A Brazilian physicist has resolved a paradox thrown up by Einstein's theory of relativity. According to the theory, objects travelling at close to the speed of light appear to get shorter when viewed by stationary observers. But from the viewpoint of those on the moving object, the observers - who are receding at close to the speed of light - appear shortened instead. Other dimensions remain the same. When these notions are applied to a submarine just below the water's surface, an inconsistency seems to arise. Spectators on an anchored ship would see the submarine shrink as it moves parallel to the surface at near-light speed. The resulting density increase would sink the vessel. The submarine crew would see the opposite: water rushing past them would contract and get denser, making the submarine more buoyant and causing it to rise. Relativity insists that both viewpoints are equally valid - so does the sub sink or swim?It sinks, says George Matsas of the State University of São Paulo in Brazil. He has used the theory of general relativity to include the effect of the different reference frames on the space-distorting force of gravity. Although the surrounding water does look denser to submariners, they also experience gravity as being stronger, creating a net downward force.
View: Full Article | Source: nature.com
