Relativity and the Block Universe: What physics avoids facing

When the very way of posing a question is fixed for over a century, it is not surprising that the answers remain confined within the original framework. This repetition can sometimes stem from a form of ipsedixitism — the acceptance of a statement solely because it comes from a recognized authority, without critical examination. Yet it is entirely legitimate — and even necessary — to approach a subject from a different angle in order to test its limits.

So I frame things differently, in three logical steps:

1. First question: 
Does the "invariance of the speed of light in one-way propagation" imply the relativity of simultaneity "at the physical level", and not merely as a convention of dating events? 
→ "Yes." And this should be recognized as a direct consequence of the postulate. However, on this point, ambiguity persists: simultaneity is indeed said to be relative, but "discussions often remain at the level of appearances or timing conventions", without ever clearly stating that this implies a relativity of the very "existence" of events. 
Yet this is a known implication, since we routinely speak of the "block universe" model, in which past, present, and future coexist within a 4D structure. 
In other words, the idea is accepted, but its full consequences are avoided.
As for me, I take this ontological aspect seriously, and I carry the reasoning through to the end — which, curiously, physicists do not. They stop at the operational level. That is a mistake.

2. Second question: 
Does this relativity of simultaneity, when all its implications are taken into account — as in the shuttle and missile objection — not lead to a logical contradiction with itself, particularly regarding the existence or non-existence of an event depending on a change of reference frame? 
→ "Yes." For if one and the same fact — a launched missile — can be said to be "real" in one frame and "not yet realized" in another, then we are dealing with a contradiction in being, not just in measurement.

3. Third question: 
Does the affirmative answer to the first two questions lead us to challenge the invariance of the speed of light in a one-way direction, "at least as a universal axiom" applicable in all situations? 
→ "Yes." For a logical contradiction in the consequences of a postulate calls into question the postulate itself.

Two Incompatible Logics at the Heart of Relativity

To assert that light has traveled from point A to point B at speed c, one must be able to assume that, at a given instant, it was located at a specific position between A and B. In other words, this requires the ability to assign a common time to spatially separated points — that is, to points separated by a spacelike interval, which, according to relativity, are not connected by a causal relation.

This is where an internal tension within relativity becomes apparent. It relies on two distinct logical frameworks:
– a logic specific to timelike and lightlike intervals, where causality is preserved;
– another applying to spacelike intervals, where no causal connection can be established.

The difficulty arises when a change of inertial frame allows a temporal order, defined within a causal framework, to be transposed into a region of spacetime where such a framework is no longer valid.

Let us take an example: far behind the train, hundreds of billions of kilometers away, a light ray is emitted (event 1). For both observers standing on the station platform, this event occurs while they are at rest in the same inertial frame.

After this moment, one of the two station observers accelerates and then joins the observer on the train—before, according to the latter, the light ray has been emitted.

The station observer who remained at rest says to the one who accelerated: “The light ray was indeed emitted when you were still in the same inertial frame as I was, before your acceleration. In fact, I received it at such-and-such a date.” This is a lightlike interval. And since both observers were in the same inertial frame at that time, this dating must also be valid for the one who later changed frame.

But the train observer replies: “When you joined me, the light ray had not yet been emitted. It was only emitted later. In fact, we both received it on such-and-such a date.” This, again, is a lightlike interval. And since, at that point, the observer who changed frame is now in the same frame as the train observer, this dating must also be valid for him.

The result is a contradiction: two different datings are attributed to the same event for same observer, in two distinct configurations. In both cases, the dating is based on a lightlike interval—that is, an interval in which causality is supposed to be preserved. If we accept that the event (the emission of the light ray) actually occurred, then the same observer cannot assign it two different dates, both based on causal relations. This contradiction highlights an internal inconsistency if one grants a physical reality to events while maintaining the relativity of simultaneity as a real property of the physical world.

The causal approach in relativity is a convention that depends on the invariance postulate. And if this postulate leads to a logical contradiction (as revealed by the shuttle-missile objection), then the entire framework becomes open to question.

Conclusion :

Within the dominant paradigm, questions are rarely reframed from a different perspective. The system’s coherence is preserved by interpreting apparent contradictions as technical or conventional issues. Paradoxes linked to the relativity of simultaneity are reduced to problems of clock synchronization. More importantly, it is often unclear whether the invariance of the speed of light refers to the one-way or the two-way case — and this ambiguity prevents a proper examination of the logical consequences that true one-way invariance would entail.

Such resistance can be understood. But just because a system has endured over time doesn’t mean it is free from inconsistency. When a flaw emerges, one must still have the courage to point it out and to explore all its consequences.

Convention or Physical Reality? A Choice Must Be Made

If the discussion keeps going in circles, it is often because a fundamental point has not been clearly stated from the outset. It is therefore necessary to pose the question in a simple and decisive way:

Should the relativity of simultaneity be regarded as a mere convention of synchronization (operational in nature), or as a real physical property of the world?

If it is of conventional nature, then a line of reasoning based on the existence of events and their dating through lightlike intervals — where causality is assumed to be preserved — cannot be invalidated by arguments relying solely on that convention. A convention cannot override a logical contradiction arising from a reasoning based on real events.

If, on the contrary, the relativity of simultaneity is held to be a physical property — in other words, if it reflects a reality of space-time — then all of its logical consequences must be acknowledged, including those revealed by the so-called shuttle-and-missile objection. Among them is a striking contradiction: the same observer, after changing inertial frames, can assign two different dates to the same event, in configurations where causality is supposed to be preserved.

This is not a matter of subjective interpretation, but of a clear-cut logical alternative:
– either the relativity of simultaneity is conventional,
– or it is physical — but in that case, one must accept everything it entails, even what is unsettling.

It is therefore essential that this question be asked clearly — and that the answer be equally clear.