmic clock
2912.46 -> Roma noticed that the timing of io's
2915.52 -> eclipses drifted he realized that the
2919.18 -> timing of the eclipse of IO was somehow
2921.22 -> tied to the Earth's orbit changing from
2923.98 -> earlier to later and back again when the
2926.26 -> Earth was either closest to or further
2928.24 -> from Jupiter and it was then Roma
2931.06 -> realized the culprit was the light and
2934.359 -> in particular it speed he reasoned that
2937.78 -> the drift in io's eclipses must be due
2939.94 -> to a finite speed of light as the Earth
2942.46 -> moved in its orbit the distance to
2944.38 -> Jupiter changed and the change in time
2946.96 -> was because light had to Traverse these
2949.24 -> differing distances his initial estimate
2951.88 -> for the speed was fast very fast 220
2957.4 -> 000 kilometers every second and
2960.099 -> eventually more accurate measurements
2961.72 -> tied the speed of light to almost 300
2964.72 -> 000 kilometers per second
2966.76 -> but just what was this speed relative to
2972.579 -> it had been the belief for centuries
2974.38 -> that there existed a medium The Ether
2976.66 -> that carried light waves surely
2978.88 -> therefore light speed was relative to
2981.22 -> this medium from Plato to Newton this
2984.16 -> ether had long been suggested as a
2986.079 -> solution to various questions in physics
2988.18 -> but never firmly detected experiments in
2991.42 -> search of evidence having failed time
2993.819 -> and time again and so it was that in
2996.52 -> 1905 during his miracle year Einstein
3000.24 -> rang the final death now for this
3002.4 -> invisible medium
3004.079 -> special relativity
3006.06 -> the truth was that it was the speed of
3008.76 -> light that was the universal absolute
3011.099 -> and invariant measured to be the same
3013.859 -> value for all observers across the
3016.68 -> cosmos A lot has been written about
3018.839 -> special relativity and although much of
3021 -> it seems confused and paradoxical there
3023.4 -> is a simple Central message at its heart
3027.06 -> particles with mass such as electrons
3030.06 -> chart out their own time as they travel
3033.599 -> through space-time
3037.68 -> imagine two clocks sitting at the same
3040.26 -> location synced to show exactly the same
3043.14 -> time
3044.94 -> now take these clocks on two separate
3047.22 -> Journeys speeding them up and slowing
3049.44 -> them down in Newton's view of the
3051.78 -> universe of absolute time if you were to
3054 -> bring these clocks together again and
3055.8 -> compare their faces they would have
3057.48 -> remained synchronized but this is not
3060.72 -> the case in Einstein's the relative
3063.599 -> motion of the two clocks would have
3065.339 -> influenced their relative passage of
3067.14 -> time and as they trace out their
3069.42 -> different paths through space-time when
3072.059 -> they reunite their times will now be out
3076.02 -> of sync
3078 -> this mind-bending aspect of Relativity
3080.76 -> seems too strange to be true but
3082.859 -> numerous experiments have shown this to
3084.599 -> be the way the universe works from
3086.819 -> globetrotting atomic clocks to
3088.68 -> high-speed particles and accelerators
3090.78 -> time is definitively relative
3095.52 -> but what does this mean for light light
3099.78 -> had taken a central place in Einstein's
3102.119 -> New Vision of the cosmos everyone in
3104.64 -> space-time should measure the speed of
3106.38 -> light to be precisely the same value but
3109.68 -> in demanding this something else had to
3113.04 -> give and so space and time themselves
3116.819 -> had to bend become flexible and rubbery
3120.119 -> to accommodate the consistency of the
3122.339 -> speed of light indeed one immediate
3124.859 -> consequence of Einstein's insights was
3127.2 -> that light would feel the existence of
3129.24 -> gravity and as it traveled through the
3131.22 -> universe light's path would be deflected
3133.38 -> by the presence of mass Newton's claim
3136.44 -> of two centuries prior reborn indeed
3140.4 -> experiments have worn this out again and
3142.319 -> again with the results becoming more and
3144.059 -> more accurate massive objects such as
3146.7 -> stars and galaxies can even behave as
3149.4 -> gravitational lenses magnifying distant
3152.819 -> galaxies from the very early universe
3154.98 -> and revealing the presence of dark
3157.559 -> matter
3158.94 -> the beauty of these natural telescopes
3160.98 -> is clearest in deep space images
3163.859 -> such as the first revealed by the James
3167.04 -> Webb Space Telescope
3170.7 -> and so the flexible nature of space and
3173.4 -> time had truly seen the end of Newton's
3175.8 -> view of a rigid universe
3178.38 -> but again
3179.819 -> what about
3182.04 -> light
3183.68 -> what did this mean for light's
3186.42 -> experience of space and time traveling
3190.619 -> at the fastest speed possible in the
3192.48 -> universe the effects of Relativity
3194.52 -> become extreme
3196.619 -> very extreme all distances shrink to
3201.48 -> zero as does the time taken to cover
3204.119 -> these zero distances
3206.099 -> and so for photons no matter how far
3209.4 -> they travel across the universe
3211.92 -> not a single instant of time
3214.38 -> we'll take by even though this light may
3217.319 -> have existed in time and space for many
3219.42 -> years or light years even though it
3221.94 -> would have been clearly formed by one
3223.5 -> electron in one location and vanished
3225.72 -> when absorbed by another electron in
3227.7 -> another location the space-time distance
3230.4 -> between these two events would be
3232.98 -> exactly zero
3235.859 -> Photon it is born and dies at precisely
3240 -> the same moment we began this story by
3244.319 -> following a lone Photon from its
3246.119 -> creation just after the beginning of
3247.859 -> time to its ultimate destruction in the
3250.26 -> detector of a telescope orbiting our
3252.24 -> planet today
3254.22 -> and yet the photon itself saw nothing of
3257.94 -> this not the intense light of Stellar
3260.46 -> birth the catastrophic explosions that
3262.74 -> come with Stellar death or the formation
3265.38 -> of planets and eventual Rise Of Life on
3268.44 -> our own pale blue dots
3272.28 -> the photon
3273.839 -> noticed nothing
3277.06 -> [Music]
3283.8 -> you've been watching the entire history
3285.48 -> of the universe don't forget to like And
3287.76 -> subscribe and leave a comment to tell us
3289.44 -> what you think
3290.64 -> thanks for watching and we'll see you
3293.16 -> next time
3294.05 -> [Music]
3296.64 -> foreign
Source: https://www.youtube.com/watch?v=bAedYtUredI