You can think of physics as being divided along three lines…
You can think of physics as being divided along three lines.
Galilean vs Einsteinian
Non-statistical vs statistical mechanics
Classical vs Quantum
Thus, physics is a cube with 8 regions on each corner. However, there are really only 6 regions because some possibilities don't really work. In particular, if you are doing Einsteinian physics, then you can't really have quantum mechanics or statistical mechanics without the other.
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The first of these divisions refers to what is usually called "nonrelativistic" vs the "relativistic" physics of Einstein. However, the Principle of Relativity, which says that any body in uniform motion can consider itself "at rest" from its own perspective and will observe identical physics, was first stated by Galileo. Thus all physics since the Renaissense has been relatavistic.
What Einstein did was to restore locality to physics. In Galilean relativity, because velocity is not capped, effectively anything can affect anything no matter how far away it is. In fact, it appears that communication between two distant bodies can be instantaneous, if there is a long-range force connecting them, like gravity or electromagnetism.
In Einstein's physics, nothing can go faster than light and hence there is a minimum amount of time before a distant region can affect a nearby region.
The second of these divisions refers to the theory of heat, which is now understood to be a kind of motion among bodies that is too small to be directly observed. In statistical mechanics, a body is understood to be more than simply a position and momentum. Instead it is a probability distribution over a range of positions and momenta that represents many small particles.
The connection between heat and motion took a long time for people to understand. Before it was understood, the principle of the conservation of energy, which is now central to all physics, could not be understood because it appeared that two bodies could interact in a way that caused both of them to slow down until they were at rest relative to one another. It is now understood that the coherent motion of the two bodies is converted into incoherent motion of their particles, which is experienced by us as heat.
In non-thermal physics, the notion of entropy does not exist.
There is a theory called thermodynamics which models heat as a fundamental quantity, like mass or charge. This theory is deterministic, like everyday classical physics. However,
Did one or more of your posts end up marked private CosmosStag ?
I ask because your thread ended on “However,”. It’s easily done by accident, or maybe you just went to bed?