What is space

Space is the boundless three-dimensional extent in which objects and events have relative position and direction.^[1] Physical space is often conceived in three lineardimensions, although modern physicistsusually consider it, with time, to be part of a boundless four-dimensional continuumknown as spacetime. The concept of space is considered to be of fundamental importance to an understanding of the physical universe. However, disagreement continues betweenphilosophers over whether it is itself an entity, a relationship between entities, or part of aconceptual framework.

Debates concerning the nature, essence and the mode of existence of space date back to antiquity; namely, to treatises like the Timaeusof Plato, or Socrates in his reflections on what the Greeks called khôra (i.e. "space"), or in thePhysics of Aristotle (Book IV, Delta) in the definition of topos (i.e. place), or in the later "geometrical conception of place" as "spacequa extension" in the Discourse on Place(Qawl fi al-Makan) of the 11th-century Arab polymath Alhazen.^[2] Many of these classical philosophical questions were discussed in theRenaissance and then reformulated in the 17th century, particularly during the early development of classical mechanics. In Isaac Newton's view, space was absolute—in the sense that it existed permanently and independently of whether there was any matter in the space.^[3] Other natural philosophers, notably Gottfried Leibniz, thought instead that space was in fact a collection of relations between objects, given by their distance and direction from one another. In the 18th century, the philosopher and theologian George Berkeley attempted to refute the "visibility of spatial depth" in hisEssay Towards a New Theory of Vision. Later, the metaphysician Immanuel Kant said that the concepts of space and time are not empirical ones derived from experiences of the outside world—they are elements of an already given systematic framework that humans possess and use to structure all experiences. Kant referred to the experience of "space" in his Critique of Pure Reason as being a subjective "pure a priori form of intuition".

In the 19th and 20th centuries mathematicians began to examine geometries that are non-Euclidean, in which space is conceived as curved, rather than flat. According to Albert Einstein's theory ofgeneral relativity, space around gravitational fields deviates from Euclidean space.^[4]Experimental tests of general relativity have confirmed that non-Euclidean geometries provide a better model for the shape of spa