The Matter of Time (1994–2005) is Richard Serra’s most complete rumination on the physicality of space and the nature of sculpture. Permanently installed in the largest gallery of the Frank Gehry-designed museum, seven new commissioned sculptures join Serra’s Snake (1994–97)—created for the museum’s inauguration—and comprise a site-specific installation of a scale and ambition unrivalled in modern history. The Matter of Time enables the spectator to perceive the evolution of the artist’s sculpted forms, from his relatively simple double ellipse to the more complex spiral. The final two works in this evolution are built from sections of toruses and spheres to create environments with differing effects on movement and perception. Shifting in unexpected ways as viewers walk in and around them, these sculptures create a dizzying, unforgettable sensation of space in motion.