Home » Physics (Page 7)
Category Archives: Physics
The Discovery of Global Warming
The idea that manmade caused global warming could occur isn’t new. Most people don’t know this, but this was first understood as far back as the late 1800s! This is because it is basic physics: adding more greenhouses gases into an atmosphere increases the amount of heat that it will hold.
Dr. Spencer Weart is a historian specializing in the history of modern physics and geophysics. Until his retirement in 2009 he was Director of the Center for History of Physics of the American Institute of Physics (AIP) in College Park, Maryland, USA, and he continues to be affiliated with the Center.
Spencer Weart writes in the summary overview to his book:
In 1896 the Swedish scientist Svante Arrhenius published a new idea. By burning fossil fuels such as coal, thus adding CO2 to Earth’s atmosphere, humanity would raise the planet’s average temperature. This “greenhouse effect,” as it later came to be called, was only one of many speculations about climate change, and not the most plausible.
The few scientists who paid attention to Arrhenius used clumsy experiments and rough approximations to argue that our emissions could not change the planet. Most people thought it was already obvious that puny humanity could never affect the vast global climate cycles, which were governed by a benign “balance of nature.”
In the 1930s, measurements showed that the United States and North Atlantic region had warmed significantly during the previous half-century. Scientists supposed this was just a phase of some mild natural cycle, probably regional, with unknown causes. Only one lone voice, the English steam engineer and amateur scientist Guy Stewart Callendar, published arguments that greenhouse warming was underway. If so, he and most others thought it would be beneficial.
In the 1950s, Callendar’s claims provoked a few scientists to look into the question with far better techniques and calculations than earlier generations could have deployed. This research was made possible by a sharp increase of government funding, especially from military agencies that wanted to know more about the weather and geophysics in general.
Not only might such knowledge be crucial in future battles, but scientific progress could bring a nation prestige in the Cold War competition. The new studies showed that, contrary to earlier crude assumptions, CO2 might indeed build up in the atmosphere and bring warming. In 1960 painstaking measurements of the level of the gas in the atmosphere by Charles Keeling, a young scientist with an obsession for accuracy, drove home the point. The level was in fact rising year by year.
(This essay covers only developments relating directly to carbon dioxide, with a separate essay for Other Greenhouse Gases. Theories are discussed in the essay on Simple Models of Climate.)
The Discovery of Global Warming: A hypertext history of how scientists came to (partly) understand what people are doing to cause climate change.
Books
The Discovery of Global Warming: Revised and Expanded Edition, by Spencer R. Weart, Harvard University Press, 2008
________________________________________
This website is educational. Materials within it are being used in accord with the Fair Use doctrine, as defined by United States law.
§107. Limitations on Exclusive Rights: Fair Use. Notwithstanding the provisions of section 106, the fair use of a copyrighted work, including such use by reproduction in copies or phone records or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use, the factors to be considered shall include: the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes; the nature of the copyrighted work; the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and the effect of the use upon the potential market for or value of the copyrighted work. (added pub. l 94-553, Title I, 101, Oct 19, 1976, 90 Stat 2546)
Astronomical engineering: a strategy for modifying planetary orbits
In a world of high-stakes testing and test-driven curriculums, we teachers need to make time for exploration and inspiration. In the past, did students fall in love with physics due to standardized tests? Of course not. They became interested in becoming a physicist due to great experience, like reading a great science fiction story, or having a science teacher discuss such stories in class, Such conversations about the big ideas can catch one’s imagination.
As such, I encourage physics teachers to go beyond the standards, and do what the classic teachers of past generations did: make room for wonder!
How’s this for an idea for a science-fiction story?
The sun has unexpectedly started to swell into a red giant – which would engulf and destroy the Earth. So, “to save humanity, the world’s governments have banded together and constructed thousands of rocket engines across the Earth’s surface. Once installed, they propel the planet out of its solar system and onto a 2,500 year journey to resettle in Alpha Centauri.” (Grant Watson.)
The Wandering Earth (Chinese: 流浪地球) is a 2019 Chinese science fiction film directed by Frant Gwo, loosely based on the novella of the same name by author Liu Cixin. Here’s an image of one of the many “Earth Engines.”
Our question – Could this be done in real life?
What science in the film did they get wrong?
Helium flash – brief thermal runaway nuclear fusion of large quantities of helium in the core of low mass stars during their red giant phase
Thrusting the Earth out of orbit with rockets: consider, how much reaction mass would we need to do this?
Even if you could build engines large enough, mining the Earth (as these engines do in the film) causes a problem. There would barely be any Earth left by the point you mined enough dirt to thrust the planet to Proxima Centauri, 4.2 light-years away. “It would take about 95 percent of the mass of Earth to do this,” Elliott estimates.
Stopping the rotation of the Earth?
Gravitational slingshot around Jupiter
Surviving the radiation around Jupiter
External links
Could ‘The Wandering Earth’ Actually Happen? Here’s What a NASA Engineer Says
Wandering Earth: Rocket scientist explains how we could move our planet. ARS Technia
Other options
We could eventually move human civilization to Mars, which become habitable.
Could we actually change Earth’s orbit?
G. Korycansky, Gregory Laughlin, and Fred C. Adams write
The Sun’s gradual brightening will seriously compromise the Earth’s biosphere within ~ 1E9 years. If Earth’s orbit migrates outward, however, the biosphere could remain intact over the entire main-sequence lifetime of the Sun.
In this paper, we explore the feasibility of engineering such a migration over a long time period. The basic mechanism uses gravitational assists to (in effect) transfer orbital energy from Jupiter to the Earth, and thereby enlarges the orbital radius of Earth.
This transfer is accomplished by a suitable intermediate body, either a Kuiper Belt object or a main belt asteroid. The object first encounters Earth during an inward pass on its initial highly elliptical orbit of large (~ 300 AU) semimajor axis.
The encounter transfers energy from the object to the Earth in standard gravity-assist fashion by passing close to the leading limb of the planet. The resulting outbound trajectory of the object must cross the orbit of Jupiter; with proper timing, the outbound object encounters Jupiter and picks up the energy it lost to Earth.
With small corrections to the trajectory, or additional planetary encounters (e.g., with Saturn), the object can repeat this process over many encounters. To maintain its present flux of solar energy, the Earth must experience roughly one encounter every 6000 years (for an object mass of 1E22 g). We develop the details of this scheme and discuss its ramifications.
Astrophys.Space Sci.275:349-366, 2001. Astronomical Engineering: A Strategy For Modifying Planetary Orbits
Cite as: arXiv:astro-ph/0102126 (or arXiv:astro-ph/0102126v1 for this version)
Astronomical engineering: a strategy for modifying planetary orbits
D. G. Korycansky, Gregory Laughlin, Fred C. Adams (7 Feb 2001)
Moving our sun and entire solar system
Could a species conceivably move an entire solar system? In principle, physics does seem to allow this as a possibility. Although, we must stress, the engineering required to do this is far beyond anything we can imagine for the near term future, and even if possible it would take huge amounts of time to actually move our solar system.
The Caplan thruster was conceived of by Matthew Caplan from Illinois State University.
These images are from How to Move the Sun: Stellar Engines by Kurzgesagt – In a Nutshell.
and
from Scientist figures out how to move our sun to avoid space collisions, BigThink
Stellar engines: Design considerations for maximizing acceleration, Acta Astronautica, 12/2019
Paul Ratner writes
Caplan envisions two stellar engine designs, with one of them based on the idea of encapsulating the sun in a megastructure that would take advantage of its energy. Another engine would make use of a giant sail to move the solar system by about 50 light years during the course of a million years….
One big reason would be to move the solar system if we’re anticipating running into a mega-explosion from a supernova or some such cataclysmic scenario. Of course, we’d need to be way more ahead technologically for any such endeavor.
If you were to be moving the solar system, the convenient thing is that theoretically everything inside it would move along at the same time. Being pulled by the sun’s gravity would keep the contents of the system in consistent orbit.
One of the stellar engine designs involves a thin mirror-like solar sail, like the “Shkladov thruster”. The reflective material would be thinner than a red blood cell. The sail would be positioned over the poles of the sun and would not be orbiting.
It would be important to install it in such a way that it won’t interfere with the Earth’s temperature. This would also affect the direction in which we’d be steering the solar system.
Thrust for the sail design would be created by solar radiation reflecting onto the mega-mirror. This is definitely not the fastest way to travel, with the sun being pushed along at the rate of 100 light-year in 230 million years. That’s actually not fast enough to get out of the way of a supernova explosion, admits Caplan.
What would work better is a speedier “active” thruster, called the “Caplan thruster” by Kurzgesagt, which initially approached Caplan to design such engines. It would be propelled by thermonuclear blasts of photon particles. This thruster is a modified version of the “Bussard ramjet,” conceptualized in the 1960s, which works on fusion energy.
The engine would need millions of tons of fuel per second to function, creating fusion from matter it collects in the solar wind by utilizing a giant electromagnetic field. More energy would also be gathered by a Dyson sphere megastructure, built around the sun.
Caplan imagines the engine having two jets, with one using hydrogen pointed at the sun, to prevent colliding with it, and another, employing helium, directed away from the star. This would cause net momentum, like from a tug boat, and move the thruster forward.
The astrophysicist calculates this type of thruster would be fast enough to escape a supernova. It could also redirect the galactic orbit of our solar system in as little as 10 million years.
The Shkadov Thruster was conceived of by Leonid M. Shkadov (1927–2003) scientist, engineer from the Central Aerohydrodynamic Institute in Russia.
Excerpted from a painting by Neil Blevans
Painting above from here.
Related articles
Gregory Benford and Larry Niven solved the problems with Shkavdov thrusters for a propulsion system for moving stars
“On the Possibility of Detecting Class A Stellar Engines Using Exoplanet Transit Curves,” Journal of the British Interplanetary Society
See this video
Learning Standards
2016 Massachusetts Science and Technology/Engineering Curriculum Framework
8.MS-ESS1-2. Explain the role of gravity in ocean tides, the orbital motions of planets, their moons, and asteroids in the solar system.
HS-PS2-4. Use mathematical representations of Newton’s law of gravitation and Coulomb’s law to both qualitatively and quantitatively describe and predict the effects of gravitational and electrostatic forces between objects.
Next Generation Science Standards
HS-PS2.B.1 ( High School Physical Sciences ): Newton’s law of universal gravitation and Coulomb’s law provide the mathematical models to describe and predict the effects of gravitational and electrostatic forces between distant objects.
Next Generation Science Standards Appendix F: Science and Engineering Practices
Ask questions that arise from careful observation of phenomena, or unexpected results, to clarify and/or seek additional information.
Ask questions that arise from examining models or a theory, to clarify and/or seek additional information and relationships.
Ask and/or evaluate questions that challenge the premise(s) of an argument, the interpretation of a data set, or the suitability of a design.
A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas (2012)
PS2.B: TYPES OF INTERACTIONS: Gravitational, electric, and magnetic forces between a pair of objects do not require that they be in contact. These forces are explained by force fields that contain energy and can transfer energy through space. These fields can be mapped by their effect on a test object (mass, charge, or magnet, respectively). Objects with mass are sources of gravitational fields and are affected by the gravitational fields of all other objects with mass. Gravitational forces are always attractive. For two human-scale objects, these forces are too small to observe without sensitive instrumentation. Gravitational interactions are non-negligible, however, when very massive objects are involved. Thus the gravitational force due to Earth, acting on an object near Earth’s surface, pulls that object toward the planet’s center. Newton’s law of universal gravitation provides the mathematical model to describe and predict the effects of gravitational forces between distant objects.
Science teaching methods
“Pedagogy is the study of teaching methods, including the aims of education and the ways in which such goals may be achieved. The field relies heavily on educational psychology, which encompasses scientific theories of learning, and to some extent on the philosophy of education, which considers the aims and value of education from a philosophical perspective.”
~ Encyclopædia Britannica
What type of teaching works with NGSS?
No one model of pedagogy is best for every topic or every teacher. Different teachers are enthusiastic about different approaches. Experienced science teachers change the mode of instruction to match the phenomenon which they are presenting.
Philip Bell and Andrew Shouse write
People often assume that a particular instructional model is best for engaging students in the NGSS practices. In fact, there are multiple models that can be used effectively.
NGSS and the underlying NRC Framework do not say anywhere that there is only one instructional approach for engaging students in the practices. But specific curricula, instructional resources, and PD can reinforce this view by focusing on only one model at a time. There are actually multiple instructional models that can be productively used to implement the learning goals of NGSS.
Explore the practice-focused instructional models listed in the table and select one(s) that fit your situation and personal preferences.
Selecting an instructional model that fits a particular classroom should be based on local circumstances. This can involve supporting instruction that fits a teacher’s personal history, goals, or commitments. Or it can be based on what instructional model is in use in the local curriculum. The district’s or school’s instructional strategy or a professional learning community may also shape teachers’ orientation to an instructional model.
From Are there multiple instructional models that fit with the science and engineering practices in NGSS?, STEM Teaching Tools
Image by Gerd Altmann, Pixabay, Free for commercial use
Flipped classroom
The flipped classroom intentionally shifts instruction to a learner-centered model. Students take responsibility to learn the content at home, usually through video lessons prepared by the teacher or third parties, and readings from textbooks. In-class lessons include activity learning, homework problems, using manipulatives, doing labs, presentations, project-based learning, skill development, etc.
An early example of this was called Peer Instruction by Harvard Professor Eric Mazur, in the early 1990s.
Just-in-Time Teaching
There is no hard line between approaches Just-In-Time teaching may be considered halfway between traditional teaching methods and the flipped classroom.
JiTT relies on pre-class assignments completed by students before class meetings. These assignments are usually completed online. The pre-class assignments cover the material that will be introduced in the subsequent class, and should be answered based on students’ reading or other preparation. The idea is to create incentive for students to complete the assigned reading before class. At college level, teachers make the pre-class assignment due at least 1 hour before class. This allows the faculty member to review the students’ answers before class.
Apps/interactive simulations
Science apps are sometimes called Physlets, Chemlets, etc. In the past many ran on Flash or JAVA. Today they are increasingly being written to run on any browser with HTML5 standards.
Apps help make the visual and conceptual models of expert scientists accessible to students.
Example: PhET Interactive Simulations
Classroom response systems (“clickers”)
A classroom response system (sometimes called a personal response system, student response system, or audience response system) is a set of hardware and software that facilitates teaching activities such as the following.
-
A teacher poses a multiple-choice question via an overhead or computer projector.
-
Each student submits an answer to the question using a clicker.
-
Software collects the answers and produces a bar chart showing how many students chose each of the answer choices.
-
The teacher makes “on the fly” choices in response to the bar chart.
Ranking Task Exercises
Conceptual physics exercises that challenges readers to make comparative judgments about a set of variations on a particular physical situation. Exercises encourage readers to formulate their own ideas about the behavior of a physical system, correct any misconceptions they may have, and build a better conceptual foundation of physics.
Interactive Lecture Demonstrations
See Interactive Lecture Demonstrations, Active Learning in Introductory Physics, by David Sokoloff and Ronald Thornton.
Start with a scripted activity in a traditional lecture format. Because the activity causes students to confront their prior understanding of a core concept, students are ready to learn in a follow-up lecture.
Interactive Lecture Demonstrations use three steps in which students:
Predict the outcome of the demonstration. Individually, and then with a partner, students explain to each other which of a set of possible outcomes is most likely to occur.
Experience the demonstration. Working in small groups, students conduct an experiment, take a survey, or work with data to determine whether their initial beliefs were confirmed (or not).
Reflect on the outcome. Students think about why they held their initial belief and in what ways the demonstration confirmed or contradicted this belief. After comparing these thoughts with other students, students individually prepare a written product on what was learned.
https://serc.carleton.edu/introgeo/demonstrations/index.html
GIFs as step-by-step animations
Textbooks and lectures use static diagrams. For many students it is hard to visualize the scientific process being taught. GIFs help students visualize a complex process.
GIFs add to our toolbook. For instance, one can model an electric series circuit with two resistors in many ways. We can model this circuit with math, with a circuit diagram, or with a GIF. With the GIF we can see how the battery adds potential energy to the electrons in a circuit, while the electrons lose this potential energy as they go through any circuit element with resistance.
https://www.stem.org.uk/news-and-views/opinions/using-gifs-classroom
http://blog.cdnsciencepub.com/science-communicators-get-your-gif-on/
http://blogs.nottingham.ac.uk/makingsciencepublic/2014/01/24/how-to-do-things-with-gifs/
Cooperative group problem solving
Cooperative Group Problem-solving – Students work in groups using structured problem-solving strategy. In this way they can solve complex, context-rich problems which could be difficult for them to solve individually.
Students in introductory physics courses typically begin to solve a problem by plunging into the algebraic and numerical solution — they search for and manipulate equations, plugging numbers into the equations until they find a combination that yields an answer (e.g. the plug-and-chug strategy).
They seldom use their conceptual knowledge of physics to qualitatively analyze the problem situation, nor do they systematically plan a solution before they begin numerical and algebraic manipulations of equations. When they arrive at an answer, they are usually satisfied — they rarely check to see if the answer makes sense.
To help students integrate the conceptual and procedural aspects of problem solving so they could become better problem solvers, we introduced a structured, five-step problem solving strategy.
5E Model (a modelling method)
The 5E model is a constructivist science learning method created in the late 1980s by the Biological Sciences Curriculum Study (BSCS Science Learning) team. The method usually has 5 steps –
Engage, student’s interest is captured,
Explore, student constructs knowledge through facilitated questioning and observation
Explain, students are asked to explain what they have discovered. Instructor leads discussion of topic to refine the students’ understanding.
Extend (Elaborate), students asked to apply what they have learned to different situations,
Evaluate.
Tutorials in Introductory Physics
Guided-inquiry worksheets for small groups in recitation section of intro calculus-based physics. Instructors engage groups in Socratic dialogue.
RealTime Physics
A series of introductory laboratory modules that use computer data acquisition tools to help students develop physics concepts and acquire lab skills.
Modeling Instruction
Instruction organized around active student construction of conceptual and mathematical models in an interactive learning community. Students engage with simple scenarios to build, test and apply the handful of scientific models that represent the content core of physics.
Force Concept Inventory
“The FCI is a test of conceputal understanding of Newtonian mechanics, developed from the late 1980s. It consists of 30 MCQ questions with 5 answer choices for each question and tests student understanding of conceptual understanding of velocity, acceleration and force. Many distracters in the test items embody commonsense beliefs about the nature of force and its effect on motion. ”
Developed by Hestenes, Halloun, Wells, and Swackhamer (1985.) Sample question:
Problem with relying solely on modeling methods
The major issues with relying solely on modeling methods, such as 5E, is that if we really followed this methodology for all topics then it would take many years to get a student through one year of a high school science class.
After all, it took some of the world’s smartest people 2,000 years of intellectual exploration to notice and understand the scientific phenomenon that make up just a one year high school science course.
There is no hope of having most high school students do all the steps in 5E for more than a small percent of physics, chemistry, or biology phenomenon in just one year.
When in science teacher discussion communities I haven’t found many people who advocated for year-long modeling as the sole or primary way to teach. The push for these methods seems to come from massive, for-profit, textbook publishing companies. They sell various 5E and NGSS labeled curricula. Older teachers have noticed that these companies always dump their own curricula and replace it with a new one every 15 years or so.
To be clear – I am not critiquing anyone who uses modeling teaching. I just am saying that there is not enough time for students to discover every phenomenon. We also need some traditional instruction: assigning reading and lecturing.
Different types of learners?
Daniel T. Willingham writes:
Question: What does cognitive science tell us about the existence of visual, auditory, and kinesthetic learners and the best way to teach them?
The idea that people may differ in their ability to learn new material depending on its modality—that is, whether the child hears it, sees it, or touches it—has been tested for over 100 years. And the idea that these differences might prove useful in the classroom has been around for at least 40 years.
What cognitive science has taught us is that children do differ in their abilities with different modalities, but teaching the child in his best modality doesn’t affect his educational achievement. What does matter is whether the child is taught in the content’s best modality.
See more at Do Visual, Auditory, and Kinesthetic Learners Need Visual, Auditory, and Kinesthetic Instruction?
External resources
www.physport.org Teaching Methods
How to teach AP Physics
ASU Modeling Instruction modeling.asu.edu/R&E/Research.html
Stars are powered by nuclear fusion
Stars are powered by nuclear fusion
Before reading this section, you will first need to know
-
Atoms are the smallest stable building blocks of matter in the universe
-
Atoms are not solid. They are made of protons, neutrons, and electrons.
-
All solids, liquids, gases and plasma in our universe are made of these particles.
-
All matter is attracted to other matter through gravity. If you have enough mass floating around in space, over time, large amounts of matter will be attracted together to form giant gas clouds – nebulas.
-
Nebulas themselves can contract, due to gravity. This leads to the development of stars
-
Generally speaking, all matter in our universe is conserved (conservation of matter)
-
Generally speaking, all energy in our universe is conserved (conservation of energy)
-
Here’s the wacky bit: scientists discovered fascinating and unexpected violations of those supposedly inviolable laws, but instead of that being magic, it pointed towards an even greater discovery: the law of conservation of matter and energy. This was discovered by Albert Einstein, and is known as mass–energy equivalence.
As such, first read our lesson on the discovery of nuclear physics and radioactivity.
At this point you now have the background for what comes next.
Inside a star, gravity pulls billions of tons of matter towards the center. Atoms are pushed very close together. So close that sometimes two atoms will fuse into one, heavier atom. The mass of this new atom is slightly less than the mass of the pieces that it was made of in the first place? Where the did missing go? It effectively becomes energy – which we see as photons, or as the heat/motion energy of other particles.
As an example, here we see deuterium fusing with tritium. The resulting product has less mass than the parts going in to the collision. That missing mass we see becomes 3.5 mega electron-volts of energy,
Here we some typical nuclear fusion reactions that go on inside yellow dwarf stars like our sun.
Here is a step-by-step cascade showing how hydrogen atoms can fuse to create Helium, giving off gamma rays and neutrinos in the process.
In a different form we see the same process here.
(More text TBA)
Particle Physics lesson
Your job: Produce a document, with pictures, putting together what you have learned today. Ways that you can do this:
* Handwrite
* Create a PowerPoint presentation
* Google Docs (typing or voice-to-text)
* Create a poster – pencils, colored pencils, pens, markers.
Intro
Inside atoms we have protons, neutrons and electrons. Now we learn that protons and neutrons are not “solid”. They are built from smaller subatomic particles!
The particle zoo
http://hetdex.org/dark_energy/particle_zoo.html
Animation: Atoms to Quarks
https://www.learner.org/courses/physics/visual/vis_bytype.html?type=animation
Videos: Out Of Sight – Building From Quarks To Atoms to Molecules
https://www.youtube.com/watch?v=H8ZMmZ_2BnI
CERN: Two protons collide and create new particles
https://home.cern/resources/video/physics/atlas-physics-process-animations
CK-12 Chemistry Fundamental Particles
https://www.ck12.org/chemistry/fundamental-particles-in-chemistry/lesson/Fundamental-Particles-MS-PS/
At the end of this website launch and explore the “CK-12 Interactive”
Advanced topics
Quarks are particles within protons and neutrons.
Labs (Physics)
Physics labs
Image from Imaginary Numbers Are Real, Welch Labs
Build projects/Engineering
Hovercraft build project
Mousetrap racers
Catapult and trebuchet build projects
Traditional physics labs
How to write a lab report
How to measure mass
Kinematics
Finding Pi, circle lab
Reaction time lab
Magnetism
Magnetism labs
Gravity
Why Is There a Tidal Bulge Opposite the Moon?
Forces & Newton’s laws
Mechanical equilibrium lab
Inertial balance lab
Finding the coefficient of friction lab
Virtual labs
PhET
Science Sims @ CCNY
BU Physics ~ Duffy HTML5 sims
HTML 5 Physics Lab Simulations: The Physics Aviary
Open Source Physics sims
The Physics Classroom interactives
Coding labs
Programming Labs for Physics
Science catalogs/supplies
Science catalog & supplier list
Earth’s magnetic field
The Earth has a magnetic field. Sometimes called geomagnetic.
When we use a compass, we make use of this field.
Combining a compass and a map allows us to navigate over the landscape.
We’re tempted to view the Earth as a big rock with a giant bar magnet stuck through it.
English scientist William Gilbert observed 400 years ago that Earth behaves like a giant bar magnet.
It is as if there is one magnetic pole up in the Arctic (near the geographic north pole) and another pole down in Antarctica (near the geographic south pole).
What do we mean that the magnetic pole is “near” the geographic pole!? Aren’t they the same thing? Contrary to popular belief, nope. Not the same.
The geographic poles are the places that the Earth spins around.
The spinning is absolutely real. (But there’s no actual axis, as the image shows.)
The north and south places where the Earth is spinning around are called the geographic poles.
But as we see here, the magnetic north pole is south of the geographic north pole.
More than that, the magnetic pole slowly moves over time?
This is a huge clue that our magnetic field doesn’t come from some giant bar magnet.
No, my friends, something more flexible and changeable is clearly making this magnetic field.
Image from commons.wikimedia.org, Magnetic_North_Pole_Positions.
Red circles mark magnetic north pole positions as determined by direct observation, blue circles mark positions modelled using the GUFM model (1590–1980) and the IGRF model (1980–2010) in 2 year increments.
How is our planet’s magnetic field generated?
Earth has a molten metal core, surrounded by a highly metallic shell of magma.
Photo by RK (c) 2019
Like in a wire, electrons move through this metal.
image from Francisco Esquembre , Universidad de Murcia; Maria Jose Cano; lookang http://weelookang.blogspot.sg/
And as we learn in our unit on electromagnetism, the motion of electrons creates a magnetic field!
The Earth itself is slowly spinning, so we end up with slow-moving mantle and core currents within the Earth.
So now we have currents of moving metal inside a giant spinning sphere!
These currents affect the flow of electrons, thus affecting the resulting magnetic field.
How strong is this planetary magnetic field?
Earth’s magnetic field is weak compared to gravity.
For a compass to be able to show tiny effects of Earth’s magnetism, we have to minimize the effects of these other forces. That’s why compass needles are
* lightweight (so gravity has less effect on them)
* mounted on frictionless bearings (less resistance for the magnetic force to overcome)
http://www.explainthatstuff.com/how-compasses-work.html
Where the Earth’s magnetic field comes from
By Chris Rowan
The Earth’s magnetic field may approximate to a simple dipole, but explaining precisely how that dipole is generated and maintained is not simple at all.
The field originates deep in the Earth, where temperatures are far too high for any material to maintain a permanent magnetisation.
The dynamism that is apparent from the wandering of the magnetic poles with respect to the spin axis (secular variation), and the quasi-periodic flips in field polarity, also suggest that some process is actively generating and maintaining the geomagnetic field.
Geophysicists therefore look to the most dynamic region in the planetary depths, the molten outer core, as the source of the force that directs our compass needles…
The Earth’s interior generates a magnetic field. It reaches out into space.
This magnetic field protects us from some types of radiation.
Earth’s North geographic pole has a South magnetic field
The “north” pole of a compass – by definition – is pulled to a “south” magnetic pole.
If we hold a compass in our hands, and call the part pointing to the land of Polar bears “north”, then we’d have to call the part attracting it “south.”
Magnetic field reversals
The magnetic field of the Earth is not stable; it has flip-flopped throughout geologic time.
Evidence: (to be added)
“In the meantime, scientists are working to understand why the magnetic field is changing so dramatically. Geomagnetic pulses, like the one that happened in 2016, might be traced back to ‘hydromagnetic’ waves arising from deep in the core1. And the fast motion of the north magnetic pole could be linked to a high-speed jet of liquid iron beneath Canada2.”
Earth’s magnetic field is acting up and geologists don’t know why. Nature Jan 19
Geomagnetic acceleration and rapid hydromagnetic wave dynamics in advanced numerical simulations of the geodynamo, Aubert, Julien, Geophys. J. Int. 214, 531–547 (2018).
An accelerating high-latitude jet in Earth’s core. Livermore, P. W., Hollerbach, R. & Finlay, C. C. Nature Geosci. 10, 62–68 (2017).
_______________________________
App: The solar wind and Earth’s magnetic field
http://esamultimedia.esa.int/multimedia/edu/PlanetaryMagneticFields.swf
Learning about Earth’s magnetic field: ESA’s Swarm mission
The Physics of Interstellar Travel
Why should humanity eventually colonize the stars?
Painting: The Prologue and the Promise, Robert McCall
http://www.mccallstudios.com/the-prologue-and-the-promise/
“Ask ten different scientists about the environment, population control, genetics and you’ll get ten different answers, but there’s one thing every scientist on the planet agrees on. Whether it happens in a hundred years or a thousand years or a million years, eventually our Sun will grow cold and go out. When that happens, it won’t just take us. It’ll take Marilyn Monroe and Lao-Tzu, Einstein, Morobuto, Buddy Holly, Aristophanes .. and all of this .. all of this was for nothing unless we go to the stars.”
– Writer J. Michael Straczynski, from a character’s speech (Commander Sinclair) in Babylon 5, season 1, “Infection”
This a resource on possible ways humans could achieve interstellar travel.
How to use this resource
Can be read as enrichment.
Resource for a science club project.
Use space travel as a NGSS phenomenon or to create a storyline; one may teach about chemistry topics:
chemical reactions
practical use of reactions – chemical rockets
ions versus atoms
practical use of ions – ion drives for space travel
atoms and anti-atoms: basic subatomics particles of matter/antimatter
energy levels/quantum jumps
Use space travel as a NGSS phenomenon or to create a storyline: one may teach about modern physics topics:
nuclear fission
nuclear fusion
magnetic fields – practical uses of fields (Bussard ramjet)
black holes and wormholes
quantum jumps (chemistry/physics)
Einstein’s theory of relativity (relates to warp drive)
Introduction
Realistically, we currently have no technology that would let us send unmanned, let alone manned, spacecraft to even the nearest star. The Voyager spacecraft – launched in 1977 – is traveling away from our Sun at a rate of 17.3 km per second.
If Voyager were to travel to our nearest star, Proxima Centauri, it would take over 73,000 years to arrive.
Yes, if we built this today, we could – with some effort – bring it to a speed ten times faster, but that still would 7300 years to reach another star.
To understand the size of this space probe, here is an image of it under construction.
What do we think about, when we think of interstellar travel?
We’re all familiar with FTL (faster than light) space travel in Star Trek…
or from movies like Star Wars.
Star Wars The Force Awakens, Millennium Falcon
But nothing like this currently exists. We’re not even if sure if anything like warp drive or hyperspace could exist – although we’ll get to those ideas at the end of this unit. So we need to start with what we currently have. What kinds of space travel technology do we have right now? All of our rocketships are powered by chemical reactions.
These are the manned rocketships that we have used from the 1960 up to today.
First, we need to know – What are chemical reactions?
We then need to know what combustion is.
Here we see a SpaceX falcon 9 rocket lifting off, carrying a Crew Dragon reusable manned spacecraft (see in the above image.)
public domain pxhere.com/en/photo/1080045
Chemical reaction powered rockets are good for manned or unmanned missions within our solar system. But they are relatively slow and require huge amounts of fuel.
Solar sail spaceships
These are application of Newton’s laws of motion and conservation of momentum.
Solar sails feel the photon wind of our sun in much the same way that traditional sailboats capture the force of the wind.
The first spacecraft to make use of the technology was IKAROS, launched in 2010.
The force of sunlight on the ship’s mirrors is akin to a sail being blown by the wind. High-energy laser beams could be used as a light source to exert much greater force than would be possible using sunlight.
Solar sail craft offer the possibility of low-cost operations combined with long operating lifetimes.
These are very low-thrust propulsion system, and they use no propellant. They are very slow, but very affordable.
Newton’s laws of motion
Momentum
image from Photon Illustration
Ionic propulsion spacecraft
We first learn What are atoms? and What are ions?
These ideas are then related to Newton’s laws of motion and conservation of momentum.
Ionic rockets have low acceleration, and it takes a long time for a spacecraft to build up much speed. However they are extremely efficient.
Uses engines such as the Hall-effect thruster (HET). Used in European Space Agency’s (ESA) SMART-1 mission. They are good for unmanned missions within our solar system.
image from dayton.hq.nasa.gov
nuclear propulsion (working engines already designed!)
These systems have already been built and tested here on Earth.
Nuclear Electric propulsion – In this kind of system, thermal energy from a nuclear fission reactor is converted to electrical energy. This is then used to drive an ion thruster.
Nuclear Thermal Rocket – Heat from a nuclear fission reactor adds energy to a fluid. This fluid is then expelled out of a rocket nozzle, creating thrust.
Here is where we may learn about nuclear fission
Matt Williams writes
In a Nuclear Thermal Propulsion (NTP) rocket, uranium or deuterium reactions are used to heat liquid hydrogen inside a reactor, turning it into ionized hydrogen gas (plasma), which is then channeled through a rocket nozzle to generate thrust.
A Nuclear Electric Propulsion (NEP) rocket involves the same basic reactor converting its heat and energy into electrical energy, which would then power an electrical engine. In both cases, the rocket would rely on nuclear fission or fusion to generates propulsion rather than chemical propellants, which has been the mainstay of NASA and all other space agencies to date.
Although no nuclear-thermal engines have ever flown, several design concepts have been built and tested over the past few decades, and numerous concepts have been proposed. These have ranged from the traditional solid-core design – such as the Nuclear Engine for Rocket Vehicle Application (NERVA) – to more advanced and efficient concepts that rely on either a liquid or a gas core.
However, despite these advantages in fuel-efficiency and specific impulse, the most sophisticated NTP concept has a maximum specific impulse of 5000 seconds (50 kN·s/kg). Using nuclear engines driven by fission or fusion, NASA scientists estimate it would could take a spaceship only 90 days to get to Mars when the planet was at “opposition” – i.e. as close as 55,000,000 km from Earth.
But adjusted for a one-way journey to Proxima Centauri, a nuclear rocket would still take centuries to accelerate to the point where it was flying a fraction of the speed of light. It would then require several decades of travel time, followed by many more centuries of deceleration before reaching it destination. All told, were still talking about 1000 years before it reaches its destination. Good for interplanetary missions, not so good for interstellar ones.
Torchships
“Have you simply had it up to here with these impotent little momma’s-boy rockets that take almost a year to crawl to Mars? Then you want a herculean muscle-rocket, with rippling titanium washboard abs and huge geodesic truck-nuts! You want a Torchship! Who cares if the exhaust can evaporate Rhode Island? You wanna rocket with an obscenely high delta V, one that can crank out one g for days at a time. Say goodbye to all that fussy Hohmann transfer nonsense, the only navigation you need is point-and-shoot. – Winchell D. Chung Jr.“
Torchsips are what we think of from many classic science fiction stories.
Shockingly, we already have the technology to build a Torship powered by multiple, small nuclear-fission explosions – Project Orion.
Project Orion was a study conducted between the 1950s and 1960s by the United States Air Force, DARPA, and NASA – [it would be a spaceship] propelled by a series of explosions of atomic bombs behind the craft via nuclear pulse propulsion. Early versions of this vehicle were proposed to take off from the ground; later versions were presented for use only in space. Six non-nuclear tests were conducted using models.
The Orion concept offered high thrust and high specific impulse at the same time. Orion would have offered performance greater than the most advanced conventional or nuclear rocket engines then under consideration. Supporters of Project Orion felt that it had potential for cheap interplanetary travel, but it lost political approval over concerns about fallout from its propulsion. The Partial Test Ban Treaty of 1963 is generally acknowledged to have ended the project.
Designs were considered that would actually allow us to build interstellar spacecraft! An Orion torchship could achieve about 10% of the speed of light. At this speed such a ship could reach the closest star, Alpha Centauri in just 44 years.
Our SpaceFlight Heritage: Project Orion, a nuclear bomb and rocket – all in one.
Project Orion
Realistic Designs: Atomic Rockets
Project Orion. Medium.com
Project Orion: The Spaceship Propelled By Nuclear Bombs
The Nuclear Bomb Powered Spaceship – Project Orion
And there’s more – Project Orion was just the first Torch ship designed, and that only uses 1960s level nuclear fission. In the last generation more flexible and safer methods using nuclear fission have been developed. Similarly we have made many advances in nuclear fusion – see the next section.
Torchships – nuclear fusion
Nuclear fusion is the process that powers our sun, and all stars in the universe. Inside a star, gravity pulls billions of tons of matter towards the center. Atoms are pushed very close together. Two atoms are fused into one, heavier atom.
Yet the mass of this new atom is slightly less than the mass of the pieces that it was made of in the first place. Where the did missing energy go? It becomes energy – which we see as photons, or as the heat/motion energy of other particles. This is also the process by which nuclear bombs work.
How can we possibly replicate the energy of stars here on Earth? For the last 70 years people have been working on this. It has been extremely challenging to do this, but progress is slowly being made.
Read more here about nuclear power.
Here is a great article about Torchships that realistically are possible.
and Torch Drives: An Overview
Very speculative technologies
Fusion (Bussard) Ramjet
Proposed by physicist Robert W. Bussard in 1960. It uses nuclear fusion. An enormous electromagnetic funnel “scoops” hydrogen from the interstellar medium and dumps it into the reactor as fuel.
As the ship picks up speed, the reactive mass is forced into a progressively constricted magnetic field, compressing it until thermonuclear fusion occurs. The magnetic field then directs the energy as rocket exhaust through an engine nozzle, thereby accelerating the vessel.
Without any fuel tanks to weigh it down, a fusion ramjet could achieve speeds approaching 4% of the speed of light and travel anywhere in the galaxy.
However, the potential drawbacks of this design are numerous. For instance, there is the problem of drag. The ship relies on increased speed to accumulate fuel, but as it collides with more and more interstellar hydrogen, it may also lose speed – especially in denser regions of the galaxy.
Second, deuterium and tritium (used in fusion reactors here on Earth) are rare in space, whereas fusing regular hydrogen (which is plentiful in space) is beyond our current methods.
Design by writer Brice Cassenti, artwork by Winchell Chung
See http://www.projectrho.com/public_html/rocket/slowerlight3.php
Antimatter-Matter annihilation powered rocket
What is antimatter?
https://www.symmetrymagazine.org/article/april-2015/ten-things-you-might-not-know-about-antimatter
https://sciencenotes.org/what-is-antimatter-definition-and-examples/
https://www.facebook.com/theuniqueknowledge/posts/935607460207906
Find source for the next quote
Fans of science fiction are sure to have heard of antimatter. But in case you haven’t, antimatter is essentially material composed of antiparticles, which have the same mass but opposite charge as regular particles. An antimatter engine, meanwhile, is a form of propulsion that uses interactions between matter and antimatter to generate power, or to create thrust.
In short, an antimatter engine involves particles of hydrogen and antihydrogen being slammed together. This reaction unleashes as much as energy as a thermonuclear bomb, along with a shower of subatomic particles called pions and muons. These particles, which would travel at one-third the speed of light, are then be channeled by a magnetic nozzle to generate thrust.
The advantage to this class of rocket is that a large fraction of the rest mass of a matter/antimatter mixture may be converted to energy, allowing antimatter rockets to have a far higher energy density and specific impulse than any other proposed class of rocket. What’s more, controlling this kind of reaction could conceivably push a rocket up to half the speed of light.
Pound for pound, this class of ship would be the fastest and most fuel-efficient ever conceived. Whereas conventional rockets require tons of chemical fuel to propel a spaceship to its destination, an antimatter engine could do the same job with just a few milligrams of fuel. In fact, the mutual annihilation of a half pound of hydrogen and antihydrogen particles would unleash more energy than a 10-megaton hydrogen bomb.
It is for this exact reason that NASA’s Institute for Advanced Concepts (NIAC) has investigated the technology as a possible means for future Mars missions. Unfortunately, when contemplating missions to nearby star systems, the amount if fuel needs to make the trip is multiplied exponentially, and the cost involved in producing it would be astronomical (no pun!)
How Long Would It Take To Travel To The Nearest Star?
NASA PDF PowerPoint: Realistic Interstellar Travel
Ask Ethan: Is Interstellar Travel Possible? Forbes
Technologies at the very edge of possibility
Wormhole (traversable black holes)
Some sci-fi novels postulate a technology called a jump drive – This allows a starship to be instantaneously teleported between two points. The specific way this is done is glossed over.
Some physicists have offered tentative ideas about how it might be possible. In Stargate, and the science fiction story Contact, the characters use a traversable wormhole – a connection between two distant black holes.
So let’s start with this – What are black holes?
H. K. Wimmer’s rendition of a black hole modified by Attractor321, for Wikipedia. “Black-hole continuum and its gravity well”
Here is one hypothesis about how one might create a transversable wormhole.
A wormhole connects distant locations in space. Wormhole mouths in space connected by a tunnel, called a throat.
and see https://kardashev.fandom.com/wiki/Wormhole
Hyperspace
In Star Wars and Babylon 5 spaceships have a hyperdrive, to send a ship through hyperspace.
From Star Wars, here is a view from the cockpit of hyperspace.
Star Wars The Force Awakens, Millennium Falcon
Hyperspace is a very different concept than warp drive. Hyperspace is a speculative, different dimension, in which faster than light speed are possible. So, in this idea, a spaceship would somehow jump out of our universe and into this realm.
No form of hyperspace has ever been discovered by science; its existence was initially merely supposed by science fiction writers. Although in recent years, theoretical physics work on superstrings has led to something called Brane theory, which indicates the possible existence of hyperspaces of various sorts.
Presumably a spaceship would reach a point in hyperspace that corresponds to the destination in our space that they want; at this point they need to jump out of hyperspace and back into our space.
https://starwars.fandom.com/wiki/Hyperspace
https://en.wikipedia.org/wiki/Hyperspace
https://babylon5.fandom.com/wiki/Hyperspace
What realistic way could limit an FTL drive to only travelling between stars?
Warp drive
You are likely familiar with methods of interstellar travel that currently only exist in science fiction. For instance, in Star Trek, spaceships have a warp drive. Warp drive allows a spaceship to travel through our space, regular space, at FTL (faster than light) speeds.
Many people are familiar with warp drive as a form of FTL (Faster Than Light travel.) Its most popular use is in the science-fiction series Star Trek. According to the laws of physics could this potentially be possible?
Possibility of a real life warp drive, The Alcubierre drive. (KaiserScience)
Warp Drive Research Key to Interstellar Travel, Scientific American
External resources and articles
Physics of interstellar travel Michio Kaku
Space.com articles on interstellar travel
Pros and Cons of Various Methods of Interstellar Travel, Universe Today
Space.StackExchange – [interstellar-travel]
“Concepts for Deep Space Travel: From Warp Drives and Hibernation to World Ships and Cryogenics“, Current Trends in Biomedical Engineering and Biosciences
Videos
The Big Problem With Interstellar Travel, YouTube, RealLifeLore
Interstellar Travel: Approaching Light Speed. Jimiticus
Interstellar Travel – Speculative Documentary HD
Learning Standards
Massachusetts Curriculum Frameworks Science and Technology/Engineering (2016)
6.MS-ESS1-5(MA). Use graphical displays to illustrate that Earth and its solar system are one of many in the Milky Way galaxy, which is one of billions of galaxies in the universe.
A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas (2012)
By the end of grade 8. Patterns of the apparent motion of the sun, the moon, and stars in the sky can be observed, described, predicted, and explained with models. The universe began with a period of extreme and rapid expansion known as the Big Bang. Earth and its solar system are part of the Milky Way galaxy, which is one of many galaxies in the universe.
Next Generation Science Standards
4-PS3 Energy, Disciplinary Core Ideas, ETS1.A: Defining Engineering Problems
Possible solutions to a problem are limited by available materials and resources (constraints). The success of a designed solution is determined by considering the desired features of a solution (criteria). Different proposals for solutions can be compared on the basis of how well each one meets the specified criteria for success or how well each takes the constraints into account. (secondary to 4-PS3-4)
Common Core State Standards Connections: ELA/Literacy
RST.6-8.8 Distinguish among facts, reasoned judgment based on research findings, and speculation in a text. (MS-LS2-5)
RI.8.8 Trace and evaluate the argument and specific claims in a text, assessing whether the reasoning is sound and the evidence is relevant and sufficient to support the claims. (MS-LS-4),(MS-LS2-5)
WHST.6-8.2 Write informative/explanatory texts to examine a topic and convey ideas, concepts, and information through the selection, organization, and analysis of relevant content. (MS-LS2-2)
The Greatest Mistake In The History Of Physics
In optics, the Poisson spot (also called the Arago or Fresnel spot) is an unexpected bright point that appears at the center of a circular object’s shadow – something that common sense would imply is impossible. The spot turns out to be due to the wave nature of light, specifically Fresnel diffraction.
This phenomenon played an important role in the discovery of the wave nature of light. There’s a great articles on this, The Greatest Mistake In The History Of Physics, Ethan Siegel, Forbes, 8/26/2018
French educational card, late 19th/early 20th century.
We all love our most cherished ideas about how the world and the Universe works. Our conception of reality is often inextricably intertwined with our ideas of who we are. But to be a scientist is to be prepared to doubt all of it each and every time we put it to the test. All it takes is one observation, measurement, or experiment that conflicts with the predictions of your theory, and you have to consider revising or throwing out your picture of reality.
If you can reproduce that scientific test and show, convincingly, that it is inconsistent with the prevailing theory, you’ve set the stage for a scientific revolution. But if you aren’t willing to put your theory or assumption to the test, you might just make the greatest mistake in the history of physics.
Which is why, in the early 19th century, the young French scientist, Augustin-Jean Fresnel, should have expected the trouble he was about to get into.
Although it isn’t as well-known today as his work on mechanics or gravitation, Newton was also one of the pioneers in explaining how light worked. He explained reflection and refraction, absorption and transmission, and even how white light was composed of colors. Light rays bent when they went from air into water and back again, and at every surface there was a reflective component and a component that was transmitted through.
Newton’s “corpuscular” [particle] theory of light was particle-based, and his idea that light was a ray agreed with a wide variety of experiments.
Although there was a wave theory of light that was contemporary with Newton’s, put forth by Christiaan Huygens, it couldn’t explain the prism experiments. Newton’s Opticks, like his mechanics and gravitation, was a winner.
But right around the dawn of the 19th century, it started to run into trouble. Thomas Young ran a now-classic experiment where he passed light through a double slit: two narrow slits separated by an extremely small distance.
Instead of light behaving like a corpuscle, where it would either pass through one slit or the other, it displayed an interference pattern: a series of light-and-dark bands.
This shows a typical experimental set-up.
Moreover, the pattern of the bands was determined by two tunable experimental parameters: the spacing between the slit and the color of the light.
If red light corresponded to long-wavelength light and blue corresponded to short-wavelength light, then light behaved exactly as you’d expect if it were a wave.
Young’s double-slit experiments only made sense if light had a fundamentally wavelike nature.
Still, Newton’s successes couldn’t be ignored. The nature of light became a controversial topic in the early 19th century among scientists.
In 1818, the French Academy of Sciences sponsored a competition to explain light. Was it a wave? Was it a particle? How can you test it, and how can you verify that test?
Augustin-Jean Fresnel entered this competition despite being trained as a civil engineer, not as a physicist or mathematician. He had formulated a new wave theory of light that he was tremendously excited about, largely based on Huygens’ 17th century work and Young’s recent experimental results.
The stage was set for the greatest mistake in all of physics to occur.
After submitting his entry, one of the judges, the famed physicist and mathematician Simeon Poisson, investigated Fresnel’s theory in gory detail.
If light were a corpuscle, as Newton would have it, it would simply travel in a straight line through space.
But if light were a wave, it would have to interfere and diffract when it encountered a barrier, a slit, or an “edge” to a surface.
Different geometric configurations would lead to different specific patterns, but this general rule holds.
Poisson imagined light of a monochrome color: a single wavelength in Fresnel’s theory. Imagine this light makes a cone-like shape, and encounters a spherical object.
In Newton’s theory, you get a circle-shaped shadow, with light surrounding it.
But in Fresnel’s theory, as Poisson demonstrated, there should be a single, bright point at the very center of the shadow. This prediction, Poisson asserted, was clearly absurd.
Poisson attempted to disprove Fresnel’s theory by showing that it led to a logical fallacy: reductio ad absurdum. Poisson’s idea was to derive a prediction made by the light-as-a-wave theory that would have such an absurd consequence that it must be false.
If the prediction was absurd, the wave theory of light must be false. Newton was right; Fresnel was wrong. Case closed.
Except, that itself is the greatest mistake in the history of physics! You cannot draw a conclusion, no matter how obvious it seems, without performing the crucial experiment.
Physics is not decided by elegance, by beauty, by the straightforwardness of arguments, or by debate. It is settled by appealing to nature itself, and that means performing the relevant experiment.
THOMAS REISINGER, CC-BY-SA 3.0, E. SIEGEL
Thankfully, for Fresnel and for science, the head of the judging committee would have none of Poisson’s shenanigans. Standing up for not only Fresnel but for the process of scientific inquiry in general, François Arago, who later became much more famous as a politician, abolitionist, and even prime minister of France, performed the deciding experiment himself.
He fashioned a spherical obstacle and shone monochromatic light around it, checking for the wave theory’s prediction of constructive interference. Right at the center of the shadow, a bright spot of light could easily be seen.
Even though the predictions of Fresnel’s theory seemed absurd, the experimental evidence was right there to validate it. Absurd or not, nature had spoken.
A great mistake you can make in physics is to assume you know what the answer is going to be in advance. An even greater mistake is to assume that you don’t even need to perform a test, because your intuition tells you what is or isn’t acceptable to nature itself.
But physics is not always an intuitive science, and for that reason, we must always resort to experiments, observations, and measurable tests of our theories.
Without that approach, we would never have overthrown Aristotle’s view of nature. We never would have discovered special relativity, quantum mechanics, or our current theory of gravity: Einstein’s General Relativity. And, quite certainly, we would never have discovered the wave nature of light without it, either.
History, context, and the end of classical physics
Arago later noted that the phenomenon had already been observed by Joseph-Nicolas Delisle (1715) and Giacomo Maraldi (1723) a century earlier. However, those scientists had not worked out the math and were not trying to use this experiment to distinguish between the different interpretations of physics.
They had made good, solid scientific observations, absolutely. Yet this is a good example of the fact that data, by itself, is only of limited usefulness without a theory to put it in context. Data needs an interpretation to have meaning
It turned out much later (in one of Albert Einstein’s Annus Mirabilis papers) that light can be equally described as a particle. Normally, this would be a paradox – surely light must either be a particle, or a wave. It certainly shouldn’t be both at the same time.
However, the indisputable experimental proof eventually was revealed:
light absolutely does have wave-like properties, and they are clearly predictable and observable in certain circumstances.
Yet light also absolutely does have particle-light properties, which is also predictable and observable in other circumstances.
This at first paradoxical result led to perhaps the greatest development in the history of physics – the overturning of classical physics and the push into the modern, quantum understanding of reality. See articles on wave–particle and quantum mechanics.
From The greatest mistake in the history of physics
See our articles on light, on waves, and on the scientific method.
Particle Detectors
A particle detector is a device used to detect, track, and/or identify ionizing particles.
These particles may have been produced by nuclear decay, cosmic radiation, or reactions in a particle accelerator.
Particle detectors can measure the particle’s energy, momentum, spin, charge, particle type, in addition to merely registering the presence of the particle.
Cloud Chamber
(Adapted from Wikipedia)
A cloud chamber, also known as a Wilson cloud chamber, is a particle detector used for visualizing the passage of ionizing radiation.
A cloud chamber consists of a sealed environment containing a supersaturated vapor of water or alcohol.
An energetic charged particle (for example, an alpha or beta particle) interacts with the gaseous mixture:
it knocks electrons off gas molecules via electrostatic forces during collisions
This results in a trail of ionized gas particles. They act as condensation centers : a mist-like trail of small droplets form if the gas mixture is at the point of condensation.
These droplets are visible as a “cloud” track that persist for several seconds while the droplets fall through the vapor.
These tracks have characteristic shapes. For example, an alpha particle track is thick and straight, while an electron track is wispy and shows more evidence of deflections by collisions.
Cloud chambers played a prominent role in the experimental particle physics from the 1920s to the 1950s, until the advent of the bubble chamber.
This is a Diffusion Cloud Chamber used for public demonstrations at the Museum of Technology in Berlin. The first part shows the alpha and beta radiation occurring around us all the time, thanks to normal activity in the atmosphere. Then a sample of Radon 220 (half-life 55 sec) is inserted into the chamber and all hell breaks loose as an alpha-decay party ensues!
Source: Derek McKenzie, Physics Footnotes, http://physicsfootnotes.com/radon-cloud-chamber/
Here is an example of two particles colliding within an accelerator, and decaying into a variety of other products.
.
Let’s look at some detailed examples. We’ll see photographs of the particle detector, then we’ll see cutaway diagrams showing us what is inside the detector.
While each detector is different – designed for a different task – they all have some basic elements in common. Each has a set of wires that make a signal if a particle flies through them. These wires are arrayed around the target area – the place where the particles are forced to collide.
When a collision occurs, some particles are broken free and fly outwards.
More remarkably, when a collision occurs, some particles are actually created – we generate particles that weren’t even there before. How is that possible? Short version, Einstein’s theory of mass-energy equivalence means that matter can be converted into energy, or vice-versa. The massive energy in these collisions creates many new sub-atomic particles. Some of these may be permanent, others might exist for only short periods of time.
ALICE, A Large Ion Collider Experiment in the LHC at CERN
This animation shows what happens when electrons and positrons collide in the ILD detector, one of the planned detectors for the future ILC. Many collisions will happen at the same time around the clock, producing a vast array of possible events. This shows one possible collision event involving the Higgs boson.
Conundrums
“With the uncertainty principle and the observer effects in mind, how do these devices measure both the position and momentum of sub-atomic particles with the kind of accuracy that they seem to get, with the beautiful color pictures?”
How do these devices measure both the position and momentum of particles without violating the Heisenberg Uncertainty principle?
Infographics
.
Apps
The Particle Adventure app lets us discover: The Standard Model, Accelerators and Particle Detectors, Higgs Boson Discovered, Unsolved Mysteries, Particle Decays and Annihilations.
Android – The Particle Adveture . iOS (Apple) The Particle Adventure
Interactive website sims
The Particle Adventure
CPEP Contemporary Physics Education Project
Further reading
Symmetry Magazine (for high school students)
Learning Standards
SAT Subject Test: Physics
Quantum phenomena, such as photons and photoelectric effect. Atomic, such as the Rutherford and Bohr models, atomic energy levels, and atomic spectra. Nuclear and particle physics, such as radioactivity, nuclear reactions, and fundamental particles.
Relativity, such as time dilation, length contraction, and mass-energy equivalence
A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas (2012)
Electromagnetic radiation can be modeled as a wave of changing electric and magnetic fields or as particles called photons. The wave model is useful for explaining many features of electromagnetic radiation, and the particle model explains other features. Quantum theory relates the two models…. Knowledge of quantum physics enabled the development of semiconductors, computer chips, and lasers, all of which are now essential components of modern imaging, communications, and information technologies.
KaiserScience 
