## Articles

A model of backward causation in which the future affects the past could help unite quantum mechanics and general relativity – and satisfy a challenge thrown down almost a century ago by Arthur Eddington.

Mapping the ancestral history of spacetime in an effort to unite quantum mechanics and general relativity.

A new model argues the forces between particles in the early universe loosed time’s arrow, creating temporal order from chaos.

Can you find a path through on this city map that crosses every bridge exactly once? Euler's answer to this problem started off the filed of graph theory.

Can you move a knight on a chessboard so that it visits every square exactly once? Euler was one of the first to analyse this problem systematically, but some questions about it are still open today.

Euler may not have cracked this problem completely, but it led to a lot of important work, including on what we today know as sudoku.

This surprising result about 3D shapes tells us something deep about the nature of space.