This nOde last updated January 27th, 2019 and is permanently morphing...
"The present" raises the question: "How is
it that all sentient beings experience now at the same time?" There is
no logical reason why this should be the case and no easy answer to the
Buddhism and many of its associated paradigms emphasize the importance of living in the present moment — being fully aware of what is happening, and not dwelling on the past or worrying about the future. This does not mean that they encourage hedonism, but merely that constant focus on one's current position in space and time (rather than future considerations, or past reminiscence) will aid one in relieving suffering. They teach that those who live in the present moment are the happiest. A number of meditative techniques aim to help the practiser live in the present moment.
The original intent of the light cone
diagram was to portray a 3-dimensional object having access to the past,
present, and future in the present moment (4th dimension).
It follows from Albert Einstein's Special Theory of Relativity that there is no such thing as absolute simultaneity. When care is taken to operationalise "the present", it follows that the events that can be labeled as "simultaneous" with a given event, can not be in direct cause-effect relationship. Such collections of events are perceived differently by different observers. Instead, when focusing on "now" as the events perceived directly, not as a recollection or a speculation, for a given observer "now" takes the form of the observer's past light cone. The light cone of a given event is objectively defined as the collection of events in causal relationship to that event, but each event has a different associated light cone. One has to conclude that in relativistic models of physics there is no place for "the present" as an absolute element of reality. Einstein phrased this as: "People like us, who believe in physics, know that the distinction between past, present, and future is only a stubbornly persistent illusion".
In physical cosmology, the present time in
the chronology of the universe is estimated at 13.8 billion years after
the singularity determining the arrow of time. In
terms of the metric expansion of space, it is in the
dark-energy-dominated era, after the universe's matter content has
become diluted enough for metric expansion to be dominated by vacuum
energy (dark energy). It is also in the universe's Stelliferous Era,
after enough time for superclusters to have formed (at about 5 billion
years), but before the accelerating expansion of the universe has
removed the local supercluster beyond the cosmological horizon (at about
150 billion years).
Philosophical presentism is the view that
neither the future nor the past exist. In some versions of presentism,
this view is extended to timeless objects or ideas (such as numbers).
According to presentism, events and entities that are wholly past or
wholly future do not exist at all. Presentism contrasts with eternalism
and the growing block theory of time which hold that past events, like
the Battle of Waterloo, and past entities, like Alexander the Great's
warhorse Bucephalus, really do exist, although not in the present.
Eternalism extends to future events as well.
Augustine of Hippo proposed that the present is analogous to a knife edge placed exactly between the perceived past and the imaginary future and does not include the concept of time. This should be self-evident because, if the present is extended, it must have separate parts – but these must be simultaneous if they are truly a part of the present. According to early philosophers, time cannot be simultaneously past and present and hence not extended. Contrary to Saint Augustine, some philosophers propose that conscious experience is extended in time. For instance, William James said that time is "the short duration of which we are immediately and incessantly sensible". Other early presentist philosophers include the Indian Buddhist tradition. Fyodor Shcherbatskoy, a leading scholar of the modern era on Buddhist philosophy, has written extensively on Buddhist presentism: "Everything past is unreal, everything future is unreal, everything imagined, absent, mental... is unreal. Ultimately, real is only the present moment of physical efficiency [i.e., causation]."
According to J. M. E. McTaggart's "The Unreality of Time", there are two ways of referring to events: the 'A Series' (or 'tensed time': yesterday, today, tomorrow) and the 'B Series' (or 'untensed time': Monday, Tuesday, Wednesday). Presentism posits that the A Series is fundamental and that the B Series alone is not sufficient. Presentists maintain that temporal discourse requires the use of tenses, whereas the "Old B-Theorists" argued that tensed language could be reduced to tenseless facts (Dyke, 2004).
Arthur N. Prior has argued against un-tensed theories with the following ideas: the meaning of statements such as "Thank goodness that's over" is much easier to see in a tensed theory with a distinguished, present now. Similar arguments can be made to support the theory of egocentric presentism (or perspectival realism), which holds that there is a distinguished, present self.
In modern theory of relativity, the conceptual observer is at a geometric point in both space and time at the apex of the 'light cone' which observes the events laid out in time as well as space. Different observers may disagree on whether two events at different locations occurred simultaneously depending on whether the observers are in relative motion (see relativity of simultaneity). This theory depends upon the idea of time as an extended thing and has been confirmed by experiment, thus giving rise to a philosophical viewpoint known as four dimensionalism. Although the contents of an observation are time-extended, the conceptual observer, being a geometric point at the origin of the light cone, is not extended in time or space. This analysis contains a paradox in which the conceptual observer contains nothing, even though any real observer would need to be the extended contents of an observation to exist. This paradox is partially resolved in relativity theory by defining a 'frame of reference' to encompass the measuring instruments used by an observer. This reduces the time separation between instruments to a set of constant intervals.
Some of the difficulties and paradoxes of presentism can be resolved by changing the normal view of time as a container or thing unto itself and seeing time as a measure of changing spatial relationships among objects. Thus, observers need not be extended in time to exist and to be aware, but they rather exist and the changes in internal relationships within the observer can be measured by stable countable events.