" The first theory of this kind was proposed in 1974 by Georgi and Glashow, using SU(5) as the unifying group. A distinguishing characteristic of these GUTs is that, unlike the Standard model, they predict the existence of proton decay . In 1999, the Super-Kamiokande neutrino observatory reported that it had not detected proton decay, establishing a lower limit on the proton half-life of 6. 7× 1032 years. This and other experiments have falsified numerous GUTs, including SU(5). Another effort to address the first defect has been to develop Preon models which attempt to set forth a substructure of more fundamental particles than those set forth in the Standard Model. In addition, there are cosmological reasons why the standard model is believed to be incomplete. Model Power Trains Within it, matter and antimatter are symmetric. While the preponderance of matter in the universe can be explained by saying that the universe just started out this way, this explanation strikes most physicists as inelegant. "

" (2) prescriptive, i. e. , the model prescribes the original. If the deviation from model to original cannot be tolerated then the original has to be changed. Design models are in a prescriptive reference mode to their originals, i. e. , the implementation. Model Toy Trains (3) idealizing, i. e. "