Quantum gravity gets a new test

https://journals.aps.org/prx/pdf/10.1103/PhysRevX.14.021022

It's worth a look. The article buries a lot of interesting details. For example:

"These bodies are shaped like dumbbells, with each end weighing less than a gram..."

But in the paper we read:

"We are thus experimenting with gold spheres of mass m ≈ 1.58 × 10^−10 kg"

So yeah, that's "less than a gram" but that's kind of like saying that a gnat weighs less than a ton. It's not wrong, but it kinda buries the lede.

This experiment sounds really cool and promising. We're looking at Nobel-Prize-worthy results if it works out.

[UPDATE]

It's actually going to be even more Nobel-Prize-worthy than I thought. Turns out they're not going to be doing this experiment any time soon:

"Admittedly, this is a very challenging condition to achieve experimentally. Considering temperatures in the order of millikelvin, e.g., achievable by attaching the pendulum to a dilution refrigerator, this would still require quality factors on the order of Q = 10^10. This is 5 orders of magnitude above the largest reported quality factors for torsion pendula. For some types of wire materials, such as sapphire, improvements in quality factors are to be expected from operation at lower temperatures."

Imagine making a wire out of sapphire!

> As the pendulums oscillate, they change the size and therefore the resonant wavelength of each cavity. This change can be detected by shining laser light into the cavities and then measuring the intensity of the resulting interference pattern.

FWIU there is more information in light intensity; from https://news.ycombinator.com/item?id=37226160 :

> > The work, led by Xiaofeng Qian, assistant professor of physics at Stevens and reported in the August 17 online issue of Physical Review Research, also proves for the first time that a light wave's degree of non-quantum entanglement exists in a direct and complementary relationship with its degree of polarization. As one rises, the other falls, enabling the level of entanglement to be inferred directly from the level of polarization, and vice versa. This means that hard-to-measure optical properties such as amplitudes, phases and correlations—perhaps even these of quantum wave systems—can be deduced from something a lot easier to measure: light intensity

> [...] Qian's team interpreted the intensity of a light as the equivalent of a physical object's mass, then mapped those measurements onto a coordinate system that could be interpreted using Huygens' mechanical theorem. "Essentially, we found a way to translate an optical system so we could visualize it as a mechanical system, then describe it using well-established physical equations," explained Qian.

> Once the team visualized a light wave as part of a mechanical system, new connections between the wave's properties immediately became apparent—including the fact that entanglement and polarization stood in a clear relationship with one another.

Hypothetical unipolar magnets in free-fall.

/? hnlog Ctrl-f "quantum gravity":

- https://news.ycombinator.com/item?id=39954180 superfluid quantum gravity / SQS, demonstrated indefinite causal order in quantum systems

- n-ary entanglement; "Designing three-way entangled and nonlocal two-way entangled single particle states via alternate quantum walks" (2024) https://arxiv.org/abs/2402.05080 :

> Herein, we generate three-way entanglement from an initially separable state involving three degrees of freedom of a quantum particle, which evolves via a 2D alternate quantum walk employing a resource-saving single-qubit coin. We achieve maximum possible values for the three-way entanglement quantified by the π-tangle between the three degrees of freedom. We also generate optimal two-way nonlocal entanglement, quantified by the negativity between the nonlocal position degrees of freedom of the particle. This prepared architecture using quantum walks can be experimentally realized with a photon.

- This is a better - fluidic - sim render of sound waves between parabolic reflectors; where are the linked states in is combinatorial outcomes with itself just? "A wave traveling between two parabolic antennas" https://youtube.com/watch?v=v0cZjOIfwos

We like to model regular wavefronts, but waves do travel through fluids of various pressures and diffraction. Are gravitational waves ever so restricted, and why do they arrive after photonic waves from the same phenomena?

https://news.ycombinator.com/item?id=39956484 :

> Deflection of electromagnetic waves by pseudogravity in distorted photonic crystals" (2023) .. "Distorted crystals use 'pseudogravity' to bend light like black holes do" https://news.ycombinator.com/item?id=38008449

(Edit)

"Measuring gravity with milligram levitated masses" (2024) Fuchs, superconducting magnetic trap with Tantalum: https://www.science.org/doi/10.1126/sciadv.adk2949 https://news.ycombinator.com/item?id=39495570 :

> This regime opens the possibility of table-top testing of quantum superposition and entanglement in gravitating systems. Here, we show gravitational coupling between a levitated submillimeter-scale magnetic particle inside a type I superconducting trap and kilogram source masses, placed approximately half a meter away. Our results extend gravity measurements to low gravitational forces of attonewton and underline the importance of levitated mechanical sensors.