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Rainbows

Rainbows are produced by electromagnetic radiation – visible light – reflecting in marvelous ways from the dispersion of light.

Let’s start with the basics:

A prism separates white light into many colors

How? Each wavelength of light refracts by a different amount

The result is dispersion – each wavelength is bent by a different amount

prism-refraction-dispersion-of-visible-light-into-spectrum

The physics of rainbow formation

Rainbows: At Atmospheric optics

http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/rbowpri.html

http://www.atmo.arizona.edu/students/courselinks/spring13/atmo170a1s1/1S1P_stuff/atmos_optical_phenomena/optical_phenomena.html

Rebecca McDowell  How rainbows form

 

The shape of a rainbow

A discussion of this comic is here Explain XKCD. 1944: The End of the Rainbow

If one considers the path that light takes to form a rainbow, then it forms a two-cone structure, where the Sun (the vertex of the outer cone) emits light rays that move towards the Earth (forming the faces of the outer cone),

Then the rays reflect off water droplets located at just the right angle (the circular base) to reach our eyes (the vertex of the inner cone).

Thus, such a rainbow structure can be said to have “ends”, represented by the vertices of the two cones: one at the eye of the viewer, and another at the light source (usually the sun).

XKCD End of the rainbow 1944

from the webcomic XKCD.

Do rainbows have reflections?

It certainly seems like rainbows can have reflections.

Consider this great photo by Terje O. Nordvik, September ’04 near Sandessjøen, Norway.

http://www.atoptics.co.uk/rainbows/bowim6.htm

But rainbows aren’t real objects – and so they literally can’t have reflections!

So what are we seeing here? See Rainbow reflections: Rainbows are not Vampires

terje-nordvik-rainbow-in-norway

Learning Standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework

HS-PS4-3. Evaluate the claims, evidence, and reasoning behind the idea that electromagnetic radiation can be described by either a wave model or a particle model, and that for some situations involving resonance, interference, diffraction, refraction, or the photoelectric effect, one model is more useful than the other.

SAT subject test in Physics: Waves and optics

• General wave properties, such as wave speed, frequency, wavelength, superposition, standing wave diffraction, and Doppler effect
• Reflection and refraction, such as Snell’s law and changes in wavelength and speed
• Ray optics, such as image formation using pinholes, mirrors, and lenses
• Physical optics, such as single-slit diffraction, double-slit interference, polarization, and color.

MCAS light and optics practice problems

MCAS example problems

Which of the following statements describes what will most likely happen to the light ray after it strikes the aluminum foil?

A. The light ray will be absorbed by the shiny metal.
B. The light ray will be refracted after passing through the shiny metal.
C. The light ray will be reflected at a different angle to the normal than the incident light ray.
D. The light ray will be reflected at the same angle to the normal as the incident light ray

_________________________________________

wave-refraction-mcas-2011

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reflection-refraction-mcas-2016

2016 Physics MCAS

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reflection-mcas-2014

Physics MCAS 2014

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optics-mcas-2014

Physics MCAS 2014

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a. Identify and describe the wave behavior as the light rays pass through the glass lens.

b. Identify and describe the wave behavior as the light rays strike the mirror.

c. Copy the dotted box from the camera diagram into your Student Answer Booklet. Draw what must happen inside the box for light ray 2 to strike the viewfinder. Be sure to include
the following:
• either a lens or a mirror that is labeled
• the path of light ray 2
• a line normal to the surface where light ray 2 strikes

Schrödinger’s cat

Schrödinger’s cat is a thought experiment, sometimes described as a paradox, devised by Austrian physicist Erwin Schrödinger in 1935.

It illustrates what he saw as the problem of the Copenhagen interpretation of quantum mechanics when applied to everyday objects.

Cat static balloons

Here is how the Schrödinger’s cat thought experiment works:

Acat, a flask of poison, and a radioactive source are placed in a sealed box.

If an internal monitor detects radioactivity (i.e., a single atom decaying), the flask is shattered, releasing the poison, which kills the cat.

The Copenhagen interpretation of quantum mechanics implies that after a while, the cat is simultaneously alive and dead.

Yet, when one looks in the box, one sees the cat either alive or dead, not both alive and dead.

schrodingers-cat-experiment

This poses the question of when exactly quantum superposition ends and reality collapses into one possibility or the other.

The Copenhagen interpretation implies that the cat remains both alive and dead – until the state is observed.

Schrödinger did not wish to promote the idea of dead-and-alive cats as a serious possibility.

On the contrary, he intended the example to illustrate the absurdity of the existing view of quantum mechanics

schrodingers-cat

Since Schrödinger’s time, other interpretations of quantum mechanics have been proposed that give different answers to the questions posed by Schrödinger’s cat of how long superpositions last and when (or whether) they collapse.

This introduction has been adapted from “Schrödinger’s cat.” Wikipedia, The Free Encyclopedia, 5 Feb. 2017.

Many-worlds interpretation and consistent histories

In 1957, Hugh Everett formulated the many-worlds interpretation of quantum mechanics, which does not single out observation as a special process.

In the many-worlds interpretation, both alive and dead states of the cat persist after the box is opened, but are decoherent from each other.

schroedingers-cat-many-world-svg

In other words, when the box is opened, the observer and the possibly-dead cat split into an observer looking at a box with a dead cat, and an observer looking at a box with a live cat.

But since the dead and alive states are decoherent, there is no effective communication or interaction between them. We have created parallel universes!

Decoherence interpretation

When opening the box, the observer becomes entangled with the cat.

Therefore “observer states” corresponding to the cat’s being alive and dead are formed; each observer state is entangled or linked with the cat so that the “observation of the cat’s state” and the “cat’s state” correspond with each other.

Quantum decoherence ensures that the different outcomes have no interaction with each other. The same mechanism of quantum decoherence is also important for the interpretation in terms of consistent histories.

Only the “dead cat” or the “alive cat” can be a part of a consistent history in this interpretation.

cat-quantum-meme

External resources

https://www.newscientist.com/article/2097199-seven-ways-to-skin-schrodingers-cat/

 

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

AP Physics Curriculum Framework
Essential Knowledge 1.D.1: Objects classically thought of as particles can exhibit properties of waves.
a. This wavelike behavior of particles has been observed, e.g., in a double-slit experiment using elementary particles.
b. The classical models of objects do not describe their wave nature. These models break down when observing objects in small dimensions.

Learning Objective 1.D.1.1:
The student is able to explain why classical mechanics cannot describe all properties of objects by articulating the reasons that classical mechanics must be refined and an alternative explanation developed when classical particles display wave properties.

Essential Knowledge 1.D.2: Certain phenomena classically thought of as waves can exhibit properties of particles.
a. The classical models of waves do not describe the nature of a photon.
b. Momentum and energy of a photon can be related to its frequency and wavelength.

Content Connection: This essential knowledge does not produce a specific learning objective but serves as a foundation for other learning objectives in the course.

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

Torque

Torque in Everyday Life

When we hear the term ‘torque’ brought up, it’s most often in the context of automobiles. Torque is one of the terms commonly thrown around to describe how powerful a car is, but what exactly does it mean?

In a car, torque is the force that pistons put on the crankshaft, causing it and the wheels to turn.

– Damien Howard

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Torque is a force that causes an object to rotate about an axis.

torque-piston-crankshaft

Here we see the piston and crankshaft motion in an internal combustion engine (like in an automobile.)

Image from Wikipedia.

four-stroke-engine-gif

While often considered an automotive term, torque is actually a general physics term that has many applications.

Torque is defined as a twisting force that tends to cause rotation.

We call the point where the object rotates the axis of rotation.

You use torque every day without realizing it. You apply torque three times when you simply open a locked door:

(1) Turning the key, (2) turning the doorknob, and (3) pushing the door open so it swings on its hinges are all methods of applying a torque.

– Damien Howard, Holt McDougal Physics Chapter 4: Forces and the Laws of Motion

Biophysics

Torque is important when studying physiology (the study of how cells and organs interact to form a whole being, including skeletons, muscles, organs, etc.)

In this lesson we learn about Forces and Torques in Muscles and Joints.

Many body motions require or take advantage of torque, for instance:

A cheetah’s tail provides an excellent example of torque and angular momentum in action.

With a simple clockwise flick of the tail, the cheetah’s body (in a response which conserves angular momentum) rolls in the anti-clockwise direction (and conversely).

This enables the cheetah to position its body mid-flight so that it is ready to turn the instant its feet make contact with the ground.

http://physicsfootnotes.com/physics-of-the-cheetahs-tail/

cheetah-tail-angular-momentum-torque
l

http://physicsfootnotes.com/physics-of-the-cheetahs-tail/

Torque: Introductory physics

From Chapter 8, Rotational Motion, Section 2, Rotational dynamics

A lever arm is… (p.209)

figure 5

lever-arm-torque-opening-a-door-glencoe-physics-chap-8

Consider how tools are used:

torque-axis-of-rotation-lever-arm-glencoe-physics-chap-8

Torque is defined as a force that tends to cause rotation. It changes the rotational motion of an object.

We call the point where the object rotates the axis of rotation.

Torque = τ  (Greek letter tau)

τ = [Force applied] x [lever arm]

τ = F·r

The amount of torque applied depends on the angle, θ, so then:

τ = F·r·sin(θ)

lever arm = perpendicular distance from the axis of rotation to the line of action of the force.

Finding the net torque

net-torque-on-pencils

An example problem

net-torque-example-seesaw

PhET labs

PhET lab: Torque

PhET lab: Balancing act

PhET lab: Balancing act (HTML 5 app)

External resources

Open Stax College Physics: Statics and torque

Rotational dynamics: SparkNotes

Learning Standards

Mass High School Technology/Engineering

HS-ETS1-2. Break a complex real-world problem into smaller, more manageable problems that each can be solved using scientific and engineering principles.

HS-ETS4-1(MA). Research and describe various ways that humans use energy and power systems to harness resources to accomplish tasks effectively and efficiently.

SAT Physics test

Torque and equilibrium

“When SAT II Physics tests you on equilibrium, it will usually present you with a system where more than one torque is acting upon an object, and will tell you that the object is not rotating. That means that the net torque acting on the object is zero, so that the sum of all torques acting in the clockwise direction is equal to the sum of all torques acting in the counterclockwise direction.” – SparkNotes Rotational dynamics

AP Physics

Enduring Understanding 3F: A force exerted on an object can cause a torque on that object.

Enduring Understanding 4D: A net torque exerted on a system by other objects or systems will change the angular momentum of the system.

A Framework for K-12 Science Education, National Research Council

PS2.A: FORCES AND MOTION: How can one predict an object’s continued motion, changes in motion, or stability?

Interactions of an object with another object can be explained and predicted using the concept of forces, which can cause a change in motion of one or both of the interacting objects… At the macroscale, the motion of an object subject to forces is governed by Newton’s second law of motion… An understanding of the forces between objects is important for describing how their motions change, as well as for predicting stability or instability in systems at any scale.

Triple point

The following is from the Learner.Org Chemistry course https://www.learner.org/courses/chemistry/about/about.html

Once the gas laws were formulated, chemists could analyze how materials transitioned from one phase to another, and how temperature and pressure affected these changes.

In 1897, a British metallurgist named Sir William Chandler Roberts-Austen (1843–1902) produced what is widely regarded as an early form of a now-common tool in chemistry and related disciplines: the phase diagram.

Modern phase diagrams show relationships between different states of matter under various combinations of temperature and pressure.

A substance can exist in two different states at once—for example, as a liquid and a gas, with molecules cycling from one state to the other.

It is also possible for a material to be both solid and liquid, with both melting and freezing taking place at its edges, or to exist as a solid and a gas.

Phase diagrams show what forms a substance will take under given temperatures and pressure levels, and where these equilibrium lines (when equal numbers of molecules are changing form in both directions) are located. (Figure 2-11)

Figure 2-11. Generic Phase Diagram for a Single Substance © Science Media Group. https://www.learner.org/courses/chemistry/text/text.html?dis=U&num=Ym5WdElUQS9NeW89&sec=YzJWaklUQS9OeW89

Figure 2-11. Generic Phase Diagram for a Single Substance
© Science Media Group.
https://www.learner.org/courses/chemistry/text/text.html?dis=U&num=Ym5WdElUQS9NeW89&sec=YzJWaklUQS9OeW89

Amazing: See a flask of liquid cyclohexane brought to the brink of its triple-point:
suddenly it can boil and freeze at the same time.

http://physicsfootnotes.com/triple-point/

A volumetric flask containing liquid cyclohexane is depressurized to a very low pressure by a turbo-molecular vacuum pump. The rapid drop in pressure results in a rapid drop in temperature, causing the substance to temporarily freeze, but the system is unstable, flirting with the triple point (a point of pressure and temperature at which a substance is simultaneously solid, liquid, and gas). The result is a fluctuation between all three states of matter, in a spectacular display of chemistry and physics in action.

http://physicsfootnotes.com/triple-point/

 

 

Unification

RUNE FISKER Unification of forces

Ruth Fisker, Quanta Magazine

Where do all the forces of nature come from?

All the forces that we see in nature today have been discovered really to be aspects of four basic forces of nature.

Are these four forces totally separate, or are they themselves different aspects of one underlying aspect of reality?

MAHARISHI UNIVERSITY OF MANAGEMENT Four Fundamental Forces

  • Electromagnetism

  • Weak nuclear force

  • Strong nuclear force

  • Gravity

One may ask, why are there four basic forces in nature? Why not 3, or 5?

Why not an infinite number of different forces – or why not just one?

After 200 years of study, physicists have marshaled an amazing array of evidence which shows that three of these basic forces indeed are apparently just different aspects of one greater force.

merging-forces-gut

The technique by which we have unified the first three of these forces has produced what is known as a Grand Unified Theory (GUT).

For the last 70 years physicists have been exploring models which be able to also unify the fourth force, gravity, with the first three. Should this be possible, it would be termed a Theory of Everything (TOE).

There may be no a priori reason why the correct description of nature has to be a unified field theory.

However, this goal has led to a great deal of progress in modern theoretical physics and continues to motivate research.

Grand Unified Theory

A GUT is a model in particle physics in which at high energy, the three gauge interactions of the Standard Model which define the electromagnetic, weak, and strong interactions or forces, are merged into one single force.

This unified interaction is characterized by one larger gauge symmetry and thus several force carriers, but one unified coupling constant.

If Grand Unification is realized in nature, there is the possibility of a grand unification epoch in the early universe in which the fundamental forces are not yet distinct.

Unifying gravity with the other three interactions would provide a theory of everything (TOE), rather than a GUT. Nevertheless, GUTs are often seen as an intermediate step towards a TOE.

The novel particles predicted by GUT models are expected to have masses around the GUT scale,  a few orders of magnitude below the Planck scale – and so will be well beyond the reach of any foreseen particle collider experiments.

Therefore, the particles predicted by GUT models will be unable to be observed directly. Instead the effects of grand unification might be detected through indirect observations such as proton decay, electric dipole moments of elementary particles, or the properties of neutrinos. Some GUTs predict the existence of magnetic monopoles.

This section excerpted from https://en.wikipedia.org/wiki/Grand_Unified_Theory

drake-unification-forces-meme

Related articles

http://www.symmetrymagazine.org/article/a-gut-feeling-about-physics

Grand Unification May Be A Dead End For Physics. Ethan Siegel.

http://physics.stackexchange.com/questions/53467/unified-field-theory-in-laymans-terms

https://en.wikipedia.org/wiki/Theory_of_everything

Superstrings: A possible theory of everything

http://www.pbs.org/wgbh/nova/physics/theory-of-everything.html

http://www.smithsonianmag.com/science-nature/string-theory-about-unravel-180953637/

Learning Standards

AP Physics Curriculum Framework

Essential Knowledge 1.D.1: Objects classically thought of as particles can exhibit properties of waves.

a. This wavelike behavior of particles has been observed, e.g., in a double-slit experiment using elementary particles.
b. The classical models of objects do not describe their wave nature. These models break down when observing objects in small dimensions.

Learning Objective 1.D.1.1:
The student is able to explain why classical mechanics cannot describe all properties of objects by articulating the reasons that classical mechanics must be refined and an alternative explanation developed when classical particles display wave properties.

Essential Knowledge 1.D.2: Certain phenomena classically thought of as waves can exhibit properties of particles.
a. The classical models of waves do not describe the nature of a photon.
b. Momentum and energy of a photon can be related to its frequency and wavelength.

Content Connection: This essential knowledge does not produce a specific learning objective but serves as a foundation for other learning objectives in the course.

 

Gravitational repulsion and the Dipole Repeller

Ask Ethan: If Gravity Attracts, How Can The ‘Dipole Repeller’ Push The Milky Way?

Ethan Siegel, Contributor. Feb 4, 2017

Forbes.com Startswithabang 2017 Ask Ethan The Dipole Repeller

The relative attractive and repulsive effects of overdense and underdense regions on the Milky Way. Image credit: "The Dipole Repeller" by Yehuda Hoffman, Daniel Pomarède, R. Brent Tully, and Hélène Courtois, Nature Astronomy 1, 0036 (2017).

The relative attractive and repulsive effects of overdense and underdense regions on the Milky Way. Image credit: “The Dipole Repeller” by Yehuda Hoffman, Daniel Pomarède, R. Brent Tully, and Hélène Courtois, Nature Astronomy 1, 0036 (2017).

One of the most peculiar things about the Universe is how quickly the Milky Way appears to be moving. Despite having mapped out the cosmic masses nearby to unprecedented accuracy, there still doesn’t appear to be enough to cause the motion we actually experience. The idea of a “great attractor” doesn’t quite match up with what we see; what’s actually present isn’t quite “great” enough. But a new idea — that of a dipole repeller — might finally explain this longstanding conundrum. How would that work, and what it is, exactly? That’s what Darren Redfern wants to know:

What are the mechanics behind a dipole repeller? How can an area of space void of matter repulse galaxies to any meaningful extent (or at all?)?

If you were to look at all the galaxies accessible to us, you’d find, on average, that they were moving away from us at a specific rate: the Hubble rate. The farther away a galaxy is, the faster it appears to move away from us, and that’s a consequence of living in an expanding Universe governed by General Relativity. But that’s only on average. Each individual galaxy has an additional motion on top of that, known as peculiar velocity, and that’s due to the combined gravitational influence of every imperfection in the Universe on it.

The various galaxies of the Virgo Supercluster, grouped and clustered together. On the largest scales, the Universe is uniform, but as you look to galaxy or cluster scales, overdense and underdense regions dominate. Image credit: Andrew Z. Colvin, via Wikimedia Commons.

The various galaxies of the Virgo Supercluster, grouped and clustered together. On the largest scales, the Universe is uniform, but as you look to galaxy or cluster scales, overdense and underdense regions dominate. Image credit: Andrew Z. Colvin, via Wikimedia Commons.

The closest large galaxy to us, Andromeda, is actually moving towards us, thanks to the Milky Way’s gravitational pull. Galaxies in the closest giant cluster of galaxies — the Virgo cluster — get extra speeds of up to 2,000 km/s on top of the Hubble flow we see. And when we look at the Big Bang’s leftover glow, the Cosmic Microwave Background, we’re able to measure our own peculiar motion through the Universe.

The CMB dipole as measured by COBE, representing our motion through the Universe relative to the CMB's rest frame. Image credit: DMR, COBE, NASA, Four-Year Sky Map.

The CMB dipole as measured by COBE, representing our motion through the Universe relative to the CMB’s rest frame. Image credit: DMR, COBE, NASA, Four-Year Sky Map.

This “cosmic dipole” we see is redshifted in one direction (meaning we’re moving away from it) and blueshifted in the other (meaning we’re moving towards it), and we can reconstruct the motion of the entire local group as a result. Us, Andromeda, Triangulum and everything else is moving at a speed of 631 km/s relative to the Hubble flow, and we know that gravitation must be the cause of this. When we look out at where the galaxies are located, we can map out their masses and how much of an attractive force they exert.

 two-dimensional slice of the overdense (red) and underdense (blue/black) regions of the Universe nearby us. Image credit: Cosmic Flows Project/University of Hawaii, via http://www.cpt.univ-mrs.fr/.

two-dimensional slice of the overdense (red) and underdense (blue/black) regions of the Universe nearby us. Image credit: Cosmic Flows Project/University of Hawaii, via http://www.cpt.univ-mrs.fr/.

Thanks to the recent Cosmic Flows project, we’ve not only mapped out the nearby Universe to better precision than ever before, we discovered that the Milky Way lies on the outskirts of a giant collection of galaxies pulling us towards it: Laniakea. This is a significant contributor to our peculiar motion, but it isn’t enough to explain all of it on its own. Gravitational attraction is only half the story. The other half? It comes from gravitational repulsion. Let me explain.

Imagine you have a Universe where you have an equal number of masses evenly spaced everywhere you look. In all directions, at all locations, the Universe is filled with matter of even density. If you put an extra mass a certain distance to your left, you’ll be attracted towards your left, because of gravitational attraction.

But if you remove some of the mass that same distance to your right, you’ll also be attracted towards your left! In a perfectly uniform Universe, you’d be attracted to all directions equally, and that attractive force would cancel out. But if you remove some mass from one particular direction, it can’t attract you as strongly, and so you’re attracted preferentially in the other direction.

Dipoles are most common in electromagnetism, where we think of negative as attractive and positive as repulsive. If you thought of this gravitationally, negative would be 'extra mass' and therefore attractive, while positive would be 'less mass' and therefore, relative to everything else, repulsive. Image credit: Wikimedia Commons user Maschen.

Dipoles are most common in electromagnetism, where we think of negative as attractive and positive as repulsive. If you thought of this gravitationally, negative would be ‘extra mass’ and therefore attractive, while positive would be ‘less mass’ and therefore, relative to everything else, repulsive. Image credit: Wikimedia Commons user Maschen.

 

It’s not technically a gravitational repulsion, since gravitation is always attractive, but you’re less attracted to one direction than all the others, and so an underdense region effectively acts as a gravitational repeller. You can even imagine a situation where you have an overly dense region on one side of you with an underdense region on the other side. You’d experience the greatest magnitude of attraction and repulsion simultaneously. This is what the idea of the dipole repeller is.

The gravitational attraction (blue) of overdense regions and the relative repulsion (red) of the underdense regions, as they act on the Milky Way. Image credit: "The Dipole Repeller" by Yehuda Hoffman, Daniel Pomarède, R. Brent Tully, and Hélène Courtois, Nature Astronomy 1, 0036 (2017).

The gravitational attraction (blue) of overdense regions and the relative repulsion (red) of the underdense regions, as they act on the Milky Way. Image credit: “The Dipole Repeller” by Yehuda Hoffman, Daniel Pomarède, R. Brent Tully, and Hélène Courtois, Nature Astronomy 1, 0036 (2017).

It’s difficult to measure where an underdense region is, since regions of average density are fairly devoid of galaxies as well as the underdense ones. But a recently discovered cosmic void relatively nearby, and in the opposite direction to the large concentration of galaxies attracting us, seems to be responsible for roughly 50% of our peculiar motion, which is exactly the amount that was unaccounted for by the overdense regions alone.

Youtube video: The Dipole Repeller video, by Daniel Pomarède.  produced as part of the following publication: “The Dipole Repeller” by Yehuda Hoffman, Daniel Pomarède, R. Brent Tully, and Hélène Courtois, Nature Astronomy 1, 0036 (2017).

At long last, this could be the solution to why our Sun, galaxy and local group all exhibit the motion that they do. Gravity is never repulsive, but a less attractive force in one direction than all the others behaves indistinguishably from a repulsion. We might distinguish between a pull in one direction and a push in the opposite direction, but in astrophysics, it’s all the same thing: forces and acceleration. It doesn’t have anything to do with dark energy or a mysterious fifth force; it’s simply having an excess of matter in one direction and a dearth of matter in nearly the exact opposite direction. The result? We move through the Universe in our own particular, peculiar fashion.

Reference: The dipole repeller, Yehuda Hoffman, Daniel Pomarède, R. Brent Tully & Hélène M. Courtois, Nature Astronomy 1, Article number: 0036 (2017).

Ethan Siegel, Contributor. Feb 4, 2017

Forbes.com Startswithabang 2017 Ask Ethan The Dipole Repeller

 

Why learn computer programming

Why Johnny can’t code

By David Brin, Salom Magazine, Sept 14, 2006

from Barron’s Dictionary of Computer and Internet Terms for: BASIC

BASIC used to be on every computer a child touched — but today there’s no easy way for kids to get hooked on programming.

Also see our main page on What is mathematics, really? Is it made by humans or a feature of the universe? Math in art & poetry.
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For three years — ever since my son Ben was in fifth grade — he and I have engaged in a quixotic but determined quest: We’ve searched for a simple and straightforward way to get the introductory programming language BASIC to run on either my Mac or my PC.

Why on Earth would we want to do that, in an era of glossy animation-rendering engines, game-design ogres and sophisticated avatar worlds? Because if you want to give young students a grounding in how computers actually work, there’s still nothing better than a little experience at line-by-line programming.

Only, quietly and without fanfare, or even any comment or notice by software pundits, we have drifted into a situation where almost none of the millions of personal computers in America offers a line-programming language simple enough for kids to pick up fast. Not even the one that was a software lingua franca on nearly all machines, only a decade or so ago. And that is not only a problem for Ben and me; it is a problem for our nation and civilization.

Oh, today’s desktops and laptops offer plenty of other fancy things — a dizzying array of sophisticated services that grow more dazzling by the week. Heck, I am part of that creative spasm.

Only there’s a rub. Most of these later innovations were brought to us by programmers who first honed their abilities with line-programming languages like BASIC. Yes, they mostly use higher level languages now, stacking and organizing object-oriented services, or using other hifalutin processes that come prepackaged and ready to use, the way an artist uses pre-packaged paints. (Very few painters still grind their own pigments. Should they?)

And yet the thought processes that today’s best programmers learned at the line-coding level still serve these designers well. Renowned tech artist and digital-rendering wizard Sheldon Brown, leader of the Center for Computing in the Arts, says:

“In my Electronics for the Arts course, each student built their own single board computer, whose CPU contained a BASIC ROM [a chip permanently encoded with BASIC software]. We first did this with 8052’s and then with a chip called the BASIC Stamp. The PC was just the terminal interface to these computers, whose programs would be burned into flash memory. These lucky art students were grinding their own computer architectures along with their code pigments — along their way to controlling robotic sculptures and installation environments.”

But today, very few young people are learning those deeper patterns. Indeed, they seem to be forbidden any access to that world at all.

And yet, they are tantalized! Ben has long complained that his math textbooks all featured little type-it-in-yourself programs at the end of each chapter — alongside the problem sets — offering the student a chance to try out some simple algorithm on a computer. Usually, it’s an equation or iterative process illustrating the principle that the chapter discussed. These “TRY IT IN BASIC” exercises often take just a dozen or so lines of text. The aim is both to illustrate the chapter’s topic (e.g. statistics) and to offer a little taste of programming.

Only no student tries these exercises.

Not my son or any of his classmates. Nor anybody they know. Indeed, I would be shocked if more than a few dozen students in the whole nation actually type in those lines that are still published in countless textbooks across the land. Those who want to (like Ben) simply cannot.

Now, I have been complaining about this for three years. But whenever I mention the problem to some computer industry maven at a conference or social gathering, the answer is always the same: “There are still BASIC programs in textbooks?”

At least a dozen senior Microsoft officials have given me the exact same response. After taking this to be a symptom of cluelessness in the textbook industry, they then talk about how obsolete BASIC is, and how many more things you can do with higher-level languages. “Don’t worry,” they invariably add, “the newer textbooks won’t have any of those little BASIC passages in them.”

All of which is absolutely true. BASIC is actually quite tedious and absurd for getting done the vast array of vivid and ambitious goals that are typical of a modern programmer. Clearly, any kid who wants to accomplish much in the modern world would not use it for very long. And, of course, it is obvious that newer texts will abandon “TRY IT IN BASIC” as a teaching technique, if they haven’t already.

But all of this misses the point. Those textbook exercises were easy, effective, universal, pedagogically interesting — and nothing even remotely like them can be done with any language other than BASIC. Typing in a simple algorithm yourself, seeing exactly how the computer calculates and iterates in a manner you could duplicate with pencil and paper — say, running an experiment in coin flipping, or making a dot change its position on a screen, propelled by math and logic, and only by math and logic:

All of this is priceless. As it was priceless 20 years ago. Only 20 years ago, it was physically possible for millions of kids to do it. Today it is not.

In effect, we have allowed a situation to develop that is like a civilization devouring its seed corn. If an enemy had set out to do this to us — quietly arranging so that almost no school child in America can tinker with line coding on his or her own — any reasonably patriotic person would have called it an act of war.

Am I being overly dramatic? Then consider a shift in perspective.

First ponder the notion of programming as a series of layers. At the bottom-most level is machine code. I showed my son the essentials on scratch paper, explaining the roots of Alan Turing’s “general computer” and how it was ingeniously implemented in the first four-bit integrated processor, Intel’s miraculous 1971 4004 chip, unleashing a generation of nerdy guys to move bits around in little clusters, adding and subtracting clumps of ones and zeroes, creating the first calculators and early desktop computers like the legendary Altair.

This level of coding is still vital, but only at the realm of specialists at the big CPU houses. It is important for guys like Ben to know about machine code — that it’s down there, like DNA in your cell — but a bright kid doesn’t need to actually do it, in order to be computer-literate. (Ben wants to, though. Anyone know a good kit?)

The layer above that is often called assembler, though there are many various ways that user intent can be interpreted down to the bit level without actually flicking a series of on-off switches. Sets of machine instructions are grouped, assembled and correlated with (for example) ASCII-coded commands. Some call this the “boringest” level. Think of the hormones swirling through your body. Even a glimpse puts me to sleep. But at least I know that it is there.

The third layer of this cake is the operating system of your computer. Call it BIOS and DOS, along with a lot of other names. This was where guys like Gates and Wozniak truly propelled a whole industry and way of life, by letting the new desktops communicate with their users, exchange information with storage disks and actually show stuff on a screen. Cool.

Meanwhile, the same guys were offering — at the fourth layer — a programming language that folks could use to create new software of their very own. BASIC was derived from academic research tools like beloved old FORTRAN (in which my doctoral research was coded onto punched paper cards, yeesh). It was crude. It was dry. It was unsuitable for the world of the graphic user interface. BASIC had a lot of nasty habits. But it liberated several million bright minds to poke and explore and aspire as never before.

The “scripting” languages that serve as entry-level tools for today’s aspiring programmers — like Perl and Python — don’t make this experience accessible to students in the same way. BASIC was close enough to the algorithm that you could actually follow the reasoning of the machine as it made choices and followed logical pathways.

Repeating this point for emphasis: You could even do it all yourself, following along on paper, for a few iterations, verifying that the dot on the screen was moving by the sheer power of mathematics, alone. Wow!

(Indeed, I would love to sit with my son and write “Pong” from scratch. The rule set — the math — is so simple. And he would never see the world the same, no matter how many higher-level languages he then moves on to.)

The closest parallel I can think of is the WWII generation of my father — guys for whom the ultra in high tech was automobiles. What fraction of them tore apart jalopies at home? Or at least became adept at diagnosing and repairing the always fragile machines of that era? One result of that free and happy spasm of techie fascination was utterly strategic. When the “Arsenal of Democracy” began churning out swarms of tanks and trucks and jeeps, these were sent to the front and almost overnight an infantry division might be mechanized, in the sure and confident expectation that there would be thousands of young men ready (or trainable) to maintain these tools of war. (Can your kid even change the oil nowadays? Or a tire?)

The parallel technology of the ’70s generation was IT.

Information technology (IT) is the application of computers to store, study, transmit, and manipulate data, often in the context of a business or other enterprise.

Not every boomer soldered an Altair from a kit, or mastered the arcana of DBASE. But enough of them did so that we got the Internet and Web. We got Moore’s Law and other marvels. We got a chance to ride another great technological wave.

So, what’s the parallel hobby skill today?
What tech-marvel has boys and girls enthralled, tinkering away, becoming expert in something dazzling and practical and new?
Shooting ersatz aliens in “Halo”?
Dressing up avatars in “The Sims”?

Oh sure, there’s creativity in creating cool movies and Web pages. But except for the very few who will make new media films, do you see a great wave of technological empowerment coming out of all this?

OK, I can hear the sneers. Are these the rants of a grouchy old boomer? Feh, kids today! (And get the #$#*! off my lawn!)

Fact is, I just wanted to give my son a chance to sample some of the wizardry standing behind the curtain, before he became lost in the avatar-filled and glossy-rendered streets of Oz. Like the hero in “TRON,” or “The Matrix,” I want him to be a user who can see the lines that weave through the fabric of cyberspace — or at least know some history about where it all came from. At the very minimum, he ought to be able to type those examples in his math books and use the computer the way it was originally designed to be used: to compute.

Hence, imagine my frustration when I discovered that it simply could not be done.

Yes, yes: For three years I have heard all the rationalized answers. No kid should even want BASIC, they say. There are higher-level languages like C++ (Ben is already — at age 14 — on page 200 of his self-teaching C++ book!) and yes, there are better education programs like Logo. Hey, what about Visual Basic! Others suggested downloadable versions like q-basic, y-basic, alphabetabasic…

Indeed, I found one that was actually easy to download, easy to turn on, and that simply let us type in some of those little example programs, without demanding that we already be manual-chomping fanatics in order to even get started using the damn thing. Chipmunk Basic for the Macintosh actually started right up and let us have a little clean, algorithmic fun. Extremely limited, but helpful. All of the others, every last one of them, was either too high-level (missing the whole point!) or else far, far too onerous to figure out or use. Certainly not meant to be turn-key usable by any junior high school student. Appeals for help online proved utterly futile.

Until, at last, Ben himself came up with a solution. An elegant solution of startling simplicity. Essentially: If you can’t beat ’em, join ’em.

While trawling through eBay, one day, he came across listings for archaic 1980s-era computers like the Apple II. “Say, Dad, didn’t you write your first novel on one of those?” he asked.

“Actually, my second. ‘Startide Rising.’ On an Apple II with Integer Basic and a serial number in five digits. It got stolen, pity. But my first novel, ‘Sundiver,’ was written on this clever device called a typewrit –”

“Well, look, Dad. Have you seen what it costs to buy one of those old Apples online, in its original box? Hey, what could we do with it?”

“Huh?” I stared in amazement.

Then, gradually, I realized the practical possibilities.

Let’s cut to the chase. We did not wind up buying an Apple II. Instead (for various reasons) we bought a Commodore 64 (in original box) for $25. It arrived in good shape. It took us maybe three minutes to attach an old TV. We flicked the power switch … and up came a command line. In BASIC.

Uh. Problem solved?

I guess. At least far better than any other thing we’ve tried!

We are now typing in programs from books, having fun making dots move (and thus knowing why the dots move, at the command of math, and not magic). There are still problems, like getting an operating system to make the 5141c disk drive work right. Most of the old floppies are unreadable. But who cares? (Ben thinks that loading programs to and from tape is so cool. I gurgle and choke remembering my old Sinclair … but whatever.)

What matters is that we got over a wretched educational barrier. And now Ben can study C++ with a better idea where it all came from. In the nick of time.

Problem solved? Again, at one level.

And yet, can you see the irony? Are any of the masters of the information age even able to see the irony?

This is not just a matter of cheating a generation, telling them to simply be consumers of software, instead of the innovators that their uncles were. No, this goes way beyond that. In medical school, professors insist that students have some knowledge of chemistry and DNA before they are allowed to cut open folks. In architecture, you are at least exposed to some physics.

But in the high-tech, razzle-dazzle world of software? According to the masters of IT, line coding is not a deep-fabric topic worth studying. Not a layer that lies beneath, holding up the world of object-oriented programming. Rather, it is obsolete!

Or, at best, something to be done in Bangalore. Or by old guys in their 50s, guaranteeing them job security, the same way that COBOL programmers were all dragged out of retirement and given new cars full of Jolt Cola during the Y2K crisis.

All right, here’s a challenge. Get past all the rationalizations. (Because that is what they are.) It would be trivial for Microsoft to provide a version of BASIC that kids could use, whenever they wanted, to type in all those textbook examples. Maybe with some cool tutorial suites to guide them along, plus samples of higher-order tools. It would take up a scintilla of disk space and maybe even encourage many of them to move on up. To (for example) Visual Basic!

Or else, hold a big meeting and choose another lingua franca, so long as it can be universal enough to use in texts, the way that BASIC was.

Instead, we are told that “those textbooks are archaic” and that students should be doing “something else.” Only then watch the endless bickering over what that “something else” should be — with the net result that there is no lingua franca at all, no “basic” language so common that textbook publishers can reliably use it as a pedagogical aide.

The textbook writers and publishers aren’t the ones who are obsolete, out-of-touch and wrong. It is people who have yanked the rug out from under teachers and students all across the land.

Let me reiterate. Kids are not doing “something else” other than BASIC. Not millions of them. Not hundreds or tens of thousands of them. Hardly any of them, in fact. It is not their fault. Because some of them, like my son, really want to. But they can’t. Not without turning into time travelers, the way we did, by giving up (briefly) on the present and diving into the past. (I also plan to teach him how to change the oil and fix a tire!) By using the tools of a bygone era to learn more about tomorrow.

If this is a test, then Ben and I passed it, ingeniously. In contrast, Microsoft and Apple and all the big-time education-computerizing reformers of the MIT Media Lab are failing, miserably. For all of their high-flown education initiatives (like the “$100 laptop”), they seem bent on providing information consumption devices, not tools that teach creative thinking and technological mastery.

Web access for the poor would be great. But machines that kids out there can understand and program themselves? To those who shape our technical world, the notion remains not just inaccessible, but strangely inconceivable.

– David Brin is an astrophysicist whose international best-selling novels include “Earth,” and recently “Existence.” ” The Postman” was filmed in 1997. His nonfiction book about the information age – The Transparent Society – won the Freedom of Speech Award of the American Library Association. (http://www.davidbrin.com)

http://www.salon.com/2006/09/14/basic_2/

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)

Coal releases more radioactivity than nuclear power

 

Coal Ash Is More Radioactive Than Nuclear Waste

By burning away all the pesky carbon and other impurities, coal power plants produce heaps of radiation

By Mara Hvistendahl on December 13, 2007

PWR_nuclear_power_plant_diagram

The popular conception of nuclear power is straight out of The Simpsons: Springfield abounds with signs of radioactivity, from the strange glow surrounding Mr. Burn’s nuclear power plant workers to Homer’s low sperm count. Then there’s the local superhero, Radioactive Man, who fires beams of “nuclear heat” from his eyes. Nuclear power, many people think, is inseparable from a volatile, invariably lime-green, mutant-making radioactivity.

Coal, meanwhile, is believed responsible for a host of more quotidian problems, such as mining accidents, acid rain and greenhouse gas emissions. But it isn’t supposed to spawn three-eyed fish like Blinky.

Over the past few decades, however, a series of studies has called these stereotypes into question. Among the surprising conclusions: the waste produced by coal plants is actually more radioactive than that generated by their nuclear counterparts. In fact, the fly ash emitted by a power plant—a by-product from burning coal for electricity—carries into the surrounding environment 100 times more radiation than a nuclear power plant producing the same amount of energy. * [See Editor’s Note at end of page 2]

At issue is coal’s content of uranium and thorium, both radioactive elements. They occur in such trace amounts in natural, or “whole,” coal that they aren’t a problem. But when coal is burned into fly ash, uranium and thorium are concentrated at up to 10 times their original levels.

Fly ash uranium sometimes leaches into the soil and water surrounding a coal plant, affecting cropland and, in turn, food. People living within a “stack shadow”—the area within a half- to one-mile (0.8- to 1.6-kilometer) radius of a coal plant’s smokestacks—might then ingest small amounts of radiation. Fly ash is also disposed of in landfills and abandoned mines and quarries, posing a potential risk to people living around those areas.

https://www.scientificamerican.com/article/coal-ash-is-more-radioactive-than-nuclear-waste/

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Nuclear Danger Still Dwarfed by Coal
By Christopher Wanjek, LiveScience, 4/26/11

One must accept a risk of radiation exposure when flying in and out of Narita International Airport, the busiest airport in Japan, just east of Tokyo, but perhaps not for the reason you are thinking.

Fukushima Daiichi, the tsunami-damaged nuclear reactor site about 150 miles (241 kilometers) to the north, as the foolish crow flies, continues to leak trace amounts of radiation. Radioactive iodine-131 made it into the water supply here last month. But most, as physics would have it, has since decayed into stable xenon.

So, few in this Tokyo region have been exposed to radiation levels as high as someone just hopping off a plane. The international flyer receives a dose of about 0.10 millisievert, or the amount of ionizing radiation in two dental X-rays, from the sun’s radioactive cosmic rays. That means that folks who left Tokyo because of the threat at Fukushima likely received more radiation on the airplane flight than they would have if they had stayed at home. [Mysterious Radiation May Strike Airline Passengers]

Such is the irony of nuclear energy, so potentially dangerous yet so much remarkably safer than most other energy sources, namely coal and other fossil fuels.

Dirty, dirty coal

As bad as Japan’s nuclear emergency could have gotten, it would never be as bad as burning coal. Coal is fantastically dangerous, responsible for far more than 1 million deaths per year, according to the World Health Organization.

Start with the coal miners, thousands of whom die from mine collapses and thousands more from various lung diseases. Next, add the hundreds of thousands of deaths in the public from breathing coal’s gaseous and particulate pollution, mostly from respiratory and heart disease.

Next, add the untold deaths and disabilities resulting from mercury in coal entering into the food chain. Then add the millions of acres of land, river and lake destroyed by mining waste.

Some of China’s citizens worried about a radioactive wind blowing over from Japan, but coal-burning power plants from China are causing far more health problems for both China and Japan.

Coal even releases more radioactive material than nuclear energy — 100 times more per the same amount of energy produced, according to Dana Christensen of the U.S. Department of Energy (DOE), as reported in Scientific American in 2007.

According to WHO statistics, there are at least 4,025 deaths from coal for every single death from nuclear power. Switch to “clean” natural gas? That’s still 100 times deadlier than nuclear energy. Oil is 900 times deadlier.

Not many are expected to die from the Fukushima Daiichi accident.

The U.S. DOE predicts a yearly dose of about 2,000 millirems for some people living northwest of the nuclear facility within 19 miles (31 kilometers), which could slightly increase their cancer risk if they haven’t left the area. But Japanese health authorities were quick to warn the public not to eat certain local foods with harmful levels of radioactivity, namely milk and spinach; people living within 12 miles (19 km) of the nuclear facility have been evacuated as a precaution; more are expected to be evacuated; and radiation levels continue to fall daily.

http://www.livescience.com/13876-nuclear-energy-dangers-coal.html

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Coal and Gas are Far More Harmful than Nuclear Power
By Pushker Kharecha and James Hansen — April 2013
NASA Science Briefs, Goddard Institute for Space Studies

In a recently published paper (ref. 1), we provide an objective, long-term, quantitative analysis of the effects of nuclear power on human health (mortality) and the environment (climate). Several previous scientific papers have quantified global-scale greenhouse gas (GHG) emissions avoided by nuclear power, but to our knowledge, ours is the first to quantify avoided human deaths as well as avoided GHG emissions on global, regional, and national scales.

The paper demonstrates that without nuclear power, it will be even harder to mitigate human-caused climate change and air pollution. This is fundamentally because historical energy production data reveal that if nuclear power never existed, the energy it supplied almost certainly would have been supplied by fossil fuels instead (overwhelmingly coal), which cause much higher air pollution-related mortality and GHG emissions per unit energy produced (ref. 2).

Using historical electricity production data and mortality and emission factors from the peer-reviewed scientific literature, we found that despite the three major nuclear accidents the world has experienced, nuclear power prevented an average of over 1.8 million net deaths worldwide between 1971-2009 (see Fig. 1). This amounts to at least hundreds and more likely thousands of times more deaths than it caused. An average of 76,000 deaths per year were avoided annually between 2000-2009 (see Fig. 2), with a range of 19,000-300,000 per year.

Likewise, we calculated that nuclear power prevented an average of 64 gigatonnes of CO2-equivalent (GtCO2-eq) net GHG emissions globally between 1971-2009 (see Fig. 3). This is about 15 times more emissions than it caused. It is equivalent to the past 35 years of CO2 emissions from coal burning in the U.S. or 17 years in China (ref. 3) — i.e., historical nuclear energy production has prevented the building of hundreds of large coal-fired power plants.

https://www.giss.nasa.gov/research/briefs/kharecha_02/

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brachistochrone

brachistochrone – curve of quickest descent.
A curve on which a bead slides frictionlessly, under the influence of gravity, to an end point in the shortest time.

tautochrone- the curve for which the time taken by an object sliding without friction in uniform gravity to its lowest point is independent of its starting point.

details to be added

brachistochrone-and-tautochrone-curve

Demonstration of the Brachistochrone Curve & the Tautochrone Curve.

vSauce The Brachistochrone