Education

The Map of Physics

So physics is a huge subject thatcovers many different topics going from galaxies in the depths of spaceright down to subatomic particles. And if you don’t already know physics its difficult sometimes to see how all these different subjects are related to each other. So this is my attempt to show that in a map,so this is the map of physics.

I hope you enjoy it. Physics can be broadly broken downin to three main parts: Classical Physics, Quantum Physics, and Relativity. We’ll start with classical physicsand a good person to start with is Issac Newton.

His laws of motion describe how everythingmade of matter moves about, and his law of universal gravitation tiedtogether the motion of planets in the sky with the falling of objects on Earth into one elegant and general description.

He also invented calculus,a supremely powerful mathematical tool which has been used over the centuriesto derive new physics. Calculus is really part of mathematics but physics and mathematics are inseparable. Math is the language of physics,you can imagine it like the bedrock that the world of physics is built from.

Newton also made strides in the field of opticswhich is the physics of light and how it travels through different materials. It explains, refraction seen in prisms and lenses which are used to focus lightin telescopes, microscopes, and cameras. Telescopes enabled us to peer into the depthsof space and observe the wild array of objects there and develop astrophysics and cosmology. Optics is closely related to the theory of waves, which is basically how energy can travel through disturbances of a medium, like rippleson the surface of a pond or sound through 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 namely reflection, refraction and diffraction. This leads us to electromagnetism:the description of magnets, electricity, or more generally, electric and magnetic fields. It was a Physicist called James Clerk Maxwellwho discovered that these are two aspects of the same thing and derivedthe wonderfully elegant rules of electromagnetism and theorized that light was an electromagnetic wave. Electromagnetism also explains all of electricity.

Jumping back a little bit, classical mechanicsis related to Newton’s laws and covers the properties and motion of solid objects,how they move when forces hit them, what happens when they are joined together,like in gears or buildings, or bridges. Fluid mechanics is the descriptionof the flow of liquids and gasses. Using fluid mechanics you can work outhow much lift is generated from an aeroplane’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.

Which leads us to Chaos theory. Chaos theory is the descriptionof large complex systems and how small differences in initial conditionscan lead to very different final outcomes. Thermodynamics is the description of energyand how it passes from one form to another. It also includes entropy which is a measureof order and disorder, and basically tells you how useful different kinds of energy are. Energy is fundamental property to physicsand although I have written energy here, I should have written it everywhereon this map because everything has energy.

So that is all of classical physics, the pictureof the Universe we had around the year 1900. It told us we lived in the Universe where everythingran sort of like clockwork, if you could measure everything accurately enoughthe future was kind of predetermined. However, not everything was solved, there were just a few of holes in experiments that hinted at something more. The orbit of Mercury was slightly too fastand some strange things happened on the smallest scales with electrons and light which were all unexplained. Physicists at the time thought that they would solveand explain these problems soon enough but poking at them they unraveled the new domainsof relativity and quantum physics and turned our understanding of the Universe completely on its head.

Albert Einstein was the genius who developedthe theories of special and general relativity. Special relativity predicts that the speedof light is constant for all observers which means that when you travel really fastweird 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 timeare part of the same fabric called spacetime, and that the force of gravity comesfrom 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 electronsbeing wave-like charge distributions. Condensed matter physicsdescribes the quantum physics of many atoms together in solids and liquids,and is where many great technologies have come from like computers, lasers,and quantum information science.

Nuclear physics describes how the nucleusof atoms behave, and explains radiation, nuclear fission, the splitting of the atom usedin 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 findthe fundamental subatomic particles that everything is made of and are describedin the standard model of particle physics.

Quantum field theory captures all of quantumphysics and combines it with the special theory of relativity and is the best descriptionof the Universe we have. Unfortunately Quantum field theorydoesn’t include gravity and so physicists don’t knowhow to join together quantum physics and the general theory of relativity leading 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 we call it quantum gravity, and thereare many attempts to do this some examples are string theory or loop quantum gravityand there is many more.

But quantum gravity isn’t the only thingwe observe but don’t understand, there are also the major puzzlesof 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 mysteriesout there like the Big Bang, and no doubt there’s things beyond thatthat we don’t even know that we don’t know. Which gets to the lofty cloudwhich 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 willif we are just made of physics?” or “How do we know that the waythat 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 formatof this channel and playing around with a few different thingsand I kind of like this animation style.

So let me know in the comments if you enjoythis kind of stuff and if you want me to do more and if there are any specific subjects you wantme 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.

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