The block universe model is a conceptual model rather than a physical theory, although it is embraced by a number of modern theories.
The concept can be traced back to Parmenides in the late sixth or early fifth century BCE. The only work of his that survives is a poem, "On Nature", which describes two views of reality: 'the way of truth' (Greek: aletheia), which explains how all reality is timeless and uniform with change being impossible, and 'the way of opinion' (Greek: doxa), which explains the world of appearances, and how our sensory faculties lead to false conceptions.
In more recent times, the term is often conflated with eternalism, perdurantism, and even relativity, but these all have specific nuances of their own that get overlooked. The conflation with the space-time of relativity is particularly prevalent, and yet even the term 'block universe' can be traced back to the late 1800s, predating both Einstein's and Minkowski's work in this area.
A static block universe has no special present moment as all times are considered to coexist and be equally real (i.e. eternalism), which in turn means there can be no temporal flow. These are considered to have a psychological origin as mental states must supervene entirely on immutable physical states. The classical conception in philosophy sees time as a dimension orthogonal to the spatial ones, described as four-dimensionalism, and thus implies absolute time, which clashes with special relativity.
The 'growing block universe', as advocated by C. D. Broad, posits that the past exists but not the future, but the physicality associated with the 'laying down' of new times requires a special absolute present moment throughout the universe, and that also clashes with special relativity.
The space-time of relativity has been proved to constitute a type of block universe (cf. Rietdijk–Putnam argument), but this differs markedly from the classical four-dimensional concept. Space-time has a specific non-Euclidean geometry, even in special relativity, but time is only defined relative to the frame of reference for some hypothetical observer. In other words, time cannot be defined in terms of the underlying continuum alone, and this places a distinction between modern conceptions of the block universe and eternalism. Rather than saying that all times are equally real, we can only say that all points in space-time are equally real.
Other variants of the block universe model may also involve space and time emergent from an isotropic continuum. The thing all variants of the model have in common is an absence of presentism in any form.
As for evidence, there is no scientific evidence that directly confirms or refutes the model, just as with the case for presentism, and this means that it is equally viable. How we interpret experimental evidence is dictated by our experience of time, and so the model appears to run counter to our experience, but not to mathematical treatment, which is applicable in both models. An advantage of a block universe model is that it does not require the additional experiential axioms that we must apply in our interpretation of the mathematics.
The modern conception presented in The Parallax of Physics is scientifically grounded, but distinct from the mathematical model that we call space-time.
This page is also located via https://block-universe.com.