Scientific reference document
Drafting date: July 9, 2026
This document reflects the state of scientific knowledge at this date. Periodic updating is recommended.
The question seems simple. It is not.
In classical physics (Newtonian then Einsteinian), the future is determined: knowing the complete state of a system and the laws governing it, one can — in principle — calculate its evolution. The future already exists, virtually, in the equations. This is determinism. Laplace formulated the most radical expression with his demon: an intelligence knowing the position and velocity of all particles in the universe could predict the entirety of the past and future.
Quantum physics cracked this framework. Indeterminacy is no longer a measurement defect, but a fundamental property. The uncertainty principle (Heisenberg, 1927) shows that one can determine a particle's velocity or its position, but not both simultaneously with arbitrary precision. The more one is known, the less the other is. The wave function does not describe a determined state, but a superposition of possible states, which are determined at the moment of measurement (or collapse of the wave function).
A question remains open: does the future already exist in some form, or does it perpetually emerge from the present? Would the future be a field of possibilities, probabilistic, realized through the exercise of free will, sovereignty? And if the future pre-exists in the form of possibilities, does consciousness play an active role in the choice? Is free will itself an act of consciousness, or an independent mechanism? This tension between a future already written (block universe) and a future to choose (free will) is at the heart of the debates that follow.
This document examines the theoretical frameworks and experiments that address this question, distinguishing what is established from what is debated.
Origin: Yakir Aharonov (Tel Aviv University, Israel), Peter Bergmann and J. Lebowitz. Initially developed by Satosi Watanabe in 1955, formalized by Aharonov and collaborators.
Principle: In the standard formulation of quantum mechanics, a system is described by a state vector evolving from past to future. The TSVF (Two-State Vector Formalism) proposes a time-symmetric description: a system at instant t is characterized by two state vectors — one evolving from the past to t, the other evolving from the future to t (from a post-selection). The complete state of the system results from combining both.
Conceptual consequence: The future (via post-selection) plays a role in describing the present state. The system "knows" where it comes from and where it goes. This is not causal influence in the classical sense, but a description that gives the future an informational role.
Associated experiments: Weak measurements, developed by Aharonov, Albert and Vaidman, allow extracting information about pre- and post-selected systems without causing complete collapse of the wave function. Results experimentally confirmed in several laboratories.
Publications: Aharonov, Bergmann & Lebowitz, Physical Review (1964). Recent review: Vaidman, Lecture Notes in Physics (Springer). Dedicated entry in Stanford Encyclopedia of Philosophy.
Status: Mathematically rigorous framework, compatible with standard quantum mechanics. Ontological interpretation (the future truly influences the present) debated.
Origin: John Archibald Wheeler (USA, 1911–2008), one of the major physicists of the 20th century (Bohr collaborator, Feynman PhD supervisor). Idea expressed from 1978, formally published afterward.
Principle: In a Young's double-slit experiment, Wheeler proposes deciding after the photon has passed through the slits (but before detection) whether to observe the path taken (particle) or the interference pattern (wave). The question: Did the photon "choose" its behavior based on a future decision?
Experimental realization: Vincent Jacques et al. (École Normale Supérieure, Paris) conducted the experiment in 2007 with single photons. Result: The behavior (wave or particle) corresponds to the type of measurement chosen, even if the choice is made after passing through the slits.
Extension: The delayed-choice quantum eraser (Kim et al., 1999) complicates the setup with entangled photons. Results show correlations difficult to interpret with purely ascending causality.
Debate: A retro-causal reading (the future influences the past) is possible. A standard reading (Copenhagen) maintains that wave function collapse only occurs at the moment of measurement, without back-action. Both interpretations produce the same predictions — the difference is ontological, not experimental.
Status: Validated and reproducible experiment. Interpretation open.
Huw Price (Philosopher of Science, Trinity College, Cambridge, then University of Sydney, Australia):
Price argues that the fundamental temporal symmetry of physics suggests that if the past influences the present, there is no principled reason the future should not influence it as well. He proposes that a truly time-symmetric physics admits retrocausality as a legitimate hypothesis.
Publications: "Time-Symmetry and Retrocausality" (2012, Studies in History and Philosophy of Modern Physics). "The Past Hypothesis, the Thermodynamic Arrow, and Retrocausality" (2021, European Journal for Philosophy of Science).
Ken Wharton (Physicist, San Jose State University, USA):
Wharton develops concrete retro-causal models for Bell-type experiments. He proposes that hidden variables could be fixed by future choices without violating statistical independence.
Publications: "A Retrocausal Account of Bell-type Correlations" (2015, Foundations of Physics). "A Simple Retrocausal Model of the Bell Experiment" (2019, Physical Review A).
Rod Sutherland (University of Sydney, Australia):
Sutherland develops a mathematical framework integrating retrocausality into quantum mechanics coherently, resolving certain non-locality problems through time-symmetric causality.
Common point: These three researchers, independently, propose that retrocausality is not a curiosity but a serious research direction in foundations of quantum physics. Their work is published in peer-reviewed journals and debated in the community.
Status: Serious theoretical hypotheses. No consensus, but no refutation. The Stanford Encyclopedia of Philosophy dedicates an entire entry to retrocausality in quantum mechanics (2022 edition).
Context: John Stewart Bell (Northern Ireland, 1928–1990) published his theorem in 1964: if the locality principle is respected (no influence propagates faster than light), certain quantum correlations have an upper bound. Violation of this bound = locality is challenged.
Experiments: Alain Aspect (France), John Clauser (USA), Anton Zeilinger (Austria) conducted increasingly rigorous experiments confirming violation of Bell inequalities. 2022 Nobel Prize in Physics awarded jointly for this work.
Implication for the future: Results show that the quantum world violates either locality (action at a distance), or another fundamental intuitive principle. A retro-causal interpretation allows preserving locality by accepting that an influence travels back through time — the future of a photon can determine its past behavior. Price and Wharton defend this reading.
Status: Violation of Bell inequalities experimentally confirmed with high confidence. Interpretation of this violation: debate open. No consensus on underlying mechanism.
Origin: Philippe Guillemant, French physicist-engineer, researcher at Laboratoire de Mécanique et d'Acoustique (LMA, CNRS, Marseille).
Principle: The TDC (Double Causality Theory) proposes that classical causality (past → present) is completed by an orthogonal causality (future → present). The future already exists in the form of timelines, but is not frozen. Consciousness can, through intention, select among parallel timelines.
Key points:
Publications: The Road of Time (La Route du Temps) (2010, 2014), The Physics of Consciousness (La Physique de la Conscience) (2015). Documentary film: The Road of Consciousness (Jean-Yves Bilien, 2015).
Position in the debate: Philippe Guillemant proposes a broader framework than academic retrocausality physicists (Aharonov, Price, Wharton) as he explicitly integrates consciousness as an active agent in timeline choice. This integration is not validated by dominant academic physics. His physicist-engineer training and CNRS affiliation give his work a serious technical basis, but TDC remains a personal theory, not validated by publication in fundamental peer-reviewed physics journals.
Status: Working hypothesis. Underlying physical framework (retrocausality, temporal symmetry) draws on established scientific bases. Integration of consciousness as causal agent relates to a theoretical proposal not validated by publication in fundamental peer-reviewed physics journals.
Concept: In general relativity, the notion of "universal present" has no absolute meaning. All events — past, present and future — exist simultaneously in a four-dimensional spacetime block. This is the block universe, associated notably with Hermann Weyl and popularized by work on relativity.
Implication: The future is not "in the process of arriving" — it is already there, like the past. The flow of time would be an illusion of consciousness. The future, like the past, exists in the block.
Tension with free will: If the future already exists, how is choice possible? This is the central debate that Price, Wharton and Guillemant try to resolve through retrocausality: the future exists, but is not unique — parallel lines coexist, and consciousness can slide from one to the other.
Status: The block universe is a direct consequence of general relativity. Its philosophical interpretation (time is illusory vs time is a flow) remains open.
What do these elements say together?
Open questions:
Two-State Vector Formalism (TSVF):
Delayed-Choice Experiment (Wheeler):
Retrocausality (Price, Wharton, Sutherland):
Bell Inequalities and Nobel Prize 2022:
Double Causality Theory (Guillemant):
Block Universe: