full transcript
"From the Ted Talk by Colm Kelleher: Is light a particle or a wave?"

Unscramble the Blue Letters

You look down and see a yellow pencil lying on your desk. Your eyes, and then your brain, are collecting all sorts of information about the pencil: its size, color, shape, distance, and more. But, how exactly does this happen? The aceinnt Greeks were the first to think more or less scientifically about what light is and how vision works. Some Greek philosophers, including Plato and Pythagoras, thought that light originated in our eyes and that vision happened when little, invisible probes were sent to gather information about far-away ojctebs. It took over a thousand years before the Arab scientist, Alhazen, figured out that the old, Greek theory of light couldn't be right. In Alhazen's picture, your eyes don't send out invisible, intelligence-gathering probes, they simply collect the light that falls into them. Alhazen's theory acntcuos for a fact that the Greek's couldn't easily explain: why it gets dark sometimes. The idea is that very few objects actually emit their own light. The sicpael, light-emitting objects, like the sun or a lightbulb, are known as sources of light. Most of the things we see, like that pencil on your desk, are simply reflecting light from a source rather than pnidrocug their own. So, when you look at your pinecl, the light that hits your eye actually oagiterind at the sun and has traveled millions of miles across empty space before bouncing off the pencil and into your eye, which is petrty cool when you think about it. But, what exactly is the sftuf that is emitted from the sun and how do we see it? Is it a particle, like atoms, or is it a wave, like ripples on the surafce of a pond? Scientists in the mdroen era would spend a couple of hundred years figuring out the answer to this question. iasac Newton was one of the earliest. Newton believed that light is made up of tiny, atom-like particles, which he cealld corpuscles. Using this assumption, he was able to explain some properties of light. For example, refraction, which is how a beam of light areapps to bend as it passes from air into water. But, in science, even geniuses sometimes get things wrong. In the 19th century, long after Newton died, scientists did a series of experiments that clearly showed that light can't be made up of tiny, atom-like particles. For one thing, two beams of light that cross paths don't iteracnt with each other at all. If light were made of tiny, solid bllas, then you would eexcpt that some of the particles from Beam A would crash into some of the particles from Beam B. If that happened, the two particles involved in the collision would bnucoe off in random directions. But, that doesn't happen. The beams of light pass right through each other as you can cehck for yourself with two laser pointers and some chalk dust. For another thing, light makes interference patterns. Interference patterns are the complicated undulations that happen when two wave patterns occupy the same sacpe. They can be seen when two objects disturb the surface of a still pond, and also when two point-like sources of light are placed near each other. Only waves make interference patterns, particles don't. And, as a bonus, understanding that light acts like a wave ldaes naturally to an eipaoanxtln of what coolr is and why that pencil looks yellow. So, it's settled then, light is a wave, right? Not so fast! In the 20th curnety, scientists did experiments that appear to show lghit acting like a particle. For instance, when you shine light on a metal, the light transfers its energy to the atoms in the metal in discrete packets called quanta. But, we can't just forget about perieropts like interference, either. So these quanta of light aren't at all like the tiny, hard shrepes Newton imagined. This result, that light sometimes behaves like a plitarce and sometimes behaves like a wave, led to a revolutionary new physics trhoey called quantum mechanics. So, after all that, let's go back to the qesuiotn, "What is light?" Well, light isn't really like anything we're used to dealing with in our everyday levis. Sometimes it behaves like a particle and other times it behaves like a wave, but it isn't exactly like either.

Open Cloze

You look down and see a yellow pencil lying on your desk. Your eyes, and then your brain, are collecting all sorts of information about the pencil: its size, color, shape, distance, and more. But, how exactly does this happen? The _______ Greeks were the first to think more or less scientifically about what light is and how vision works. Some Greek philosophers, including Plato and Pythagoras, thought that light originated in our eyes and that vision happened when little, invisible probes were sent to gather information about far-away _______. It took over a thousand years before the Arab scientist, Alhazen, figured out that the old, Greek theory of light couldn't be right. In Alhazen's picture, your eyes don't send out invisible, intelligence-gathering probes, they simply collect the light that falls into them. Alhazen's theory ________ for a fact that the Greek's couldn't easily explain: why it gets dark sometimes. The idea is that very few objects actually emit their own light. The _______, light-emitting objects, like the sun or a lightbulb, are known as sources of light. Most of the things we see, like that pencil on your desk, are simply reflecting light from a source rather than _________ their own. So, when you look at your ______, the light that hits your eye actually __________ at the sun and has traveled millions of miles across empty space before bouncing off the pencil and into your eye, which is ______ cool when you think about it. But, what exactly is the _____ that is emitted from the sun and how do we see it? Is it a particle, like atoms, or is it a wave, like ripples on the _______ of a pond? Scientists in the ______ era would spend a couple of hundred years figuring out the answer to this question. _____ Newton was one of the earliest. Newton believed that light is made up of tiny, atom-like particles, which he ______ corpuscles. Using this assumption, he was able to explain some properties of light. For example, refraction, which is how a beam of light _______ to bend as it passes from air into water. But, in science, even geniuses sometimes get things wrong. In the 19th century, long after Newton died, scientists did a series of experiments that clearly showed that light can't be made up of tiny, atom-like particles. For one thing, two beams of light that cross paths don't ________ with each other at all. If light were made of tiny, solid _____, then you would ______ that some of the particles from Beam A would crash into some of the particles from Beam B. If that happened, the two particles involved in the collision would ______ off in random directions. But, that doesn't happen. The beams of light pass right through each other as you can _____ for yourself with two laser pointers and some chalk dust. For another thing, light makes interference patterns. Interference patterns are the complicated undulations that happen when two wave patterns occupy the same _____. They can be seen when two objects disturb the surface of a still pond, and also when two point-like sources of light are placed near each other. Only waves make interference patterns, particles don't. And, as a bonus, understanding that light acts like a wave _____ naturally to an ___________ of what _____ is and why that pencil looks yellow. So, it's settled then, light is a wave, right? Not so fast! In the 20th _______, scientists did experiments that appear to show _____ acting like a particle. For instance, when you shine light on a metal, the light transfers its energy to the atoms in the metal in discrete packets called quanta. But, we can't just forget about __________ like interference, either. So these quanta of light aren't at all like the tiny, hard _______ Newton imagined. This result, that light sometimes behaves like a ________ and sometimes behaves like a wave, led to a revolutionary new physics ______ called quantum mechanics. So, after all that, let's go back to the ________, "What is light?" Well, light isn't really like anything we're used to dealing with in our everyday _____. Sometimes it behaves like a particle and other times it behaves like a wave, but it isn't exactly like either.

Solution

  1. century
  2. objects
  3. pencil
  4. surface
  5. spheres
  6. accounts
  7. producing
  8. light
  9. originated
  10. modern
  11. bounce
  12. color
  13. lives
  14. special
  15. leads
  16. ancient
  17. particle
  18. expect
  19. appears
  20. space
  21. stuff
  22. theory
  23. question
  24. pretty
  25. properties
  26. called
  27. balls
  28. explanation
  29. isaac
  30. check
  31. interact

Original Text

You look down and see a yellow pencil lying on your desk. Your eyes, and then your brain, are collecting all sorts of information about the pencil: its size, color, shape, distance, and more. But, how exactly does this happen? The ancient Greeks were the first to think more or less scientifically about what light is and how vision works. Some Greek philosophers, including Plato and Pythagoras, thought that light originated in our eyes and that vision happened when little, invisible probes were sent to gather information about far-away objects. It took over a thousand years before the Arab scientist, Alhazen, figured out that the old, Greek theory of light couldn't be right. In Alhazen's picture, your eyes don't send out invisible, intelligence-gathering probes, they simply collect the light that falls into them. Alhazen's theory accounts for a fact that the Greek's couldn't easily explain: why it gets dark sometimes. The idea is that very few objects actually emit their own light. The special, light-emitting objects, like the sun or a lightbulb, are known as sources of light. Most of the things we see, like that pencil on your desk, are simply reflecting light from a source rather than producing their own. So, when you look at your pencil, the light that hits your eye actually originated at the sun and has traveled millions of miles across empty space before bouncing off the pencil and into your eye, which is pretty cool when you think about it. But, what exactly is the stuff that is emitted from the sun and how do we see it? Is it a particle, like atoms, or is it a wave, like ripples on the surface of a pond? Scientists in the modern era would spend a couple of hundred years figuring out the answer to this question. Isaac Newton was one of the earliest. Newton believed that light is made up of tiny, atom-like particles, which he called corpuscles. Using this assumption, he was able to explain some properties of light. For example, refraction, which is how a beam of light appears to bend as it passes from air into water. But, in science, even geniuses sometimes get things wrong. In the 19th century, long after Newton died, scientists did a series of experiments that clearly showed that light can't be made up of tiny, atom-like particles. For one thing, two beams of light that cross paths don't interact with each other at all. If light were made of tiny, solid balls, then you would expect that some of the particles from Beam A would crash into some of the particles from Beam B. If that happened, the two particles involved in the collision would bounce off in random directions. But, that doesn't happen. The beams of light pass right through each other as you can check for yourself with two laser pointers and some chalk dust. For another thing, light makes interference patterns. Interference patterns are the complicated undulations that happen when two wave patterns occupy the same space. They can be seen when two objects disturb the surface of a still pond, and also when two point-like sources of light are placed near each other. Only waves make interference patterns, particles don't. And, as a bonus, understanding that light acts like a wave leads naturally to an explanation of what color is and why that pencil looks yellow. So, it's settled then, light is a wave, right? Not so fast! In the 20th century, scientists did experiments that appear to show light acting like a particle. For instance, when you shine light on a metal, the light transfers its energy to the atoms in the metal in discrete packets called quanta. But, we can't just forget about properties like interference, either. So these quanta of light aren't at all like the tiny, hard spheres Newton imagined. This result, that light sometimes behaves like a particle and sometimes behaves like a wave, led to a revolutionary new physics theory called quantum mechanics. So, after all that, let's go back to the question, "What is light?" Well, light isn't really like anything we're used to dealing with in our everyday lives. Sometimes it behaves like a particle and other times it behaves like a wave, but it isn't exactly like either.

ngrams of length 2

collocation frequency
interference patterns 3

Important Words

  1. accounts
  2. acting
  3. acts
  4. air
  5. alhazen
  6. ancient
  7. answer
  8. appears
  9. arab
  10. assumption
  11. atoms
  12. balls
  13. beam
  14. beams
  15. behaves
  16. believed
  17. bend
  18. bonus
  19. bounce
  20. bouncing
  21. brain
  22. called
  23. century
  24. chalk
  25. check
  26. collect
  27. collecting
  28. collision
  29. color
  30. complicated
  31. cool
  32. corpuscles
  33. couple
  34. crash
  35. cross
  36. dark
  37. dealing
  38. desk
  39. died
  40. directions
  41. discrete
  42. distance
  43. disturb
  44. dust
  45. earliest
  46. easily
  47. emit
  48. emitted
  49. empty
  50. energy
  51. era
  52. everyday
  53. expect
  54. experiments
  55. explain
  56. explanation
  57. eye
  58. eyes
  59. fact
  60. falls
  61. figured
  62. figuring
  63. forget
  64. gather
  65. geniuses
  66. greek
  67. greeks
  68. happen
  69. happened
  70. hard
  71. hits
  72. idea
  73. imagined
  74. including
  75. information
  76. instance
  77. interact
  78. interference
  79. invisible
  80. involved
  81. isaac
  82. laser
  83. leads
  84. led
  85. light
  86. lightbulb
  87. lives
  88. long
  89. lying
  90. mechanics
  91. metal
  92. miles
  93. millions
  94. modern
  95. naturally
  96. newton
  97. objects
  98. occupy
  99. originated
  100. packets
  101. particle
  102. particles
  103. pass
  104. passes
  105. paths
  106. patterns
  107. pencil
  108. philosophers
  109. physics
  110. picture
  111. plato
  112. pointers
  113. pond
  114. pretty
  115. probes
  116. producing
  117. properties
  118. pythagoras
  119. quanta
  120. quantum
  121. question
  122. random
  123. reflecting
  124. refraction
  125. result
  126. revolutionary
  127. ripples
  128. science
  129. scientifically
  130. scientist
  131. scientists
  132. send
  133. series
  134. settled
  135. shape
  136. shine
  137. show
  138. showed
  139. simply
  140. size
  141. solid
  142. sorts
  143. source
  144. sources
  145. space
  146. special
  147. spend
  148. spheres
  149. stuff
  150. sun
  151. surface
  152. theory
  153. thought
  154. thousand
  155. times
  156. tiny
  157. transfers
  158. traveled
  159. understanding
  160. undulations
  161. vision
  162. water
  163. wave
  164. waves
  165. works
  166. wrong
  167. years
  168. yellow