Henri Bergson posited that memory is an experience and a process that does not limit itself to preserving the past, but also applies itself in, and to, the present. Déjà vu, he further reasoned, occurs in moments of conscious perception of this automatic preservation of the past in the present -- an experience in which we are made aware that we’re remembering what is happening as it happens.
Cinema does this as well - it is a spectral (i.e. intangible, immaterial, conjured by tricks of the light) visitation of the past on and in the present. No genre or convention in film embodies this more cogently than time travel cinema in which the future or the past (re)turns to the present, usually with the intention of saving the world - or at least some part of it - from some future evil.
One such film is Rian Johnson’s Looper. In the film, present-day Joe is visited by future Joe, who needs to save the future from the evil Rainmaker by killing him in the past. Through this visitation, the future and past both literally present themselves. They haunt the present: they are conjured up all at once in real-time, and this simultaneity is portrayed not only through the injection of characters from the future in the present, but also by the presence of the past depicted by way of aestheticizing the ordinary. The locations where Old Joe confronts his (and the Rainmaker's) past are depictions of Americana and of pastoral imagery (e.g. train car diners, corn fields, trains, farms) - imagery, that is, which are deeply rooted in nostalgia, or a longing for the past (nostalgia has its roots in the Ancient Greek nostos, “return home” and algos, “woe, pain”).
The omnipresence of time functions in Looper and similar time travel films as a mechanism through which the importance of presence -- and of action in the present -- is emphasized. If past and future have both left their homes to visit the present, then the past and the future have ceased to exist: everything rides on the choices we make in the present, simply because the present is all that we have.
In other words: when it comes to saving the world in Looper and in other such films, there is no time like the present, because there is no time but the present.