Time is an elusive concept. There are many definitions for time. Time is a non-spatial continuum in which events occur in apparently irreversible succession from the past through the present to the future. Time is an interval separating two points on this continuum; a duration; a number, as of years, days, or minutes, representing such an interval; a similar number representing a specific point on this continuum, reckoned in hours and minutes.
There are many questions concerning time. Scientists have studied time for many years now. The general theory of relativity and quantum mechanics are the two most fundamental theories of physics, and the Big Bang theory is the leading theory of cosmology. These relate to time. According to relativity and quantum mechanics, space-time is, loosely speaking, a collection of points called “space-time locations” where the universe’s physical events occur. Space-time is four-dimensional and a continuum and time is a distinguished, one-dimensional sub-space of this continuum. Any interval of time–any duration–is a linear continuum of instants. So, duration has a point-like structure similar to the structure of an interval of real numbers; between any two instants there is another instant, and there are no gaps in the sequence of instants.
Was there an infinite amount of time in the past? Aristotle argued “yes,” but by invoking the radical notion that God is “outside of time,” St. Augustine declared, “Time itself being part of God’s creation, there was simply no before!” (That is, no time before God created everything else but Himself). So, for theological reasons, Augustine declared time had a finite past. After advances in astronomy in the late 19th and early 20th centuries, the question of the age of the universe became a scientific question. With the acceptance of the classical Big Bang theory, the amount of past time was judged to be less than 14 billion years because this is when the Big Bang began.
The assumption is that time does not exist independently of the space-time relations exhibited by physical events. Recently, however, the classical Big Bang theory has been challenged. There could be an infinite amount of time in the past according to some proposed, but as yet untested, theories of quantum gravity based on the assumptions that general relativity theory fails to hold for infinitesimal volumes. These theories imply that the beginning of the Big Bang was actually an expansion from a pre-existing physical state. There was never a singularity. In that case our Big Bang could be just one bang among other bangs throughout an infinite past of the landscape.
Will there be an infinite amount of time in the future? Probably. According to the classical theory of the Big Bang, the answer depends on whether events will keep occurring. The best estimate from the cosmologists these days is that the expansion of the universe is accelerating and will continue forever. There always will be the events of galaxy clusters getting farther apart, and so future time will have an infinite duration, even though gravity will continue to compact much of the matter into black holes.
