“Groundbreaking Research Challenges the Reality of Dark Energy Through Supernova Insights”

The Crab Nebula, the outcome of a luminous supernova explosion witnessed by Chinese and other astronomers in 1054, located 6,500 light-years away from Earth, is captured in an image taken by the James Webb Telescope on June 3, 2024. Centrally located is a neutron star, a super-dense star formed by the supernova. This image includes the X-ray information from Chandra along with infrared data from the Webb space telescope.
| Photo Credit: Reuters

By observing light from distant exploding stars known as supernovas, astronomers made a significant discovery in 1998: the universe is not merely expanding – its expansion is accelerating. But what drives this speedup?

Introducing dark energy. It stands as one of the most disputed and captivating missing pieces in contemporary physics – a perplexing form of energy presumed to uniformly pervade all of space. In the currently prevailing model of modern cosmology, dark energy is considered the force propelling the accelerated expansion of the universe.

But what if there exists an alternative explanation that excludes dark energy? A recent investigation utilizing data from supernovas suggests that there may indeed be such an explanation, referred to as the Timescape model.

This revelation has the potential to fundamentally challenge our comprehension of the cosmos, so let’s explore further.

What is dark energy?

The foundation of modern cosmology rests on the Lambda-Cold Dark Matter (Lambda-CDM) model. This model outlines a universe where dark energy – symbolized by Λ, the Greek letter Lambda – is the key driver behind the universe’s accelerating expansion.

According to this model, galaxies are interacting through the influence of an invisible web of dark matter composed of heavy particles that remain non-interactive. The effects of this cold dark matter can be observed exclusively through gravitational pull.

Dark energy constitutes nearly 70% of the universe’s total energy budget, yet its precise nature continues to be one of the most significant enigmas in physics.

Some interpretations propose that dark energy could be associated with the energy of the vacuum, while other research has attempted to depict it as a new, evolving energy field dispersed throughout space.

A recent study from the international DESI collaboration tracking the universe’s expansion hinted that dark energy may be diminishing over time.

It is also feasible that our current gravitational theory (Einstein’s general relativity) is inadequate. It may need an extension to adequately describe gravitational interactions on cosmological scales – distances reaching millions to billions of light-years.

What is the Timescape model?

Matter – including dark matter, gas, galaxies, star clusters, and super clusters – is unevenly distributed across the cosmos.

However, for the Lambda-CDM model, we hypothesize that the universe is both homogeneous and isotropic. This implies that, at cosmic scales, the matter distribution appears even and uniform. Any clusters or voids we may observe are deemed inconsequential due to the vastness of the universe.

In contrast, the Timescape model considers the irregular distribution of matter. It posits that our complex cosmic structure – comprising galaxies, clusters, filaments, and enormous cosmic voids – directly influences our interpretation of the universe’s expansion.

This suggests that the universe is not expanding uniformly.

According to the Timescape model, the rate of expansion varies across distinct regions, contingent on their density.

The crucial parameter in the Timescape model is the “void fraction”: it measures the share of space occupied by expanding voids.

Gravity dictates that voids expand more rapidly than denser areas – they possess less matter to restrain them, enabling space to enlarge more freely. This produces an average effect that can create a perception of acceleration similar to that attributed to dark energy in the Lambda-CDM framework.

In summary, the Timescape model implies that the perceived acceleration of the universe’s expansion may be an illusion. The speed of expansion varies based on one’s location within the universe.

What did the study uncover?

The researchers of the recent study examined one of the largest compilations of Type Ia supernovas, known as the Pantheon+ dataset. These supernovas serve as a dependable standard to evaluate cosmological models.

The team analyzed two primary models: the conventional Lambda-CDM (our “vanilla” interpretation of the universe), and the Timescape model.

When assessing nearby bright supernovas, the Timescape model provided a better explanation than our standard model. However, this was solely statistical, revealing a “very strong” inclination in the data.

Even when they investigated more distant supernovas, where we’d expect a more uniform spread, Timescape still performed slightly better than the routine model.

The conclusion? The Timescape model, which emphasizes how cosmic “clumps and voids” alter our perception of the universe’s growth, may more accurately reflect the true character of our universe’s expansion. This is particularly true for our local universe – filled with numerous voids and filaments, which influence our perception of expansion.

How robust is the evidence, then?

There are significant qualifications. The analysis does not take into account peculiar velocities – random, small-scale motions of galaxies that may influence supernova readings. They also do not consider Malmquist bias, in which brighter supernovas are more likely to be captured in the data purely because they are easier to detect.

These potential errors could significantly undermine their findings. Moreover, the study did not leverage the most recent DES5yr dataset of supernovas, which is more consistent and uniform in data collection compared to Pantheon+, making it potentially more reliable for comparative analysis.

Numerous other sources, besides supernovas, currently support the Lambda-CDM model, notably baryon acoustic oscillations and gravitational lensing. Future research would need to incorporate these elements into the Timescape model.

Nevertheless, this new study presents the Timescape model as an exciting alternative to Lambda-CDM. Ultimately, the implication is that the acceleration of our universe is an illusion stemming from the uneven distribution of matter with large cosmic voids expanding quicker than denser regions.

If verified, this could signify a transformative paradigm shift in cosmology.

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