Physicists have created a 3D shape called the cosmohedron, which can be used to reconstruct the quantum wavefunction of the universe – and potentially do away with the idea of space-time as the underlying fabric of the universe

Is space-time the fabric of the universe, or is there something deeper? Shutterstock/Mohd. Afuza

What is the structure of our physical reality? Physicists have long imagined space and time interweaving into “space-time”, the metaphorical fabric that underlies the cosmos. But there may be something even more fundamental. Instead of space-time’s three spatial dimensions and one of time, the physics of our world could be encoded into a set of odd geometrical shapes – and studying them may chart a new, space-time-free path towards a theory of everything.

“The idea is that space-time somehow has to go, that it has to…

A fresh look at gravity challenges long-held assumptions about one of nature’s most familiar yet puzzling forces. In a new study, two researchers argue that gravitational attraction is not a basic force at all, but an effect that emerges from deeper quantum processes tied to electromagnetism. If confirmed, the theory could help explain mysteries that have long resisted standard models — including the origins of dark matter and the energy accelerating the universe’s expansion.

The work, published in Journal of Physics Communications, reimagines gravity not as a force stitched into the fabric of spacetime, but as something that arises from the quantum-level behavior of ordinary matter. Ruth Kastner of the University of Maryland and Andreas Schlatter at the Quantum Institute in New York developed a framework in which space and time themselves are not fundamental but result from electromagnetic interactions between charged systems like atoms and molecules.

Spacetime from photon exchanges

“The creation of a real photon creates ‘the fabric of spacetime’ by giving rise to spacetime events and their structural connection; namely the emission event, the absorption event, and the real photon which links these,” said Kastner. “In short, spacetime events, along with their structural connections, emerge from these transactions.”

They occur when atoms or molecules emit and absorb photons — the particles of light that carry the electromagnetic force. According to the theory, each transaction gives rise to a pair of events in spacetime, effectively stitching together a network of relationships that form what we perceive as space and time.

The idea builds on earlier efforts to rethink gravity as an emergent phenomenon — an effect that arises from more basic physical processes, rather than a force on its own. In this picture, the apparent curvature of spacetime described by Einstein’s general relativity is not a fundamental feature of the universe but a large-scale result of underlying interactions between matter and the electromagnetic field.

“Transactions constitute ‘measurements’ in quantum theory,” Kastner explained. “The fundamental degrees of freedom that underpin the emergent spacetime events are bound systems with charged components, such as atoms and molecules — these are the emitters and absorbers — and also the electromagnetic field, the medium of transactions.”

From thermodynamics to gravity

One of the most intriguing implications of this approach is its ability to reproduce key predictions of general relativity — including the gravitational pull between massive bodies — without invoking gravity as a distinct force. Instead, the researchers apply the principles of thermodynamics, particularly the concept of entropy, to explain why matter attracts other matter.

Entropy, which is often described as a measure of disorder, reflects the number of possible microscopic arrangements that give rise to the same large-scale state. In the new framework, the many quantum states of atoms and molecules — along with the photons they emit — define the entropy of a system. As mass increases, so does the number of these states, enhancing the likelihood of interactions and thus generating the force we interpret as gravity.

“Objects with mass, being composed of transacting components, provide ‘fuel’ for transactions,” said Kastner. “When we quantify that transactional fuel in terms of temperature, and the possible positions for masses, the gravitational potential is the result.”

Rethinking dark matter and dark energy

The researchers suggest that this entropy-based description naturally accounts for phenomena that have long challenged conventional theories. These include the unexplained motion of stars in galaxies, which led to the idea of invisible dark matter, and the apparent acceleration of the universe’s expansion, typically attributed to dark energy.

“The model predicts quantities that currently are anomalies for the standard theory, such as the galactic rotation anomalies (‘dark matter’) and the small but non-vanishing value of ‘dark energy’ and its recently observed weakening over time,” Kastner said. “Further astronomical observations may offer more precise tests for the model’s predictions in this regard.”

According to Kastner Schlatter and, there is no need to invoke unknown forms of matter or energy to explain these effects — they arise naturally from the thermodynamic behavior of ordinary matter and its electromagnetic interactions.

“In sum, our theory is a quantum theory of gravity with appropriate corrections to Einstein’s theory, although gravity is not a quantum field in this model, but a natural structural property of the emergent spacetime,” said Kastner.

Looking ahead

The team is now working to extend the theory further. A major goal is to describe gravitational waves — ripples in spacetime detected by observatories like LIGO — within this new framework. Instead of being waves in a gravitational field, these signals would result from changes in the motion of mass itself.

“We are continuing to develop the model, in particular its ability to explain gravitational waves without attributing energy directly to the ‘gravitational field’ but rather to the source masses themselves,” Kastner said.

While many questions remain, the new theory offers an intriguing alternative to the standard view of gravity, one that could eventually help unify our understanding of the universe from its smallest particles to its largest structures.

Reference: A Schlatter and R E Kastner, Gravity from transactions: fulfilling the entropic gravity program, Journal of Physics Communications (2025). DOI: 10.1088/2399-6528/acd6d7

Feature image credit: geralt on Pixabay

Some 13.8 billion years ago, the universe began with a rapid expansion we call the big bang. After this initial expansion, which lasted a fraction of a second, gravity started to slow the universe down. But the cosmos wouldn’t stay this way. Nine billion years after the universe began, its expansion started to speed up, driven by an unknown force that scientists have named dark energy.

But what exactly is dark energy?

The short answer is: We don’t know. But we do know that it exists, it’s making the universe expand at an accelerating rate, and approximately 68.3 to 70% of the universe is dark energy.

The history of the universe is outlined in this infographic. NASA

A Brief History

It All Started With Cepheids

Dark energy wasn’t discovered until the late 1990s. But its origin in scientific study stretches all the way back to 1912 when American astronomer Henrietta Swan Leavitt made an important discovery using Cepheid variables, a class of stars whose brightness fluctuates with a regularity that depends on the star’s brightness.

All Cepheid stars with a certain period (a Cepheid’s period is the time it takes to go from bright, to dim, and bright again) have the same absolute magnitude, or luminosity – the amount of light they put out. Leavitt measured these stars and proved that there is a relationship between their regular period of brightness and luminosity. Leavitt’s findings made it possible for astronomers to use a star’s period and luminosity to measure the distances between us and Cepheid stars in far-off galaxies (and our own Milky Way).

Around this same time in history, astronomer Vesto Slipher observed spiral galaxies using his telescope’s spectrograph, a device that splits light into the colors that make it up, much like the way a prism splits light into a rainbow. He used the spectrograph, a relatively recent invention at the time, to see the different wavelengths of light coming from the galaxies in different spectral lines. With his observations, Silpher was the first astronomer to observe how quickly the galaxy was moving away from us, called redshift, in distant galaxies. These observations would prove to be critical for many future scientific breakthroughs, including the discovery of dark energy.

Redshift is a term used when astronomical objects are moving away from us and the light coming from those objects stretches out. Light behaves like a wave, and red light has the longest wavelength. So, the light coming from objects moving away from us has a longer wavelength, stretching to the “red end” of the electromagnetic.

Discovering an Expanding Universe

The discovery of galactic redshift, the period-luminosity relation of Cepheid variables, and a newfound ability to gauge a star or galaxy’s distance eventually played a role in astronomers observing that galaxies were getting farther away from us over time, which showed how the universe was expanding. In the years that followed, different scientists around the world started to put the pieces of an expanding universe together.

In 1922, Russian scientist and mathematician Alexander Friedmann published a paper detailing multiple possibilities for the history of the universe. The paper, which was based on Albert Einstein’s theory of general relativity published in 1917, included the possibility that the universe is expanding.

In 1927, Belgian astronomer Georges Lemaître, who is said to have been unaware of Friedmann’s work, published a paper also factoring in Einstein’s theory of general relativity. And, while Einstein stated in his theory that the universe was static, Lemaître showed how the equations in Einstein’s theory actually support the idea that the universe is not static but, in fact, is actually expanding.

Astronomer Edwin Hubble confirmed that the universe was expanding in 1929 using observations made by his associate, astronomer Milton Humason. Humason measured the redshift of spiral galaxies. Hubble and Humason then studied Cepheid stars in those galaxies, using the stars to determine the distance of their galaxies (or nebulae, as they called them). They compared the distances of these galaxies to their redshift and tracked how the farther away an object is, the bigger its redshift and the faster it is moving away from us. The pair found that objects like galaxies are moving away from Earth faster the farther away they are, at upwards of hundreds of thousands of miles per second – an observation now known as Hubble’s Law, or the Hubble-Lemaître law. The universe, they confirmed, is really expanding.

This composite image features one of the most complicated and dramatic collisions between galaxy clusters ever seen. Known officially as Abell 2744, this system has been dubbed Pandora’s Cluster because of the wide variety of different structures found. Data from NASA’s Chandra X-ray Observatory (red) show gas with temperatures of millions of degrees. In blue is a map showing the total mass concentration (mostly dark matter) based on data from NASA’s Hubble Space Telescope, the VLT (Very Large Telescope), and the Subaru telescope. Optical data from Hubble and VLT also show the constituent galaxies of the clusters. Astronomers think at least four galaxy clusters coming from a variety of directions are involved with this collision. NASA, ESA, J. Merten (Institute for Theoretical Astrophysics, Heidelberg/Astronomical Observatory of Bologna), and D. Coe (STScI)

Expansion is Speeding Up, Supernovae Show

Scientists previously thought that the universe’s expansion would likely be slowed down by gravity over time, an expectation backed by Einstein’s theory of general relativity. But in 1998, everything changed when two different teams of astronomers observing far-off supernovae noticed that (at a certain redshift) the stellar explosions were dimmer than expected. These groups were led by astronomers Adam Riess, Saul Perlmutter, and Brian Schmidt. This trio won the 2011 Nobel Prize in Physics for this work.

While dim supernovae might not seem like a major find, these astronomers were looking at Type 1a supernovae, which are known to have a certain level of luminosity. So they knew that there must be another factor making these objects appear dimmer. Scientists can determine distance (and speed) using an objects’ brightness, and dimmer objects are typically farther away (though surrounding dust and other factors can cause an object to dim).

This led the scientists to conclude that these supernovae were just much farther away than they expected by looking at their redshifts.

Using the objects’ brightness, the researchers determined the distance of these supernovae. And using the spectrum, they were able to figure out the objects’ redshift and, therefore, how fast they were moving away from us. They found that the supernovae were not as close as expected, meaning they had traveled farther away from us faster than anticipated. These observations led scientists to ultimately conclude that the universe itself must be expanding faster over time.

While other possible explanations for these observations have been explored, astronomers studying even more distant supernovae or other cosmic phenomena in more recent years continued to gather evidence and build support for the idea that the universe is expanding faster over time, a phenomenon now called cosmic acceleration.

But, as scientists built up a case for cosmic acceleration, they also asked: Why? What could be driving the universe to stretch out faster over time?

Enter dark energy.

What Exactly is Dark Energy?

Right now, dark energy is just the name that astronomers gave to the mysterious “something” that is causing the universe to expand at an accelerated rate.

Dark energy has been described by some as having the effect of a negative pressure that is pushing space outward. However, we don’t know if dark energy has the effect of any type of force at all. There are many ideas floating around about what dark energy could possibly be. Here are four leading explanations for dark energy. Keep in mind that it’s possible it’s something else entirely.

Vacuum Energy

Some scientists think that dark energy is a fundamental, ever-present background energy in space known as vacuum energy, which could be equal to the cosmological constant, a mathematical term in the equations of Einstein’s theory of general relativity. Originally, the constant existed to counterbalance gravity, resulting in a static universe. But when Hubble confirmed that the universe was actually expanding, Einstein removed the constant, calling it “my biggest blunder,” according to physicist George Gamow.

But when it was later discovered that the universe’s expansion was actually accelerating, some scientists suggested that there might actually be a non-zero value to the previously-discredited cosmological constant. They suggested that this additional force would be necessary to accelerate the expansion of the universe. This theorized that this mystery component could be attributed to something called “vacuum energy,” which is a theoretical background energy permeating all of space.

Space is never exactly empty. According to quantum field theory, there are virtual particles, or pairs of particles and antiparticles. It’s thought that these virtual particles cancel each other out almost as soon as they crop up in the universe, and that this act of popping in and out of existence could be made possible by “vacuum energy” that fills the cosmos and pushes space outward.

While this theory has been a popular topic of discussion, scientists investigating this option have calculated how much vacuum energy there should theoretically be in space. They showed that there should either be so much vacuum energy that, at the very beginning, the universe would have expanded outwards so quickly and with so much force that no stars or galaxies could have formed, or… there should be absolutely none. This means that the amount of vacuum energy in the cosmos must be much smaller than it is in these predictions. However, this discrepancy has yet to be solved and has even earned the moniker “the cosmological constant problem.”

Quintessence

Some scientists think that dark energy could be a type of energy fluid or field that fills space, behaves in an opposite way to normal matter, and can vary in its amount and distribution throughout both time and space. This hypothesized version of dark energy has been nicknamed quintessence after the theoretical fifth element discussed by ancient Greek philosophers.

It’s even been suggested by some scientists that quintessence could be some combination of dark energy and dark matter, though the two are currently considered completely separate from one another. While the two are both major mysteries to scientists, dark matter is thought to make up about 85% of all matter in the universe.

Space Wrinkles

Some scientists think that dark energy could be a sort of defect in the fabric of the universe itself; defects like cosmic strings, which are hypothetical one-dimensional “wrinkles” thought to have formed in the early universe.

A Flaw in General Relativity

Some scientists think that dark energy isn’t something physical that we can discover. Rather, they think there could be an issue with general relativity and Einstein’s theory of gravity and how it works on the scale of the observable universe. Within this explanation, scientists think that it’s possible to modify our understanding of gravity in a way that explains observations of the universe made without the need for dark energy. Einstein actually proposed such an idea in 1919 called unimodular gravity, a modified version of general relativity that scientists today think wouldn’t require dark energy to make sense of the universe.

The Future

Dark energy is one of the great mysteries of the universe. For decades, scientists have theorized about our expanding universe. Now, for the first time ever, we have tools powerful enough to put these theories to the test and really investigate the big question: “what is dark energy?”

NASA plays a critical role in the ESA (European Space Agency) mission Euclid (launched in 2023), which will make a 3D map of the universe to see how matter has been pulled apart by dark energy over time. This map will include observations of billions of galaxies found up to 10 billion light-years from Earth.

NASA’s Nancy Grace Roman Space Telescope, set to launch by May 2027, is designed to investigate dark energy, among many other science topics, and will also create a 3D dark matter map. Roman’s resolution will be as sharp as NASA’s Hubble Space Telescope’s, but with a field of view 100 times larger, allowing it to capture more expansive images of the universe. This will allow scientists to map how matter is structured and spread across the universe and explore how dark energy behaves and has changed over time. Roman will also conduct an additional survey to detect Type Ia supernovae.

In addition to NASA’s missions and efforts, the Vera C. Rubin Observatory, supported by a large collaboration that includes the U.S. National Science Foundation, which is currently under construction in Chile, is also poised to support our growing understanding of dark energy. The ground-based observatory is expected to be operational in 2025.

The combined efforts of Euclid, Roman, and Rubin will usher in a new “golden age” of cosmology, in which scientists will collect more detailed information than ever about the great mysteries of dark energy.

Additionally, NASA’s James Webb Space Telescope (launched in 2021), the world’s most powerful and largest space telescope, aims to make contributions to several areas of research, and will contribute to studies of dark energy.

NASA’s SPHEREx (the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) mission, scheduled to launch no later than April 2025, aims to investigate the origins of the universe. Scientists expect that the data collected with SPHEREx, which will survey the entire sky in near-infrared light, including over 450 million galaxies, could help to further our understanding of dark energy.

NASA also supports a citizen science project called Dark Energy Explorers, which enables anyone in the world, even those who have no scientific training, to help in the search for dark energy answers.

*A brief note*

Lastly, to clarify, dark energy is not the same as dark matter. Their main similarity is that we don’t yet know what they are!

By Chelsea Gohd

NASA’s Jet Propulsion Laboratory

We have long taken it for granted that gravity is one of the basic forces of nature – one of the invisible threads that keeps the universe stitched together. But suppose that this is not true. Suppose the law of gravity is simply an echo of something more fundamental: a byproduct of the universe operating under a computer-like code.

That is the premise of my latest research, published in the journal AIP Advances. It suggests that gravity is not a mysterious force that attracts objects towards one another, but the product of an informational law of nature that I call the second law of infodynamics.

It is a notion that seems like science fiction – but one that is based in physics and evidence that the universe appears to be operating suspiciously like a computer simulation.

In digital technologies, right down to the apps in your phone and the world of cyberspace, efficiency is the key. Computers compact and restructure their data all the time to save memory and computer power. Maybe the same is taking place all over the universe?

Information theory, the mathematical study of the quantification, storage and communication of information, may help us understand what’s going on. Originally developed by mathematician Claude Shannon, it has become increasingly popular in physics and is used in a growing range of research areas.

In a 2023 paper, I used information theory to propose my second law of infodynamics.

This stipulates that information “entropy”, or the level of information disorganisation, will have to reduce or stay static within any given closed information system. This is the opposite of the popular second law of thermodynamics, which dictates that physical entropy, or disorder, always increases.

Take a cooling cup of coffee. Energy flows from hot to cold until the temperature of the coffee is the same as the temperature of the room and its energy is minimum – a state called thermal equilibrium. The entropy of the system is a maximum at this point – with all the molecules maximally spread out, having the same energy. What that means is that the spread of energies per molecule in the liquid is reduced.

If one considers the information content of each molecule based on its energy, then at the start, in the hot cup of coffee, the information entropy is maximum and at equilibrium the information entropy is minimum. That’s because almost all molecules are at the same energy level, becoming identical characters in an informational message. So the spread of different energies available is reduced when there’s thermal equilibrium.

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But if we consider just location rather than energy, then there’s lots of information disorder when particles are distributed randomly in space – the information required to keep pace with them is considerable. When they consolidate themselves together under gravitational attraction, however, the way planets, stars and galaxies do, the information gets compacted and more manageable.

In simulations, that’s exactly what occurs when a system tries to function more efficiently. So, matter flowing under the influence of gravity need not be a result of a force at all. Perhaps it is a function of the way the universe compacts the information that it has to work with.

Here, space is not continuous and smooth. Space is made up of tiny “cells” of information, similar to pixels in a photo or squares on the screen of a computer game. In each cell is basic information about the universe – where, say, a particle is – and all are gathered together to make the fabric of the universe.

If you place items within this space, the system gets more complex. But when all of those items come together to be one item instead of many, the information is simple again.

The universe, under this view, tends to naturally seek to be in those states of minimal information entropy. The real kicker is that if you do the numbers, the entropic “informational force” created by this tendency toward simplicity is exactly equivalent to Newton’s law of gravitation, as shown in my paper.

This theory builds on earlier studies of “entropic gravity” but goes a step further. In connecting information dynamics with gravity, we are led to the interesting conclusion that the universe could be running on some kind of cosmic software. In an artificial universe, maximum-efficiency rules would be expected. Symmetries would be expected. Compression would be expected.

And law – that is, gravity – would be expected to emerge from these computational rules.

We may not yet have definitive evidence that we live in a simulation. But the deeper we look, the more our universe seems to behave like a computational process.

Melvin M. Vopson, Associate Professor of Physics, University of Portsmouth

This article is republished from The Conversation under a Creative Commons license. Read the original article.