# Space

**Space** — The definition of space in physics is contentious. Various concepts used to try to define space have included:

— the structure defined by the set of “spatial relationships” between objects

— a manifold defined by a coordinate system where an object can be located.

— the entity that stops all objects in the universe from touching one another

In classical physics, space is a three-dimensional Euclidean space where any position can be described using three coordinates. relativistic physics examines spacetime rather than space; spacetime is modeled as a four-dimensional manifold.

Philosophical questions concerning space include: Is space absolute or purely relational? Does space have one correct geometry, or is the geometry of space just a convention?

Historical Eminences who have taken sides in these debates include Isaac Newton (space is absolute), Gottfried Leibniz (space is relational), and Henri Poincar (spatial geometry is a convention).

Two important thought-experiments connected with these questions are: Newton’s bucket argument and Poincar’s disc-world.

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