The problematic nature of synchronizing clocks consists of the use of the condition of the equality of the speed of light in opposite directions for clock synchronization in the STR, while the experimental verification of this equation is considered impossible in principle. Ein- stein, by alluding to the impossibility of measuring velocity in one direction without arbitrary assumptions, assumed that the speed of light propagation in a vacuum from point A to point B is equal to the speed of light passing from B to A. Does nature not permit us to measure the speed of light in one direction without arbitrary assumptions? Did S. Marinov and his followers measure the one way speed? In the paper method and device for measuring the speed of light in a single direction without arbitrary assumptions are discussed. A possible cause of the boundedness of the velocity of material objects is demonstrated without reference to the provisions of the special theory of relativity. A condition is formulated on the basis of which the assumption of the movement of material objects at any arbitrarily prescribed velocities proves to be self-contradictory in instances when the arbitrarily prescribed velocities of the objects exceed a certain value. This condition consists of the existence of massles signals and particles that are propagated in space and inside material objects at a velocity greater than any prescribed velocity of the material objects and particles that do have mass.