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9-12 > Physical Science
Grade level: 9-12 Subject: Physical Science Duration: Two class periods
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Understanding: Uncertainty

Students will understand the following:
1. The Heisenberg uncertainty principle, formulated by the German scientist Werner Heisenberg, states that in the world of subatomic particles, the very act of observing alters the reality being observed, and therefore, in that world of subatomic particles, one can never measure all properties exactly.
2. The “uncertainty” in the uncertainty principle cannot be done away with by better observation techniques; rather, it is part of the nature of reality itself.
3. The uncertainty principle does not apply to the world of ordinary objects, since in that world, the effect of observation on the reality observed is so small as to be negligible.

For this lesson, you will need:
Research materials on Heisenberg and the uncertainty principle
Computer with Internet access
Materials students may need to create models

1. Share the following background information with your students: In 1927, the young German physicist Werner Heisenberg was working at the Danish physicist Niels Bohr’s research institute in Copenhagen, Denmark. The two scientists worked together on theoretical investigations into quantum theory and the nature of physics. When Bohr was away on vacation, Heisenberg had an insight into the limits of physical knowledge:The act of observing alters the reality being observed.
2. Go on to explain that Heisenberg was thinking about reality at the subatomic level. His reasoning went like this: To measure the properties (position and momentum) of a particle such as an electron, one must use light, or radiation, as a measuring device. But the energy in the radiation affects the electron being observed. If you adjust the light beam to accurately measure position, the energy of the light beam will change the momentum of the electron; if you adjust the light beam to measure the momentum of the electron, the energy of the light beam will move the electron, throwing off its position.
3. To simplify further, explain that to determine the position of an electron, we shine light on it. The light strikes the electron and causes it to move a very tiny amount. This means that the “image” of the electron (if we could see it) is slightly blurred, like a photograph in which a person moved while the picture was being taken. We can defineprobablelocations for the electron but cannot locate it exactly.
4. Clarify one more concept before moving on: Uncertainty is not due to any fault on the part of the observer; rather, it is part of the nature of reality.
5. Let students know that the Heisenberg uncertainty principle applies only to the subatomic world, not to the ordinary world of macroscopic objects. It is only in the quantum mechanical world that in order to make a measurement, one must disturb the system. In other words, in order for us to know something is there, we must bump into it; in order to locate an electron, the electron must encounter a photon. In the ordinary world, this does not hold true.
6. Once students have grasped the foregoing simplified explanation of Heisenberg’s uncertainty principle, divide your class into groups. Challenge group members to design a model that would help others understand the uncertainty principle. Here are three examples of the sorts of models students might come up with:
  • One person acts as a particle, such as an electron, circling in its orbit around the nucleus of an atom. Another person acts as a photon, bumping into the “electron,” thus moving it as the two encounter each other.
  • A Ping-Pong ball represents an electron, and a hair dryer represents a beam of light. When the “beam” (i.e., the stream of air) encounters the “electron,” it causes it to move.
  • A Ping-Pong ball in an open shoe box lined with cotton represents an electron. The only way a blindfolded person can locate the ball in the box is by dropping paper clips into the box and listening for the difference in sound when a paper clip hits the ball or hits the cotton-lined bottom of the box. However, when the paper clip hits the ball, it causes the ball to move.
7. Students in each group should accompany their model with a written explanation of what each component in the model represents and how the model helps to explain Heisenberg’s principle.
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Give students the simplest possible explanation of Heisenberg’s uncertainty principle. Rather than asking them to come up with their own ideas for ways to model the principle, illustrate the principle for them by one of the example models given.
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Discussion Questions

1. Philosophers of science (physicists) now consider several realities when explaining the nature of the universe. Give examples of how other major philosophies (such as political, religious, economic) also recognize alternate realities.
2. What is meant by the phrase, “collapse of the wave function,” when physicists are trying to decide whether or not to think of an electron as a wave or as a particle?
3. “Schroedinger’s Cat” is a scientific parable explaining how physicists create reality to explain outcomes. Discuss the probabilistic nature of a wave, the certainty of a particle, and Heisenberg’s Uncertainty Principle in the context of this parable.
4. Near the end of “Understanding: Uncertainty,” the narrator asks you, the viewer, who may be taking a hard look at this program, if you feel annoyed, stupid, or have a sense of being on the edge of a new understanding. Explain how you feel after viewing this program.
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Students’ models and explanations should reflect their own grasp of the Heisenberg uncertainty principle.
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Take a Cyberspace Field Trip into the Nucleus of an Atom
“The Particle Adventure” is an award-winning multimedia interactive Web site that will take your students on a tour of the inner workings of the atom. Your students will explore the particles that exist within the atom and the nucleus, and the forces that hold them there. Frequent quizzes check your students’ understanding of what they have toured. Particle Adventure may be found atadventure.

Schroedinger’s Cat
“Schroedinger’s Cat” is a scientific parable explaining how physicists create reality to explain outcomes. Have students do research to find and understand the parable. Then invite them to discuss the probabilistic nature of a wave, the certainty of a particle, and Heisenberg’s uncertainty principle in the context of the parable.

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Suggested Readings

A Journey into the Mysteries of Relativity and Quantum Mechanics
Alphonse J. Sistino. Orland Park, Illinois: Beaudoin, 1997
This book captures the essences of ancient, classical, and modern physics, including quantum mechanics and its development, in an exploratory narrative.

Order, Chaos, Order: The Transition from Classical to Quantum
Phillip Stehle. New York: Oxford University Press, 1994
Discover the history of quantum theory in this fascinating book.

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A Perspective on Interconnectedness from Quantum Mechanical Physicist and Philosopher, David Bohm (1917-1992)
“Understanding: Uncertainty” could be your physics students’ first exposure to a deep and serious philosophical discussion on the modern view of reality among physicists. Print out this brief essay by quantum physicist David Bohm.

The Particle Adventure
This award-winning mutlimedia interactive site will in a very interesting way help allow your students to explore the particles that exist within the atom and the nucleus, and the forces that hold them there. Students are quizzed frequently.

The Page of Uncertainty
To paraphrase the author, “This page is dedicated to that enigmatic scientific law, the Heisenberg Uncertainty Principle.”

Fermi Lab: Discovering the Nature of Nature
Nobel laureate Leon Lederman was the former director of The Fermi Lab featured at this site. On your tour of one of the largest particle accelerators be sure to check out “Particle Physics” and “Education.”

Introduction to Cosmology
Certainly it is with uncertainty that we completely understand the fundamental structure of matter, space and time, and yet we allow our imagination to pull together that which we do know into interconnected cosmological theories.

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Click on any of the vocabulary words below to hear them pronounced and used in a sentence.

speaker    physics
Definition:A science that deals with matter and energy and their interactions.
Context:Physics, like science itself, is a disciplined way of coming to know and then explaining the nature of the physical world. A world made of matter in motion.

speaker    Newton’s mechanical universe (Newtonian physics)
Definition:A body of three laws, proposed by Sir Isaac Newton in the 17th century, that describes the interaction of matter and motion in cause and effect type relations.
Context:The founders of America looked for a way of governing that was based on natural principles with a government that would run objectively and mechanically as did Newton’s mechanical universe.

speaker    quantum mechanics
Definition:A theory of matter that is based on the concept of the possession of wave properties by elementary particles, that affords a mathematical interpretation of the structure and interactions of matter on the basis of these properties, and that incorporates within it quantum theory and the uncertainty principle.
Context:As physicists peered into the atom they were forced to accept new realities of matter and energy, thus a new view, a quantum mechanical view, emerges in the 20th century.

speaker    reality
Definition:Existing or occurring as fact, actual rather than imaginary, ideal, or fictitious.
Context:What is reality to a physicist is that which is measurable.

speaker    wave/particle theory
Definition:A theory that allows us to give the reality of a wave when it is successful in explaining observed and measurable phenomena, and to choose to give it the reality of a particle when that choice yields a logical explanation for observed phenomena.
Context:When photons of light pass through a diffraction grating, they interfere constructively and destructively as if they were waves. When photons bounce off a mirror, we can think of them as behaving as particles.

speaker    interference
Definition:A resulting wave form caused by the interaction of two or more waves, sometimes in a destructive manner (crest to trough) and sometimes in a constructive manner (crest to crest).
Context:The bright and dark pattern of light seen as a light wave passes through a diffraction grating is called an interference pattern.

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This lesson plan may be used to address the academic standards listed below. These standards are drawn from Content Knowledge: A Compendium of Standards and Benchmarks for K-12 Education: 2nd Edition and have been provided courtesy of theMid-continent Research for Education and Learningin Aurora, Colorado.
Grade level:9-12
Subject area:physical science
Understands basic concepts about the structure and properties of matter.
Knows the structure of an atom (e.g., negative electrons occupy most of the space in the atom; neutrons and positive protons make up the nucleus of the atom; protons and neutrons are almost 2000 times heavier than an electron; the electric force between the nucleus and electrons holds the atom together).

Grade level:9-12
Subject area:physical science
Understands motion and the principles that explain it.
Understands general concepts related to the theory of special relativity (e.g., in contrast to other moving things, the speed of light is the same for all observers, no matter how they or the light source happen to be moving; nothing can travel faster than the speed of light).

Grade level:9-12
Subject area:physical science
Understands motion and the principles that explain it.
Knows that waves (e.g., sound, seismic, water, light) have energy and can transfer energy when they interact with matter.

Grade level:9-12
Subject area:science
Understands the nature of scientific knowledge.
Understands how scientific knowledge changes and accumulates over time (e.g., all scientific knowledge is subject to change as new evidence becomes available; some scientific ideas are incomplete and opportunity exists in these areas for new advances; theories are continually tested, revised, and occasionally discarded).

Grade level:9-12
Subject area:science
Understands the nature of scientific knowledge.
Knows that from time to time, major shifts occur in the scientific view of how the world works, but usually the changes that take place in the body of scientific knowledge are small modifications of prior knowledge.

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