accurately than $ \lambda>1/\langle p \rangle$. For an ultra-relativistic system, the entropy density is $\sigma\approx 4 \rho$, therefore $$\frac{\eta}{\sigma}\stackrel{~}{>} \frac{1}{12} \;\;, 
\label{etabound}$$ which is within 5% of the string theory bound. It is the consequence of the universality of the Heisenberg uncertainty principle. Surprisingly, the QGP found at RHIC saturates this uncertainty bound and the data clearly rule out the order of magnitude larger predictions based on pQCD [@Danielewicz:ww]. See again [@Molnar:2001ux]. The long wavelength modes in the QGP are as maximally coupled as $\hbar=1$ allows.

It is “shear” good luck that the mid rapidity initial conditions at RHIC are dense enough to essentially eliminate the dilution of elliptic flow due to the imperfect hadron fluid formed after the spatial asymmetry vanishes. (Recall that $(\eta/\sigma)_H\sim (T_c/T)^{1/{c_H}^2}>1$ for $T<T_c$ [@Danielewicz:ww]). At lower energies or higher rapidities this good luck runs out and the mixture of near perfect QGP and imperfect hadronic fluid dynamics reduces the elliptic flow.

 pQCD and Jet Quenching
=======================

In addition to the breakdown of perfect fluid collectivity at high rapidity seen in Fig.(\[line1figb\]), Fig.(\[line1fig\]) clearly shows that hydrodynamics also breaks down at very short wavelengths and high transverse momenta, $p_T> 2$ GeV. Instead of continuing to rise 