Twenty Dragon Tampan Paminggir people. Lampung region of Sumatra 19th century, 65 x 81 cm. From the library of Darwin Sjamsudin, Jakarta. Photograph by D Dunlop. |

Let some well-known particle F be employed as a frame of reference. This just means that we use F to describe changing phenomena. Otherwise a reference frame is a compound quark like any other particle, so it can be characterized by its quark coefficients and wavevector $\overline{\kappa}$. For example, a rigid frame of reference always has the same radius. Another important special case is when each component of the average wavevector of F is zero

$\begin{align} \tilde{\kappa} \equiv \frac{ \overline{\kappa} }{ N } = \left( 0, 0, 0 \right) \end{align}$

then we say that F provides a perfectly **inertial** frame of reference. This condition is approximated when the total number of quarks $N$ is enormous. Because if the total number of quarks is huge, there will likely be some mix of quarks and anti-quarks making the $\Delta n$ terms in the numerator tend toward zero, even as the denominator gets larger.

Definition: If a frame of reference is rigid, inertial and non-rotating then we call it an **ideal** reference frame. We often assume that frames are ideal and then use the icon shown on the left to represent these qualities. Sensory interpretation: An ideal frame of reference is big, grey and uniform.