Quantum Superposition Yields Repulsive Gravity in New Physics Model

Sabine Hossenfelder

Destructive quantum interference from a mass in spatial superposition can impart an effective repulsive kick to probe particles, offering a pathway to prove gravity operates quantum mechanically if researchers can scale quantum coherence by six orders of magnitude.

AI-assisted summary of Scientists Have Figured Out How to Make Antigravity — original source. Check the original for full context.

Source published: 2026-07-17

Key ideas

A new theoretical paper shows that spatial quantum superpositions can cause destructive interference between gravitational wave functions, producing an effective repulsive kick on a nearby probe particle. (2:37)
Observing this repulsive kick would provide experimental proof that gravity possesses quantum properties, as a purely classical gravitational field cannot produce this interference effect. (5:02)
The proposed setup requires placing a 20-microgram source mass in superposition alongside cesium atom probes, which is roughly two million times heavier than current laboratory capabilities. (5:02)
The repulsive phenomenon does not violate energy conservation because it averages out to standard attractive gravity over statistical ensembles, occurring only in individual quantum runs. (2:37)

Detailed notes

## Background Published on YouTube by Sabine Hossenfelder on July 17, 2026, this video examines a theoretical breakthrough concerning repulsive gravity. According to the page description, while Einstein's general relativity dictates that gravity is always attractive, a new research paper outlines how quantum mechanics provides a loophole to produce antigravity, which could decisively prove that gravity possesses quantum properties.

## TL;DR In classical general relativity, gravity is strictly attractive, but a recent theoretical paper proposes that quantum mechanics can create an effective repulsive force. By placing a massive source particle into a spatial quantum superposition near a probe, the resulting destructive interference between momentum states produces an outward kick in individual runs while preserving standard conservation laws on average. If detected, this phenomenon would serve as proof of quantum gravity, though laboratory execution remains a steep challenge because the required 20-microgram source mass is roughly two million times larger than what current technology can hold in superposition. Evaluating the proposal, Hossenfelder gives it a modest 2 out of 10 on her bullshit meter, praising its theoretical ingenuity while emphasizing severe experimental hurdles.

## Atmosphere & style The presentation delivers Sabine Hossenfelder's signature blend of dry wit, accessible analogies, and unapologetic scientific skepticism. She deftly punctures sensationalist sci-fi tropes about flying to work by anchoring the discussion in rigorous quantum field dynamics and tabletop experimental limits. The mood is intellectually playful yet grounded, balancing genuine appreciation for clever theoretical modeling with an unvarnished, pragmatic appraisal of laboratory realities.

## Bulletin - [02:37](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=157s) A new theoretical paper shows that spatial quantum superpositions can cause destructive interference between gravitational wave functions, producing an effective repulsive kick on a nearby probe particle. - [05:02](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=302s) Observing this repulsive kick would provide experimental proof that gravity possesses quantum properties, as a purely classical gravitational field cannot produce this interference effect. - [05:02](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=302s) The proposed setup requires placing a 20-microgram source mass in superposition alongside cesium atom probes, which is roughly two million times heavier than current laboratory capabilities. - [02:37](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=157s) The repulsive phenomenon does not violate energy conservation because it averages out to standard attractive gravity over statistical ensembles, occurring only in individual quantum runs.

## Key takeaways - [00:00](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=0s) General relativity mandates that gravity is strictly attractive because mass-energy acts as charge in a spin-2 field where only positive values exist. - [00:00](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=0s) General relativity and quantum mechanics remain incompatible frameworks, colloquially compared to two contradictory instruction manuals for the universe. - [00:00](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=0s) Testing quantum gravity traditionally relied on hypothetical black hole energies, but modern research focuses on tabletop quantum entanglement witness tests. - [00:00](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=0s) Entanglement tests struggle experimentally because large masses required for measurable gravity decohere almost instantly from environmental interactions. - [02:37](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=157s) The proposed study uses a single source mass in a spatial superposition of two locations rather than two entangled masses. - [02:37](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=157s) A nearby probe simultaneously experiences attraction toward both source locations, enabling quantum destructive interference to create an outward repulsive force. - [02:37](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=157s) Conservation laws remain intact because averaging measurements across many experimental runs recovers normal attractive gravity toward the source's mean position. - [05:02](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=302s) The repulsion is not a new fundamental interaction, but an effective force produced by the momentum spread and wave interference of the quantum source. - [05:02](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=302s) Detecting this anomalous repulsive kick would conclusively demonstrate that gravity obeys quantum mechanical laws. - [05:02](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=302s) The paper models the experiment using cesium atoms as probes and a 20-microgram source mass. - [05:02](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=302s) The required 20-microgram mass exceeds current laboratory quantum superposition limits by a factor of about two million. - [05:02](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=302s) Experimental feasibility could improve with longer decoherence times, higher nanoscale force precision, and shorter probe-to-source spatial resolution. - [05:02](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=302s) Sabine Hossenfelder rates the paper a 2 out of 10 on her 'bullshit meter,' finding it theoretically clever despite daunting experimental ambiguities.

## Detailed walkthrough ### [00:00](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=0s) Why Gravity Is Always Attractive—And How Quantum Mechanics Finds a Loophole

The idea of making antigravity sounds absurd at first glance, yet it rests on a sound theoretical foundation. In Einstein’s theory of general relativity, gravity is strictly attractive. This behavior stems from the way mass and energy interact: in gravitational theory, energy serves the exact same role that electric charge plays in electromagnetism. However, because the gravitational field is mediated by a spin-2 field, particles with identical charges attract one another while opposite charges repel. Given that physics only recognizes positive masses and positive energies, all gravitational sources naturally pull toward each other. Despite this bedrock rule, a recent research paper proposes that quantum mechanics harbors an unexpected loophole where two attractive gravitational pulls can interfere to produce an effective repulsion under very specific conditions.

This startling conclusion was uncovered not while deliberately designing antigravity machines, but while tackling one of the deepest unsolved mysteries in modern physics: determining whether gravity itself possesses quantum properties. Theoretical physics currently relies on two mutually incompatible frameworks. On one side stands quantum mechanics, which formulates atoms and elementary particles through quantum fields; on the other stands general relativity, which models gravity as the smooth curvature of spacetime. As Sabine Hossenfelder colorfully summarizes the conflict, “It's like having two instruction manuals for the universe.” She jokes that one manual demands, “Assemble with screws,” while the other insists, “There are no screws,” only for a theorist to drop by and ask, “Have you tried 11 dimensions?”

For decades, the consensus held that testing quantum gravity would demand unattainable energies found only inside black holes or during the Big Bang. Recently, physicists discovered that laboratory tabletop experiments might actually suffice. The dominant experimental avenue relies on an “entanglement witness,” where two masses are placed into quantum superposition so that their gravitational interaction generates quantum entanglement. Because observing gravitational entanglement would decisively prove that gravity operates quantum mechanically, it serves as a golden standard. However, the experimental hurdle is immense: an object must be massive enough to generate a detectable gravitational field, yet large masses lose their quantum coherence almost instantaneously through environmental interactions, which explains why everyday objects and humans are never seen in two places at once.

```mermaid flowchart TD accTitle: Entanglement Witness Concept accDescr: Diagram showing how quantum entanglement mediated by gravity implies gravity is quantum. subgraph S1["Classical General Relativity"] A["Spin-2 Field Mediating Energy"] --> B["Like Charges Attract"] B --> C["Strictly Attractive Gravity"] end subgraph S2["Quantum Gravity Test"] D["Massive Object in Superposition"] --> E["Gravitational Interaction with Probe"] E --> F["Gravitational Entanglement Witness"] F --> G["Proof of Quantum Nature of Gravity"] end ```

[02:37](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=157s) Superpositions, Destructive Interference, and the Repulsive Kick

The authors of the new paper deviate from the traditional two-mass entanglement route by proposing a setup involving a single massive source placed into a spatial quantum superposition alongside a nearby probe particle. In this configuration, the source mass exists in two locations simultaneously, meaning the probe simultaneously experiences the gravitational field emanating from both potential positions. If the source occupied only the first position, the probe would be attracted toward that single spot; if it occupied only the second position, the probe would be pulled toward that alternative spot instead. The breakthrough comes from quantum interference: when the source exists in both places at once, the respective quantum states can undergo destructive interference, yielding a net repulsive effect on the probe.

This immediately raises the concern of whether such a repulsive result breaches core conservation laws. Hossenfelder clarifies that it does not violate fundamental physics because conservation laws hold over the statistical ensemble. When an experimenter averages out measurements over many runs, the probe behaves normally and is pulled toward the average position of the source particle. However, in individual, isolated experimental runs, the quantum dynamics manifest as an unexpected outward push.

- **Source mass setup:** One massive particle prepared in a spatial superposition of two locations. - **Probe response:** Experiences gravitational influences from both source states concurrently. - **Statistical resolution:** Averaged over multiple runs, gravity remains attractive; in individual single runs, destructive interference produces an effective repulsion.

[03:43](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=223s) Sponsor: Cognitive Testing

Hossenfelder steps aside from theoretical physics to address the prevalence of deceptive online intelligence tests. Many web-based IQ quizzes instantly assign participants genius-level marks, functioning primarily as flattering marketing funnels designed to inflate scores for profit rather than measure true cognitive ability.

To counter these misleading tools, cognitivetesting.org was created by a large Reddit community that grew frustrated with pervasive online scams. The platform offers professionally validated, scientifically rigorous tests developed by licensed psychologists. Modeled after the proctored exams used by school districts, clinical psychologists, and electoral bodies, these assessments utilize properly normed, culture-fair questions alongside adaptive testing technology that presents fresh problem sets daily. The aim is to deliver a transparent, unvarnished baseline of raw pattern recognition without ego-stroking gimmicks.

[05:02](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=302s) The Physics of Effective Forces and Laboratory Hurdles

Resuming the physics breakdown, Hossenfelder explains why the interaction mimics a repulsive force. Because quantum entities exhibit wave-particle duality, an object suspended in two locations does not carry a single fixed momentum, but rather a spread of multiple momentum states. When these wave functions superimpose and interfere destructively in a precise configuration, the resulting momentum transfer kicks the probe away rather than drawing it inward. As Hossenfelder highlights, “It's not a new fundamental force.” Instead, it represents an effective force tied exclusively to specially prepared quantum states. This subtlety is precisely why the test is valuable: a strictly classical gravitational field could never produce such a phenomenon. As Hossenfelder notes, “If the wrong-way kick is observed and all ordinary forces are ruled out, it would be evidence that gravity has quantum properties.”

```mermaid flowchart LR accTitle: Quantum Destructive Interference Leading to Antigravity accDescr: Flow showing how wave superposition yields momentum interference and an effective repulsive kick. subgraph WaveDynamics["Quantum Wave Mechanics"] A["Source Particle Superposition"] --> B["Multiple Momentum States"] B --> C["Destructive Interference"] end subgraph PhysicalOutcome["Observed Effect"] C --> D["Net Outward Momentum Transfer"] D --> E["Effective Repulsive Force"] end ```

Carrying out the proposed experiment remains a massive technological challenge because gravitational forces between microscopic objects are extraordinarily feeble. In their paper, the authors model a system utilizing cesium atoms as the probe particles, calculating that the source mass must weigh roughly 20 micrograms. While 20 micrograms sounds tiny for everyday items, it is roughly two million times heavier than the largest masses physicists can currently maintain in a quantum superposition in a laboratory. The required source mass could theoretically be reduced if researchers achieve three key breakthroughs: - Extending the quantum decoherence times of mesoscopic masses. - Increasing the precision of nanoscale force measurements. - Achieving the capability to resolve much shorter spatial distances between particles.

Hossenfelder quips that commuters hoping to float to work will be disappointed, even if current public transit makes the dream appealing. Delivering her overall assessment, she awards the paper a modest score: “I give this paper a 2 out of 10 on the bullshit meter.” Her primary reservations concern experimental ambiguity. Even if a lab detects the repulsive anomaly, definitively ruling out stray non-gravitational background forces will be near impossible. Conversely, failing to see the repulsion would merely prove that gravity does not exhibit this exact flavor of quantum behavior, leaving the broader question unresolved. Nonetheless, she praises the concept as a genuinely clever contribution to the quantum gravity literature, concluding with a lighthearted remark that if the physics pans out, she finally has an excuse for why her hair refuses to obey gravity.

## Notable quotes > [05:02](https://www.youtube.com/watch?v=XKRMbVpJ3Rc&t=302s) If the wrong-way kick is observed and all ordinary forces are ruled out, it would be evidence that gravity has quantum properties. — Sabine Hossenfelder

## Mentioned Albert Einstein, Sabine Hossenfelder, cognitivetesting.org, Reddit

## Video description Head over to https://cognitivetesting.org/ to take a legitimate IQ test

In Einstein's theory of general relativity, gravity is always attractive. But according to a new paper, quantum mechanics offers a loophole that can create antigravity. And not only this, if it was measurable that would prove that gravity has quantum properties. How does this work and how can repulsive gravity be compatible with the laws of physics that we know and like? Let's take a look.

Paper: https://arxiv.org/abs/2602.12266

#science #sciencenews #gravity #quantumphysics #physics #technology

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[Source](https://www.youtube.com/watch?v=XKRMbVpJ3Rc)

中文简报

新物理模型表明量子叠加可产生排斥引力处于空间叠加态的质量所产生的相消量子干涉可对探测粒子施加有效排斥冲量；若研究人员能将量子相干性提升六个数量级，这将为证明引力遵循量子力学机制提供途径。在经典广义相对论中，引力纯粹表现为吸引力，但近期一篇理论论文提出量子力学可以产生一种有效的排斥力。通过将大质量源粒子置于探测器附近的空间量子叠加态中，动量态之间产生的相消干涉会在单次运行中产生向外的推力，同时在统计平均上仍保持标准守恒定律。若能被探测到，该现象将成为量子引力的证明，不过实验室实现仍面临巨大挑战，因为所需的20微克源质量比当前技术能够维持叠加态的质量高出约两百万倍。在评估该提案时，Hossenfelder在其“胡扯指数”上给出了较低的2分（满分10分），在赞赏其理论独创性的同时强调了严峻的实验障碍。一篇新的理论论文表明，空间量子叠加会导致引力波函数之间发生相消干涉，从而对附近的探测粒子产生有效的排斥冲量。 (2:37) 观察到这种排斥冲量将为引力具有量子特性提供实验证据，因为纯经典的引力场无法产生这种干涉效应。 (5:02) 拟议的实验方案需要将20微克的源质量与铯原子探测器一同置于叠加态中，该质量大约是目前实验室能力上限的两百万倍。 (5:02) 这种排斥现象并不违反能量守恒，因为它只发生在单次量子运行中，在统计系综平均下仍表现为标准的吸引引力。 (2:37)

Reading summary

A recent physics paper proposes that quantum destructive interference between gravitational states could produce an effective repulsive kick, offering a potential tabletop signature for quantum gravity without requiring negative mass or violating conservation laws, according to Sabine Hossenfelder. Theoretical Conflict and Tabletop Gravity Tests (0:00) Modern physics depends on two mutually incompatible descriptions of nature: quantum mechanics, which governs atomic-scale particles through quantum fields, and general relativity, which models gravity as smooth spacetime curvature. Because general relativity relies on a spin-2 field where mass and energy are strictly positive, gravity in standard classical physics is exclusively attractive. While testing quantum gravity historically seemed to require the inaccessible energies of black holes or the Big Bang, recent efforts focus on tabletop experiments using an entanglement witness, where gravitational entanglement between superposed masses would prove gravity's quantum nature. Destructive Interference and Effective Repulsion (2:37) Rather than relying on mutual entanglement between two masses, the new proposal examines a single massive source placed into a spatial quantum superposition alongside a probe particle. Because the source exists in two locations simultaneously, the probe interacts with both gravitational configurations at once. When these quantum states undergo destructive interference, the resulting momentum transfer pushes the probe outward instead of drawing it inward. Hossenfelder stresses that this repulsive kick does not represent a new fundamental force or breach conservation laws; over a statistical ensemble of many runs, the average interaction remains attractive, while individual runs can exhibit the effective repulsion. Experimental Barriers to Laboratory Verification (5:02) Detecting this repulsive signature faces immense practical hurdles because gravity is exceptionally weak at microscopic scales. The study models a system using cesium atoms as probes, requiring a source mass of approximately 20 micrograms. Although microscopic, a 20-microgram mass is roughly two million times heavier than the largest objects physicists currently maintain in quantum superposition, which rapidly undergo environmental decoherence. Testing the effect would require substantial advances in extending decoherence times, refining nanoscale force measurement precision, and measuring interactions over far shorter spatial separations. Hossenfelder rates the paper favorably against speculative science, giving it a 2 out of 10 on her 'bullshit meter' and calling it a clever conceptual contribution. However, she notes major experimental limitations: ruling out ordinary background forces during a positive detection would be exceptionally difficult, while a null result would only rule out this specific configuration rather than resolving whether gravity is quantum.

精炼阅读摘要

物理学者 Sabine Hossenfelder 指出，最新理论研究发现处于空间量子叠加态的质量源能够通过波函数相消干涉对探测粒子产生向外的等效推斥效应，为利用桌面实验检验引力是否具备量子属性提供了突破口。经典引力吸引性与量子检验困境 (0:00) 在爱因斯坦的广义相对论中，引力由自旋-2（spin-2）场传递，能量扮演着电磁学中电荷的角色。不同于电磁学中同号相斥的规律，自旋-2场的物理特性决定了同号荷必定相互吸引；鉴于自然界仅已知存在正质量与正能量，经典引力在宏观与微观层面均严格呈现吸引特征。然而，现代物理学目前依赖的两大基石——将时空描述为平滑弯曲的广义相对论与基于量子场论的微观粒子物理学——在数学与概念上并不相容。物理学界此前长期认为检验引力是否具有量子本质需要黑洞或宇宙大爆炸级别的极端能标，直到近期研究证明低能桌面实验同样具备验证潜力。当前检验量子引力的核心思路依赖于“纠缠目击者”（entanglement witness）机制，即观察两个置于空间量子叠加态的微观质量是否能通过纯引力相互作用产生量子纠缠。若引力能够介导纠缠，即可确证引力属于量子场。然而该方案面临严峻的物理矛盾：物体必须具备足够大的质量才能产生可探测的引力，但大质量物体极易因微弱的环境扰动迅速发生量子退相干（decoherence），导致叠加态瞬间瓦解，这也是宏观世界从未观测到物体同时处于两处的原因。空间叠加相消干涉与等效引力排斥 (2:37) 最新论文提出了一种绕过双质量纠缠难题的单源方案：研究人员将单一宏观源质量制备于两个空间位置的叠加态，并在其近旁放置一个微观探测粒子（例如铯原子）。在此设定下，探测粒子会同时受到源质量在两个位置所产生的引力牵引。如果质量源仅位于单一确定位置，探测粒子只会被拉向该特定位置；但当质量源处于双位置叠加时，其对应的量子态波函数会发生相消干涉，进而在特定几何与动量构型下对探测粒子施加一个净向外的反向动量冲量。 Hossenfelder 解释道，这种等效反引力排斥并未违反能量与动量守恒等基础物理定律。守恒定律在统计系综层面严格成立：当实验人员对大量独立运行的结果取统计平均时，探测粒子依然表现为向源粒子的质心平均位置靠拢，符合经典引力吸引规律。然而，在单次独立的量子测量过程中，波函数的相消干涉确实会真实产生反常的向外推斥响应。等效力本质与两百万倍质量的技术鸿沟 (5:02) Hossenfelder 强调，这种引力排斥并非自然界中发现了全新的第五种基本相互作用力，而是特殊量子态下诱发的“等效力”（effective force）。这一特性的关键价值在于经典引力场在任何情况下都无法诱导出这种推斥行为，因此只要能在实验室中观测到该反向冲量并严格排除所有电磁与机械等常规背景力，就能直接构成引力具有量子属性的强有力证据。尽管机制成立，实验落地仍面临极其严苛的工程壁垒。论文作者以铯原子作为探测器计算得出，源质量必须达到约 20 微克（20 micrograms）。这一质量虽属微观范畴，但已比当前人类实验室内所能维持量子叠加态的最大粒子质量重约 200 万倍（two million times）。要将这一构想转化为现实，实验物理学需要在三个方向取得关键突破：大幅提升介观物体的量子退相干时间、推进纳米级极弱力测量的灵敏度，以及实现超短距离内的空间定位与力学操控能力。 Hossenfelder 认为该论文在构思上极具创造性，但对其验证前景持保留态度：在微观极弱引力尺度下，完全排除非引力杂散干扰的难度极高；此外，即使实验未能检测到推斥效应，也仅能证明引力不具备该特定的量子干涉行为，无法彻底证伪引力的量子本质。

Source quotes

[5:02] Sabine Hossenfelder: If the wrong-way kick is observed and all ordinary forces are ruled out, it would be evidence that gravity has quantum properties.

Original transcript

[0:00] Scientists have figured out how to make anti-gravity. Sounds crazy, [0:04] yet I think it might actually work. But before you go and buy ceiling furniture, let's have a [0:11] look at the "ifs and buts." In Einstein's theory of general relativity, gravity is always attractive. [0:18] The reason is quite simple. In gravity, energy plays the role that electric charges play in [0:24] electromagnetism. It's just that since gravity is mediated by a spin-2 field, like charges attract [0:30] and unlike charges repel. And since there are only positive masses and only positive energies, they [0:36] all attract each other. But according to the new paper, quantum mechanics offers a loophole. Under [0:42] the right conditions, two attractive gravitational poles can combine into an effective repulsion. [0:50] That's a stunning conclusion they arrived at by studying an entirely different question, namely [0:56] how to find out whether gravity itself is quantum. This is one of the biggest unsolved problems in [1:03] physics. We have quantum mechanics which describes atoms and elementary particles through quantum [1:11] fields and we have general relativity which describes gravity as the curvature of spaceime. [1:17] Both theories work extremely well. Unfortunately, they don't fit together. It's like having two [1:23] instruction manuals for the universe. One that says, "Assemble with screws," and the other says, [1:30] "There are no screws." And then a theorist walks in and says, "Have you tried 11 dimensions?" For [1:36] a long time, most people thought that testing quantum gravity require absurdly high energies, [1:42] like inside of black holes or at the big bang. But in recent years, physicists have finally realized [1:48] that it's possible to test quantum gravity in the laboratory. The currently most discussed ideas [1:54] to use what's called an entanglement witness. That's if you create entanglement using only the [2:00] gravitational interaction. If this is possible, then you can conclude that gravity must also [2:05] have had quantum properties. It's a difficult test because for this you have to put massive [2:12] objects into a Quantum Superposition. They have to be massive enough so that the gravitational [2:17] interaction has a measurable effect. The problem is that the quantum properties of massive objects [2:24] go away very quickly. This is why we don't normally see people being in two places at once. [2:31] It's also why the experiment has not yet been done. The authors of the new paper now suggest [2:37] a slightly different route. Their proposal is to use one massive object, the source in a superposition [2:45] of two places and nearby is another particle, the probe. The source mass is put [2:51] into two possible locations at once. The probe then feels gravity from both possible locations [2:57] of the source. If the source were in just the first place, the probe would be attracted towards [3:04] that. If the source were in the other place, the probe would also be attracted just towards this [3:11] different place. The twist is that if you have the source in two places at once, you can create [3:17] a destructive interference that leads to a net repulsion. Wait, what? Doesn't this violate some [3:23] sort of conservation law? No, it's fine, really, if you average over many runs of the experiment, [3:30] you get what you expect, namely that the probe particle is attracted to the average of the source [3:36] particle. But in single runs, you can get this repulsive effect. Have you ever taken an online [3:43] IQ test and instantly gotten a genius level score? Hate to break it to you, but most of those tests [3:50] are designed to inflate your score for profit. They sell you a flattering number, not the truth. [3:58] That's exactly why cognitivetesting.org was created. 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It looks like gravity became repulsive, but really it happens [5:09] because quantum particles are not just particles. They're also waves, and waves can interfere. If [5:14] you have a particle in two places at once, then the particle has not one particular momentum, [5:19] but many different ones. And if these add up in a weird way, the result can push you away rather [5:25] than, as you would expect, make a pole. It's not a new fundamental force. It's an effective [5:31] force that only occurs for specially prepared quantum states. But that's exactly why it's [5:37] interesting. If the gravitational interaction didn't have quantum properties, it could not [5:41] produce this effect. If the wrong-way kick is observed and all ordinary forces are ruled out, [5:47] it would be evidence that gravity has quantum properties. That said, the experiment is still [5:53] hard because the gravitational interaction between small objects is ridiculously weak. The authors [6:00] make an estimate with Cesium atoms as the probe particles and find that the source mass would have [6:06] to be about 20 micrograms. That's about 2 million times larger than what current technology allows. [6:13] Though the masses might go down if either a) the decoherence time increases, b) force measurements [6:19] become more accurate or c) shorter distances can be resolved. So no, you can't yet float to work. [6:26] But given the current state of public transport, I understand why you asked. I give this paper a [6:33] 2 out of 10 on the [ __ ] meter. I have misgivings about this sort of experiment in general because [6:40] even if the effect is observed, I think it'll be extremely difficult to rule out it was some other [6:47] interaction. And if it isn't observed, the result is inconclusive because that wouldn't mean gravity [6:53] has no quantum properties. It'd just mean it doesn't have these particular quantum properties. Still, [7:00] I have to say that this is a neat contribution to the literature and I hope the question of [7:07] repulsive gravity will receive more attention. And if this works, I finally have a scientific excuse [7:14] for why my hair does not obey gravity. Thanks for watching. See you tomorrow.