According to the theory of relativity, particles having nonzero rest mass can approach, but not reach, the speed of light, as their mass would become infinite at that speed. On the other hand, particles with zero rest mass, like photons, always travel at the speed of light. Theorists have argued that nothing in principle prohibits the existence of a third class of particles, named tachyons, whose velocity always exceeds that of light. What effect would a loss of energy have on a tachyon’s speed? Discuss

Source: The Free Dictionary

The Mali Empire flourished in West Africa between the 13th and 16th centuries. A trading empire, it developed from the upper Niger River state of Kangaba, whose inhabitants were middlemen in the gold trade in ancient Ghana. It expanded for a few centuries but eventually outgrew its political and military strength, and many of its subject areas revolted. Which Mali ruler distributed so much gold during his pilgrimage to Mecca that the metal was devalued in Egypt for more than a decade? Discuss

Source: The Free Dictionary

Simonetta was the Genoese wife of the Italian nobleman Marco Vespucci of Florence. Renowned as the greatest beauty of her age, she was the subject of countless portraits, including many by the Italian master Sandro Botticelli. Some claim that the goddess depicted in Botticelli’s masterpiece, Birth of Venus, was modeled after Simonetta, even though she died at the age of 22—several years before it was completed. What fact about Botticelli’s burial place lends credence to the theory? Discuss

Source: The Free Dictionary

In order for certain insects, crustaceans, and reptiles to grow, they must periodically shed, or molt, their outer layer of skin or other covering in a process known as ecdysis. Prior to shedding, a new soft and expandable layer is laid down underneath the existing one. Then the inner layers of the old cuticle are digested by a molting fluid secreted by the epidermal cells, the animal emerges from the old covering, and the new cuticle hardens. How often do insects undergo ecdysis? Discuss

Source: The Free Dictionary