**How can Einstein’s theory of gravity be unified with quantum mechanics? It is a challenge that could give us deep insights into phenomena such as black holes and the birth of the universe. Now, a new article in Nature Communications, written by researchers from Chalmers University of Technology, Sweden, and MIT, USA, presents results that cast new light on important challenges in understanding quantum gravity.**

A grand challenge in modern theoretical physics is to find a ‘unified theory’ that can describe all the laws of nature within a single framework – connecting Einstein’s general theory of relativity, which describes the universe on a large scale, and quantum mechanics, which describes our world at the atomic level. Such a theory of ‘quantum gravity’ would include both a macroscopic and microscopic description of nature.

“We strive to understand the laws of nature and the language in which these are written is mathematics. When we seek answers to questions in physics, we are often led to new discoveries in mathematics too. This interaction is particularly prominent in the search for quantum gravity – where it is extremely difficult to perform experiments,” explains Daniel Persson, Professor at the Department of Mathematical Sciences at Chalmers university of technology.

An example of a phenomenon that requires this type of unified description is black holes. A black hole forms when a sufficiently heavy star expands and collapses under its own gravitational force, so that all its mass is concentrated in an extremely small volume. The quantum mechanical description of black holes is still in its infancy but involves spectacular advanced mathematics.

#### A simplified model for quantum gravity

“The challenge is to describe how gravity arises as an ‘emergent’ phenomenon. Just as everyday phenomena – such as the flow of a liquid – emerge from the chaotic movements of individual droplets, we want to describe how gravity emerges from quantum mechanical system at the microscopic level,” says Robert Berman, Professor at the Department of Mathematical Sciences at Chalmers University of Technology.

In an article recently published in the journal Nature Communications, Daniel Persson and Robert Berman, together with Tristan Collins of MIT in the USA, showed how gravity emerges from a special quantum mechanical system, in a simplified model for quantum gravity called the ‘holographic principle’.

“Using techniques from the mathematics that I have researched before, we managed to formulate an explanation for how gravity emerges by the holographic principle, in a more precise way than has previously been done,” explains Robert Berman.

#### RIpples of dark energy

The new article may also offer new insight into mysterious dark energy. In Einstein’s general theory of relativity, gravity is described as a geometric phenomenon. Just as a newly made bed curves under a person’s weight, heavy objects can bend the geometric shape of the universe. But according to Einstein’s theory, even the empty space – the ‘vacuum state’ of the universe – has a rich geometric structure. If you could zoom in and look at this vacuum on a microscopic level, you would see quantum mechanical fluctuations or ripples, known as dark energy. It is this mysterious form of energy that, from a larger perspective, is responsible for the accelerated expansion of the universe.

This new work may lead to new insights into how and why these microscopic quantum mechanical ripples arise, as well as the relationship between Einstein’s theory of gravity and quantum mechanics, something that has eluded scientists for decades.

“These results open up the possibility to test other aspects of the holographic principle such as the microscopic description of black holes. We also hope to be able to use these new connections in the future to break new ground in mathematics,” says Daniel Persson.

The scientific article, “Emergent Sasaki-Einstein geometry and AdS/CFT” is published in *Nature Communications* and is written by Robert Berman, Tristan Collins and Daniel Persson at Chalmers University of Technology, Sweden, and Massachusetts Institute of Technology, USA.

Reference: “Emergent Sasaki-Einstein geometry and AdS/CFT” by Robert J. Berman, Tristan C. Collins and Daniel Persson, 18 January 2022, *Nature Communications*.

DOI: 10.1038/s41467-021-27951-9

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This Is a question not a a comment. Gravity, speed of light, energy, all have a dimensional component. Distance. Einstein accelerated relative time in order to accomodate the speed of light constant. Is ir possible to modify or relativize the 3D space structure, instead of Time? So, the distance between A and B is relative to when this distance is measured. The structure Is Time, no the 3d universo as we experience ir.

Minkowski spacetime is flawed in its conception as time is not scalar but a compact dimension. Neutron decay cosmology and associated topology accounts for baryon asymmetry, electron half spin, fine tuning and black hole paradoxes by accepting time as having a very real and total duration of a single Planck second.

Neutron decay cosmology is Inevitable

If observed blueshift is an effect partly conforming to observer gravity not an effect conforming only to light source gravity, flipping the magnitude of an observed shift restores realism to remote gravity measurements, undoing the light channel’s cumulative effects, also it conforms to supposing all changes to falling rates, and to frequency rates, must run together in the same direction. However, not taking shifts literally but instead taking them flipped inside out would disagree with the trampoline-type “matter stretches spacetime” lensing theory used to explain the paths of mass particles and light bending toward mass. Despite that flipping around frequency shifts would agree with a round mass compressing the closest space around it the most, just like it compresses another mass the most on its surface, the curved spacetime theory for flipped gravity shift remote inference-making (anti deSitter space) says mass must repel light and bits of matter in space. Ultimately, neither of the two complementary bent spacetime tropes is completely realistic.

Faster light is not the same as faster seconds or slower seconds: Don’t stretch it in front of the class:

When light (and space and time) is laterally compressed more when closer to a mass and compressed less when farther, what draws light toward mass faster than drawing it away? Answer is nothing, not even time reversal. When light (and space and time) is laterally stretched more when closer to a mass and less when farther, what draws light toward mass faster than drawing it away? Best answer GR is a model where stretchable space fabric gets pulled down by gravity pushing on top of it. When light is faster closer to mass and slower when further, what draws light toward mass faster than drawing it away? Answer is flat time, bent time, backward time, any kind of time.

Believe it or not: Unbent time and unbent space also have the benefit of giving an easy accurate accounting of energy:

Keeping wavelength constant while letting frequency vary means initially redshifted light realistically must be light initially slowed by decreased gravity. Same with a passing rumble-strip effect. Light frequency is independent of photon rate, meaning a constant-rate countable photon (or light pulse) source gives the only reliable light-based indicator for time rate. Heisenberg’s uncertainty applied to light says a tight frequency source is a loose phase timing source, so atomic clock frequency means practically nothing about photon rate.