The concept of a "block-time" universe is closely related to the philosophy of time and the nature of temporal existence. In a block-time universe, also known as a "four-dimensionalist" view of time, the past, present, and future are all considered to exist simultaneously as an unchanging four-dimensional block.
According to this view, the universe is like a static, timeless entity that encompasses all events and moments, from the beginning of time to its end. In other words, the entire history of the universe, from the Big Bang to the eventual heat death or any other potential endpoint, is already fully determined and "preexistent" within this block of time.
This perspective challenges the traditional linear view of time, where events unfold sequentially from the past, through the present, and into the future. In the block-time view, the past, present, and future are all equally real and coexist, although they may be experienced subjectively as a succession of moments by conscious beings within the universe.
It's important to note that the block-time view is a philosophical and theoretical concept, primarily discussed in the realms of metaphysics and philosophy of time. There is ongoing debate among philosophers and physicists regarding the nature of time, but currently, there is no consensus on whether a block-time universe accurately represents the fundamental nature of reality.
In contemporary physics, time is often described within the framework of spacetime, as proposed by Albert Einstein's theory of general relativity. Spacetime is a four-dimensional manifold that combines three dimensions of space with one dimension of time. While general relativity allows for certain phenomena, such as time dilation and the bending of spacetime, it doesn't directly imply a block-time universe.
The question of whether a block-time universe exists and whether the past, present, and future are truly simultaneous is a topic of ongoing philosophical and scientific inquiry. It's worth noting that our current scientific understanding is based on the concept of a linearly progressing time, where events unfold sequentially.