‘Space and Time are the modes by which we think, not the conditions in which we live’–Albert Einstein
‘The only reason for time is so that everything doesn't happen at once’–Albert Einstein
‘Time is an illusion. Lunchtime doubly so’–Douglas Adams
SPACE AND TIME IN COSMOLOGY
The question about the nature of space and time is intimately linked with the question of cosmology: Did space and time have a beginning? Do they go on forever? Space and time form the framework for our picture of cosmology, while our large-scale view of the Universe puts the limits on what space and time are.
The nature of space and time underwent a radical change from Newton to Einstein. As Newton set out in his Principia Mathematica, space and time was an unchanging Aristotelian background to the unfolding play of particles and waves. But even this seemingly innocuous assumption caused Newton problems. Gravity acted instantaneously everywhere (action at a distance); a radical idea for the 1770s used to the idea that every effect had a direct cause. If the Universe was infinite in extent, the forces acting on any given point would depend instantaneously on the influence of all of the matter throughout the Universe. But because the volume of space increases rapidly with distance these forces would accumulate and increase without limit in an infinite Universe. These problems were mainly swept under the carpet as Newtonian gravity clearly gave an excellent local approximation to the motion of the moon and planets.