The status of lattice QCD may be summed up as: under way. Already there have been some nice results in the context of the quenched approximation, but the lattices are still too coarse and too small to give definitive results. Results for full QCD are going to take orders of magnitude more computer time, but we now have an algorithm-Hybrid Monte Carlo-which puts real simulations within reach.
When will the computer power be sufficient? In Figure 4.11, we plot the horsepower of various QCD machines as a function of the year they started to produce physics results. The performance plotted in this case is the real sustained rate on actual QCD codes. The surprising fact is that the rate of increase is very close to exponential, yielding a factor of 10 every two years! On the same plot, we show our estimate of the computer power needed to redo correct quenched calculations on a lattice. This estimate is also a function of time, due to algorithm improvements.
Figure 4.11: MFLOPS for QCD Calculations
Extrapolating these trends, we see the outlook for lattice QCD is rather bright. Reasonable results for the phenomenologically interesting physical observables should be available within the quenched approximation in the mid-1990s. With the same computer power, we will be able to redo today's quenched calculations using dynamic fermions (but still on today's size of lattice). This will tell us how reliable the quenched approximation is. Finally, results for the full theory with dynamical fermions on a lattice should follow early in the next century (!), when computers are two or three orders of magnitude more powerful.