Eternalism's strongest scientific support comes from special relativity's relativity of simultaneity: two events that one observer, moving at a certain velocity, judges to happen at exactly the same moment, another observer, moving differently, will judge to happen at different times, with neither observer's frame of reference privileged as the correct one, which makes the very idea of a single, objective present moment shared across the universe difficult to sustain physically.
If there is no privileged present, eternalists argue, then there is no principled physical basis for saying the past has ceased to exist while the future has not yet begun to; instead, all events at all times are equally real, differing from one another only in their position along the time dimension, much as different places differ only in their position along a spatial dimension, an analogy that gives the view its common name, the block universe. On this picture, change and the felt passage of time are not features built into the fabric of reality itself but features of how a conscious observer, embedded at one location within the block, experiences moving through it, in something like the way a person reading a novel experiences the story unfolding page by page even though the entire book, beginning to end, already exists complete on the shelf.