Physics is what explains the very, very small and very, very large things.

Time: August 20, 2017
Place: At home in the Pacific Northwest
Pointer from: My pops
Note type: Direct

Physics is what explains the very, very small and very, very large things.

Physics, or more specifically cosmology, is the only discipline that currently studies what happens at such large scales. This remains so for galaxy clusters and galaxies and interstellar space, which fall into the area of astrophysics.

If we get to even smaller scales, to the size of atoms of about an Angstrom, physics starts taking over again. First there is atomic physics, then there is nuclear physics, and then there is particle physics, which deals with quarks and electrons and photons and all that. Beyond that... nobody knows. But to the extent that it’s science at all, it’s safely in the hands of physicists.

One would need an enormously high energy to probe such short distances, much higher than what our particle accelerators can reach. Such energies, however, were reached at the big bang, when our universe started to expand. And so, if we look out to very, very large distances, we actually look back in time to high energies and very short distances. Particle physics and cosmology are therefore close together and not far apart.

Not everything in physics, however, is classified by distance scales. Rocks fall, water freezes, planes fly, and that’s physics too. There are two reasons for that.

First, gravity and electrodynamics are forces that span over all distance scales.

And second, the tools of physics can be used also for stuff composed of many small things that behave similarly, like solids fluids and gases. But really, it could be anything from a superconductor, to a gas of strings, to a fluid of galaxies. The behavior of such large numbers of similar objects is studied in fields like condensed matter physics, plasma physics, thermodynamics, and statistical mechanics.