Space is the boundless three-dimensional extent in which objects and events have relative position and direction. Physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum known as spacetime. The concept of space is considered to be of fundamental importance to an understanding of the physical universe. However, disagreement continues between philosophers over whether it is itself an entity, a relationship between entities, or part of a larger structure.
Debates concerning the nature of space date back to antiquity; namely, to treatises like Aristotle’s Physics and Euclid’s Elements. In the nineteenth century, two debates dominated the philosophy of space. The first debate concerned the whether points or extended objects occupied space; this was resolved by Immanuel Kant’s Critique of Pure Reason (1781), where he argued that neither points nor extended objects can occupy space: only relationships can do so. The second debate concerned the geometry of space; this was resolved by Bernhard Riemann’s 1854 essay “On the hypotheses which lie at the foundations of geometry”. He showed that there are infinitely many possible geometries for spaces with any number of dimensions. These results were incorporated into Albert Einstein’s theory of relativity (1905), which transformed our understanding not just of geometry but also mechanics and electromagnetism by unifying them under one set of equations valid for all observers regardless their state of motion.
The nature and structureof spacetime has been further explored in recent years through theories such as string theory and loop quantum gravity which attempt to unify Einstein’s theory with quantum mechanics – something that Einstein himself was not able to do despite his lifelong efforts. One consequenceof these theories is that they imply the existenceof extra spatial dimensions beyond those we are awareof through our everyday experience; anotheris that they predict various novel phenomena suchas wormholes connecting distant regionsof spacetime or microscopic black holes createdin high-energy collisions at particle accelerators