Where are fundamental forces of physics in real life?

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.

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.

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?

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?

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.

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.

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

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

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

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.

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.

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

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.

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.

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.

Why You Should Read A Brief History of Time

For a man who was given just a few years to live in his twenties, not only did Stephen Hawking beat the odds but also revolutionized physics for next half a century. Let us see what makes his book A brief history of time special and why you should read it.

The cover quite nicely summarizes the book: This book marries a child's wonder to a genius's intellect. The introduction to A brief history of time is written by an equally famous scientist, American astronomer Carl Sagan, who declares Hawking a worthy successor to Newton and Dirac.

Hawking wrote the book for non-specialist readers who have no prior knowledge of physics or astronomy. He clearly possessed a natural teacher's gifts: easy good-natured humour and the ability to illustrate the complexities of physics with well thought out analogies.

As the book progresses, Hawking takes on the role of a narrator, unfolding the stories of man's struggle for knowledge and wisdom.

Hawking briefly touches upon the important contributions made by Copernicus, Kepler and Galileo that debunked the 2000-year-old accepted world views of Aristotelian science.

The consequences were not in their favour as Copernicus was mysteriously put to death for his daring questioning and Galileo imprisoned for life for his very stubborn resistance against the church.

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The first scientific movement was crushed by the figures of authority but it paved a way for later scientists like Newton and Huygens. Hence, the famous saying attributed to Newton: If I have seen further, it is by standing on the shoulders of giants.

Throughout the book, Hawking has discussed various integrations in physics as they happened: Newton's laws that explained celestial mechanics, Maxwell's equations unifying the phenomena of electricity and magnetism, Einstein's energy-mass equivalence, wave-particle duality and so on.

Hawking has touched upon his collaboration with mathematician Roger Penrose with whom he worked on deriving a set of results in general relativity which attempt to answer the question of when gravitation produces singularities. With this, Hawking earned his PhD in 1965.

Two chapters are devoted to black holes, Hawking's specialization. In 1970, a young physicist named Jacob Bekenstein made a proposal that the surface area of a black hole's event horizon might be the measure of its entropy.

But if an object has entropy, it must also have a temperature, and if it has temperature, then it must radiate energy. Since the whole point of black hole is that nothing gets out of it, not even light, the idea seemed absurd at first.

While initially Hawking set out to prove Bekenstein wrong, to his surprise, he found that Bekenstein was correct. In doing so, Hawking brought together relativity and quantum mechanics and discovered the formula of black hole radiation.

In the book, there is also a discussion on time in which Hawking argues that intelligent life could not exist in the contracting phase of the universe, that is, when time is running backwards. Only the expanding universe is suitable for the humans to exist, as it contains a strong thermodynamic arrow.

For example: in order to live and function properly, we must consume food – an ordered form of energy and convert it into heat – the disordered form of energy. That clearly points to a thermodynamic arrow of time moving forwards.

All in all, A Brief History of Time is a masterpiece that makes sense because it sold more than 10 million copies and got translated into 30 languages. It is the single best book on physics and astronomy covering a large number of topics on science and philosophy.

In his conclusion to the book, Hawking says: "If we find the answer to why we and the universe exist, it would be the ultimate triumph of human reason, for then we would know the mind of God."

The last line irked his academic colleagues and confused critics since Hawking was known for being an outspoken atheist. Hawking later explained in an interview that he had used the word God only as a metaphor.

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This book infuses our questioning and thinking with a spiritual aspect: why there is something rather than nothing? Does the universe need a supernatural creator or is it governed by natural laws? Can time run backwards? How do we know what's true and what's not true?

In A brief history of time, Stephen Hawking tries to unveil answers to questions of such intriguing nature that add to the beauty and mystery of science. His book is not only a source of great learning but also a messenger of science to the wider public.

Movies Every Physics Student Should Watch

Physics movies often make us wow due to the combined impact of scenery and music, technical detail and philosophical dialogue, futuristic lighting and a multitude of other special effects, that can't be found in run of the mill films. So, take a look at the following spoiler-free list of 20 science movies that everyone should watch in their lifetime.

Primer (IMDb 6.9)

This 2004 film is based on the physics of time. The principles of time travel in the film are inspired by Feynman diagrams in which there is no difference between watching an interaction happen forward or backward in time.

The film is so mind-bending that it makes Back To The Future look like a children's cartoon. It has deep philosophical implications and complex technical terminology in the dialogue which make us want to Google their meanings.

The film was written, directed, produced, edited and scored by Shane Carruth, who also is the protagonist of the story. In real life, he is a mathematics major (no surprises) who has previously worked as software developer before becoming a full-time filmmaker.

The Theory of Everything (IMDb 7.7)

This 2014 movie is less about physics and more about life. It is based on Professor Stephen Hawking who is played almost effortlessly by Eddie Redmayne. The film has multiple themes including science, love, life and religion. It is a beautiful mix of everything; you can watch on Amazon prime.

Hawking (IMDb 7.5)

Compared to The Theory of Everything, this 2004 film is a little less known. However, it has more substance to it than its successor. Starring Benedict Cumberbatch as Professor Stephen Hawking, the movie has more physics in it and less of philosophy.

The film has debates and arguments on the Steady State and the Big Bang theories which were part of Hawking's early years as a PhD student. Benedict received his first nomination for a BAFTA Award for his role in the film.

Infinity (IMDb 6.2)

This movie is based on the autobiography of Richard Feynman in which the Nobel Prize winning physicist has described his early childhood, his work during the second World War and his relationship with the love of his life, Arline Greenbaum. You can watch it on Amazon prime; it was released in 1996 starring Matthew Broderick and Patricia Arquette.

Copenhagen (IMDb 7.4)

This 2002 film is based on the chemistry between two genius physicists, Niels Bohr and Werner Heisenberg. It has actors Daniel Craig and Stephen Rea as Heisenberg and Bohr respectively.

The movie is quite serious as it is set against the backdrop of the second World War. It has a running time of 90 minutes followed by an epilogue by physicist Michio Kaku.

Interstellar (IMDb 8.6)

This 2014 epic science fiction film directed by Christopher Nolan is probably the most scientifically accurate film. It has a star cast of Matthew McConaughey, Anne Hathaway, Jessica Chastain and Matt Damon. Nobel Prize winning theoretical physicist Kip Thorne was the executive producer of the film.

The film has portrayed the correct depiction of the Penrose Process which is a means by which energy can be extracted from a rotating black hole. It was widely praised by eminent scientists such as Michio Kaku, Stephen Hawking and Neil deGrasse Tyson; watch it on Amazon prime.

Coherence (IMDb 7.2)

This is a science fiction thriller movie which is based on the many worlds interpretation of quantum mechanics. It has the idea of multiple realities in a single location. The film was released in 2013 starring Emily Baldoni in the lead role.

Einstein and Eddington (IMDb 7.3)

This is a British drama movie based on the friendship of Albert Einstein and Arthur Eddington and their groundbreaking work on the theory of general relativity.

The film has David Tennant and Andy Serkis as Eddington and Einstein respectively. It is a story about the pursuit of truth against a background of war, violence, nationalism, subterfuge, and prejudice.

Predestination (IMDb 7.5)

This is not just another time travel movie: if you want your mind to be blown, then this is the one to watch. The entirety of the film is full of twists and turns and the ending is absolutely jaw-dropping. It has Ethan Hawke in the lead role.

A Serious Man (IMDb 7)

This 2009 comedy movie is fully based on the concept of Schrödinger's cat. The idea is simple: if you place a cat and something which could kill the cat in a box and sealed it, you would not know if the cat was dead or alive until you opened the box so that until the box was opened, the cat was, in some sense, both "dead and alive".

Contact (IMDb 7.4)

This film is based on the prize winning novel written by Carl Sagan. It is the story of a radio astronomer who has found strong evidence of extraterrestrial life.

It has Jodie Foster and Matthew McConaughey in the lead roles. The film has been described as the most accurate cinematic study of alien life.

2001: A Space Odyssey (IMDb 8.3)

This movie was released way back in 1968 but it is on par with Interstellar due to its stunning ahead of the time special effects for which it even received an Oscar. The main theme of the film was artificial evolution of intelligence: from tool-making ancestors to sentient machines in the future.

Gravity (IMDb 7.7)

This film is the winner of seven academy awards; starring Sandra Bullock and George Clooney. It is the story of astronauts who are stranded in space after mid orbit destruction of their Space Shuttle and attempt to return to Earth. Watch it on Amazon Prime.

Flatland: The Movie (IMDb 6.9)

Flatland is a romance of many dimensions. It is an animated movie with a voice cast of Martin Sheen, Kristen Bell and Tony Hale. Based on the 1884 novel written by Edwin Abbott; it is a combination of science, maths and philosophy.

October Sky (IMDb 7.8)

Released in 1999 starring Jake Gyllenhaal and Laura Dern, this is a film about a coal miner's son who wants to become a NASA engineer, against his father's wishes. The good thing is that the story is based on real events, which is why, the movie is deeply motivational, especially for young, growing minds.

Back To The Future (IMDb 8.5)

This is probably the best science fiction comedy of all time. The theme is time travel and its bizarre implications such as the grandfather paradox. The movie was released in 1985, has Michael J. Fox in the lead, and earned a Saturn Award for Best Science Fiction Film. Watch it on Amazon Prime.

The Martian (IMDb 8)

It is the story of an astronaut who becomes stranded on Mars after his team members assume him dead. He must rely on his ingenuity to find a way to signal to Earth that he is alive. Starring Matt Damon and Jessica Chastain, this is one of the most scientifically accurate films.

Marie Curie: More Than Meets The Eye (IMDb 7.5)

This is a movie on the life of Marie Curie who is remembered for her discovery of radium and polonium and her contributions to finding treatment for cancer. The film is set amidst the backdrop of world war starring Kate Trotter as Marie Curie.

Particle Fever (IMDb 7.4)

This 100 minute film is a story of the large hadron collider at CERN and its discovery of the Higgs Boson particle in 2012. Particle fever is so well made that you don't have to be a physics student to enjoy it.

Apollo 13 (IMDb 7.6)

This film was released in 1995 starring Tom Hanks as Apollo 13 Commander Jim Lovell. Based on a true story; nominated for nine academy awards; most technically accurate film because it was executed by NASA engineers and actors took a crash course in physics.

10 Real Scientists On The Big Bang Theory

The Big Bang Theory had a successful run on TV having broadcast a total 279 episodes over the course of twelve years. The show was centered around the lives of Caltech physicists Sheldon Cooper and Leonard Hofstadter, Indian-origin astrophysicist Rajesh Koothrappali and MIT-trained engineer and astronaut Howard Wolowitz.

While them four were reel-life scientific people, did you know that they had the pleasure of sharing the screen time with actual geniuses in the field? This post is a list of extraordinarily intelligent personalities in sciences and technology who made casual appearances on the longest running sit-com.

George Smoot

He is an American Nobel Prize winning astrophysicist who is known for his work on the cosmic microwave background radiation. He did a cameo in season two episode The Terminator Decoupling. Smoot had admitted in an interview that he was a fan of the show's often physics-based plots.

Sheldon: "You won the Nobel Prize what, three years ago? You must be dealing with a whole lot of, what has Smoot done lately?" So I thought.. we continue my research, as a team and when we win the Nobel Prize, you will be back on top!"

George has also written a joke for the episode The Dead Hooker Juxtaposition which is told by Penny. He appeared again in the last season on the episode The Laureate Accumulation.

Mayim Bialik

She played the role of Amy Farrah Fowler on the show from season four onwards. Mayim has a PhD in neuroscience from UCLA so she's the real-life doctor among the cast members. Neuroscientists study the development and function of the brain.

For her role as Fowler, Mayim has been nominated four times for the Primetime Emmy Award. She has also acted as scientific consultant for the show along with professor David Saltzberg of UCLA.

Brian Greene

Brian Greene is an American theoretical physicist, mathematician, and string theorist who is the chairman of the World Science Festival since co-founding it in 2008. He appeared in the episode The Herb Garden Germination speaking to a small crowd about the contents of his most recent book.

Greene's area of research is string theory which is a candidate for the theory of everything. He is most well known for his popular books such as The Elegant Universe, The Fabric of the Cosmos and The Hidden Reality.

Elon Musk

He is the renowned South African-American engineer and technology entrepreneur who has founded companies like PayPal, Tesla and SpaceX. Musk appeared in an episode as himself volunteering at a soup kitchen with Howard Wolowitz.

Musk asks if Howard ever thinks about going back into space. Howard lights up: “Is that a job offer? Cuz I really want to go to Mars!” Musk tells him, “We’re not quite there yet, but we’re always looking for engineers, so let me give you my email, and we can stay in touch.

Neil deGrasse Tyson

Popular American astrophysicist and science communicator first appeared on the show alongside Rajesh Koothrapalli. Sheldon just happened to stop by and they exchange a friendly banter. He is quite unhappy with Tyson's role in the demotion of Pluto from planetary status.

In season 12, Neil and Raj get caught up in a Twitter war in which he called Neil "Mike Tyson's little sister." Neil, enraged, goes on to phone Rajesh and challenges him to a face to face duel, "I am the guy who kicked Pluto out of the solar system," he says.


Bill Nye

He is an American science educator who studied mechanical engineering at Cornell University in 1977. His enthusiasm for science deepened after meeting astronomer Carl Sagan. Bill Nye became well known as "The Science Guy" and for his other appearances on television.

He guest starred in episode The Proton Displacement. Sheldon Cooper befriends Nye and brings him in to teach Leonard Hofstader a lesson after Professor Proton, played by Bob Newhart, helps Leonard with an experiment instead of Sheldon.

Steve Wozniak

American electronics engineer and programmer who co-founded the Apple Computers company in 1976 which went on to become the largest company in the world..

While dining in The Cheesecake Factory where Penny works, Woz is approached by Sheldon via telepresence on a self-made robot. Leonard tries to explain to Penny who Wozniak is, but she says she already knows him from Dancing with the Stars.


Stephen Hawking

He was an English theoretical physicist, probably the most famous genius of the modern age, best known for Hawking radiation. Hawking had a recurring role in the show having appeared a total six times. The first cameo is the funniest when Sheldon goes to great lengths to meet his hero. When the moment comes, Sheldon messes up big time and faints!

He was a fan of The Big Bang Theory since season one and requested to watch a rehearsal. Howard Wolowitz does an impression of Hawking's voice in the episode; Simon Helberg who plays the character felt slightly uncomfortable mimicking Hawking but Hawking seemed to enjoy the impression.

Kip Thorne

He is an American Nobel Prize winning physicist who appeared in the final season of the show. After their Nobel prize competitors, Pemberton and Campbell, go on a publicity tour, Sheldon and Amy seek support from a trio of Nobel laureates which included Kip Thorne.

Frances Arnold

She is an American Nobel Prize winning chemist and engineer who appeared in the same season as Kip Thorne as one of the laureates whose support Amy and Sheldon seek.