Does gravity create reality? A shocking path to a theory of everything

At times, after working hard on a problem, you might find you’ve been approaching it the wrong way. Imagine trying to squeeze a large antique piano through a narrow doorway. You’ve tried every technique—rotating, disassembling, pushing—but it just won’t fit. Eventually, you realize that building a room for the piano where it currently is might be a better solution.

Some physicists are facing a similar situation. The traditional method of unifying physics’ fundamental forces has involved trying to fit gravity into the framework of quantum mechanics. Quantum mechanics effectively explains three of the four fundamental forces, making this approach sensible. Yet, nearly a century on, gravity remains a puzzle.

This has led some unconventional thinkers to propose a different method. They suggest that altering quantum mechanics equations—essentially creating a new framework for gravity—could clarify how the peculiar world of particles forms our everyday reality.

Several experimental paths are being explored to investigate this idea, from levitating diamonds and glowing metals to swinging pendulums and ticking clocks. These experiments aim to illuminate the workings of the quantum world and aid in the quest for a more comprehensive understanding of the universe. “This is like venturing into the open ocean without a clear route,” says Angelo Bassi, a physicist from the University of Trieste in Italy. “But perhaps by going in the wrong direction, we’ll find the right path.”

The world we experience is definite. Books rest firmly on shelves, clocks tick forward, and cats are visibly alive. However, in the atomic realm, certainty dissolves. Quantum mechanics describes particle properties, like position, in terms of probability. You can predict the likelihood of finding a particle in various places, but its exact position remains unknowable until measured. Before measurement, the object exists in a wave-like superposition of possibilities, mathematically described as a wave function.

This presents two major challenges in quantum theory. Firstly, it’s unclear how and when quantum fuzziness transitions into classical reality. Secondly, this probabilistic nature clashes with Einstein’s classical gravity theories. Attempts to translate Einstein’s gravity into particle terms, like string theory, have been awkward and nearly untestable.

The belief that everything fundamentally adheres to quantum principles has persisted. Despite a century since quantum mechanics emerged, physicists continue to grapple with forming a cohesive narrative. “There must be more to understand,” says Bassi. “The key is pushing quantum mechanics to its boundaries.”

One approach to probing these boundaries involves the superposition principle, a quantum mechanics oddity. Scientists routinely put particles in states of being in two places simultaneously, verified by interference patterns. However, measuring the particle collapses it to a single state, like left or right.

Various interpretations explain this measurement phenomenon. The many-worlds view suggests each possible scenario unfolds in separate realities, while the Copenhagen interpretation advises trusting the mathematical calculations.

Another set of explanations seeks a physical cause. In the 1980s, physicists Giancarlo Ghirardi, Alberto Rimini, and Tullio Weber suggested an unseen process disrupts quantum waves, causing them to collapse. Later, physicist Lajos Diósi from the Wigner Research Centre for Physics in Hungary and University of Oxford mathematician Roger Penrose proposed that gravity might be responsible. The Diósi-Penrose model posits that in the clash between quantum mechanics and gravity, quantum mechanics gives way first. They argued that placing a large mass into superposition would force space-time to bend in two ways, which it cannot allow, leading to the collapse of quantum waves.

If this theory holds, superpositions would only last inversely proportional to the square of their mass. Thus, while quantum objects can remain in superposition for long periods, larger objects would collapse faster. This could explain why large objects aren’t observed in superposition—their gravity quickly forces a collapse. This idea also addresses the measurement issue, as any device capable of measuring a quantum system would disturb it gravitationally. This concept shifted the focus from interpreting quantum theory to revising it.

Ever-larger superpositions

In the past two decades, physicists have been developing larger superpositions to test these predictions. Advances in interferometry, which exploits quantum matter’s dual particle-wave nature, have significantly increased the size of objects that can be put into superposition. Earlier this year, physicists achieved a new milestone with sodium nanoparticles containing over 7,000 atoms, larger than some viruses.

Recent work by Penrose and his team indicates that experiments can, in theory, test his collapse proposal. A paper, not yet peer-reviewed, published online in December 2025 by a team led by Ron Folman at Ben-Gurion University in Israel, demonstrated a rubidium atom in a superposition of two states: one stationary and the other in freefall. The interference pattern observed provided insights into how the atom’s quantum state evolved due to this interaction. The results matched a century-old prediction, confirming that, at least on a microscopic scale, the superposition principle aligns with general relativity.

This experiment’s setup might help identify when this compatibility breaks down. Penrose suggests that repeated tests with larger masses might yield different results. In Folman’s experiment, Earth’s gravity acted on the free-falling object. However, if the object is sufficiently large, its gravitational pull could emerge between its two states, potentially leading to self-interaction. If the object is simultaneously in two places, it might sense its own gravitational influence. Penrose predicts that, in such cases, the interference pattern will vanish, indicating a collapse due to gravitational self-interaction.

Cătălina Curceanu, a physicist at the National Institute for Nuclear Physics in Frascati, Italy, finds the experiment’s technical prowess impressive. “It’s absolutely fascinating,” she remarks. As experiments scale up, she foresees “the disappearance of quantumness before our eyes.”

Should they achieve a superposition of diamonds separated by 2 micrometers, predictions indicate gravitationally induced collapse could occur in under a second.

Others express skepticism about the timeline. “Currently, the molecules aren’t large enough for a genuine test of these collapse theories,” states Bassi. “The day will come, but it will be a prolonged journey.”

While some physicists aim to expand quantum superpositions, others focus on the opposite: understanding gravity at the smallest scales.

For decades, physicists have sought to reconcile quantum mechanics, which deals in probabilities, with general relativity, which assigns exact values at every point in space and time. Now, some are converging on a bold proposal: make gravity random. If space-time is inherently noisy, objects wouldn’t follow straight gravitational paths but would exhibit inherent, unpredictable motion. This could account for tiny objects existing in superposition without violating space-time and explain why quantum measurements yield random outcomes.

Random gravity

In 2023, Jonathan Oppenheim at University College London refined this concept into a “post-quantum” theory, a hybrid model allowing different behaviors at microscopic and macroscopic scales while maintaining interaction. “There’s a single premise: the gravitational field is classical,” he explains. “Everything else follows.”

The theory builds on work by Diósi and Antoine Tilloy at PSL University in France in 2016, which demonstrated a mathematically consistent way for gravity to be random. Oppenheim argues that a classical, random gravitational field is enough to disturb quantum superpositions without invoking measurement or additional collapse mechanisms. Unlike earlier hybrid models trying to keep space-time classical, his proposal aligns well with Einstein’s general relativity, enhancing its credibility. Oppenheim and his colleagues also outlined an experiment to test these ideas by precisely observing the mass of a gravity-affected object.

Not everyone supports randomizing gravity. Ivette Fuentes at the University of Southampton, UK, a close collaborator of Penrose, believes that proposing a fluctuating gravitational field without clarifying the source of randomness is a way of avoiding the problem. “Although I disagree with what he does, I admire it,” she says. “He proposes an alternative and suggests an experiment to test it.”

Additionally, post-quantum gravity is now aiding in the exploration of gravitational collapse models more broadly. Recently, physicists examined the effects of a classical gravitational field interacting with quantum matter. They found that if gravity is classical, it must randomly collapse quantum waves upon interaction, causing some shaking in the wave function describing quantum states. In the past year, separate studies led by Bassi and Daniel Carney at Lawrence Berkeley National Laboratory in California determined the minimum size of these fluctuations. Their analyses open new opportunities for testing these models.

New experiments

In recent years, three primary experimental channels have emerged in the search for signs of randomness in the gravitational field.

The first type of test seeks heat generated by quantum matter being agitated by gravity. A random gravitational field acting on charged particles would make them jiggle, causing them to emit radiation. Scientists search for this radiation by placing materials in well-shielded environments to protect them from other heat sources.

Curceanu and her colleagues have been using a piece of germanium, wrapping it in lead, burying it over a kilometer underground, and then monitoring for any unexpected light emissions. Recent experiments by her team haven’t detected significant anomalous radiation, narrowing the constraints on these ideas and, in some cases, eliminating entire models. But Curceanu insists negative results don’t rule out collapse theories entirely. “When you eliminate the simplest models,” she says, “the real work begins.”

Another channel focuses on oscillating pendulums, seeking subtle deviations in their movement caused by gravitational randomness. Some researchers monitor tiny wiggling cantilevers for unexplained motion attributed to gravity. Others study small metal cubes in constant freefall on the European Space Agency’s LISA Pathfinder satellite, which has provided some of the most precise constraints yet. Last year, Bassi and his colleagues proposed conducting pendulum experiments at much colder temperatures to reduce noise interference.

Recently, a third experimental avenue emerged, potentially leading to profound insights about the universe. A team led by Nicola Bortollotti at Sapienza University of Rome demonstrated that all collapse models involving gravity also impact time itself. They argue that a random gravitational field causing matter to vibrate would set a fundamental limit on time precision.

The ultimate time limit

This limit surpasses the Planck time, previously thought to be the smallest measurable interval. “The ultimate fuzziness of time may not require extreme quantum gravity but can arise from more accessible physics,” says Curceanu, who co-authored the paper.

Though this limit remains beyond the reach of today’s most precise clocks, which use atomic oscillations, future advancements in timekeeping could provide a new method to test these collapse models. If correct, the age-old pursuit of creating increasingly accurate clocks might someday hit a universal boundary, revealing the quantum-classical divide. Since different collapse models predict varying rates of decline in clock precision, this method could help differentiate models experimentally.

“You anticipate a smooth time flow, but with very small clocks, randomness in time measurement might emerge,” says Bortollotti. If confirmed, he concludes, “we’ll need to rethink our concept of time.”

Even if future experiments rule out this approach, physicists believe the process will yield valuable insights into how our structured reality arises from atoms’ uncertain dance. “They are constrained from different directions, platforms, and mass ranges,” says Bassi. These experiments are gradually narrowing the theoretical space for models attempting to integrate gravity into quantum mechanics. “Either they collectively reduce it to zero, ending the quest, or they uncover something significant.”

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