The Wave-Particle Duality of Quanta
The exact nature of matter has puzzled scientists for centuries. We have discovered the building blocks of matter, but what is the nature of these blocks? How do they behave? The ultimate question boils down to whether these ‘blocks’ behave as waves, or as particles.
The quest for the answer to this question first focused on light. We now know that light is composed of the boson named the photon, but what is its nature? Greek scientists from the ancient Pythagorean discipline postulated that every visible object emits a steady stream of particles, while Aristotle determined that light travels in a manner similar to waves in the ocean.
Throughout the eighteenth century, two theories about the nature of light were in strong competition for acceptance. One theory, proposed by Dutch physicist and astronomer Christiaan Huygens during the seventeenth century (which was also held by a English contemporary of Newton’s named Robert Hooke), asserted that light traveled as small waves (wave theory). Although the wave theory successfully accounted for many of the observed properties of light such as interference and diffraction, it required a medium (like the water in which ocean waves move through). This medium, given the name ether or Æther, continued to elude physicists.
Around the same time, a second theory emerged, put forth by English physicist Sir Isaac Newton. In 1672, Newton published his first scientific paper on light and color in the Philosophical Transactions of the Royal Society. The paper was generally well received but Hooke and Huygens objected to Newton's attempt to prove, by experiment alone, that light consists of the motion of small particles rather than waves. And in his 1687 work Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy). Newton continued to show that light consisted of a series of tiny particles or "corpuscles". This corpuscular, or particle, theory explained why light traveled in straight lines and why it did not need a medium to travel through. But several problems remained with this particle theory, including trying to explain why light was able to cross paths without being deflected (surely the particles would collide with each other like cars running a red light). The two theories vied for acceptance for more than two centuries and many prominent scientists took opposing views and argued their positions with great conviction.
Proponents of the particle nature of light pointed towards the Photoelectric Effect as one experiment that required light to behave as a particle. In this experiment, when light shines on a metal surface, the surface emits electrons. If light were indeed a wave, its energy would be a measure of its amplitude (the taller the ocean wave, the more power it has). Thus, if the light intensity striking the metal plate was increased, the electrons emitted should have more energy. However, the experiment showed that this is NOT the case. Increasing the intensity of the light only increases the number of electrons, not the energy of the electrons released. Thus, light behaves as a particle, where increasing the intensity of the light only sends more particles to hit the metal atoms, but each particle has the same energy as in the less intense light. This is like using a machine gun and increasing the rate of fire to increase the intensity. In fact, the only way to change the energy of the electrons emitted is to change the wavelength of the light (use bigger bullets). Higher-frequency photons have more energy, so they make the electrons come flying out faster; thus, switching to light with the same intensity but a higher frequency increases the maximum energy of the emitted electrons. If you leave the frequency the same but crank up the intensity, more electrons come out (because there are more photons to hit them), but they don't come out any faster, because each individual photon still has the same energy. Einstein would later win the Nobel Prize for his work on the photoelectric effect (not for his more famous theory of relativity).
By the start of the 19th century, Newton’s corpuscular theory of light was widely accepted, albeit not universally.
In 1801, a British scientist named Thomas Young performed an experiment using a double slit apparatus to test the nature of light. He reasoned that if light consisted of particles, it would travel in straight lines from a source, through two slits in a barrier, and on to a screen placed at the back of the apparatus; at the screen, it would appear as two stripes of light. If, on the other hand, light consisted of waves, it would radiate outward from the source toward the two slits, pass through the two slits, and begin radiating anew from each of the two slits as it traveled toward the back screen. Where the path of the light from the two slits overlaps, the waves would interfere with each other. On the screen, it would appear as a series of stripes of light, representing the interference pattern typical of overlapping, symmetrical waves.
For example, when two water waves intersect, a new wave pattern is set up. Two wave peaks can coincide and form an amplified peak. Likewise, two wave troughs can coincide to form a deeper trough in a relationship known as constructive interference. Where a peak and trough coincide, however, they cancel each other out in a phenomenon known as destructive interference. On Young's screen, bright bands or lines would evidence constructive interference; dark lines or bands would evidence destructive interference.
The complete article is found on our website here
The quest for the answer to this question first focused on light. We now know that light is composed of the boson named the photon, but what is its nature? Greek scientists from the ancient Pythagorean discipline postulated that every visible object emits a steady stream of particles, while Aristotle determined that light travels in a manner similar to waves in the ocean.
Throughout the eighteenth century, two theories about the nature of light were in strong competition for acceptance. One theory, proposed by Dutch physicist and astronomer Christiaan Huygens during the seventeenth century (which was also held by a English contemporary of Newton’s named Robert Hooke), asserted that light traveled as small waves (wave theory). Although the wave theory successfully accounted for many of the observed properties of light such as interference and diffraction, it required a medium (like the water in which ocean waves move through). This medium, given the name ether or Æther, continued to elude physicists.Around the same time, a second theory emerged, put forth by English physicist Sir Isaac Newton. In 1672, Newton published his first scientific paper on light and color in the Philosophical Transactions of the Royal Society. The paper was generally well received but Hooke and Huygens objected to Newton's attempt to prove, by experiment alone, that light consists of the motion of small particles rather than waves. And in his 1687 work Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy). Newton continued to show that light consisted of a series of tiny particles or "corpuscles". This corpuscular, or particle, theory explained why light traveled in straight lines and why it did not need a medium to travel through. But several problems remained with this particle theory, including trying to explain why light was able to cross paths without being deflected (surely the particles would collide with each other like cars running a red light). The two theories vied for acceptance for more than two centuries and many prominent scientists took opposing views and argued their positions with great conviction.Proof I dare say?
Proponents of the particle nature of light pointed towards the Photoelectric Effect as one experiment that required light to behave as a particle. In this experiment, when light shines on a metal surface, the surface emits electrons. If light were indeed a wave, its energy would be a measure of its amplitude (the taller the ocean wave, the more power it has). Thus, if the light intensity striking the metal plate was increased, the electrons emitted should have more energy. However, the experiment showed that this is NOT the case. Increasing the intensity of the light only increases the number of electrons, not the energy of the electrons released. Thus, light behaves as a particle, where increasing the intensity of the light only sends more particles to hit the metal atoms, but each particle has the same energy as in the less intense light. This is like using a machine gun and increasing the rate of fire to increase the intensity. In fact, the only way to change the energy of the electrons emitted is to change the wavelength of the light (use bigger bullets). Higher-frequency photons have more energy, so they make the electrons come flying out faster; thus, switching to light with the same intensity but a higher frequency increases the maximum energy of the emitted electrons. If you leave the frequency the same but crank up the intensity, more electrons come out (because there are more photons to hit them), but they don't come out any faster, because each individual photon still has the same energy. Einstein would later win the Nobel Prize for his work on the photoelectric effect (not for his more famous theory of relativity).
By the start of the 19th century, Newton’s corpuscular theory of light was widely accepted, albeit not universally.
Thomas Young’s double-slit experiment
In 1801, a British scientist named Thomas Young performed an experiment using a double slit apparatus to test the nature of light. He reasoned that if light consisted of particles, it would travel in straight lines from a source, through two slits in a barrier, and on to a screen placed at the back of the apparatus; at the screen, it would appear as two stripes of light. If, on the other hand, light consisted of waves, it would radiate outward from the source toward the two slits, pass through the two slits, and begin radiating anew from each of the two slits as it traveled toward the back screen. Where the path of the light from the two slits overlaps, the waves would interfere with each other. On the screen, it would appear as a series of stripes of light, representing the interference pattern typical of overlapping, symmetrical waves.For example, when two water waves intersect, a new wave pattern is set up. Two wave peaks can coincide and form an amplified peak. Likewise, two wave troughs can coincide to form a deeper trough in a relationship known as constructive interference. Where a peak and trough coincide, however, they cancel each other out in a phenomenon known as destructive interference. On Young's screen, bright bands or lines would evidence constructive interference; dark lines or bands would evidence destructive interference.
The complete article is found on our website here
posted by The Universe Of Power at 6:53 PM
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