Physics for Alice & Julien
Objects and forces.
Physics used to be about four fundamental things: objects and forces interacting in space over time. Special relativity showed that space and time were linked and had no fixed coordinates, while general relativity showed that forces could be a result of objects falling into dents in curved spacetime, caused by other objects, at large scales.
At the small scale forces can be the exchange of objects (particles) too, so this leaves two things: force exchanging objects interacting in spacetime at the small scale and objects interacting in force creating spacetime at the large. The objects and the spacetime may come from the same stuff, as objects can be created from spacetime itself.
For a grand unified theory of physics there may just be relationships between different aspects of one type of thing if we can resolve what happens with very large masses (general relativity) which are simultaneously small in size (quantum mechanics).
Unfortunately, these conditions only exist in extreme circumstances such as black holes, very high energy particle collisions or shortly after the big bang. So this will be hard.
If we are able to do this, and the relationships between aspects of one kind of universal stuff are in very specific amounts (lots of unknown constants), then maybe there is some meta-law that allows these constants to self-configure for the universe to work as it does, e.g. the laws of physics themselves evolve.
At the small scale, everything is made up of atoms (which was meant to mean they are indivisible, except they aren’t). Atoms are made of a nucleus and electrons. The nucleus is made of particles called protons and neutrons and these in turn are made of quarks. Particles can have 4 attributes: charge; color charge; mass energy and spin.
All particles can also behave like waves (fluctuations of a spacetime field, rather than droplets rolling about in it).
Particles do not sit in a physical spacetime medium (ether), they are part of it. Spacetime is a curved 4 dimensional field of points which constitute ‘events’ (things that happen at a particular time and place relative to an observer).
There used to be three known forces: electricity, magnetism and gravity.
Maxwell combined electricity and magnetism and later two new forces were discovered: weak nuclear and strong nuclear, to give four fundamental forces of nature: electromagnetism; weak nuclear; strong nuclear and gravity.
QED combined electromagnetism and weak nuclear and QCD added the strong nuclear to the explanation, to effectively leave two fundamental forces: particle forces and gravity.
Forces (at the small, quantum, scale) can be considered as particles.
Forces (at the large, general relativistic, scale) are a result of curled up geometry of spacetime.
A resolution of the two would possibly mean that forces are particles which are the result of curled up dents and balls of spacetime.