So physics is a huge subject that covers many different topics
going from galaxies in the depths of space right 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 down in to three main parts:
Classical Physics, Quantum Physics, and Relativity.
We’ll start with classical physics and a good person to start with is Issac Newton.
His laws of motion describe how everything made of matter moves about,
and his law of universal gravitation tied together 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 centuries to 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 optics which 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 light in telescopes, microscopes, and cameras.
Telescopes enabled us to peer into the depths of 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 ripples on 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 Maxwell who discovered that these are two aspects
of the same thing and derived the 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 mechanics is 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 description of the flow of liquids and gasses.
Using fluid mechanics you can work out how 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 description of large complex systems
and how small differences in initial conditions can lead to very different final outcomes.
Thermodynamics is the description 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 fundamental property to physics and although I have written energy here,
I should have written it everywhere on this map because everything has energy.
So that is all of classical physics, the picture of the Universe we had around the year 1900.
It told us we lived in the Universe where everything ran sort of 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 of 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 that they would solve and explain these problems soon enough
but poking at them they unraveled the new domains of relativity and quantum physics
and turned 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
which 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, and is where many great technologies have come from
like computers, lasers, and quantum information science.
Nuclear physics describes how the nucleus of atoms behave, and 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 and 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 and 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 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 there are many attempts to do this some examples
are string theory or loop quantum gravity and there is 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’s 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 and 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.