<P> The rate of change in the distance between two objects in a frame of reference with respect to which both are moving (their closing speed) may have a value in excess of c . However, this does not represent the speed of any single object as measured in a single inertial frame . </P> <P> Certain quantum effects appear to be transmitted instantaneously and therefore faster than c, as in the EPR paradox . An example involves the quantum states of two particles that can be entangled . Until either of the particles is observed, they exist in a superposition of two quantum states . If the particles are separated and one particle's quantum state is observed, the other particle's quantum state is determined instantaneously (i.e., faster than light could travel from one particle to the other). However, it is impossible to control which quantum state the first particle will take on when it is observed, so information cannot be transmitted in this manner . </P> <P> Another quantum effect that predicts the occurrence of faster - than - light speeds is called the Hartman effect: under certain conditions the time needed for a virtual particle to tunnel through a barrier is constant, regardless of the thickness of the barrier . This could result in a virtual particle crossing a large gap faster - than - light . However, no information can be sent using this effect . </P> <P> So - called superluminal motion is seen in certain astronomical objects, such as the relativistic jets of radio galaxies and quasars . However, these jets are not moving at speeds in excess of the speed of light: the apparent superluminal motion is a projection effect caused by objects moving near the speed of light and approaching Earth at a small angle to the line of sight: since the light which was emitted when the jet was farther away took longer to reach the Earth, the time between two successive observations corresponds to a longer time between the instants at which the light rays were emitted . </P>

Which of the following is closest to the speed of light in a vacuum