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Physics can be divided into three main areas: classical physics, quantum physics, and relativity.

Let's start with classical physics, and a great person to introduce is Isaac Newton. His laws of motion describe how everything made of matter moves, and his law of universal gravitation ties together the motion of planets in the sky with the falling of objects on Earth into one elegant and general description.

Newton also invented calculus, a powerful mathematical tool that has been used over the centuries to derive new physics. Calculus is a part of mathematics, but physics and mathematics are inseparable. You can think of math as the foundation of the world of physics.

Newton also made progress in optics, which is the study of light and how it travels through different materials. It explains refraction, seen in prisms and lenses, which are used to focus light in telescopes, microscopes, and cameras. Telescopes allowed us to peer into the depths of space and observe the vast array of objects there, leading to the development of astrophysics and cosmology.

Optics is closely related to the theory of waves, which describes how energy can travel through disturbances in a medium, such as ripples on the surface of a pond or sound in the air. Light doesn't need a medium to travel through; it can travel through the vacuum of space, but it still follows the same principles as all waves: reflection, refraction, and diffraction.

This leads us to electromagnetism, which describes magnets, electricity, or more generally, electric and magnetic fields. It was a physicist called James Clerk Maxwell who discovered that these are two aspects of the same thing. Maxwell derived the wonderfully elegant rules of electromagnetism and theorized that light is an electromagnetic wave. Electromagnetism also explains all of electricity.

Classical mechanics is related to Newton's laws and covers the properties and motion of solid objects. It explains how objects move when forces hit them and what happens when they are joined together, such as in gears, buildings, or bridges.

Fluid mechanics describes the flow of liquids and gases. Using fluid mechanics, you can work out how much lift is generated from an airplane's wing or how aerodynamic a car is. Fluid mechanics is notoriously difficult, mostly because motions of tiny things like molecules get really complicated really fast.

This leads us to chaos theory, which describes large complex systems and how small differences in initial conditions can lead to very different final outcomes.

Thermodynamics is the study of energy and how it passes from one form to another. It also includes entropy, which is a measure of order and disorder, and basically tells you how useful different kinds of energy are. Energy is a fundamental property of physics, and although I have written about energy here, I should have written it everywhere on this map because everything has energy.

So that's all of classical physics, the picture of the Universe we had around the year 1900. It told us we lived in a Universe where everything ran like clockwork. If you could measure everything accurately enough, the future was kind of predetermined. However, not everything was solved. There were just a few holes in experiments that hinted at something more. The orbit of Mercury was slightly too fast, and some strange things happened on the smallest scales with electrons and light, which were all unexplained.

Physicists at the time thought they would solve and explain these problems soon enough. But poking at them, they unraveled the new domains of relativity and quantum physics, turning our understanding of the Universe completely on its head.

Albert Einstein was the genius who developed the theories of special and general relativity. Special relativity predicts that the speed of light is constant for all observers. This means that when you travel really fast, weird stuff starts happening, like time slowing down. It also states that energy and matter are different aspects of the same thing through the famous formula E=mc2. General relativity says that space and time are part of the same fabric called spacetime, and that the force of gravity comes from objects bending spacetime, making other objects fall in towards them.

While relativity describes the very big, other physicists were busy at work on the very small in the world of Quantum Physics. Atomic theory probed the nature of the atom, and more and more detailed descriptions of the atom were developed. From a tiny sphere to electron orbits, to energy levels, and then to the electrons being wave-like charge distributions.

Condensed matter physics describes the quantum physics of many atoms together in solids and liquids. This is where many great technologies have come from, such as computers, lasers, and quantum information science.

Nuclear physics describes how the nucleus of atoms behave. It explains radiation, nuclear fission, the splitting of the atom used in our nuclear power plants, and nuclear fusion, which takes place in the Sun and will hopefully soon be harnessed here on Earth.

Particle physics probes even deeper to find the fundamental subatomic particles that everything is made of. These are described in the standard model of particle physics.

Quantum field theory captures all of quantum physics and combines it with the special theory of relativity. It is the best description of the Universe we have. Unfortunately, quantum field theory doesn't include gravity, and so physicists don't know how to join together quantum physics and the general theory of relativity. This leads to the giant chasm of ignorance.

One day in the future, we hope to close this chasm and come up with a theory of all of physics, called quantum gravity. There are many attempts to do this, some examples are string theory or loop quantum gravity, and there are many more.

But quantum gravity isn't the only thing we observe but don't understand. There are also the major puzzles of dark energy and dark matter, which seem to make up 95% of the Universe. So all of our physics only really describes 5% of what we know about, and everything else, at the moment, is a mystery.

There are many other mysteries out there, like the Big Bang, and no doubt there are things beyond that that we don't even know that we don't know.

Which gets to the lofty cloud which floats over all of physics: philosophy. Although many physicists make fun of philosophy, it is the big philosophical questions that motivate a lot of physics. Like, "What is the fundamental nature of reality?""How come the Universe even exists?" "Do we have free will if we are just made of physics?" or "How do we know that the way that we do physics and science actually gets to the fundamental truth of the Universe?" And, just, why is all of physics like the way it is?

Well, those are the big questions, ones which we may or may never answer. But that is no reason to give up trying. After all, physicists are not quitters.

And that was the map of physics. So that's the end, thanks for watching the video. I hope you enjoyed it. Um. I'm still kind of working on the format of this channel and playing around with a few different things. I kind of like this animation style. So let me know in the comments if you enjoy this kind of stuff and if you want me to do more. And if there are any specific subjects you want me to cover, I'm totally open to ideas. I've got a whole bunch of videos that are coming down the pipe so keep your eyes peeled for those.

So until next time. See ya.

questions:

How are optics and wave theory related?

Who formulated the laws of electromagnetism, and what discovery did he make about the nature of light?

What does classical mechanics do, and how is it related to Newton's laws?

What does fluid mechanics describe?

What is chaos theory, and what phenomenon does it explain?