and Hendrik Lorentz, which assumes an absolute (though experimentally indiscernible) frame of reference, no twin paradox arises due to the fact that clock slowing (along with length contraction and velocity) is regarded as an actuality, hence the actual time differential between the reunited clocks. That interpretation of relativity, which John A. Wheeler calls "ether theory B (length contraction plus time contraction)", did not gain as much traction as Einstein's, which simply disregarded any deeper reality behind the symmetrical measurements across inertial frames. There is no physical test which distinguishes one interpretation from the other. In 2005, Robert B. Laughlin (Physics Nobel Laureate, Stanford University), wrote about the nature of space: "It is ironic that Einstein's most creative work, the general theory of relativity, should boil down to conceptualizing space as a medium when his original premise [in special relativity] was that no such medium existed ... The word 'ether' has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it rather nicely captures the way most physicists actually think about the vacuum. ... Relativity actually says nothing about the existence or nonexistence of matter pervading the universe, only that any such matter must have relativistic symmetry (i.e., as measured)." In Special Relativity (1968), A. P. French wrote: "Note, though, that we are appealing to the reality of A's acceleration, and to the observability of the inertial forces associated with it. Would such effects as the twin paradox exist if the framework of fixed stars and distant galaxies were not there? Most physicists would say no. Our ultimate definition of an inertial frame may indeed be that it is a frame having zero acceleration with respect to the matter of the universe at large." See also Bell's spaceship paradox Clock hypothesis Ehrenfest paradox Herbert Dingle Ladder paradox List of paradoxes Supplee's paradox Time dilationTime for the StarsPrimary sources Secondary sources Further reading The ideal clock The ideal clock is a clock whose action depends only on its instantaneous velocity, and is independent of any acceleration of the clock. Gravitational time dilation; time dilation in circular motion External links Twin Paradox overview in the Usenet Physics FAQ The twin paradox: Is the symmetry of time dilation paradoxical? From Einsteinlight: Relativity in animations and film clips. FLASH Animations: from John de Pillis.'' (Scene 1): "View" from the Earth twin's