" If neutrinos have non-zero mass, they necessarily travel slower than the speed of light. Therefore, it would be possible to "overtake" a neutrino, choosing a reference frame in which its direction of motion is reversed without affecting its spin (making it right-handed) . Since then, physicists have revised the Standard Model to allow neutrinos to have mass, which make up additional free parameters beyond the initial 19. A further extension of the Standard Model can be found in the theory of supersymmetry, which proposes a massive supersymmetric "partner" for every particle in the conventional Standard Model. Supersymmetric particles have been suggested as a candidate for explaining dark matter. Although supersymmetric particles have not been observed experimentally to date, the theory is one of the most popular avenues of research in theoretical particle physics. References Textbooks Griffiths, David J. San Diego Model Railroad Museum (1987) Introduction to Elementary Particles, Wiley, John & Sons, Inc. ISBN 0471603864 Journal Articles Y. "

" It was sold in the beginning at a price of $850 when competing cars often cost $2000-$3000. By the 1920s the price had fallen to $300 (about $3,300 in 2005 inflation-adjusted dollars) because of increasing efficiencies of assembly line technique and volume. On May 27, 1927, Ford Motor Company stopped manufacturing Model T cars. However Model T motors continued to be produced until August 4, 1941. Almost 170,000 motors were built after car production ceased. Many Model T parts are still manufactured today, particularly fibreglass replicas of their distinctive bodies, which are popular for T-bucket style hot rods (as immortalized in the Jan and Dean surf music song, "Bucket T", which was later recorded by The Who). The Standard Model of particle physics is a theory which describes the strong, weak, and electromagnetic fundamental forces, as well as the fundamental particles that make up all matter. Model Railroad Simulator Developed between 1970 and 1973, it is a quantum field theory, and consistent with both quantum mechanics and special relativity. To date, almost all experimental tests of the three forces described by the Standard Model have agreed with its predictions. "