Do We Live in a Block Universe?
A Series Exploring Causality in Relativity
Einstein’s theory of relativity transformed our view of the universe, challenging our most basic intuitions about time and space. These changes took an even more radical turn when Hermann Minkowski introduced the notion of spacetime: a four-dimensional structure in which space and time play seemingly identical roles. Einstein himself initially resisted this development before later embracing it.
But some thinkers have taken Minkowski’s picture further, suggesting it compels us to view spacetime as a fixed ‘block’ where past, present, and future all coexist, and the flow of time is an illusion. If true, the future would be as settled as the past, and our experience of choice and genuine change merely illusory. This idea, the block universe, is often presented as scientific justification for predetermination: that everything that will ever happen has, in some sense, already happened.
Does spacetime physics really force this view upon us? This series argues that it does not. The step from physical theory to metaphysical conclusion rests on subtle misunderstandings, especially about the relativity of simultaneity: the result from relativity theory that forms the crux of the block universe argument.
Why This Series?
The block universe idea persists partly through lack of clarity about the key concepts and the mechanics of using different reference frames. Yet discussions of the subject tend either to remain at a popular level, which leaves crucial distinctions unexplored, or to become more technical without fully clarifying the key concepts.
This subject demands precision. Relativity is notorious for its ‘paradoxes’: aspects that appear self-contradictory even to physicists on first encounter. Students must grapple with these paradoxes as part of learning the theory. Physicists debated the ’twin paradox’ for decades before atomic clocks settled the matter in the 1970s, despite the physics pointing clearly to the resolution all along. The concepts aren’t mathematically complex, but they’re profoundly counter-intuitive, requiring us to rethink fundamental assumptions about reality. Mastering them takes time and repeated engagement. A shaky grasp invites serious error.
Unlike the twin paradox, the block universe debate appears immune to experimental testing. This makes careful reasoning essential. My aim in these essays is to provide that clarity. Proponents of the block universe correctly recognise that relativity demands we rethink time and existence. But I contend they misidentify what that rethinking requires. The third essay in this series illuminates what the relativity of simultaneity actually reveals: insights that are real, but not those claimed by the block universe argument.
The Essays: A Guide
I’ve written a series of three essays addressing different aspects and audiences, plus two companion explainers that fill in the physics.
Rethinking the Andromeda Paradox
The first essay in the series examines a simple, popular thought experiment known as the Andromeda Paradox. This serves as a useful introduction for readers new to the block universe idea. The reasoning is accessible to a general audience, and the flaw, once explained, is relatively straightforward to grasp. Yet the error here is essentially the same as in academic arguments, making this a good entry point for the key issues.
This essay can be read with only a brief glossary for orientation. By using Minkowski’s spacetime diagrams I am able to avoid the need for formal mathematics. These deceptively simple yet powerful visual tools allow rigorous analysis whilst remaining accessible. For readers who still find the ideas difficult to grasp (or to accept), there are links from the glossary to the explainer essays (see below).
The second essay addresses more technical versions of the argument, including the forms independently developed by Rietdijk and Putnam in the 1960s. The explainer essays will be particularly helpful here, though not essential.
The final essay presents a framework for thinking about time and space in relativity that respects what the physics tells us whilst making sense of the conceptual changes relativity requires. I suggest that the debate has not fully worked through these adjustments, leading to ideas like the block universe.
A Guide to the Language of Relativity
The first of the ’explainer’ essays is written in a series of short sections, each an expansion of (and linked from) an item in the first essay’s glossary. The key ideas, especially those most challenging, are explained in a level of detail that would have interrupted the argument in the main essays.
Explainer 2 goes deeper, explaining how the relativity of simultaneity and related concepts arise from the theory. This will help readers who want more than assertions about relativity’s strange claims; those who rightly feel that deeper knowledge of the physics will aid philosophical understanding; and those simply curious to understand this fascinating subject more fully. The spacetime diagrams really come into their own here, allowing us to see how the structure of the theory leads to its counter-intuitive results.
October 2025