What follows is the general script I used for the video linked in this post, “What is Physics”, in which I go over the 4 main branches of physics:
Classical Mechanics, Electromagnetic wave theory, Quantum Mechanics and Relativity

My goal is to put the material out there for anyone that wants to learn more, I thought I would make the video’s transcript more easily text searchable, so below is the script I used:

Physics is the natural science that studies matter,^[a] its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force.^[2]

Physics Fundamental science, studies everything in the physical universe. It’s subject of study is literally the entire universe, by that I mean that it’s a science in which nothing is designated as too in depth, there is no phenomenon that is considered too fundamental to study, there will be nothing left to another field to review, describe or study, its the science where everything can be derived by first principle. That’s not to say it’s the most important science, since we need the other science to understand and study the different parts of the physical universe, and to derive useful understanding and applications from them. I’m not saying that physics is the most important or the best science. As a society we need people that try to study all levels of nature, from first principle, to observational application. Societies need more than just 1 type of professional or person, besides a world of just physicist would be pretty boring. We need engineers, chef, logistical, manufacturing personnel, artist, communicators and leaders for our society to run.

Beside, physics will tell you the soil is hot, and when, but not the best time to plant. Physics can tell you how two molecules interact, but not which medical molecules are need to cure a sickness or condition. Physics can tell us the way in which molecules rearrange themselves, but not how to ferment bread to make the beer we need to cope with reality

Physics relies on the scientific method to create hypothesis, collect data, review it, and correct assumptions based on new data. It’s away to correct for mistakes in light of new data, and communicate those findings and data to others.

Physics in society, how it’s seen, how it contributes. Our ability to manufacture, travel, stay healthy, have food, comfort have all be vastly enhanced by our knowledge of physics and the other sciences, and it’s application via the development of applied technologies

Fate of empires and nations have been decided by their level of technological and scientific determination. Knowing how to forge iron as opposed to copper in the old world. Modern wars are also defined by the combatants level of industrialization and scientific know how. Hell, the Asian front in WWII was partially ended due to the success of the most expensive science research effort ever

Physics is like art and spirituality, tries to explain the world around us. It’s one of the oldest human endevours, to look around, gaze at the stars, the natural forces around us, to attempt to explain and make sense of everything around us. Like the art and the faiths of our civilizations, Physics and the sciences are our attempts to understand and make sense of what would appear chaos

Science is considered as a national strategic priority. The Fed govt pours tons of money into the sciences, making sure universities have the funding for their science departments, to funding the national labs, NSF, NASA and the defense research efforts. The scientific and engineering sectors of the private industry also spend billions if not trillions of years into research and development. Some sectors of industry like tech, are defined by their adoption of technological and scientific tools and principles.

I like the image of erudite scholars that understood these old and mysterious ways. The image of the scientist in movies, as experts that can interpret or understand things happening around them in ways that others can’t. The image of the tinkerer who is able to macgyver clever new inventions. I was fascinated by the idea of technology, and the tools that we can build if we better understand how the universe operates. Of how more efficient we can be in construction, agriculture, manufacturing with more and more advanced tools and understanding. I was amazed by how societies and cultures evolved and changed in their physical conditions as they developed more advanced science and technologies.

Special thanks to the NSF, whose financing puts thousands of scientists in the United States through college. The NSF’s and federal funding has also led to the USA being the world leader in graduate research programs, with lots of well funded programs where faculty and students have access to expensive scientific equipment to use for training and research.

Before talking about Physics, we need to talk about the language of physics

In this video, first we’ll talk about the language of physics, and then we’ll have a quick overview of 4 of the main branches of physics. There is disagreement on how physics should be divided or organized and some would say I’m leaving out important parts by using this way of organizing physics

Mathematics (from Ancient Greek μάθημα; máthēma: ‘knowledge, study, learning’) is an area of knowledge that includes such topics as numbers (arithmetic and number theory),^[1] formulas and related structures (algebra),^[2] shapes and the spaces in which they are contained (geometry),^[1] and quantities and their changes (calculus and analysis)

Why do we use mathematics? It’s an universal unambiguous language that we use to describe phenomena accurately. Some of the key reasons mathematics is used as the language of physics is exactness and universality.

Exactness refers to the ability to achieve a necessary language of precisions. A car goes fast, a car goes 60 mph

Universality means that values and meanings will be interpreted the same regardless of the interpreter. There is no dependency of interpretation of the meaning of the messaged that’s affected by age, creed, nationality or time (well… mostly)

Mathematics presents the tools that physicists need to try to describe or hypothesize behavior in the physics world. 

Equalities allow us to break down the way different variables relate to each other. 

Calculus and partial differential equations tells us behavior changes with respect to others, and can be used to tell us how something behaves over a distance or time. 

Linear algebra gives us framework for working in a high number of dimensions like in Quantum or String theory. 

Einstein notation, Riemann sums, bracket notation, matrix operations all gives us the tools to describe, and communicate a behavior or phenomenon. They also allow us to play with them, change them, to see what insights we can discover about the world around us, through just observing how we can move parts around with the math tools that we have.

And i should take a moment to talk about communication. The discovery of science, the pushing forward of human knowledge is not task for a single person. A person has biases, limitations, a finite lifetime, but a large group of people, like an international society of collaborators, can develop theories and laws of the physical universe, but working together to overcome limitations, all brains work a little different and sometimes you need people that think differently than you, and work over long periods of time by passing down information over generations. So science is inherently collaborative and additive. Someone learning science today anywhere in the world will receive basically the same education, based on the cumulative accumulation of human knowledge. 

You are inheriting a little part of experience of thousands of wanderers and explorers that came before you. Like, art and religion, science and physics have been with us since the dawn of our species.

There is no American physics, or Russian quantum, it’s all our collective inheritance 

So, moving on to physics, I’ll go over 4 parts of physics that anyone that moves through the academic process has to go through. 4 parts of physics that samples from the diverse fields, and most physicist will have a decent level of fluency in them. Most physicist would encounter them in college undergraduate. It also excludes quantum field theory because I don’t know anything about that. Once you hit the sub particle level is when my competency starts to drop off. You’ll have to find someone that stayed in school longer if you want to learn about muons and leptons and tacyhons

There are many different ways to divide the sciences and physics, depending on what criteria you are using

Classical Mechanics so trajectories of objects we can see, stresses, orbits, ballistics. NASA

Electromagnetic wave theory think electronics and long range communication. Optics could also be put here. Electricity

Quantum Mechanics Schrodinger’s equation, used in electronics, semiconductors, nuclear and particle phenomenon, eventually spintronics and quantum computing

Relativity widely used in aerospace and communications. Satellites can travels at relativistic speeds. Astrophysics and Time travel. Also goes into the effects of gravity on space time. Gravity being the most mysterious and least understood of the 4 fundamental forces of the universe.

I’ve worked on as an engineer, I don’t have a PhD, and particle and quantum physics are my weakest points, so keep that in mind when you consider my biases in anything i say.

Classical Mechanics

Usually it’s everyone’s first introduction to physics, when you study it in college or high-school.

Developed over millennium as mathematics developed (algebra note not a western word since we use Arabic numerals). Used in medieval architecture and ancient calculations of motion of the stars

Was able to accurately predict the motion of celestial bodies when Newton developed calculus.

Cover the moment of celestial and terrestrial objects and is the one that we have the most sense of intuition of

Present some typical examples of home work problems. Ballistics, kinematics, train heading east, mechanic stresses, so forces on a box on a sloped plane.

Name some applications in ballistics and aerodynamics, civil engineering with stress and strain, thermodynamics (I think)

Used to calculate orbits and space travel, but more on that later

Newton’s 3 laws

Stuff in rest stays in rest

F= ma Force is proportional to acceleration, point out that it’s an equality that allows us to calculate either force, mass, acceleration from any 2 of the 3

F = mg (gravity as a force)

Work and energy F = -delta work

Classical mechanics is also what i used to calculate everything related with aerodynamics and space travel, the motion of bodies, stresses, speed, drag, acceleration, distance travelled and so forth. Lagrangian points and mention JW space telescope resting at a moon earth Lagrangian points.

This is where we get the famous three body problem. The Three body problem can be approximated with numerical solutions (brute force), but no analytical solution exists using differential equations and Newton’s laws

Electromagnetic wave theory

Covers anything involving light, or radiation, electricity, and magnetism. So optical fiber, radio waves, electronics and circuits, alternating engines, electricity, induction, energy generation all fall into the field of study of electromagnetic wave theory.

The flow of energy through the universe

A wave of electromagnetism is a couple of oscillation of a magnetic and electric field that travels through space or the air at C, the speed of light. The speed of light depends on the medium Find a medium where it travels slowly, and have visual aids

Both waves oscillate and travel together, they cannot be separated.

Go over the spectrum of radiation, and mention the visible spectrum of light

James Maxwell, Scottish mathematician pioneer in electricity and magnetism, Regarded the father of electrical engineering, since the Maxwell field equations are fundamental to modern electronics, circuits and transistors. 

Modern electronics, communications, satellites, internet, optics, wouldn’t be possible without EM wave theory

though there were many other scientist working at the time making tons of discoveries, this was a time of rapid development and progress and science and math.

Based on maxwell’s wave equations, these fun little guis over here

Some of the other major concepts in EM are

• Induction: The generation of current by a changing magnetic field, it’s how electricity is generated.

•  Lenz’s law, analogous to Newton’s 3rd law, with equal and opposite reactions

, strap some big ole magnetics to something that moves it, water, wind, nuclear boiled steam, coil generated steam and so on. The inverse is true too, a you can run a current through a conductor to generate a magnetic field, an electromagnet, like how electric motors work.

electromagnet has to do with spin alignment of bound electrons aligning due to an outside force, but that’s beyond the scope of this video, and how magnets work

• Coulomb repulsion: Equal charges repulse and different charges attract. Electric fields have a lot of parallels with magnetic field and how gravity seems to work. More on this during the relativity chapter, but gravity is very mysterious and we don’t know much about it, comparatively

The attraction between electrons is what makes current, and electricity possible, and consequently electronics and circuirts possible. Maxwell’s and Coulombs research gives us the tools to make all these devices and machines.

Ok, moving on to Quantum.

We’ve talked about the 2 fields of physics that we have a sense of intuition for, in that we can see these effects and forces with our own senses. We’ve interacted with them, and can related laws to real world behaviors

For the next two, this sense of familiarity might be gone. We don’t intuitively know how time dilation or quantum tunneling works, we don’t interact with these behaviors everyday. Even though they are still valid parts of the physical universe, their behavior might seem a bit odd to us at first.

Quantum mechanics

For the next two fields of physics we are going over, we will no longer have an intuitive sense based on experience on how they operate

We interact with the forces of electricity, gravity and motion everyday, but we don’t with time dilation or quantum tunneling. What i’m getting at, is that for relativity and quantum mechanics, we usually don’t have an intuitive sense of how things work. Quantum behaviors, if extrapolated to macroscopic scale does make sense and makes it seem magical.

Which is a good segway to how quantum is presented in the media and a personal pet peeve. In movies it’s usually a label you put on a mcguffin and functionally it means magical. Need a plot device or a way for something to happen, just say it’s quantum. Not that movies need to be scientific accurate, not why we watch them, i’m just saying they could be a bit more creative and just say “science is magic”.

https://www.quora.com/Why-does-every-science-fiction-movie-use-quantum-physics-as-an-answer-to-any-and-every-questionable-thing-or-plot-hole

Also, i recommend that you are careful with anyone that mixes quantum and philosophy. In my experience, at least some years ago, it seemed like there was a trend of using quantum behaviors to justify a philosophical outlook. I think some writers might rely on the obscurity of quantum as a way to get legitimacy. I’ll be going a few of things that anyone having studied quantum in a academic setting would know.

Quantum mechanics aims to study and detail the behavior of very small objects, or on this scale, particles. Usually when we’re talking about quantum we are talking about things that are happening on the scale of a nucleus or electron of an atom. Quantum behavior doesn’t really manifests on the macroscopic scale

A few notes on quantum, and how it’s different than what we’ve already gone over. Mechanics and EM are deterministic, events, objects things, values have definitive values. A bag weights a pound, a house is there. An object has a start and an end, there is no fuzzyness there.

At the quantum scale electrons no longer are discrete objects that orbit a nucleus, but rather probability clouds that surround the nucleus. The probability cloud that the electrons orbit in changes with the electron level, or the amount of energy it’s carrying. Sort of like how a moon would orbit a planet, but in a distribution cloud

Quantum is probabilistic. Instead of saying a thing is in a location, we talk about possibilities, we say there is a chance this object is in this area. The distribution of probabilities is described using wavefunctions, that we say collapse, once a measurement is taken and we know the location of something

The first concept that you learn in quantum mechanics is Schrodinger’s equation, there’s a lot to unpack here, and we’re just doing a quick survey

In this form, we see a double space derivative equated to a time, or temporal, derivative. So relating the change along an axis, and the passage of time.

To not, we have i here, which is an imaginary number, sqrt of -1. Here it can represent the phase and angle of the wavefunction, and if squared is equal to -1, which can be useful in maintaining an equality

Another important concept in quantum mechanics is Heisenberg uncertainty principle, which basically states that there’s a limit on the details you can know of a system, in terms of time and location. The more you know of one, the less you can find out about the other. Again, with the theme of probabilistic wave functions

Quantum tunneling is also a key idea in quantum. Basically it covers the concept that at the quantum scale, a particle can tunnel through a barrier, if it’s going fast enough, and the barrier thin enough. On a macroscale that’d be like throwing a ball at the way and it going through.

Another famous experiment in quantum is the double slit experiment, which is what established the dual wave particle behavior of electrons. The short version is that if you shoot a single electron through a double slit, you’d expect it go through one slit, or the other, and landing within a distribution of places on the sensor. Rather, what happens is that you get a probability distribution that shows interaction between two waves, resulting in a interferometric pattern on the sensor. This occurs on the phenomenon that a wave of light can be added or subtracted, either amplifying the wave, or canceling out. So where you’d expect the behavior of a particle through the double slit, you get the behavior of dual waves, so the electron has behaviors of a wave, and a particle

Quantum mechanics is key to understand the behavior of subatomic particles. You could make the argument that a big part of the manhattan project was quantum mechanics along with relativity, and the most expensive science project ever. Back then scientist would have access to the white house to advise the president. Imagine that, a president listening to experts!!

Quantum mechanics are also becoming more and more important in semiconductor manufacturing and chip making. As features get smaller and smaller with the advancement of Moore’s law, which states that the density of transistors doubles every two years, quantum behavior become more apparent and dominant

Current generation transistors are made with lithography as small as 4 nm, which is maybe 10s of atomic layers, getting real close to the limits of quantum behaviors. As these quantum behaviors become more dominant, most notably quantum tunneling, it will require a lot of creative engineering to overcome their effects, or to take advantage of them. Time will tell. Time will tell

In response to this, we have effort to push for quantum computing, thinking that one day we’ll have to radically revamp how computer chips are made and organized. Spintronics, where the force messengers is a spin oscillation. So instead of an electron traveling, it’s a perturbation of the spin alignment of a series of electrons, but that’s a whole other can of worms

So wavefunctions, probability distributions, electron clouds, Schrodinger’s equation and Heisenberg’s uncertainty principle

Moving on to the last part of this quick tour:

Relativity

Famously discovered and developed by Einstein, before during and after WWII. The famous equation E=MC^2 (though there’s more to that equation) equates a relationship between mass and energy. Note the C^2, which we know is 3×10^8 m/s, which squared is a massive number. This relationship mediated by C squared is at the center of nuclear energy, the conversion of mass to energy through fusion or fission. The conversion from mass to energy is also what powers the sun and stars

Einstein postulated two theories that shook the world of physics, the principle of general relativity, and special relativity. I’m only going to go over these briefly since these there’s so much here.

Special relativity postulates two things:

The laws of physics are the same in all inertial frames of reference

The nuance here is on the inertial, implying some differences for systems under acceleration, specifically with space time, so that’s where you get time dilation and stuff like that

Speed of light is the same in all frames of reference. This ones is tricky, since it leads to time and space contraction and dilation. No matter how you look at light, when, where and how you measure it, it will always measure at C in vacuum, 3 x10 ^8

So if two observers are heading towards each other at a high speed, and they both measure the speed a beam of light, they will both measure the same speed. How can this be, how can the laws of physics be consistent> And this is where we get time and space dilation, space or time would have to contract in one of the frames of reference, for both observers to measure light moving at C

Which leads to the theory of general relativity

Basically the theory of general relativity tells us that mass is able to affect the curvature of space time, presenting an explanation for the force of gravity. An object in orbit around a planet is traveling in a straight line in it’s own frame of reference, but might be traveling in curved space time in the frame of reference from the planet, that’s how bodies stay in orbit of larger bodies. How the Earth stays in the orbit of the sun, the sun is very massive, so it curves space time around it, which has trapped the planets of the solar system. Leading to the orbits of the planets around the sun, and the same story with the moons of the different planets in the solar systems.

Time dilation is also explained with the theory of general relativity. As space time is curved, the way that time is experienced also changes. That’s why an astronaut traveling in space, will feel time pass a little slower than someone that stayed on Earth. The faster the astronaut is traveling, closer to the speed of light, the bigger the difference in how the astronaut would experience the passage of time.

Note, that we don’t have any way to accelerate large objects to anywhere near the speed of light, even in space, so the relativistic feelings a person can experience are pretty minor. Particle accelerators are able to accelerate neutrons or other small particles to close to the speed of light, but that takes mile long tunnels with super powerful magnets and lots of power