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Introduction

Modern physics faces the challenge of reconciling quantum mechanics (the physics of the very small) with general relativity (the theory of gravity and the cosmos). One intriguing approach is the block universe concept, where time is treated as another dimension and all events (past, present, future) exist in a fixed 4D structure. This picture is inherently deterministic – the entire history of the universe is laid out like a tapestry. To support this view, physicists have been gathering evidence that quantum processes might be time-symmetric and deterministic at a deeper level, despite appearing indeterministic when observed. Below, we survey recent experimental findings and theoretical arguments that reinforce a deterministic, block-universe interpretation of reality. In particular, we highlight:

• Experiments demonstrating time-reversal symmetry and two-way flow of time in quantum systems (e.g. photon interference and quantum “eraser” setups).
• Phenomena suggesting retrocausality or entanglement across time (quantum correlations that span time or have no definite causal order).
• The discovery of time crystals and their implications for non-classical temporal order.
• Mechanisms by which classical determinism emerges from quantum wavefunction evolution.
• The prevalence of power-law behavior in complex systems as a sign of deterministic structure across scales.
• Deterministic quantum models addressing cosmic mysteries (dark matter, dark energy).
• Evidence that all matter and forces are composed of quantum building blocks, suggesting time and gravity should likewise have quantum or deterministic underpinnings.

Throughout, we draw from peer-reviewed studies, university press releases, and reputable science journalism. The discussion is organized by topic, with key experiments and theories summarized. A summary table at the end recaps major findings and their implications.

Time-Reversal Symmetry in Quantum Experiments

One fundamental hint of determinism in quantum physics is its time-reversal symmetry: the basic equations (like Schrödinger’s equation) work equally well if time runs forward or backward. While everyday phenomena exhibit an irreversible “arrow of time,” recent quantum experiments show that at small scales this arrow can be flipped or erased under controlled conditions. For example, a 2019 study used IBM’s quantum computer to reverse the evolution of a simple quantum state, effectively “rewinding” a particle to an earlier state (Researchers reverse the flow of time on IBM’s quantum computer). The researchers simulated a particle scattering (analogous to ripples from a stone in a pond) and then applied an algorithm that caused the quantum wave pattern to un-spread and re-localize, as if time ran backward (Researchers reverse the flow of time on IBM’s quantum computer) (Researchers reverse the flow of time on IBM’s quantum computer). Remarkably, the procedure succeeded ~85% of the time for a two-qubit system (Researchers reverse the flow of time on IBM’s quantum computer). This is a striking validation that, absent external interference, quantum dynamics are reversible. The forward and reverse trajectories of a quantum system can, in principle, mirror each other (Fig. 1), consistent with a block-universe view where past and future are symmetric. Researchers note that irreversibility in quantum processes seems to arise only when a measurement or environment interaction introduces an arrow of time (Researchers reverse the flow of time on IBM’s quantum computer). In other words, the underlying laws do not prefer a direction – a concept long suspected because fundamental physics equations “do not inherently favor a single direction” of time (Physicists uncover evidence of two arrows of time emerging from the quantum realm).

(Physicists uncover evidence of two arrows of time emerging from the quantum realm) Figure 1: Illustration of forward vs. reverse evolution in a quantum system. In a recent study, physicists found that opposing arrows of time can emerge from the same quantum process under different conditions (Physicists uncover evidence of two arrows of time emerging from the quantum realm). The left panel shows a system’s state $\psi(x,t)$ evolving forward in time, while the right panel shows the time-reversed evolution $\Theta \psi(x,-t)$. Blue arrows indicate momentum flow in the forward-time case and red arrows in the reversed case. Such results emphasize that quantum laws are fundamentally time-symmetric, and only external conditions select a forward arrow. (Physicists uncover evidence of two arrows of time emerging from the quantum realm) (Physicists uncover evidence of two arrows of time emerging from the quantum realm)

Another famous example of time symmetry in quantum mechanics is the delayed-choice experiment, originally proposed by John Wheeler. In these interference experiments, the decision of whether to observe a particle as a wave or a particle is made after it has entered the interferometer. Quantum mechanics predicts – and experiments confirm – that the outcome (wave-like interference or particle-like detection) still respects the future choice, as if the particle’s behavior is decided retroactively. Wheeler noted the seeming paradox: “a last-minute decision made on Earth on how to observe a photon could alter a situation established millions of years earlier” (Delayed-choice quantum eraser – Wikipedia). Indeed, modern delayed-choice experiments with light from distant quasars (emitted billions of years ago) find the same results as lab experiments, implying the photon has no definite reality (wave or particle) until measurement (Wheeler’s delayed-choice experiment – Wikipedia). While the standard quantum view avoids true paradox by saying the photon was in a superposition (neither wave nor particle) until measured (Delayed-choice quantum eraser – Wikipedia), the block-universe interpretation would say the choice and outcome are consistent parts of one spacetime complete story – no signal is actually sent backward, but past and future are correlated because they’re fixed together. These experiments demonstrate bidirectional consistency in time: you can insert or remove a detection apparatus after the particle is in flight, and the interference pattern (or lack thereof) adjusts accordingly, as seen in quantum eraser setups (Delayed-choice quantum eraser – Wikipedia). Such findings fuel interpretations of quantum mechanics that are time-symmetric or retrocausal, suggesting the flow of time in quantum events can be surprisingly flexible and hinting at a deterministic block picture where cause and effect can be woven in non-traditional ways.

Retrocausality and Entanglement Across Time

Closely related to time symmetry is the idea of retrocausality – future events influencing the past – and the existence of quantum entanglement that is not constrained by the usual time order. Quantum entanglement is typically discussed for particles separated in space, but recent work shows entanglement can also bridge separation in time. In 2013, physicists succeeded in entangling two photons that never coexisted – one photon was created and absorbed before the other was even emitted (Physics team entangles photons that never coexisted in time) (Physics team entangles photons that never coexisted in time). Using a clever sequence of entanglement-swapping measurements, the team entangled photon P1 with P2, then later entangled photon P3 with P4, and by a joint measurement effectively entangled P2 with P3. Photon P1 was detected (and destroyed) before photon P4 was created, yet P1 and P4 ended up in an entangled state (Physics team entangles photons that never coexisted in time) (Physics team entangles photons that never coexisted in time). In other words, “the first photon was detected even before the other was created,” yet the results showed they had become entangled (Physics team entangles photons that never coexisted in time). This striking experiment proves that entanglement is not a synchronistic connection in real time, but rather a correlation that can span time; as the researchers put it, “this new work shows that [particles] can be linked via time as well” (Physics team entangles photons that never coexisted in time). It suggests that what we call a “quantum state” can extend across time, consistent with a block-universe picture where quantum correlations are fixed across the timeline.

Beyond specific particles, even the order of events can be entangled or indefinite. In classical terms, for event A to cause B, A must precede B in time. But quantum mechanics allows scenarios of indefinite causal order in which it’s impossible to say which of two events happened first. In the past decade, physicists have realized that “in principle, both versions of the story can happen at once” – that is, both “A causes B” and “B causes A” can be simultaneously true in a quantum process (Quantum Mischief Rewrites the Laws of Cause and Effect | Quanta Magazine). This sounds paradoxical, but experiments have demonstrated exactly such phenomena using a setup called the quantum switch. In 2017, the first experimental quantum switch showed that two operations (for example, two logic gates applied to a quantum bit by Alice and Bob) could be applied in a superposition of orders – effectively A then B and B then A at the same time (Quantum Mischief Rewrites the Laws of Cause and Effect | Quanta Magazine) (Quantum Mischief Rewrites the Laws of Cause and Effect | Quanta Magazine). The result is an entangled causal order that has no single, objective sequence of events. In these experiments, measurement forces a definite order in hindsight, but until then the causal sequence is fuzzy. Such indefinite causality violates our normal intuitions of time and cause-effect, yet it is allowed (and indeed realized) in quantum theory. It indicates that causality itself may be an emergent, scale-dependent concept – at fundamental levels, nature’s description might be a tenseless network (a “block”) of events where cause and effect are not absolute. Retrocausal interpretations of quantum theory build on this, positing that constraints from both past and future define quantum outcomes in a self-consistent way (much like how solving a puzzle might require applying boundary conditions at both ends) (Understanding Retrocausality and Blockworld – Physics Forums). While still debated, these ideas show that relaxing classical one-way causality can resolve quantum paradoxes and align naturally with the timeless block-universe paradigm.

Time Crystals: Persistent Temporal Order

If time is indeed a dimension on par with space in a block universe, one might expect structures in time analogous to structures in space. A recent breakthrough in quantum physics is the creation of time crystals, a novel phase of matter that exhibits regular, repeating structure in time rather than space. In a normal crystal (like a salt crystal), atoms are arranged in a repeating lattice pattern in space. In a time crystal, the system’s configuration repeats periodically in time – it oscillates indefinitely without energy input, breaking the usual symmetry of time-translation. First theorized in 2012, time crystals were experimentally realized in 2017 and more definitively in 2021. For example, a team involving Stanford and Google used a quantum processor (Google’s Sycamore chip) to create a genuine time crystal (Time crystal in a quantum computer | Stanford Report) (Time crystal in a quantum computer | Stanford Report). In their system, quantum spins flipped in a stable, recurring cycle with a period that was a multiple of the driving period – like a beat that skips – and this oscillation persisted without energy gain or loss. “Just as a crystal’s structure repeats in space, a time crystal repeats in time and, importantly, does so infinitely and without any further input of energy – like a clock that runs forever without batteries,” explained the Stanford news release (Time crystal in a quantum computer | Stanford Report). This seemingly “perpetual motion” does not violate thermodynamics because the system is not in equilibrium and no work is extracted; in fact, the entropy of the time crystal state stays constant over time, satisfying the second law (it doesn’t decrease, it just doesn’t increase) (Time crystal in a quantum computer | Stanford Report). The key point is that time crystals establish that stable, non-decaying order can exist purely in the time dimension. This is a profound insight: it means time can host phases of matter the way space does. In a block-universe sense, a time crystal is like a standing wave etched across the time axis of the block – a deterministic pattern that extends through time. The existence of time crystals underscores that time is not just an abstract background for events; it can have its own quantum structure and order. This lends credence to the idea that time itself might emerge from or be constrained by quantum rules. If time can crystallize, it hints that time is a tangible aspect of reality that could, at base, be quantum-mechanical. As more time crystals are developed (in nuclei, solids, quantum circuits, etc.), they provide concrete systems to study non-classical temporal dynamics and perhaps how a time-ordered deterministic pattern can coexist with quantum fluctuations.

(First ‘Time Crystal’ Built Using Google’s Quantum Computer | Quanta Magazine) Figure 2: Conceptual illustration of a time crystal. Like a spatial crystal repeats periodically in space, a time crystal’s configuration cycles periodically in time without consuming energy (First ‘Time Crystal’ Built Using Google’s Quantum Computer | Quanta Magazine). In experiments, time crystals have been realized in quantum systems that oscillate indefinitely (within coherence time limits) by spontaneously breaking time-translation symmetry. This suggests that time, like space, can support persistent structures – a hint towards time being a fundamental quantum dimension. (Time crystal in a quantum computer | Stanford Report) (Time crystal in a quantum computer | Stanford Report)

From Quantum Wavefunction to Classical Determinism

Quantum mechanics is famously probabilistic – the outcomes of measurements are described only by probabilities (the Born rule) in the standard interpretation. Yet, between measurements, the quantum state evolves in a perfectly deterministic way given by the wave equation (Schrödinger’s equation or its relativistic variants). This dichotomy raises a question: how does the familiar classical determinism of everyday life emerge from the underlying quantum description? Several lines of evidence suggest that when many particles or interactions are involved, quantum systems naturally give rise to definite, classical behavior, without the need for any mysterious collapse. One key mechanism is decoherence – the process by which a quantum system interacting with its environment loses its quantum interference effects and “chooses” a classical state. Decoherence has been extensively studied and shows that once information about a quantum system’s state leaks into the environment, the system’s wavefunction appears to collapse for all practical purposes. In effect, the environment measures the system and picks out a consistent outcome, yielding the illusion of a sudden collapse even though the overall system (system + environment) still evolves deterministically.

Recent theoretical work using numerical simulations provides strong support for this emergence of classicality. In a 2024 study in Physical Review X, researchers simulated large quantum systems and found that on large scales, the weird quantum interference effects vanish, leaving behavior that matches classical physics (Numerical simulations show how the classical world might emerge from the many-worlds universes of quantum mechanics). Lead author Philipp Strasberg noted that while single particles like electrons or photons behave in non-intuitive quantum ways, if one “zooms out” to coarse-grained quantities (like the position of a baseball or the temperature of coffee), the quantum interference washes out (Numerical simulations show how the classical world might emerge from the many-worlds universes of quantum mechanics). Their findings “indicate that quantum interference effects, which are responsible for weird quantum behavior, vanish” at macroscopic scales (Numerical simulations show how the classical world might emerge from the many-worlds universes of quantum mechanics). In the simulations, classical features (like a definite trajectory) emerged from a variety of quantum models, suggesting this is a general result (Numerical simulations show how the classical world might emerge from the many-worlds universes of quantum mechanics). Notably, the team framed their results in the context of the Many-Worlds Interpretation of quantum mechanics. In Many-Worlds (a deterministic interpretation), the wavefunction never collapses; instead, it branches into multiple non-communicating outcomes. The simulations showed how our single classical reality can emerge as one branch, with the other branches effectively invisible, thus “the classical world we see can emerge from the many-worlds picture of quantum mechanics” (Numerical simulations show how the classical world might emerge from the many-worlds universes of quantum mechanics). In that picture, every measurement’s possible outcomes all happen in different branches, and because of decoherence these branches don’t interfere – yielding the appearance of randomness in each branch even though the wavefunction’s evolution is fully deterministic.

Other deterministic interpretations like de Broglie–Bohm’s pilot-wave theory similarly attribute quantum probabilities to ignorance of initial conditions, not fundamental randomness. In pilot-wave theory, particles have well-defined positions at all times and are guided by a “pilot wave” (the wavefunction); if one had complete information, the theory is fully deterministic. In such interpretations, quantum uncertainty is epistemic (due to hidden variables or branching worlds), whereas the underlying law is as deterministic as classical mechanics. The success of classical physics emerging from quantum rules in these studies and interpretations reinforces the notion that quantum mechanics can be viewed as a deterministic theory at the fundamental level, with apparent indeterminism arising only because we observe just one branch or lack information. This dovetails with a block-universe view: if the entire timeline of the wavefunction’s evolution (and all its branches) is laid out, every event is determined within that whole. Our perception of chance would then just reflect our limited access to the whole picture. In short, unitary quantum evolution is deterministic, and when combined with mechanisms like decoherence, it yields the consistent, classical world — suggesting no “mystery factor” is needed to go from quantum to classical, just the complex interplay of many quantum parts following simple rules ( A simple guide to chaos and complexity – PMC ).

Power Laws and Deterministic Patterns Across Scales

Determinism in physics often reveals itself through patterns that persist across different scales. Power-law distributions – where a quantity’s frequency scales as a power of its size – are widespread in nature (from earthquake magnitudes to stock market fluctuations to galaxy clustering). Such distributions often signal an underlying scale-free process, which in many cases is rooted in deterministic dynamics (for instance, chaotic systems or critical phenomena). Complex systems science has shown that even systems with many components and random-seeming behavior can be governed by simple, deterministic rules that produce complexity. A chaotic system is a prime example: it is deterministic (no randomness in the equations), yet its output appears random due to extreme sensitivity to initial conditions. The behavior of a chaotic system appears random, but is generated by simple, non-random, deterministic processes ( A simple guide to chaos and complexity – PMC ). The complexity lies in the iterative evolution of the system, not in any inherent randomness ( A simple guide to chaos and complexity – PMC ). This insight, as noted in a Chaos and Complexity review, highlights that things like strange attractors and fractal patterns (which often follow power laws or self-similarity) arise from deterministic equations iterated over time ( A simple guide to chaos and complexity – PMC ).

For example, the logistic map (a simple deterministic equation) can produce a fractal bifurcation diagram with regions described by power laws. Likewise, at the critical point of phase transitions, systems exhibit scale invariance and power-law correlations – a hallmark of underlying rules that do not have a preferred length scale. These phenomena support the idea of a deterministic structure extending across scales: the same mathematical forms (power laws) appear in systems as vast as galactic networks and as small as electron trajectories in a chaotic quantum system. In the context of a block universe, such self-similar patterns hint that the universe’s fabric might be woven by recursive, deterministic principles. If one zooms out from the microscopic laws to the macroscopic world, a continuity of pattern (like fractal self-similarity or conserved quantities) suggests the absence of arbitrary randomness injected at intermediate scales. In short, the ubiquity of power-law behavior in nature “exhibits self-similarity” and an absence of characteristic scale, which is easier to reconcile with deterministic (or at least law-governed) processes than with pure chance (Power law: universality in nature | by Francisco Rodrigues – Medium) (Chaos theory – Wikipedia). This doesn’t prove the universe is a strict clockwork, but it provides circumstantial evidence that from chaotic pendulums to complex ecosystems, simple rules can govern rich behavior – consistent with an underlying deterministic order.

Deterministic Quantum Models Tackling Cosmic Mysteries

One motivation for seeking a unified, deterministic quantum-relativistic framework is to demystify cosmic puzzles like dark matter and dark energy. Dark matter and dark energy are “fixes” to make our current cosmological models work: unseen mass is inferred to explain galaxy motions, and a mysterious energy is invoked to explain the accelerating expansion of the universe. But what if our theories themselves need revision instead of adding unseen entities? Some physicists have proposed that a deeper quantum theory of spacetime might eliminate the need for dark matter or dark energy by explaining those phenomena as emergent effects. A notable example is Erik Verlinde’s emergent gravity theory. Verlinde suggests that gravity is not fundamental but arises from quantum information – essentially viewing spacetime as built from microscopic quantum bits (“qubits”) entangled with each other (Doubting darkness – CERN Courier). In his model, space and time themselves emerge from an underlying deterministic network of quantum information. When Verlinde applied this idea to cosmic scales, he found an extra “entropy force” appears in the equations due to the presence of dark energy (a positive cosmological constant) (Doubting darkness – CERN Courier) (Doubting darkness – CERN Courier). This extra term behaves like an additional gravitational pull at large scales. In fact, “in a universe with a positive dark energy, there is a contribution to the entanglement entropy that… results in the phenomena that we currently attribute to dark matter” (Doubting darkness – CERN Courier). In short, the anomalous gravity in galaxies (usually blamed on dark matter) could be explained by modifications to gravity from quantum entanglement in spacetime, according to this model (Doubting darkness – CERN Courier). Here, dark matter is not a new particle but an emergent, deterministic effect – the interplay of matter with the quantum structure of space-time.

While Verlinde’s theory is still speculative and being tested, it exemplifies how deterministic quantum frameworks can simplify cosmic mysteries. By attributing cosmic phenomena to known ingredients (quantum information, entropy, etc.) rather than unknown substances, such models strive for a more cohesive picture of the universe. Another proposal, by Julian Barbour and collaborators, envisions the universe’s history as a path in a timeless configuration space (a “Janus point” cosmology) – in their view, what we perceive as the Big Bang might be a low-entropy turning point that gives rise to two oppositely arrowed time evolutions, potentially addressing the arrow of time and maybe eliminating the need for dark energy-driven expansion as an independent puzzle. There are also hypotheses that the dark energy driving cosmic acceleration could be related to quantum vacuum energy or the wavefunction of the universe itself (e.g. the Hartle-Hawking wavefunction) (What Physicists Have Been Missing – Nautilus Magazine). These ideas remain speculative, but they share a common thread: they attempt to derive cosmic dynamics from quantum principles and often do so in a way that keeps the overall evolution deterministic. In Oppenheim’s recent “post-quantum gravity” proposal, for instance, gravity is kept classical but imbued with a fundamental randomness to mesh with quantum physics, yielding a unified theory that reportedly can account for cosmic expansion and galaxy rotation without dark matter (The End of the Dark Universe? – Nautilus) (The End of the Dark Universe? – Nautilus). Although Oppenheim’s approach explicitly introduces randomness in gravity, it underscores how adjusting the framework can remove the need for dark components (The End of the Dark Universe? – Nautilus) (The End of the Dark Universe? – Nautilus) – the ultimate goal being a simpler, law-governed universe.

The block-universe perspective complements these attempts by suggesting that if we view the universe’s spacetime as a whole, dark matter/energy might not be separate ingredients but rather parts of the geometry or quantum state of the block. For example, what appears as an unexplained acceleration (dark energy) could be a natural property of a block universe with certain boundary conditions. Indeed, some theorists have speculated that what we call dark energy could be linked to a global condition on the universe’s wavefunction or a teleological constraint (a final condition in time, as in some retrocausal models). While concrete evidence for these specific ideas is pending, the trend is clear: by extending quantum mechanics to encompass spacetime (or vice versa), we can potentially explain “dark” phenomena without invoking mysterious new forces or particles. In doing so, we lean into deterministic quantum structure – a hopeful sign that the biggest mysteries in cosmology might find resolution in a unified, block-universe theory where everything from particle interactions to the expansion of space derives from one coherent quantum reality.

Quantum Building Blocks of Reality

Any argument for time and gravity having quantum or deterministic properties must contend with a basic fact: all known non-gravitational forces and matter are described by quantum theory. The Standard Model of particle physics is a quantum field theory that successfully explains three of the four fundamental forces – electromagnetism, the strong nuclear force, and the weak nuclear force – as well as all known elementary particles of matter (The Standard Model | CERN). In this model, particles of matter (fermions like quarks and electrons) interact by exchanging force-carrying particles (bosons like the photon, gluon, and W/Z bosons) (The Standard Model | CERN). Each force has a quantum field and associated quanta: for example, the electromagnetic field’s quantum is the photon. All matter around us is made of elementary quantum particles, the building blocks such as quarks and leptons (The Standard Model | CERN). These particles obey quantum mechanics and have no substructure in current theory – they are the “atoms” of our theories in the original Greek sense of indivisible units. Even phenomena that once seemed continuous (like light, or the energy in atoms) are now understood as quantized. Given this enormous success of quantum reductionism, it is natural to suspect that gravity and even time itself are also built from some quantum pieces – or at least that they obey quantum-like laws.

Indeed, the only fundamental force not yet integrated into the quantum framework is gravity. Physicists hypothesize a particle called the graviton as the quantum of gravity (analogous to the photon for electromagnetism), but gravitons have not been observed and a full quantum theory of gravity remains elusive (The Standard Model | CERN). The difficulty lies in making Einstein’s general relativity (which is deterministic and continuous) mesh with quantum mechanics (which is probabilistic and discrete in some aspects) (The Standard Model | CERN). However, virtually all approaches to unification – from string theory to loop quantum gravity – assume that spacetime at the Planck scale has quantum properties. Loop quantum gravity, for instance, predicts that space is made of finite “chunks” (quantized volumes and areas) and that time too may be discrete. Other approaches like the holographic principle suggest spacetime emerges from a deeper quantum system (e.g., quantum entanglement patterns). The success of the Standard Model (and its extension to include the recently confirmed Higgs field) in explaining all known particles and their interactions as excitations of quantum fields strongly supports the idea that nature is quantum all the way down. If time and gravity are fundamental parts of nature, it would be logically inconsistent for them alone to resist quantization. Most likely, they too are either emergent from quantum entities or have dual descriptions as quantum fields in a yet-to-be-discovered theory. Furthermore, a deterministic block universe would mean that the “randomness” in quantum experiments is only apparent – perhaps due to hidden variables or branching worlds – and that if we had the full picture (the entire 4D block), we would see that every event is seamlessly connected. As Einstein once suspected, “God does not play dice”; instead, the complexity of quantum outcomes might stem from our limited perspective within time.

Table 1 below summarizes some of the key experiments and theoretical developments we have discussed, highlighting how each supports the convergence of quantum mechanics, time, and gravity into a single deterministic framework.

Experiment / Theory	Key Finding	Implication for Deterministic Block-Universe
Quantum time reversal (2019) – Lesovik et al., Sci. Reports (Researchers reverse the flow of time on IBM’s quantum computer) (Researchers reverse the flow of time on IBM’s quantum computer)	Reversed a quantum evolution on a quantum computer, sending a two-qubit state a “fraction of a second” back in time.	Quantum laws are time-symmetric and reversible; the arrow of time can be flipped in isolated quantum systems, consistent with a 4D block view where past↔future symmetry exists.
Delayed-choice quantum eraser (1999) – Y.-H. Kim et al. (Delayed-choice quantum eraser – Wikipedia)	Future measurement choices (whether to erase which-path info) affect interference patterns from photons emitted earlier.	Apparent retrocausality in quantum experiments; suggests that measurement outcomes across time are correlated as a single whole, as expected if events are fixed in a block universe (no true signal backward, but block consistency).
Entanglement across time (2013) – Eisenberg group (Physics team entangles photons that never coexisted in time) (Physics team entangles photons that never coexisted in time)	Two photons entangled despite one being measured before the other existed. Verified entanglement with timelike separation.	Quantum entanglement is not constrained by “ simultaneity ” – supports the idea of quantum states extending across time. The block universe can contain entangled relations between past and future events, reinforcing time as just another dimension for quantum correlations.
Indefinite causal order (2017–2020) – Quantum switch experiments ([Quantum Mischief Rewrites the Laws of Cause and Effect	Quanta Magazine](https://www.quantamagazine.org/quantum-mischief-rewrites-the-laws-of-cause-and-effect-20210311/#:~:text=burns%20himself%20on%20the%20stove,Alice%20to%20drop%20a%20plate))	Demonstrated processes where event A happens and doesn’t happen before B (no definite order) using a superposition of causal sequences.
Time crystal formation (2017, 2021) – Monroe, Google teams ([Time crystal in a quantum computer	Stanford Report](https://news.stanford.edu/stories/2021/11/time-crystal-quantum-computer#:~:text=For%20example%2C%20the%20creation%20of,now%20finally%20come%20to%20fruition)) ([Time crystal in a quantum computer	Stanford Report](https://news.stanford.edu/stories/2021/11/time-crystal-quantum-computer#:~:text=match%20at%20L182%20closer%20look,of%20thermodynamics%20by%20not%20decreasing))
Emergence of classical order (2024) – Strasberg et al., PRX (Numerical simulations show how the classical world might emerge from the many-worlds universes of quantum mechanics) (Numerical simulations show how the classical world might emerge from the many-worlds universes of quantum mechanics)	Simulations show that large-scale observables of quantum systems follow classical (non-interference) behavior, aligning with one branch of many-worlds.	A single determinate classical reality can emerge from underlying quantum determinism (wavefunction evolution). No true randomness is needed if all outcomes exist – aligns with block universe determinism (the entire set of branches is fixed, we experience one branch as “reality”).
Verlinde’s emergent gravity (2016) – Sci. Rep. & others (Doubting darkness – CERN Courier) (Doubting darkness – CERN Courier)	Gravity derived as an entropic force from quantum entanglement; additional “elastic” effect from positive vacuum energy reproduces dark matter-like effects.	Space, time, and gravity might emerge from quantum information in a deterministic way. Cosmic “unknowns” (dark matter/energy) could be accounted for by quantum structure of spacetime, reducing the need for undetermined free parameters in the cosmos.
Standard Model of Particles (1970s–) – High-energy physics ([The Standard Model	CERN](https://home.cern/science/physics/standard-model#:~:text=Three%20of%20the%20fundamental%20forces,electromagnetic%2C%20strong%20and%20weak%20forces)) ([The Standard Model	CERN](https://home.cern/science/physics/standard-model#:~:text=fundamental%20force%20has%20its%20own,The%20quantum%20theory%20used))

Table 1: Selected experiments and theories that bridge quantum mechanics, time-symmetry, and gravitation, supporting a deterministic block-universe perspective. Each finding removes a bit of the “mystery” or indeterminacy from the physical world by showing how outcomes can be predicted or correlated through underlying structure, even when they appear random or acausal in a classical sense.

Conclusion

The convergence of evidence from the quantum realm and insights from relativity is painting a picture of a universe that is, at its core, a unified, deterministic whole – much like the “block universe” envisioned in relativistic physics. Experiments showing time reversibility, retrocausal-like correlations, and indefinite causal structures highlight that the linear flow of time and strict cause-effect are not absolute at the quantum level. At the same time, quantum systems exhibit patterns (like time crystals and scale-invariant distributions) and give rise to the stable classical world in ways that strongly suggest there is no fundamental randomness at play – only complexity. All physical phenomena we understand can be reduced to quantum constituents, and it stands to reason that gravity and time will eventually be understood in similar terms, whether that means quantizing them or uncovering an underlying deterministic principle from which they emerge. The block universe theory provides an appealing framework to reconcile these ideas: it posits that the universe’s spacetime is an immutable four-dimensional entity. Within that block, what we perceive as probabilistic or irreversible is in fact just one path through a much richer, pre-existing structure.

No experiment to date has violated the core tenet of quantum theory’s unitarity (deterministic evolution) – instead, experiments challenge our intuitions about time and locality, nudging us toward interpretations where past and future are entwined and all outcomes have their place. In quantum gravity research, treating spacetime as emergent from quantum entanglement or other quantum information concepts is an approach very much in the spirit of a block universe: spacetime (and time’s arrow) is not fundamental, but arises from deeper laws that likely run both forward and backward without preference (Physicists uncover evidence of two arrows of time emerging from the quantum realm) (The End of the Dark Universe? – Nautilus). While we do not yet have a final theory uniting quantum mechanics and general relativity, the pieces we have examined – from laboratory photonics to cosmic observations – reinforce the notion that determinism has not lost its place in modern physics. Instead, it has evolved: no longer the clockwork determinism of classical physics, but a subtler quantum determinism in which the universe can be thought of as “a completed puzzle,” already consistent across all time, waiting for us to understand how the pieces fit.

In summary, current experimental evidence and theoretical advances lend support to the vision of a universe where quantum mechanics and relativity meet in a time-symmetric, all-encompassing framework. The block universe may ultimately serve as the stage on which quantum processes unfold in a preordained way – a stage where every force and particle is quantum, every event is connected, and time itself is part of the script rather than the mystery behind the scenes.

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• Wheeler, J.A. delayed-choice thought experiment discussed in (Delayed-choice quantum eraser – Wikipedia) (see also Science 315, 966 (2007) for experimental realization).
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• Quanta Magazine (2021) – Wolchover, N., “Quantum Mischief Rewrites the Laws of Cause and Effect” (Quantum Mischief Rewrites the Laws of Cause and Effect | Quanta Magazine).
• Quanta Magazine (2021) – Wolchover, N., “Eternal Change for No Energy: A Time Crystal Finally Made Real” (First ‘Time Crystal’ Built Using Google’s Quantum Computer | Quanta Magazine) (First ‘Time Crystal’ Built Using Google’s Quantum Computer | Quanta Magazine).
• Stanford University News (2021) – “Time crystal in a quantum computer” (Time crystal in a quantum computer | Stanford Report) (Time crystal in a quantum computer | Stanford Report).
• Appell, D. (2024). Phys.org – “Numerical simulations show how the classical world might emerge from the many-worlds universes of quantum mechanics” (Numerical simulations show how the classical world might emerge from the many-worlds universes of quantum mechanics) (Numerical simulations show how the classical world might emerge from the many-worlds universes of quantum mechanics).
• Adams, B. et al. (2022). Chaos, 32, 032101 – on deterministic chaos and complexity ( A simple guide to chaos and complexity – PMC ).
• Verlinde, E. (2016). Sci. Rep., 6, 31922 – “Emergent Gravity and the Dark Universe” (interview in CERN Courier) (Doubting darkness – CERN Courier) (Doubting darkness – CERN Courier).
• CERN – “The Standard Model” (2017) (The Standard Model | CERN) (The Standard Model | CERN).
• Hossenfelder, S. (2024). Nautilus – “The End of the Dark Universe?” (discussing Oppenheim’s post-quantum gravity) (The End of the Dark Universe? – Nautilus) (The End of the Dark Universe? – Nautilus).
• Additional references as cited in-line above.