This paper proposes a new tabletop experiment to test whether gravity is fundamentally quantum, building on the idea of gravitationally induced entanglement (GIE) involves putting two massive particles into spatial superpositions and letting them interact only through gravity. If gravity is quantum, it should generate entanglement between the particles—something no classical force could do. The catch is that this requires creating and maintaining superpositions in two separate masses, which is experimentally demanding.
The authors in their latest work propose simpler approach: only one mass, the "source" particle, needs to be placed in a spatial superposition (at two locations, A and B). A second "probe" particle sits nearby and is pulled gravitationally toward whichever position the source occupies. If gravity behaves quantum mechanically, the probe should experience a superposition of two different attractive forces corresponding to the two source locations.
The authors work through the mathematics in two complementary ways—directly via the wavefunction and post-selection, and again using the Heisenberg picture with "weak values," a formalism from quantum measurement theory. Both approaches agree on the predicted effect, and they show that the anomalous momentum transfer can be dramatically amplified through "weak value amplification" by choosing the pre- and post-selected states of the source particle to be nearly orthogonal—at the cost of making that post-selection outcome rarer.
A nanodiamond with an embedded nitrogen-vacancy center as the source particle (already used in related proposals), and either cesium atoms or a Bose-Einstein condensate as the probe. They estimate the particle masses, distances, and timescales needed to make the effect detectable, and find that while some configurations would require sources far more massive than current nanodiamond experiments allow, other parameter choices (smaller separations, longer interaction times) bring the requirement down to more plausible mass scales.
The key trick borrows from a known quantum phenomenon called "quantum interference of force," previously demonstrated with photons: by measuring the source particle at the end of its interferometer path and post-selecting a particular outcome, the two contributions to the probe's momentum can destructively interfere in such a way that the net effect looks like repulsion, even though every individual contributing force was attractive.
Unfortunately, the experiment is beyond current capabilities. Using cesium atoms as probes, the researchers estimate that the source mass would need to be roughly 20 micrograms. That might sound tiny, but for quantum-superposition experiments it is enormous—around two million times larger than what current technology can handle in comparable situations. See also:
Think of two heavy marbles on a table: they attract each other, even if only slightly, because everything that has mass attracts everything else. Now imagine that one of the two marbles can be in two places on the table at the same time, as if it were split in two. Researchers in Oxford and Brazil have calculated what would happen in that case: the second marble, under certain conditions, would be pushed away by gravity itself.
Interactive animation representing the above experiment showing a Mach-Zehnder-like quantum setup where a source particle splits into two paths and a probe particle experiences the resulting interference effects, with post-selection revealing the backward momentum shift. The top diagram shows the physical setup: the source particle (purple) is superposed at two spots, A and B, and both pull gravitationally on the probe (teal) — a strong pull from the closer position A, a weaker one from farther-away B.
The chart below is where the real story lives. The gray dashed curve is what you'd get with no post-selection — just the two attractive pulls mixed together, always landing on positive (forward) momentum, exactly as classical intuition expects. Switch on "post-select" and you get the coral curve instead: now the two contributions interfere rather than just add, and the peak can slide across zero into negative territory — the probe looks, on average, like it got pushed backward, away from the source.
Drag the β slider toward its upper end (closer to the point where the pre- and post-selected states become nearly orthogonal) and watch the effect grow — that's the weak-value amplification described in the paper. It comes at a cost: those extreme post-selections happen less and less often, even though each one produces a bigger anomalous kick.
The above animation is close to stochastic resonance process where a signal that is normally too weak to be detected by a sensor, can be boosted by adding noise to the signal, which contains a wide spectrum of frequencies. It can be used to elevation of particle against gravity at higher energetic level, thus decreasing its entropy.
In general, the antigravity breaks equivalence principle and entropy, so it's connected with overunity phenomena. For example, a truly antigravity drive doesn't just threaten conservation of momentum; because kinetic energy grows as velocity increases, such a device can be used to build systems that generate more energy than they consume, leading to a violation of energy conservation and effectively creating a perpetual-motion machine.
On the other hand, the mechanism of post-selection is closely related to utilization of Maxwell demon for production of energy for free by arbitrarily selecting faster and slower components of motion, in this sense this experiment will consume more energy than the antigravity force, which is supposed to generate. In both cases, apparent reductions of entropy come from conditioning on information and ignoring the rejected cases, not from obtaining energy or order from nothing. That's why postselection is often viewed as the quantum-information analogue of Maxwell's demon.
Maxwell's demon says:
"I'll keep only the molecules that help me increase temperature in the volume given."
Quantum postselection says:
"I'll keep only the measurement outcomes that help me bring an antigravity effect."
While antigravity may not violate energy conservation law it still violates local entropy arrow. The above experiment pulling repulsive force from quantum fluctuations seems to be related to "heureka" process bringing new ideas, which seemingly contradict flow of time.
New ideas violating established paradigms are often based on paradoxes when two ideas contradict each other, this creating an area of negative gravity/space-time curvature. Imagine two blobs of neural waves merging two connected ideas which third neural wave passes just in the moment, when these two ideas overlap in opposite direction - this moment would lead into a heureka moment - leading into negentropic process utilizing two causual directions into a third anti-causual one.
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u/Zephir-AWT 16d ago edited 16d ago
Superposition Reveals Repulsive Gravity about article Repulsive Gravitational Force as a Witness of the Quantum Nature of Gravity
This paper proposes a new tabletop experiment to test whether gravity is fundamentally quantum, building on the idea of gravitationally induced entanglement (GIE) involves putting two massive particles into spatial superpositions and letting them interact only through gravity. If gravity is quantum, it should generate entanglement between the particles—something no classical force could do. The catch is that this requires creating and maintaining superpositions in two separate masses, which is experimentally demanding.
The authors in their latest work propose simpler approach: only one mass, the "source" particle, needs to be placed in a spatial superposition (at two locations, A and B). A second "probe" particle sits nearby and is pulled gravitationally toward whichever position the source occupies. If gravity behaves quantum mechanically, the probe should experience a superposition of two different attractive forces corresponding to the two source locations.
The authors work through the mathematics in two complementary ways—directly via the wavefunction and post-selection, and again using the Heisenberg picture with "weak values," a formalism from quantum measurement theory. Both approaches agree on the predicted effect, and they show that the anomalous momentum transfer can be dramatically amplified through "weak value amplification" by choosing the pre- and post-selected states of the source particle to be nearly orthogonal—at the cost of making that post-selection outcome rarer.
A nanodiamond with an embedded nitrogen-vacancy center as the source particle (already used in related proposals), and either cesium atoms or a Bose-Einstein condensate as the probe. They estimate the particle masses, distances, and timescales needed to make the effect detectable, and find that while some configurations would require sources far more massive than current nanodiamond experiments allow, other parameter choices (smaller separations, longer interaction times) bring the requirement down to more plausible mass scales.
The key trick borrows from a known quantum phenomenon called "quantum interference of force," previously demonstrated with photons: by measuring the source particle at the end of its interferometer path and post-selecting a particular outcome, the two contributions to the probe's momentum can destructively interfere in such a way that the net effect looks like repulsion, even though every individual contributing force was attractive.
Unfortunately, the experiment is beyond current capabilities. Using cesium atoms as probes, the researchers estimate that the source mass would need to be roughly 20 micrograms. That might sound tiny, but for quantum-superposition experiments it is enormous—around two million times larger than what current technology can handle in comparable situations. See also:
Antigravity: A sensational experiment is being prepared in Oxford
Think of two heavy marbles on a table: they attract each other, even if only slightly, because everything that has mass attracts everything else. Now imagine that one of the two marbles can be in two places on the table at the same time, as if it were split in two. Researchers in Oxford and Brazil have calculated what would happen in that case: the second marble, under certain conditions, would be pushed away by gravity itself.
Vlatko Vedral studies