I've read some papers recently that talk about gapped Hamiltonians or gapless systems, but what does it mean? Edit: Is an XX spin chain in a magnetic field gapped? Why or why not?
I asked a question recently where I wanted to know whether it was physically meaningful to talk about the arrow of time in other universes. Although many people apparently have an intuitive notion of ...
Can someone please explain what a potential is? Example. velocity potential in ideal flows, acoustic potential (gradient of which gives the particle velocity in a sound wave). Whenever I see potential ...
There are six types of quarks, known as flavors. Why where these types called flavors? Why do the flavors have such odd names (up, down, charm, strange, top, and bottom)?
Impedance is a concept that shows up in any area of physics concerning waves. In transmission lines, impedance is the ratio of voltage to current. In optics, index of refraction plays a role similar ...
I've been using the term "sound" all my life, but I really have no clue as to what sound exactly is or how it is created. What is sound? How is it produced? Can it be measured?