Showing posts with label Concept. Show all posts
Showing posts with label Concept. Show all posts

This Is How Dirac Predicted Antimatter

how did paul dirac predict antimatter dirac sea quantum mechanics

For those who don't know anything about English theoretical physicist Paul Dirac: he has often been compared to one of the fathers of physics, Sir Isaac Newton. Both were genius mathematicians; socially awkward; they made their greatest breakthroughs in their twenties; both held the Lucasian chair of Mathematics at Cambridge University.

But some may consider Dirac an even greater scientist due to many reasons. While Newton, in his day, became much involved with pseudosciences such as alchemy; he even attempted to reconcile science with faith through his writings. Paul Dirac, on the other hand, an outspoken agnostic, remained true to scientific path, and went on to make many significant contributions to the theory of everything.

Furthermore, while Newton was considered arrogant, too full of himself, who often made use of his authority to dismiss others' opinions. Dirac, on the other hand, was a lean, meek, shy young fellow, who suffered agonies if forced into any kind of small talk. He coined the term Fermion after Italian physicist Enrico Fermi, despite him having worked on the equation which governed the behavior of Fermions.

So that was a little background information on the man that was Paul Dirac. Unfortunately, he never was popularized enough, in fact, hardly anyone knows anything about who he was or what he did in his scientific career. Even so, his work is of primary importance to electronics, especially how electrons flow in the transistor, devices which form the building blocks of any modern-day computer.

What's more: his biggest discovery, prediction of anti-particle, has inspired numerous science fiction writers to create a mirror world in their stories, the collision of which with the real world, would lead to a whole lot of catastrophic activity in the lives of their characters. This is based upon Dirac's work that when matter and antimatter collide, they annihilate one another.

In the early twentieth century, Dirac, who had just completed his engineering degree, was unemployed. But this made him choose math as a career and thank goodness he did so! Because, a great quantum revolution was ongoing and Dirac, who had merely remained an observer, was keen on becoming a part of it.

Everybody at that time was talking about a young Austrian physicist named Erwin Schrödinger. He just had formulated wave mechanics, that is, an equation which explained the behavior of electron inside an atom. The wave equation, so it was called, gave the probability of finding the electron at any given point inside the atom.

Dirac realized that Schrödinger's wave equation was inconsistent with special theory of relativity. In other words, even though the equation was enough to describe the electronic motion at low velocity, it was yet unable to do the same at speeds approaching that of light. Dirac took this challenge upon himself to find a solution for it.

Unlike other physicists, those who insisted that revelations in physics be firmly grounded on experimental data, (and rightly so) Dirac relied heavily on mathematical consistency instead. To him, if the equation he found had mathematical beauty, then he just assumed that he was going on the correct path. This just goes on to show that Paul Dirac was more of a mathematician rather than a staunch physicist.

After many years, in 1928, Dirac modified the Schrödinger's equation to make it agreeable with Einstein's special relativity. His groundbreaking equation also defined the concepts of spin and magnetic moment of electron. While developing his equation, Dirac realized that Einstein's famous energy-mass relation, E=mc², was only partially right. The correct formula, he claimed, should be E=±mc², the minus sign because one has to take the square root of E²=m²c^4, which was a subtle correction indeed.

But then, according to an axiom of physics, matter particles always tend to the state of lowest energy - for stability. Therefore, the negative sign in E=mc² would imply that all the electrons tumble down to infinitely large negative energy. That is, an electron in a positive energy state (bound or free) should be able to emit a photon and make a transition to a negative energy state. This process could continue forever giving off an infinite amount of light!

Clearly, that isn't the case in the actual, stable universe; real electrons do not behave in such a way. So it made Dirac think of a solution to the problem: he proposed a theoretical model called the Dirac Sea in which he imagined that all the negative energy states were already occupied, meaning, that an electron in positive state could not tumble down to negative energy (since according to Pauli's exclusion principle, no two electrons could share a single energy state).

If a particle of this negative energy sea is given sufficient energy it is possible for it to rise into a positive energy state. A resulting "hole" would be created in the negative energy sea. This hole should have the same mass as the original electron but behave like a positively-charged particle.


Dirac wrote in 1931, after being suggested by Oppenheimer, that this hole was an anti-electron; a re-combination with electron should annihilate both of them. Because, when the electron comes into contact with the hole it spontaneously fills the hole and consequently must release the excess energy that went in.

In 1932, while examining the composition of cosmic rays, high-energy particles that move through space at nearly the speed of light, American physicist Carl Anderson discovered the positron. He observed that a particular particle in the ray behaved out of the ordinary. The trajectory suggested that it had to be positively charged but at the same time 1/1,836 the mass of a proton, exactly that of an electron.

In his 1933 Nobel Prize lecture, Dirac suggested that particle-antiparticle should be a fundamental symmetry of nature. He interpreted the Dirac equation to mean that for every particle there existed a corresponding antiparticle, exactly matching the particle mass but with opposite charge. In 1955, antiproton was discovered by University of California, Berkeley physicists.

The success of Dirac equation shows that a mathematical result can manifest itself in the real world. Paul Dirac had once said, "If you are receptive and humble, mathematics will lead you by the hand." That is pretty much true; his work has been described fully on par with the works of Newton, Maxwell, and Einstein before him. Dirac was undoubtedly a genius.

Where are fundamental forces of physics in real life?

applications of fundamental forces in daily life weak strong gravity electromagnetism

All the visible interactions in nature can be explained in terms of just four fundamental forces. Most physicists think that these four forces must have separated as the universe expanded but which must have essentially been the same under those hot conditions that existed at the Big Bang.

Which is why they are looking for a theory of everything which will set to unify them and reveal a complete understanding of the universe. The string theory and standard model are two such grand unification theories which aim to do so but haven't yet succeeded.

In this post, we will look at how the four fundamental forces apply in day to day life. Two of those forces namely gravitation and electromagnetism we are all well aware of. That is because they are large scale fundamental forces whereas weak and strong forces, which are small scale, hardly catch out our attention.


Electromagnetism

This fundamental force is actually a unification of two forces: electric and magnetic. From pioneering experiments of Michael Faraday, genius mathematician James Clerk Maxwell built a set of equations which combined the two forces into one.

applications of fundamental forces in daily life weak strong gravity electromagnetism
one of the first color photographs taken by Maxwell in 1861

Wherever you look in the modern society, electromagnetic force is apparent. Prominent examples include television, radio and computer. With advances in technology our devices got smaller and began to fit in the palm of our hands. With just a click of a button, we are connected with the world through the internet, which is again, an electromagnetic gift to the whole of humanity.

Also, many electromagnetic waves are used for medical treatment as well. Examples: To generate a picture of brain activity an MRI machine uses radio waves or which bone is broken could be seen with x-rays or ultraviolet rays which treat diseases such as Jaundice or gamma rays which are employed to kill cancerous cells.

Furthermore, what we see with our eyes is the visible light, a small part of the full spectrum, colors from violet to red, such as in the rainbow. This is why electromagnetic force is the one we are most familiar with because it is everywhere to be seen; whether in selfies we click or films we shoot.


Gravitation

The Earth goes around the Sun once in a year because it is pulled in by the gravitational field of the Sun. If there was no gravity to keep the earth spinning, would we get to celebrate the New Year's with our friends and family?

The planets and comets and asteroids and other debris are all held together by the gravity of Sun. This suggests that gravity is quite a long range force. Even so, there is a limit to it such as with increasing distance gravitational force declines considerably in its strength.

applications of fundamental forces in daily life weak strong gravity electromagnetism
Stephen Hawking takes a zero gravity flight

At this moment, there are hundreds of satellites circling the earth out of which 24 are fully dedicated to the GPS technology. Think about this: without gravity keeping them in stable orbit, there would have been no google maps and we would be lost without direction in a strange place!

The universal law of gravitation is a unification of terrestrial and celestial mechanics as it was done by Sir Isaac Newton in the seventeenth century. Today, we can understand the origin of the universe by knowing what causes gravitation. Some physicists also can predict how the universe may end by studying how gravity would respond against other forces of nature.


Weak Force

It was known to common people that inside the earth was warm and molten since there were the occasional volcanoes to testify. Then, scientists discovered that the earth was four billion years old which put them to confusion because how could it remain warm for so long? Also, what kept iron melted in the core and enabled the Earth’s magnetic field?

In the twentieth century, it was found that within the earth were radioactive elements in plenty, such as, Uranium and Thorium, which decayed spontaneously thus keeping the earth warm on the inside. Energy from these reactions was explained by Einstein's famous equation which stated that mass and energy were equivalent.

In the decay, neutrinos are emitted which interact only by means of the weak force. Such high speed particles were first detected in 2005 by scientists in the KamLAND collaboration based in Japan. Thus, the inherent heat and temperature of the Earth's core are explained by the weak interaction.

If this had not been the case there would be no molten iron hence no magnetic field around the earth to protect it from the blazing solar wind. As a result, the ozone layer would disappear and we would all be put to death. Thus, beta decay, which is a manifestation of weak force is fundamental to our existence.

What's more the weak force is also responsible for radioactive decays which help to generate light in the Sun and which help to determine age of a fossil on the Earth.


Strong Force

Since protons are positive charges and since like charges repel one another and since the distance between them within the nucleus is so small, the electric repulsion should be so high that they should fly apart! What is it then that binds them together?

applications of fundamental forces in daily life weak strong gravity electromagnetism

Strong force is the glue that holds the nuclei together; so naturally it should be a very short range force but with an enormous strength advantage over electromagnetic force. And you know what is interesting? Most of the mass of a proton (or neutron) is the result of the strong force field energy. This means that most of our own mass is just a manifestation of that same energy.

Life without strong force would not exist because without it protons would not come together in the first place. But, due to strong force, the protons can bind together to become an unstable Helium. Then which decays under the guidance of the weak force and visible light is made in the process. Using which fruits and vegetables be made on the Earth. Consumed by animals. Like us.

Weak and strong forces are both short range forces so they hardly have any large scale technological applications yet we know for sure that there would be nothing without them and that in itself is beautiful isn't it!?


Summing up

Two forces govern all the macro scale activities in the universe whereas the other two more important forces rule the micro world. As mentioned before, scientists are looking for a theory of everything which would unify all the four forces of nature into one coherent system. But, what if there is a fifth force of nature?

10 Documentaries All Physics Students Should Watch

“best

Great American astronomer, Carl Sagan, said in the original Cosmos: "Imagination will carry us to the worlds that never were but without it we go nowhere."

Carl Sagan was probably the first mainstream scientist who started campaigning for public understanding of science on a very large scale through media and TV.

A great many documentaries have been made for educational purposes by esteemed scientists which are watched by millions of people around the world. Following is a list of some of the best physics documentaries.


Einstein and The Theory of General Relativity

This documentary was released to mark 100 years of Einstein's famous theory of gravity. It was created by leading physicists in the world as a tribute to Albert Einstein. The experts in the field have developed new experiments with advanced technology and even hundred years after first publication, the theory still works.


Cosmos: A Personal Voyage

Thirteen episode series, rated 9.3 out of 10 on IMDb, created by Carl Sagan, based on his best-selling book of the same name. The visual effects are old but each and every topic is explained with great emphasis and detail. No doubt the show was much ahead of its time.

“best

Cosmos: a personal voyage covers a wide range of scientific subjects, including the origin of life and a perspective of our place in the universe. Since 1980, it has been broadcast in more than 60 countries and seen by over 500 million people.


Cosmos: A Spacetime Odyssey

This much needed sequel of Cosmos, released in 2014, was created by American astrophysicist Neil deGrasse Tyson. The visuals are improved and animations have been included making it a wholesome documentary series. The show has received highly positive reviews getting a Metacritic rating of 83 out of 100 based on 19 reviews


Into The Universe

Physicist Stephen Hawking brings his vision of the universe to the screen for the first time to delve into questions like how the universe began, whether life exists on other planets, and whether time travel is possible.

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Hawking appears on the show in linking scenes using his own synthesized voice while the voice over narration is provided in character as Hawking by renowned actor Benedict Cumberbatch. It was released on Discovery Channel.


Wonders of The Universe

“best

Particle physicist Brian Cox discusses various aspects of the universe featuring a wonder related to each topic. The topics include nature of time, life cycle of stars and the effect of gravity in the creation of the universe.


Secrets of Quantum Physics

British physicist Jim Al-Khalili shows how quantum physics is in every day life such as robins navigate using quantum entanglement, how our sense of smell is influenced by quantum vibrations and that quantum physics might play a role in biological evolution. You can watch it on Amazon Prime.


The Elegant Universe

American physicist Brian Greene explains the eleven dimensions, parallel universes, and a world made out of strings. This is not science fiction; this is a proper mathematical framework called the string theory. You can watch it here.


Lise Meitner: The Mother of the Atom Bomb

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Lise Meitner led the small group of scientists who first discovered nuclear fission of uranium when it absorbed an extra neutron. Her research into nuclear fission helped to pioneer nuclear reactors to generate electricity as well as the development of nuclear weapons in the second world war. This is also available on Amazon Prime.


Fun To Imagine

In 1983, BBC aired this special by Nobel laureate Richard Feynman who used physics to explain how the everyday world worked like why rubber bands are stretchy, why tennis balls can't bounce forever, and what you're really seeing when you look in the mirror.


The Amazing Science of Empty Space

How can the universe come from nothing? This question has haunted scientists and common people for a long time; different explanations have been provided throughout history. However, physicist Jim Al Khalili explores the meaning of nothing in the scientific terms. His journey ends with perhaps the most profound insight about reality that humanity has ever made: everything came from nothing. You can watch it on Amazon Prime.


Bonus: Universe In A Nutshell

This is entry level educational video produced by Big Think and hosted by Professor Michio Kaku. for the lay people. It has a holistic approach towards physics; a brief history, applications and what the future holds for physicists.

4 Applications of Einstein's Famous Equation E=mc²

E=mc² albert einstein equation applications physics world war

Just like electric and magnetic phenomena are two sides of the same coin, in similar way, matter and energy, according to Albert Einstein, are also equivalent.

Einstein said, "It followed from the special theory of relativity that mass and energy are different manifestations of the same thing, a somewhat unfamiliar conception for the average mind. Furthermore, the equation in which energy is equal to mass, multiplied by the square of the velocity of light, showed that very small amounts of mass may be converted into a very large amount of energy and vice versa."

In the Second World War, Einstein feared that Germans might develop an atomic weapon based on his groundbreaking discovery. Despite being a long-time pacifist, he wrote a letter to President of the United States, out of necessity, to urge him to develop the atomic bomb before the Germans.

America succeeded, the unfortunate bombings of Hiroshima and Nagasaki happened, the Great War came to a close but at Great Cost. Robert Oppenheimer, part of the Manhattan Project, quoted from Bhagavad Gita, "Now I am become death; the destroyer of worlds."

In 1948, Einstein regretted, "If I had foreseen Hiroshima and Nagasaki, I would have torn up my formula of 1905," he said in an interview. But just how much energy is locked inside matter? Here's an example: shortly after Einstein's death in 1955 his brain was removed and weighed at 1.23 kilogram.

E=mc² albert einstein equation applications physics world war

That would equal 26,000 kilotons of TNT worth of energy. Compare this to the bomb which burned 70% of Hiroshima: it was only 15 kilotons of TNT. This means that an average human brain would have roughly 1,700 times more explosive energy than the bomb which destroyed an entire city!

No doubt Einstein was worried. But to everyone's surprise, despite having Heisenberg by their side, although his involvement in the war is disputed by some historians, the Germans were unable to complete the bomb.

On the other hand, nuclear arms race began between the United States and Soviet Union; a competition for supremacy in the world; which ultimately led to greater tension; a possibility that some eccentric politician might blow up the whole earth.

But apart from war, the equation is useful in other instances. For example, in a nuclear reaction, mass of the atoms that come out is less than mass of the atoms that go in. The difference of which shows up as heat and light.

This would make a good alternative to fossil fuels. Clean energy is the need of the planet because just think how long can we rely on fuel from the dead? Furthermore, space travel in the distant future may also depend on such power.

E=mc² albert einstein equation applications physics world war

Einstein's formula also explains why the crust of our planet is inherently warm. It is due to energy mass conversions occurring within radioactive elements such as uranium and thorium in earth's crust.

Uranium can be found almost everywhere: in rocks, soils, rivers, and oceans. It is in fact 40 times more common than silver in the crust. Thus, the built-in temperature of Earth crust, is directly related to E=mc².

Also the source of sunlight is mass energy conversion. The Sun is made up of 70% Hydrogen. In its core, where temperature is high enough, four hydrogen atoms fuse together to become a helium nucleus, which is slightly less massive than the four combining hydrogen nuclei. The lost mass was converted to light.

Without that sunlight, there'd be no life on earth. Without it, there is no growth in the plants hence no food; all the animals would ultimately starve to death. Hence, we owe our existence to E=mc². Thus, Einstein's little equation is a triumph of the power and simplicity of physics.

How To Teach Physics Like Richard Feynman

how to teach physics science teacher

Physics is a beautiful subject, apparent and applicable in the day-to-day life. The mysterious phenomena of nature have sparked human interest since time immemorial. But if the education system is unable to keep the curiosity alive then something must not be right.

In this post, you will learn how best to teach physics by using the IRADE technique, a teaching method of taking multiple approaches. It is based on American physicist Richard Feynman's philosophy: "The best way to teach is to be very chaotic, in the sense, that you use every possible way of doing it."



Introduce

Narrate the history of the concept in a story-like format. How and why something being taught was discovered is a good way to start. Make use of humor whenever possible. This will take students on a ride and peak their interest. Then, define the concept with a bookish definition along with the equation associated with that concept.


Relate

Give at least three real-world examples of the concept. For example, suppose you are teaching the third law of motion. It is visible in many instances of life, such as while walking, jumping, swimming, recoiling of gun, rocket propulsion, etc.

how to teach physics science teacher

This is an important step because otherwise their understanding is merely bookish, that is, robotic in a sense. If students know examples, the next time they observe similar phenomena they will immediately recall the associated concept in physics.


Apply

Solve at least two numerical problems from the textbook. From the beginner level to the advanced. Make sure that students understand the approach. Accept questions from students if they have any doubts.


Demonstrate

Visual demos are necessary for science teaching because they implant the concept in the mind of the learner. In the case of third law of motion, you could use balloon in a controlled propulsion activity.

how to teach physics science teacher

You may even start the lesson with demonstration (before narrating that history) or insert it in the middle somewhere. There is always at least one experiment for each physics concept. Try to find it on the internet and replicate in class if possible.


Examine

In the end, test your students (but make it fun, like a quiz). You may group them into teams and even give incentive to the winner. Students will look forward to this event and it will not only strengthen their understanding but also develop teamwork. You may also examine students more formally once this activity is done.


Summing up

Teaching is a noble profession but half-hearted teaching benefits no one. By using the IRADE technique, any science teacher can become a rock star for their students. More importantly, physics classes will not bore students like it used to before. So please share this post with a fellow science teacher.
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