Comprehending the expansion of the universe without using 'Dark Energy'

Why is the universe expanding at an ever-increasing rate? This is one of the most exciting yet unresolved questions in modern physics. Because it cannot be fully answered using our current physical worldview, researchers assume the existence of a mysterious "dark energy." However, its origin remains unclear to this day.

An international research team has come to the conclusion that the expansion of the universe can be explained—at least in part—without dark energy.

In physics, the evolution of the universe has so far been described by the general theory of relativity and the so-called Friedmann equations. However, in order to explain the observed expansion of the universe on this basis, an additional "dark energy term" must be manually added to the equations.

This unsatisfactory solution prompted the researchers to take a different approach. Their findings, published in the Journal of Cosmology and Astroparticle Physics, are based on an extension of general relativity (GR) by the later developed model of Finsler gravity. Unlike the original explanatory approach of GRT, the Finsler model allows for a more accurate modeling of the gravitational force of gases, as it is based on a more general spacetime geometry than GRT.

When the research team calculated the Finsler extension of the Friedmann equations, they made an exciting discovery: The Finsler-Friedmann equations already predict an accelerated expansion of the universe in a vacuum—without the need to introduce additional assumptions or "dark energy" terms.

We may now be able to explain the accelerated expansion of the universe without dark energy, based on a generalized spacetime geometry, say the researchers. The new geometry opens up completely new possibilities for better understanding the laws of nature in the cosmos.

Christian Pfeifer et al, From kinetic gases to an exponentially expanding universe—the Finsler-Friedmann equation, Journal of Cosmology and Astroparticle Physics (2025). DOI: 10.1088/1475-7516/2025/10/050. On arXiv (2025). DOI: 10.48550/arxiv.2504.08062

Bats' brains reveal a global neural compass that doesn't depend on the moon and stars

Some 40 kilometers east of the Tanzanian coast in East Africa lies Latham Island, a rocky, utterly isolated and uninhabited piece of land about the size of seven soccer fields. It was on this unlikely patch of ground that  researchers recorded—for the first time ever—the neural activity of mammals in the wild.

In their study, published in Science, the team used a tiny device to record, at the level of single neurons, the brain activity of fruit bats as they flew around the island. The scientists discovered that the bats' neuronal "compass" is global: It provides stable directional information across the entire island and does not depend on the moon or stars.

Many species share the behavioral ability to orient themselves using an "internal compass," and it is quite possible that humans rely on the same neural mechanism that was studied in these bats.

They found that every time the bats flew with their heads pointing in a particular direction—north, for instance—a unique group of neurons became active, creating an "internal compass." Navigation by means of directional neurons had previously been observed in the lab, but this was the first evidence that it happens in nature as well. When the researchers analyzed the recordings from different parts of the island, they discovered that the activity of the head-direction cells was consistent and reliable across the entire island, enabling the bats to orient themselves over a large geographical area.

 The compass is global and uniform: No matter where the bat is on the island and no matter what it sees, specific cells always point in the same direction—north stays north and south stays south. 

 Shaked Palgi et al, Head-direction cells as a neural compass in bats navigating outdoors on a remote oceanic island, Science (2025). DOI: 10.1126/science.adw6202. www.science.org/doi/10.1126/science.adw6202

Scientists Just Discovered a Whole New Type of Connection Between Neurons

Super-resolution microscopes have revealed a whole new type of connection between neurons in mouse and human brains.

In the lab,  researchers identified tiny tubular bridges in the branching tips of cultured neurons. In further tests on mouse models of Alzheimer's disease, it appeared the bridges were shuttling calcium and disease-related molecules directly between cells.

Similar] structures can transport a vast range of materials, from small ions (10⁻¹⁰m) to large mitochondria (10⁻⁶ m)," the team writes in their paper.

In cultured neurons, we observed these nanotubes forming dynamically and confirmed that they possessed a distinct internal structure, setting them apart from other neuronal extensions.

Neurons are well known for passing rapid messages to each other using synapses to transmit both electrical and chemical information. Yet, other cell types are known to use physically connecting bridging tubes to exchange molecules. Researchers have just confirmed that a similar type of tube bridge occurs in neurons too, using advanced imaging and machine learning.

The researchers observed the nanotubes transporting amyloid-beta molecules that they had injected into mouse brain cells. These molecules have been implicated in neurodegenerative diseases like Alzheimer's, where they tend to clump together abnormally. When researchers stopped the bridges from forming, the amyloid-beta stopped spreading between cells, too, confirming that the nanotubes acted as direct conduits.

The computational model supported these findings, predicting that overactivation in the nanotube network could accelerate the toxic accumulation of amyloid in specific neurons, thereby providing a mechanistic link between nanotube alterations and the progression of Alzheimer's pathology," the researchers explain. 

https://www.science.org/doi/10.1126/science.adr7403