Physics relies heavily on math. Many posts include mathematical notation, rendered using the Javascript library MathJax. If you see dollar signs with what appear to be LaTeX commands between them, it just means that MathJax isn't working properly for you. In this case, make sure that your browser has Javascript enabled and, if you use a script blocker, that scripts from mathjax.org are enabled.

Including mathematical notation in your own posts should be easy if you are familiar with TeX/LaTeX. MathJaX uses a very similar syntax; in particular, most core math commands from LaTeX as well as the environments from the amsmath package are supported.

If you're not familiar with LaTeX, see Mathematics Meta for an overview of the most useful MathJax notation. The full documentation of everything you can use in MathJaX is available on the MathJax website.

Using MathJax on Physics Stack Exchange

• Inline formulas are surrounded by single dollar signs:

  This is an inline formula: $f(x) = ax^2 + bx + c$
  

  renders as

  This is an inline formula: $f(x) = ax^2 + bx + c$

• Block formulas are surrounded by double dollar signs.

  $$x = \frac{-b \pm \sqrt{b^2 - 4ac} }{2a}$$
  

  renders as

  $$x = \frac{-b \pm \sqrt{b^2 - 4ac} }{2a}$$

• To create Dirac notation, use \langle, \rangle, \lvert, and \rvert.

  \langle\phi\rvert M\lvert\psi\rangle
  

  renders as

  $$\langle\phi\rvert M\lvert\psi\rangle$$

• The hermitian conjugate is generally denoted by ^\dagger.