The Standard Model is the best model so far for characterizing the fundamental constituents of our physical world, with the following caveats:
– It is admittedly incomplete, as it does not contain gravity. Thus it alone can’t fully describe our physical world.
– In its current formulation, or at least the formulation appearing in most text books, it assumes neutrinos have no mass. Mass oscillation experiments such as the Super-K experiment in Japan and the MINOS experiment in the U.S. have shown that neutrinos oscillate between different flavors (i.e. different types), which implies that they do have mass. This however does not spell doom for the Standard Model, as it can be extended to include massive neutrinos via the “seesaw mechanism”, though this in turn predicts a very massive, non-interacting “sterile” neutrino, so named as it doesn’t interact with other particles except via gravity. So far there is no definitive evidence of sterile neutrinos.
– We still haven’t found the Higgs particle, which is an integral part of the Standard Model. If the Higgs particle exists, we should find it after the Large Hadron Collider (LHC) has been taking data for three years or so (around 2012). If the Higgs is not found at the LHC, then the Standard Model will be wrong as formulated.
With those admittedly large qualifications, and the realization that the Standard Model is definitely not the end word in subatomic physics, it is a very successful theory which describes experimental observations amazingly well. Its prediction of the mass of the Z boson, for example, agrees with experiment exactly, up to each one’s error bar of about 0.2%. It also predicted the W and Z bosons and the charm and top quarks before they were observed, with experiments later confirming these predictions. A theory that has predicted 4 new particles and agrees with experiments to 3 decimal places is definitely doing something right. Any new theory would have to incorporate the Standard Model as an effective theory, similar to the recovery of Newtonian gravity in certain limits from general relativity. It is by far the best theory that we have to describe the subatomic world and most competing theories are extensions of the Standard Model in some way, shape, or form. Its successes insure that it will have a place in physics even after a new theory has displaced it as a more fundamental description of reality.
