 # If you hear men talking about “bras” and “cats”, then they are physicists.

The other day I updated the Language section of my CV, stating that I have “working knowledge” in Mathematical Physics. Most people are afraid of Mathematics because it introduces a lot of new objects (or concepts) and different ways to use them. And thats just like a language, with word and grammar. If you hear another language and youre immediately asked to talk it, then its normal to be at least reluctant.

One distinct feature of the “science guys” is laziness. We would find the easiest (least effort needed) to do even the most mundane/trivial things. And talking the mathematical language is not an exception. For example, the continuity of real-valued functions at a point c: $(\forall \epsilon > 0)( \exists \delta > 0):( \forall x \in D) ( 0 < |x-c| < \delta \Rightarrow |f(x) - f(c)|$ Physics may make you famous one day, but thats not why you do it.

This literally means: For any positive number epsilon, there exists a positive number delta such that for any number x in the interval D, if the absolute difference between x and the point of interest c is less than delta, then the absolute difference between the value of the function at point x and point c is less than epsilon, which is a very fancy way of saying that if you start drawing the function, you cannot lift your pen from the paper until you finish.

If thats not an efficient language, then what is Spanish?

Let me now explain the joke in the title (if a joke needs explanations, then yes, it is a lousy one). Just like normal verbiage, the defi nitions (“words”) are usually taken to be as simple and straightforward as they can be. In quantum mechanics, Dirac notations is generally favoured for its simplicity. Here, a common notation (for scalar product) is the following: $\left< \Psi | \Psi \right>$. This is commonly seen as two functions in angular brackets. If you divide the two, you obtain: $\left< \Psi \right|$ (a bra) and $\left| \Psi \right>$ (a ket). They are simply taken to be a bra-c-kets. Therefore, the physicists would talk about bras (“bras”) and ket`s (“cats”).

Ironically, the more efficient the language, the harder it is to learn it. After almost 12 years of education and hard work, I barely have working knowledge, whereas I obtained the same thing for German in 3 years with minimum effort.

Be like a proton, stay positive!