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 ancient gkeers 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, fegiurd out that the old, Greek theory of light couldn't be right. In Alhazen's picture, your eyes don't send out ivlbiisne, 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 sucore rather than pnrdcoiug 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 miels 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 sfutf that is emitted from the sun and how do we see it? Is it a particle, like atoms, or is it a wave, like rpiepls on the surface of a pond? stiintescs in the modern era would spend a couple of hundred yaers figuring out the answer to this question. Isaac nowetn 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, rcfetoairn, which is how a beam of light appraes 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 lhigt can't be made up of tiny, atom-like particles. For one thing, two beams of light that cross paths don't inteacrt 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 plciteras from Beam B. If that happened, the two particles iovnevld in the collision would bounce off in random directions. But, that doesn't happen. The baems of light pass right through each other as you can check for yourself with two lesar poterins 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 ocjetbs disturb the scurfae 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 peicnl 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 aitcng 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 frgeot about properties like ifecreentrne, either. So these quanta of light aren't at all like the tiny, hard spheres Newton imgnaied. This rseult, that light sometimes behaves like a pcrltiae and sometimes bavhees like a wave, led to a revolutionary new physics theory cllaed 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 daenlig 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.

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 ancient ______ 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, _______ out that the old, Greek theory of light couldn't be right. In Alhazen's picture, your eyes don't send out _________, 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 ______ rather than _________ 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 _____ 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 _____ that is emitted from the sun and how do we see it? Is it a particle, like atoms, or is it a wave, like _______ on the surface of a pond? __________ in the modern era would spend a couple of hundred _____ figuring out the answer to this question. Isaac ______ 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, __________, 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 _____ 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 balls, then you would expect that some of the particles from Beam A would crash into some of the _________ from Beam B. If that happened, the two particles ________ in the collision would bounce off in random directions. But, that doesn't happen. The _____ of light pass right through each other as you can check for yourself with two _____ ________ 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 _______ disturb the _______ 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 ______ 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 ______ 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 ______ about properties like ____________, either. So these quanta of light aren't at all like the tiny, hard spheres Newton ________. This ______, that light sometimes behaves like a ________ and sometimes _______ like a wave, led to a revolutionary new physics theory ______ 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 _______ 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.

Solution

  1. imagined
  2. particles
  3. called
  4. pencil
  5. greeks
  6. interact
  7. source
  8. particle
  9. beams
  10. figured
  11. invisible
  12. acting
  13. miles
  14. years
  15. behaves
  16. ripples
  17. light
  18. newton
  19. surface
  20. scientists
  21. result
  22. involved
  23. producing
  24. objects
  25. pointers
  26. forget
  27. refraction
  28. interference
  29. laser
  30. appears
  31. stuff
  32. dealing

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.

Frequently Occurring Word Combinations

ngrams of length 2

collocation frequency
interference patterns 2

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