The concept of time has been a subject of philosophical, scientific, and metaphysical inquiry for centuries. Various theories and perspectives on time have emerged over time.

These theories are not mutually exclusive, and some can coexist or be combined in various ways. The nature of time remains a complex and ongoing topic of exploration and debate in philosophy, physics, and other fields of study. Different theories of time have implications not only for our understanding of the physical universe but also for our philosophical and existential perspectives on life and reality.

Below is my attempt at categorizing these theories, based on different aspects that might make them incompatible with each other.

Theories on the Tense of Time

Presentism, Tensed Theory of Time

Presentism is the view that only the present moment is real. Past and future events do not have an objective existence but are mere abstractions. In other words, only the "now" exists, and the past has ceased to exist while the future has not yet come into existence. This perspective is often associated with a common-sense understanding of time but is somewhat challenged by modern physics, which suggests that all moments in time are equally real.

This is also known as "A-Theory of Time" (as coined by Richard Gale). A-theorists argue that events are not equally real at all points in time. The past events have occurred and no longer exist, while future events do not yet exist. Only the present moment is real.

This perspective often aligns with our everyday experience of time, where we feel the flow of time and our own existence moving through it.

Eternalism (Block Universe), Tenseless Theory of Time

Eternalism, also known as the block universe theory, posits that past, present, and future all exist simultaneously and are equally real. According to this view, time is a fourth dimension, and all events in time are fixed and unchanging, forming a static "block" of spacetime. This perspective is more aligned with the theory of relativity in physics, where spacetime is treated as a four-dimensional continuum.

This is also known as "tenseless theory" or the "B-Theory of Time". It argues that the flow of time is only a subjective illusion, that the past, present, and future are equally real, and that time is tenseless.

Growing Block Universe

The growing block universe theory is a compromise between presentism and eternalism. It suggests that the past and present are real, but the future is not. As time progresses, the future becomes real and adds to the growing "block" of spacetime. This view acknowledges the reality of the past and present while allowing for the openness of the future.

Theories on the Emergence of Time

Relational Theories

Relational theories of time emphasize the relational nature of time, suggesting that it exists as a relationship between events or objects. According to these theories, time is not an absolute entity but is defined by the relationships and interactions between different events or objects. The theory of relativity in physics, for instance, can be seen as a relational theory of time because it describes how the perception of time depends on one's relative motion and gravity.

Phenomenological Theories

Phenomenological theories of time focus on subjective human experiences of time. These theories explore how individuals perceive and experience time, taking into account psychological and cultural factors. They often emphasize the fluid and variable nature of human temporal experiences.

Quantum Theories of Time

In the realm of quantum physics, there are various interpretations of time. Some interpretations suggest that time is an emergent property of quantum processes, while others propose that time is fundamental but behaves differently at the quantum level compared to the macroscopic world.

Theories on the Start/End of Time

Cyclic or Recurrent Theories

Some theories propose that time is cyclical, with the universe undergoing a never-ending cycle of birth, expansion, contraction, and rebirth. These cyclic models suggest that the universe repeats itself over infinite cycles, and time is not linear but rather a continuous loop.

This is what many ancient cultures, like the Greek and the Hundu, believed. With he Universe going through cycles of creation and destruction.

The Technological Singularity Future

In some variants of this theory, it is believed that time might eventually come to an end when all human consciousness merge into a Singularity, into some form of intelligent machine.