These labs were designed by Prof. Chris Orban for Physics 1250 at The Ohio State University at Marion. They are useful at the high school and college level. No calculus knowledge or prior programming experience is required.

The nice part about these programming labs is that there is no software to install. The compiling and executing and visualization is all done within your web browser! This is accomplished using a programming framework called p5js.org which is very similar to C/C++.

Introduction to the p5.js programming framework

Earth’s magnetic field

January 13, 2019 12:11 am

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.

http://www.nationalparks.gov.uk/press/press-images?result_256754_result_page=3

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.

http://commons.wikimedia.org/wiki/File:Earth’s_Axis.gif

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.

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!

http://www.abc.net.au/science/articles/2011/11/09/3359365.htm

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…

http://all-geo.org/highlyallochthonous/2008/03/where-the-earths-magnetic-field-comes-from/

The Earth’s interior generates a magnetic field. It reaches out into space.

This magnetic field protects us from some types of radiation.

http://euanmearns.com/the-laschamp-event-and-earths-wandering-magnetic-field/

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

http://www.esa.int/Our_Activities/Observing_the_Earth/The_Living_Planet_Programme/Earth_Explorers/Swarm/ESA_s_magnetic_field_mission_Swarm

The Physics of Interstellar Travel

January 2, 2019 1:29 am

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

CloudyLabs https://www.youtube.com/watch?v=ZiscokCGOhs&feature=youtu.be

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.

http://kenobi-wan-obi.tumblr.com/post/64983465809/nasa-releases-movie-of-suns-canyon-of-fire-a

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.

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

November 22, 2018 9:45 pm

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

Augustin-Jean Fresnel, French physicist and engineer

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.

$Two slits diffraction pattern Young's Double slit$

This shows a typical experimental set-up.

$Double slit diffraction pattern REALITY$

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.

$Poisson spot Fresnel diffraction experiment$

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.

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

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

November 19, 2018 6:44 pm

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/

diffusion-cloud-chamber-with-radon-gas

Here is an example of two particles colliding within an accelerator, and decaying into a variety of other products.

particles colliding LHC

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

how Particle Accelerators Work

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

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.

There Was No Big Bang Singularity

October 23, 2018 5:26 pm

Backup articles for students – There Was No Big Bang Singularity, Ethan Siegel, Forbes, 7/27/2018

Almost everyone has heard the story of the Big Bang. But if you ask anyone, from a layperson to a cosmologist, to finish the following sentence, “In the beginning, there was…” you’ll get a slew of different answers. One of the most common ones is “a singularity,” which refers to an instant where all the matter and energy in the Universe was concentrated into a single point. The temperatures, densities, and energies of the Universe would be arbitrarily, infinitely large, and could even coincide with the birth of time and space itself.

Big Bang metric expansion of space represented by circular sections.

http://en.wikipedia.org/wiki/Big_Bang

But this picture isn’t just wrong, it’s nearly 40 years out of date! We are absolutely certain there was no singularity associated with the hot Big Bang, and there may not have even been a birth to space and time at all. Here’s what we know and how we know it.

When we look out at the Universe today, we see that it’s full of galaxies in all directions at a wide variety of distances. On average, we also find that the more distant a galaxy is, the faster it appears to be receding from us. This isn’t due to the actual motions of the individual galaxies through space, though; it’s due to the fact that the fabric of space itself is expanding.

This was a prediction that was first teased out of General Relativity in 1922 by Alexander Friedmann, and was observationally confirmed by the work of Edwin Hubble and others in the 1920s. It means that, as time goes on, the matter within it spreads out and becomes less dense, since the volume of the Universe increases. It also means that, if we look to the past, the Universe was denser, hotter, and more uniform.

If you were to extrapolate back farther and farther in time, you’d begin to notice a few major changes to the Universe. In particular:

you’d come to an era where gravitation hasn’t had enough time to pull matter into large enough clumps to have stars and galaxies,
you’d come to a place where the Universe was so hot you couldn’t form neutral atoms,
and then where even atomic nuclei were blasted apart,
where matter-antimatter pairs would spontaneously form,
and where individual protons and neutrons would be dissociated into quarks and gluons.

Each step represents the Universe when it was younger, smaller, denser, and hotter. Eventually, if you kept on extrapolating, you’d see those densities and temperatures rise to infinite values, as all the matter and energy in the Universe was contained within a single point: a singularity.

The hot Big Bang, as it was first conceived, wasn’t just a hot, dense, expanding state, but represented an instant where the laws of physics break down. It was the birth of space and time: a way to get the entire Universe to spontaneously pop into existence. It was the ultimate act of creation: the singularity associated with the Big Bang.

Yet, if this were correct, and the Universe had achieved arbitrarily high temperatures in the past, there would be a number of clear signatures of this we could observe today. There would be temperature fluctuations in the Big Bang’s leftover glow that would have tremendously large amplitudes. The fluctuations that we see would be limited by the speed of light; they would only appear on scales of the cosmic horizon and smaller. There would be leftover, high-energy cosmic relics from earlier times, like magnetic monopoles.

And yet, the temperature fluctuations are only 1-part-in-30,000, thousands of times smaller than a singular Big Bang predicts. Super-horizon fluctuations are real, robustly confirmed by both WMAP and Planck. And the constraints on magnetic monopoles and other ultra-high-energy relics are incredibly tight. These missing signatures have a huge implication: the Universe never reached these arbitrarily large temperatures.

CMB Cosmic Microwave Background COBE WMAP

Instead, there must have been a cutoff. We cannot extrapolate back arbitrarily far, to a hot-and-dense state that reaches whatever energies we can dream of. There’s a limit to how far we can go and still validly describe our Universe.

In the early 1980s, it was theorized that, before our Universe was hot, dense, expanding, cooling, and full of matter and radiation, it was inflating. A phase of cosmic inflation would mean the Universe was:

filled with energy inherent to space itself,
which causes a rapid, exponential expansion,
that stretches the Universe flat,
gives it the same properties everywhere,
with small-amplitude quantum fluctuations,
that get stretched to all scales (even super-horizon ones),

and then inflation comes to an end.

When it does, it converts that energy, which was previously inherent to space itself, into matter and radiation, which leads to the hot Big Bang. But it doesn’t lead to an arbitrarily hot Big Bang, but rather one that achieved a maximum temperature that’s at most hundreds of times smaller than the scale at which a singularity could emerge. In other words, it leads to a hot Big Bang that arises from an inflationary state, not a singularity.

The information that exists in our observable Universe, that we can access and measure, only corresponds to the final ~10^-33 seconds of inflation, and everything that came after. If you want to ask the question of how long inflation lasted, we simply have no idea. It lasted at least a little bit longer than 10^-33 seconds, but whether it lasted a little longer, a lot longer, or for an infinite amount of time is not only unknown, but unknowable.

So what happened to start inflation off? There’s a tremendous amount of research and speculation about it, but nobody knows. There is no evidence we can point to; no observations we can make; no experiments we can perform. Some people (wrongly) say something akin to:

Well, we had a Big Bang singularity give rise to the hot, dense, expanding Universe before we knew about inflation, and inflation just represents an intermediate step. Therefore, it goes: singularity, inflation, and then the hot Big Bang.

There are even some very famous graphics put out by top cosmologists that illustrate this picture. But that doesn’t mean this is right.

Big Bang Singularity Inflation Gravitational Waves

NATIONAL SCIENCE FOUNDATION (NASA, JPL, KECK FOUNDATION, MOORE FOUNDATION, RELATED)

In fact, there are very good reasons to believe that this isn’t right! One thing that we can mathematically demonstrate, in fact, is that it’s impossible for an inflating state to arise from a singularity.

Here’s why: space expands at an exponential rate during inflation. Think about how an exponential works: after a certain amount of time goes by, the Universe doubles in size. Wait twice as long, and it doubles twice, making it four times as large. Wait three times as long, it doubles thrice, making it 8 times as large. And if you wait 10 or 100 times as long, those doublings make the Universe 2¹⁰ or 2¹⁰⁰ times as large.

Which means if we go backwards in time by that same amount, or twice, or thrice, or 10 or 100 times, the Universe would be smaller, but would never reach a size of 0. Respectively, it would be half, a quarter, an eighth, 2^-10, or 2^-100 times its original size. But no matter how far back you go, you never achieve a singularity.

How Universe Grows Time Before Singularity

Image by E. Siegel

There is a theorem, famous among cosmologists, showing that an inflationary state is past-timelike-incomplete. What this means, explicitly, is that if you have any particles that exist in an inflating Universe, they will eventually meet if you extrapolate back in time.

This doesn’t, however, mean that there must have been a singularity, but rather that inflation doesn’t describe everything that occurred in the history of the Universe, like its birth. We also know, for example, that inflation cannot arise from a singular state, because an inflating region must always begin from a finite size.

http://en.wikipedia.org/wiki/Big_Bang

Every time you see a diagram, an article, or a story talking about the “big bang singularity” or any sort of big bang/singularity existing before inflation, know that you’re dealing with an outdated method of thinking.

The idea of a Big Bang singularity went out the window as soon as we realized we had a different state — that of cosmic inflation — preceding and setting up the early, hot-and-dense state of the Big Bang.

There may have been a singularity at the very beginning of space and time, with inflation arising after that, but there’s no guarantee. In science, there are the things we can test, measure, predict, and confirm or refute, like an inflationary state giving rise to a hot Big Bang. Everything else? It’s nothing more than speculation.

Related articles by Ethan Siegel

The Big Bang Wasn’t The Beginning, After All 9/2017

What Was It Like When The Universe Was Inflating? 6/2018

How Well Has Cosmic Inflation Been Verified? 5/2019

Did Time Have A Beginning? 7/2019

What Came First: Inflation Or The Big Bang? 10/2019

The science wars: postmodernism as a threat against truth and reason

October 5, 2018 11:17 am

The science wars was an intellectual war between scientific realists and postmodernist critics.

The debate was about whether anything that humans could learn or talk about actually has meaning – or whether all words (even for science and math) ultimately only conveyed internal biases and feelings. Thus, in this view, nothing could ever be objectively said about the world.

Misunderstanding the debate

The science wars were often misunderstood by observers. Outsiders imagined that the debate was whether the intellectual paradigms of a culture affected the way data was interpreted. After all, it is noted, the same data can cause the investigator to reach different conclusions based on their internal biases.

However, this had nothing to do with the science wars. Scientists acknowledge that all people operate within intellectual paradigms, and that this of course affects how people might interpret data.

Rather, in the science wars, deconstructionists and postmodernists went much further: Many held that science tells us nothing about the real world. Some said things such as “DNA molecules are a myth of Western culture;” “the idea that 2 + 2 = 4 is white colonialist thinking,” etc. Some in this group denied that math and science had any more existence or legitimacy than “other ways of thinking” about subjects.

Ironically, this kind of thinking was foreseen by George Orwell.

In the end, the Party would announce that two and two made five, and you would have to believe it. It was inevitable that they should make that claim sooner or later: the logic of their position demanded it. Not merely the validity of experience, but the very existence of external reality, was tacitly denied by their philosophy.
– George Orwell, Nineteen Eighty-Four

Scientific realists (such as Norman Levitt, Paul R. Gross, Jean Bricmont and Alan Sokal) understand and explain that scientific knowledge is real.

In contrast, many postmodernists and deconstructionists openly reject the reality and useful of science itself. Many openly reject scientific objectivity, the scientific method, Empiricism, and scientific knowledge.

Postmodernists and deconstructionists interpret Thomas Kuhn‘s ideas about scientific paradigms to mean that scientific theories are only social constructs, and not actual descriptions of reality.

Some philosophers like Paul Feyerabend argued that other, non-realist forms of knowledge production were just as valid. Therefore, for example:

a Native American thinking about nature would come up with his or her own ideas that are different from ideas in supposed “colonialist” science textbooks, and that those ideas – even when never backed by experiment – would literally be just as “true” as the ideas found by science (ideas which actually have been tested, and found to be true no matter the ethnicity of the person involved.)

a woman thinking about nature would come up with her own ideas that are different from ideas in supposed “male” science textbooks, and that those ideas – even when never backed by experiment – would literally be just as “true” as the ideas found by science (ideas which actually have been tested, and found to be true no matter the ethnicity of the person involved.)

There were attempts to bring postmodernism/deconstructionism into science back in the 1990s. There is a new attempt to do so today in the 2020s under the misleading motto “decolonize the curriculum.”

Some of these postmodernist attempts to do so at first look like a parody, but it turns out that the authors are serious.

For example, an increasing number of postmodernists claim that math itself is “colonialist.” The example shown below is becoming increasingly common.

$Decolonize Math 1$

Can you imagine what would happen if we allowed people to “decolonize” math, science, and engineering practices? Every piece of technology created by people indoctrinated with this view would be dangerous.

$Decolonize math 2$

In the 1990’s, Scientific realists were quick to realize the danger. Large swaths of deconstructionist and postmodernist writings rejected any possibility of objectivity and realism. This not only undercut the entire idea of mathematics, and all of science, but also of philosophy and human rights.

The works of Jacques Derrida, Gilles Deleuze, Jean-François Lyotard and others claimed to say something about reality, but realists (scientists and anyone who believed in rational thought) recognized that such postmodern writings were deliberately incomprehensible or meaningless.

Example of how postmodernists understand basic logic

Some people misunderstand (or deliberately misrepresent) images like this to promote the idea that “truth is relative.” They say things like “The object is a triangle when viewed by one person, but a square when viewed by someone else, and a circle when seen by yet another person. So reality is relative, not absolute.”

The problem of course is that their claims are not only false, they are irrational.

In this example there is an actual three dimensional object (a fact in the real world.) The geometric projection of this object contains only a small part of information about the object as a whole.

Thus, a viewer who only looks at the object from one direction only receives some of the information, and does not yet know about the rest. Yet that lack of knowledge doesn’t change the reality of what the three dimensional object actually is.

If a postmodernist concluded, “I see a circle, therefore it is a circle” and then make a mathematical model of the object as a circle or sphere, their model would have predictions which immediately turn out to be wrong. Not “wrong” from one culture’s point of view, or from one religion’s point of view, or one gender’s point of view, but actually objectively wrong in reality.

News

Fake News Comes to Academia How three scholars gulled academic journals to publish hoax papers on ‘grievance studies.’

Book reviews

Richard Dawkins’ review of Intellectual Impostures by Alan Sokal and Jean Bricmont.

Lenz’s law

September 7, 2018 1:42 pm

Lenz’s law demonstration

Lenz’s law is named after the physicist Heinrich Friedrich Emil Lenz (pronounced /ˈlɛnts/) who formulated it in 1834.

The direction of the electric current induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes the initial changing magnetic field.

It is a qualitative law that specifies the direction of induced current.

This law tells us nothing about the current’s magnitude.

Lenz’s law predicts the direction of many effects in electromagnetism, such as:

the direction of voltage induced in an inductor or wire loop by a changing current
the drag force of eddy currents exerted on moving objects in a magnetic field.

Lenz’s law is not really a law of physics on its own. It is a phenomenon which can be predicted from a more general law of physics, Faraday’s law of induction.

Faraday’s law of induction itself is a subset of the even more fundamental MAXWELL’s EQUATIONS.

Step-by-step explanation

Take a copper tube (conductive but non-magnetic.) Drop a piece of steel down through the tube.

The piece of steel will fall through, as you might expect.

It accelerates very close to the acceleration due to gravity.

Only air friction and possible rubbing against the inside of the tube prevent it from reaching the acceleration due to gravity.

Now take the same copper tube and drop a strong magnet through it

Neodymium or other rare earth magnets work the best. Now the magnet falls very slowly.

This is because the copper tube experiences a changing magnetic field from the falling magnet.

This changing magnetic field induces a current in the copper tube.

The induced current in the copper tube creates its own magnetic field ,

one that opposes the magnetic field that created it!

RegentsPrep archived notes

This lesson has been archived ScienceJoyWagon and from regentsprep.org, Oswego City School District, NY.

TBA – create link to this in Electromagnetic Induction