## What is a Magnetic Field?

Everyone knows just how fun magnets can be. As a child, who among us didn’t love to see if we could make our silverware stick together? And how about those little magnetic rocks that we could arrange to form just about any shape because they stuck together? Well, magnetism is not just an endless source of fun or good for scientific experiments; it’s also one of basic physical laws upon which the universe is based.

The attraction known as magnetism occurs when a magnetic field is present, which is a field of force produced by a magnetic object or particle. It can also be produced by a changing electric field and is detected by the force it exerts on other magnetic materials. Hence why the area of study dealing with magnets is known as electromagnetism.

## Definition:

Magnetic fields can be defined in a number of ways, depending on the context. However, in general terms, it is an invisible field that exerts magnetic force on substances which are sensitive to magnetism. Magnets also exert forces and torques on each other through the magnetic fields they create.

They can be generated within the vicinity of a magnet, by an electric current, or a changing electrical field. They are dipolar in nature, which means that they have both a north and south magnetic pole. The Standard International (SI) unit used to measure magnetic fields is the Tesla, while smaller magnetic fields are measured in terms of Gauss (1 Tesla = 10,000 Guass).

Mathematically, a magnetic field is defined in terms of the amount of force it exerted on a moving charge. The measurement of this force is consistent with the Lorentz Force Law, which can be expressed as F= qvB, where F is the magnetic force, q is the charge, v is the velocity, and the magnetic field is B. This relationship is a vector product, where F is perpendicular (->) to all other values.

## Field Lines:

Magnetic fields may be represented by continuous lines of force (or magnetic flux) that emerge from north-seeking magnetic poles and enter south-seeking poles. The density of the lines indicate the magnitude of the field, being more concentrated at the poles (where the field is strong) and fanning out and weakening the farther they get from the poles.

A uniform magnetic field is represented by equally-spaced, parallel straight lines. These lines are continuous, forming closed loops that run from north to south, and looping around again. The direction of the magnetic field at any point is parallel to the direction of nearby field lines, and the local density of field lines can be made proportional to its strength.

Magnetic field lines resemble a fluid flow, in that they are streamlined and continuous, and more (or fewer lines) appear depending on how closely a field is observed. Field lines are useful as a representation of magnetic fields, allowing for many laws of magnetism (and electromagnetism) to be simplified and expressed in mathematical terms.

A simple way to observe a magnetic field is to place iron filings around an iron magnet. The arrangements of these filings will then correspond to the field lines, forming streaks that connect at the poles. They also appear during polar auroras, in which visible streaks of light line up with the local direction of the Earth’s magnetic field.

## History of Study:

The study of magnetic fields began in 1269 when French scholar Petrus Peregrinus de Maricourt mapped out the magnetic field of a spherical magnet using iron needles. The places where these lines crossed he named “poles” (in reference to Earth’s poles), which he would go on to claim that all magnets possessed.

During the 16th century, English physicist and natural philosopher William Gilbert of Colchester replicated Peregrinus’ experiment. In 1600, he published his findings in a treaties (De Magnete) in which he stated that the Earth is a magnet. His work was intrinsic to establishing magnetism as a science.

In 1750, English clergyman and philosopher John Michell stated that magnetic poles attract and repel each other. The force with which they do this, he observed, is inversely proportional to the square of the distance, otherwise known as the inverse square law.

In 1785, French physicist Charles-Augustin de Coulomb experimentally verified Earths’ magnetic field. This was followed by 19th century French mathematician and geometer Simeon Denis Poisson created the first model of the magnetic field, which he presented in 1824.

By the 19th century, further revelations refined and challenged previously-held notions. For example, in 1819, Danish physicist and chemist Hans Christian Orsted discovered that an electric current creates a magnetic field around it. In 1825, André-Marie Ampère proposed a model of magnetism where this force was due to perpetually flowing loops of current, instead of the dipoles of magnetic charge.

In 1831, English scientist Michael Faraday showed that a changing magnetic field generates an encircling electric field. In effect, he discovered electromagnetic induction, which was characterized by Faraday’s law of induction (aka. Faraday’s Law).

Between 1861 and 1865, Scottish scientist James Clerk Maxwell published his theories on electricity and magnetism – known as the Maxwell’s Equations. These equations not only pointed to the interrelationship between electricity and magnetism, but showed how light itself is an electromagnetic wave.

The field of electrodynamics was extended further during the late 19th and 20th centuries. For instance, Albert Einstein (who proposed the Law of Special Relativity in 1905), showed that electric and magnetic fields are part of the same phenomena viewed from different reference frames. The emergence of quantum mechanics also led to the development of quantum electrodynamics (QED).

## Examples:

A classic example of a magnetic field is the field created by an iron magnet. As previously mentioned, the magnetic field can be illustrated by surrounding it with iron filings, which will be attracted to its field lines and form in a looping formation around the poles.

Larger examples of magnetic fields include the Earth’s magnetic field, which resembles the field produced by a simple bar magnet. This field is believed to be the result of movement in the Earth’s core, which is divided between a solid inner core and molten outer core which rotates in the opposite direction of Earth. This creates a dynamo effect, which is believed to power Earth’s magnetic field (aka. magnetosphere).

Such a field is called a dipole field because it has two poles – north and south, located at either end of the magnet – where the strength of the field is at its maximum. At the midpoint between the poles the strength is half of its polar value, and extends tens of thousands of kilometers into space, forming the Earth’s magnetosphere.

Other celestial bodies have been shown to have magnetic fields of their own. This includes the gas and ice giants of the Solar System – Jupiter, Saturn, Uranus and Neptune. Jupiter’s magnetic field is 14 times as powerful as that of Earth, making it the strongest magnetic field of any planetary body. Jupiter’s moon Ganymede also has a magnetic field, and is the only moon in the Solar System known to have one.

Mars is believed to have once had a magnetic field similar to Earth’s, which was also the result of a dynamo effect in its interior. However, due to either a massive collision, or rapid cooling in its interior, Mars lost its magnetic field billions of years ago. It is because of this that Mars is believed to have lost most of its atmosphere, and the ability to maintain liquid water on its surface.

When it comes down to it, electromagnetism is a fundamental part of our Universe, right up there with nuclear forces and gravity. Understanding how it works, and where magnetic fields occur, is not only key to understanding how the Universe came to be, but may also help us to find life beyond Earth someday.

We have written many articles about the magnetic field for Universe Today. Here’s What is Earth’s Magnetic Field, Is Earth’s Magnetic Field Ready to Flip?, How Do Magnets Work?, Mapping The Milky Way’s Magnetic Fields – The Faraday Sky, Magnetic Fields in Spiral Galaxies – Explained at Last?, Astronomy Without A Telescope – Cosmic Magnetic Fields.

If you’d like more info on Earth’s magnetic field, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Sources:

## Physicists Maybe, Just Maybe, Confirm the Possible Discovery of 5th Force of Nature

For some time, physicists have understood that all known phenomena in the Universe are governed by four fundamental forces. These include weak nuclear force, strong nuclear force, electromagnetism and gravity. Whereas the first three forces of are all part of the Standard Model of particle physics, and can be explained through quantum mechanics, our understanding of gravity is dependent upon Einstein’s Theory of Relativity.

Understanding how these four forces fit together has been the aim of theoretical physics for decades, which in turn has led to the development of multiple theories that attempt to reconcile them (i.e. Super String Theory, Quantum Gravity, Grand Unified Theory, etc). However, their efforts may be complicated (or helped) thanks to new research that suggests there might just be a fifth force at work.

In a paper that was recently published in the journal Physical Review Letters, a research team from the University of California, Irvine explain how recent particle physics experiments may have yielded evidence of a new type of boson. This boson apparently does not behave as other bosons do, and may be an indication that there is yet another force of nature out there governing fundamental interactions.

As Jonathan Feng, a professor of physics & astronomy at UCI and one of the lead authors on the paper, said:

“If true, it’s revolutionary. For decades, we’ve known of four fundamental forces: gravitation, electromagnetism, and the strong and weak nuclear forces. If confirmed by further experiments, this discovery of a possible fifth force would completely change our understanding of the universe, with consequences for the unification of forces and dark matter.”

The efforts that led to this potential discovery began back in 2015, when the UCI team came across a study from a group of experimental nuclear physicists from the Hungarian Academy of Sciences Institute for Nuclear Research. At the time, these physicists were looking into a radioactive decay anomaly that hinted at the existence of a light particle that was 30 times heavier than an electron.

In a paper describing their research, lead researcher Attila Krasznahorka and his colleagues claimed that what they were observing might be the creation of “dark photons”. In short, they believed that they might have at last found evidence of Dark Matter, the mysterious, invisible mass that makes up about 85% of the Universe’s mass.

This report was largely overlooked at the time, but gained widespread attention earlier this year when Prof. Feng and his research team found it and began assessing its conclusions. But after studying the Hungarian teams results and comparing them to previous experiments, they concluded that the experimental evidence did not support the existence of dark photons.

Instead, they proposed that the discovery could indicate the possible presence of a fifth fundamental force of nature. These findings were published in arXiv in April, which was followed-up by a paper titled “Particle Physics Models for the 17 MeV Anomaly in Beryllium Nuclear Decays“, which was published in PRL this past Friday.

Essentially, the UCI team argue that instead of a dark photon, what the Hungarian research team might have witnessed was the creation of a previously undiscovered boson – which they have named the “protophobic X boson”. Whereas other bosons interact with electrons and protons, this hypothetical boson interacts with only electrons and neutrons, and only at an extremely limited range.

This limited interaction is believed to be the reason why the particle has remained unknown until now, and why the adjectives “photobic” and “X” are added to the name. “There’s no other boson that we’ve observed that has this same characteristic,” said Timothy Tait, a professor of physics & astronomy at UCI and the co-author of the paper. “Sometimes we also just call it the ‘X boson,’ where ‘X’ means unknown.”

If such a particle does exist, the possibilities for research breakthroughs could be endless. Feng hopes it could be joined with the three other forces governing particle interactions (electromagnetic, strong and weak nuclear forces) as a larger, more fundamental force. Feng also speculated that this possible discovery could point to the existence of a “dark sector” of our universe, which is governed by its own matter and forces.

“It’s possible that these two sectors talk to each other and interact with one another through somewhat veiled but fundamental interactions,” he said. “This dark sector force may manifest itself as this protophopic force we’re seeing as a result of the Hungarian experiment. In a broader sense, it fits in with our original research to understand the nature of dark matter.”

If this should prove to be the case, then physicists may be closer to figuring out the existence of dark matter (and maybe even dark energy), two of the greatest mysteries in modern astrophysics. What’s more, it could aid researchers in the search for physics beyond the Standard Model – something the researchers at CERN have been preoccupied with since the discovery of the Higgs Boson in 2012.

But as Feng notes, we need to confirm the existence of this particle through further experiments before we get all excited by its implications:

“The particle is not very heavy, and laboratories have had the energies required to make it since the ’50s and ’60s. But the reason it’s been hard to find is that its interactions are very feeble. That said, because the new particle is so light, there are many experimental groups working in small labs around the world that can follow up the initial claims, now that they know where to look.”

As the recent case involving CERN – where LHC teams were forced to announce that they had not discovered two new particles – demonstrates, it is important not to count our chickens before they are roosted. As always, cautious optimism is the best approach to potential new findings.

Further Reading: University of California, Irvine

## Why Can’t We See the Big Bang?

Since telescopes let us look back in time, shouldn’t we be able to see all the way back to the very beginning of time itself? To the moment of the Big Bang?

You’ve probably heard that looking out into space is like looking back in time. As it takes light 1 second to get from the Moon to us. Whenever we view it, we’re seeing it 1 second in the past. The Sun is 8 light minutes away, and the light we see from it is from 8 minutes into the past.

A better example might be Andromeda, it’s 2.5 million light years away… and you guessed it, we’re seeing it 2.5 million years in the past. Since the Big Bang happened 13.7 billion years ago, using this idea, shouldn’t we be able look all the way back to the beginning of time, even if we’ve misplaced the key to our Tardis?

At the very beginning of the Universe, seconds after the Big Bang, everything was mushed together. Energy and matter were the same thing. Dogs and cats lived together. There was no difference between light and radiation, it was all just one united force.

You couldn’t see it, because light didn’t actually exist. There were no such thing as photons.

However, if you’re still insisting there’s no such thing as photons, you might want to check yourself. After these things started to separate. Photons and particles became actual things. Electromagnetism and the weak nuclear force split off and formed new bands, but could never quite get the momentum of the original lineup.

By the end of the first second, neutrons and protons were around, and they were getting mashed by the intense heat and pressure into the first elements. But you still couldn’t see that because the whole Universe was like the inside of a star. Everything was opaque. It was Scarlett Johansson hot, and too crazy to form stable atoms with electrons as we see today.

After the Universe was about 380,000 years old, it had cooled down to the point that proper atoms could form. This is the moment when light could finally move, and travel distances across the Universe to you and get caught up in your light buckets. In fact, this light is known as the cosmic microwave background radiation.

So, how come we don’t see all this freed light in all directions with our eyes? It’s because the region of space where it exists is so far away, and travelling away from us so quickly. The light’s wavelengths have been stretched out to the point that light has been turned into microwaves. It’s only with sensitive radio telescopes and space missions that astronomers can even detect it.

Unfortunately, we’ll never be able to see the Big Bang. Even though we’re looking back in time, right to the edge of the observable Universe, it’s just beyond our reach. If you could look at the Universe at any point in time, what would it be? Tell us in the comments below.

And if you like what you see, come check out our Patreon page and find out how you can get these videos early while helping us bring you more great content!

## Minute Physics: Real World Telekinesis

How do magnets affect things at a distance? How does the Sun heat our planet from 93 million miles away? How can we send messages across the world with our cell phones? We take these seemingly simple things for granted, but in fact there was a time not too long ago when the processes behind them were poorly understood, if at all… and, to the uninformed, there could seem to be a certain sense of “magic” about them.

This video from MinutePhysics, featuring director of the Perimeter Institute for Theoretical Physics Neil Turok, illustrates how our understanding of electromagnetic fields was developed and why there’s nothing magic about it… except, perhaps, how they pack all that excellent info into 5 minutes. Enjoy!

Video: MinutePhysics (Created by Henry Reich.) In conjunction with The CBC Massey Lectures.

## An Anti-Gravity User Interface

Researcher Jinha Lee at MIT has developed a remarkable way to interact with computers — via a programmable, intelligent and gravity-defying metal ball.

The concept, called “ZeroN”, is demonstrated in the video above. Fascinating!

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Using magnets and computer-controlled motors, ZeroN hovers in mid-air between two control units. Its movements can be pre-programmed or it can react to objects in its environment, and it can apparently “learn” new movements as it is interacted with.

Lee demonstrates how it could be used to control camera positions in 3D applications, and (my favorite) model the motions of planets and stars.

“ZeroN is about liberating materials from the constraints of space and time by blending the physical and digital world,” Lee states on his website.

ZeroN is still in its development stages and obviously needs refining (the 3D camera isn’t much use if the ball is wobbling) but the premise is interesting. I can see something like this being, at the very least, a mesmerizing interactive display for museums, classrooms and multimedia presentations.

Of course, with a little ingenuity a whole world of applications could open up for such a zero-g interface. (I’m sure Tony Stark already has a dozen on pre-order!)

## What is Electromagnetic Induction?

It is hard to imagine a world without electricity. At one time, electricity was a humble offering, providing humanity with unnatural light that did not depend on gas lamps or kerosene lanterns. Today, it has grown to become the basis of our comfort, providing our heat, lighting and climate control, and powering all of our appliances, be they for cooking, cleaning, or entertainment. And beneath most of the machines that make it possible is a simple law known as Electromagnetic Induction, a law which describes the operation of generators, electric motors, transformers, induction motors, synchronous motors, solenoids, and most other electrical machines. Scientifically speaking it refers to the production of voltage across a conductor (a wire or similar piece of conducting material) that is moving through a magnetic field.

Though many people have been thought to have contributed to the discovery of this phenomenon, it is Michael Faraday who is credited with first making the discovery in 1831. Known as Faraday’s law, it states that “The induced electromotive force (EMF) in any closed circuit is equal to the time rate of change of the magnetic flux through the circuit”. In practice, this means that an electric current will be induced in any closed circuit when the magnetic flux (i.e. the amount of magnetic field) passing through a surface bounded by the conductor changes. This applies whether the field itself changes in strength or the conductor is moved through it.
Whereas it was already known at this time that an electric current produced a magnetic field, Faraday demonstrated that the reverse was also true. In short, he proved that one could generate an electric current by passing a wire through a magnetic field. To test this hypothesis, Faraday wrapped a piece of metal wire around a paper cylinder and then connected the coil to a galvanometer (a device used to measure electric current). He then moved a magnet back and forth inside the cylinder and recorded through the galvanometer that an electrical current was being induced in the wire. He confirmed from this that a moving magnetic field was necessary to induce an electrical field, because when the magnet stopped moving, the current also ceased.
Today, electromagnetic induction is used to power many electrical devices. One of the most widely known uses is in electrical generators (such as hydroelectric dams) where mechanical power is used to move a magnetic field past coils of wire to generate voltage.
In mathematical form, Faraday’s law states that: ? = – d?B/dt, where ? is the electromotive force and ?B is the magnetic flux, and d and t represent distance and time.

We have written many articles about electromagnetic induction for Universe Today. Here’s an article about electromagnets, and here’s an article about generators.

We’ve also recorded an entire episode of Astronomy Cast all about Electromagnetism. Listen here, Episode 103: Electromagnetism.

## What are Magnets Made Of

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Magnets are the unsung heroes of the Modern Age. However most people don’t really understand what are magnets made of and how they even work. The issue is that we just know that magnets attract iron and nickel. However, magnets have a very interesting origin and can be seen as a physical manifestation of the electromagnetic force.

All magnets are made of a group of metals called the ferromagnetic metals. These are metals such as nickel and iron. Each of these metals have the special property of being able to be magnetized uniformly. When we ask how a magnet works we are simply asking how the object we call a magnet exerts it’s magnetic field. The answer is actually quite interesting.

In every material there are several small magnetic fields called domains. Most of the times these domains are independent of each other and face different directions. However, a strong magnetic field can arrange the domains of any ferromagnetic metal so that they align to make a larger and stronger magnetic field. This is how most magnets are made.

The major difference among magnets is whether they are permanent or temporary. Temporary magnets lose their larger magnetic field over time as the domains return to their original positions. The most common way that magnets are produced is by heating them to their Curie temperature or beyond. The Curie temperature is the temperature at which a ferromagnetic metals gains magnetic properties. Heating a ferromagnetic material to its given temperature will make it magnetic for a while. While heating it beyond this point can make the magnetism permanent. Ferromagnetic materials can also be categorized into soft and hard metals. Soft metals loses their magnetic field over time after being magnetized while hard metals are likely candidates for becoming permanent magnets.

Not all magnets are manmade. Some magnets occur naturally in nature such as lodestone. This mineral was used in ancient times to make the first compasses. However, magnets have other uses. With the discovery of the relation between magnetism and electricity, magnets are now a major part of every electric motor and turbine in existence. Magnets have also been used in storing computer data. There is now a type of drive called a solid state drive that allows data to still be saved more efficiently on computers.

We have written many articles about magnets for Universe Today. Here’s an article about the Earth’s magnetic field, and here’s an article about the bar magnet.

If you’d like more info on Magnets, check out NASA’s Discussion on Magnets, and here’s a link to an article about Magnetic Fields.

We’ve also recorded an entire episode of Astronomy Cast all about Magnetism. Listen here, Episode 42: Magnetism Everywhere.

Sources:
NASA
Wikipedia

## Electromagnetism

The short version: electromagnetism is one of the four fundamental forces (the strong force, the weak force, and gravitation are the other three), responsible for all magnetic, electrical, and electromagnetic phenomena.

The long version is a little more complicated.

Start with history … phenomena we today call electrical have been known for millennia (e.g. static electricity), as have their magnetic counterparts (e.g. lodestone). The 17th and 18th centuries saw considerable scientific study of each, as separate forces, with Ørsted and Ampère uniting the two into electromagnetism, around 1820. Maxwell consolidated (in 1864) everything known about electromagnetism into what today we call Maxwell’s equations … and predicted electromagnetic waves (or radiation), a prediction verified by Hertz, two decades later. However, Maxwell’s equations opened a can of worms (to do with the aether, and the speed of light) … which lead to Einstein and special relativity. In parallel, a series of discoveries lead to photons (the quanta of electromagnetic radiation) and quantum mechanics, and these in turn to the recognition that the spectacular success of classical electromagnetism (i.e. Maxwell’s equations) actually depends on quantum field theory (with all its counter-intuitives).

Fast forward to the 1940s, and Quantum Electrodynamics (QED), which has electrically charged particles interacting via exchanges of photons (real or virtual), and describes all electromagnetic phenomena. QED is the most successful theory in physics, period (it has been tested, and found accurate, to one part in 1012!).

Here’s a fun fact: QED incorporates special relativity … and an electric charge (with no magnetic field) becomes an electric current (with an associated magnetic field), in relativity, simply by switching to a frame of reference moving with respect to the (stationary) electrical charge.

So, in its classical form, electromagnetism is an instantaneous ‘action at a distance’ type of force; in its quantum form; it’s an exchange of virtual photons, at the speed of light.

Now for more complication.

In 1979 Sheldon L. Glashow, Abdus Salam, and Steven Weinberg shared the Nobel Prize for Physics, for their contributions to the unification of electromagnetism and the weak force … which goes under the name electroweak interaction. So electromagnetism is just one manifestation of something more general, just as electricity and magnetism are two manifestations of one underlying thing, electromagnetism.

Want to learn more? Try Stargazers’ Electromagnetism, Math Pages on Maxwell’s equations, Richard Feynman’s excellent non-technical book on QED, and the 1979 Nobel Press Release on the electroweak interaction.

To get a handle on how diverse the roles of electromagnetism are, in astronomy, check out these Universe Today articles (just some of the many): Stellar Jets are Born Knotted,
Magnetic “Ropes” Connect the Northern Lights to the Solar Wind, and Spitzer Spies Ghostly Magnetar.

Astronomy Cast has an episode devoted to electromagnetism, called Electromagnetism. Some others you may also find interesting, on this topic, are The Search for the Theory of Everything, and The Important Numbers in the Universe.

Sources:
Wikipedia
University of Oregon
NASA