Proposal for an experiment to demonstrate the block universe

📝 Abstract

While the concept of the block universe has a most respectable scientific provenance, many physicists nevertheless do not accept that future events are just as embedded in spacetime as are those of the present and the past. This paper proposes an experiment to demonstrate the block universe using interplanetary distances and high relative speeds such as those accessible through the NASA Mars Reconnaissance Orbiter. The proposed experiment hinges on signals exchanged between Earth and the Orbiter which reveal a time interval of some tens of milliseconds in the future of the Earth which is already in the past of the Orbiter. Since this experiment can be performed at any time, and since the magnitude of the time interval can in principle be increased in proportion to the distances and speeds over which it is performed, an observer can always be found for whom the past is in the future of another observer. The only explanation that fits these observations is a block universe in which all events in the past, present and future of any observer are equally enfolded into spacetime.

💡 Analysis

While the concept of the block universe has a most respectable scientific provenance, many physicists nevertheless do not accept that future events are just as embedded in spacetime as are those of the present and the past. This paper proposes an experiment to demonstrate the block universe using interplanetary distances and high relative speeds such as those accessible through the NASA Mars Reconnaissance Orbiter. The proposed experiment hinges on signals exchanged between Earth and the Orbiter which reveal a time interval of some tens of milliseconds in the future of the Earth which is already in the past of the Orbiter. Since this experiment can be performed at any time, and since the magnitude of the time interval can in principle be increased in proportion to the distances and speeds over which it is performed, an observer can always be found for whom the past is in the future of another observer. The only explanation that fits these observations is a block universe in which all events in the past, present and future of any observer are equally enfolded into spacetime.

📄 Content

Proposal for an experiment to demonstrate the block universe Alan McKenzie Lately of University Hospitals Bristol NHS Foundation Trust, Bristol UK

Abstract

While the concept of the block universe has a most respectable scientific provenance, many physicists nevertheless do not accept that future events are just as embedded in spacetime as are those of the present and the past. This paper proposes an experiment to demonstrate the block universe using interplanetary distances and high relative speeds such as those accessible through the NASA Mars Reconnaissance Orbiter.
The proposed experiment hinges on signals exchanged between Earth and the Orbiter which reveal a time interval of some tens of milliseconds in the Earth’s future which is already in the Orbiter’s past. Since this experiment can be performed at any time, and since the magnitude of the time interval can in principle be increased in proportion to the distances and speeds over which it is performed, an observer can always be found for whom the past is in another observer’s future. The only explanation that fits these observations is a block universe in which all events in the past, present and future of any observer are equally enfolded into spacetime.

Introduction

Arguments over the question of free will can be traced back to the Ancient Greeks and doubtlessly stem from the millennia before recorded history. For many, Hermann Minkowski settled the debate with his formulation of spacetime and the resulting block universe, in which, for any observer, the future is just as embedded as the past and present. The theory was all the more credible, having “sprung from the soil of experimental physics” as Minkowski himself put it [1]. Sceptics, though, were encouraged by the burgeoning quantum theory, equally grounded in experiment, and which demonstrated the essential randomness of quantum events. So we are apparently left with fundamentally undetermined quantum outcomes in a completely “predetermined” block universe.

Any worthy theory of the universe must unravel this paradox to the satisfaction of both parties. Everett’s Many Worlds interpretation (MWI) [2] and its successors (e.g., [3], [4], [5]) go some way to resolving the dilemma, but not entirely: in MWI, while events in a given observer’s past and present are fixed as in the block universe, the future nevertheless contains an infinite number of branches. In order to obviate this problem, McKenzie [6] proposed a multiverse of individual, stand-alone block

2 universes populated with quantum outcomes determined at the multiverse level by a discrete formulation of the familiar equations of quantum mechanics.

A solution such as this is so radical, however, that any remaining doubts as to the validity of the block universe need to be readdressed. Even with strong support for the block universe from authors in the 1960s such as Rietdijk [7] and Putnam [8], who probably felt they had written the last words on the matter, the old arguments have resurfaced like the Hydra’s heads. Even the vivid encapsulation of these ideas in Penrose’s so-called Andromeda Paradox [9] did not satisfy a significant number of physicists, who regard Minkowski spacetime as an idealized concept not capable of accounting for the time evolution of real, complex systems (see, for instance, Ellis [10], Sorkin [11]).

In the final analysis, the problem seems to be this: while quantum uncertainty can be demonstrated directly (for instance, by a single-photon, two-slit experiment), it is only the underlying concepts of the block universe that are rooted in experiment (such as the null result of the Michelson-Morley experiment): no experiment has yet exposed the block universe directly.

Ingredients of an experiment

S V U event in Alice’s future time space information transmitted from V to U information transmitted from U to S Bob informs Alice of her future. This experiment would convince most of those who are sceptical about the Block Universe. Minkowski spacetime diagram

Figure 1: While this experiment might convince all but the most sceptical, it is clearly unrealistic. Nevertheless, it contains the ingredients of a more plausible experiment.

So that is the purpose of this paper – to propose an experiment that will demonstrate the block universe as directly as possible. Figure 1 shows the type of experiment that would be most likely to convince the majority of those who are sceptical about the block universe. If Alice’s future is “already written” (strictly a meaningless phrase

3 for a timeless block universe, but it captures the sentiment), then, if the information about her future could somehow be transmitted to Bob at an earlier time, he could, in turn, inform Alice of her future.

Of course, such an experiment is unachievable. Basically, it fails because it would require part of the wave fun

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