# Time (Analog)

Time[1][2] is something we don't even have a bad definition for. Let alone a rigorous scientific definition.

Crystals In Time by Frank Wilczek, Scientific American, November 2019, p. 28.

• Crystals are orderly states of matter in which the arrangements of atoms take on repeating patterns. In the language of physics, they are said to have “spontaneously broken spatial symmetry.”
• Time crystals, a newer concept, are states of matter whose patterns repeat at set intervals of time rather than space. They are systems in which time symmetry is spontaneously broken.
• In physics Space Symmetry holds the Laws of Physics apply everywhere equally. Time Symmetry holds the Laws of Physics apply at any time equally. Time Symmetry is denoted by $$\tau$$.

So what is time symmetry?

Amir Pnueli, Temporal Logic