Saturday, December 21, 2024

dark energy debate timescape expansion

Dark Energy Debate: Physicists Question Its Role in Expanding the 'Lumpy' Universe

Introduction to the Dark Energy Debate

Artistic depiction of the cosmic web with galaxy clusters, voids, and an overlay comparing dark energy and timescape models.

Researchers investigating the expansion of the universe propose that dark energy, long considered one of science's greatest mysteries, may not exist.

The results of their analysis are published in the journal Monthly Notices of the Royal Astronomical Society Letters.

The Traditional Assumption: Isotropic Cosmic Expansion

Over the past 100 years, scientists have generally operated under the assumption of isotopic cosmic expansion, with dark energy serving as a provisional explanation for mysterious, poorly understood physics.

The New Challenge: Irregular, "Lumpier" Universe Expansion

Researchers at the University of Canterbury in Christchurch, New Zealand, are challenging conventional views, employing refined supernovae light curve analysis to suggest the universe expands in a more irregular, "Lumpier" manner.

The Timescape Model of Cosmic Expansion

The findings bolster the "Timescape" model of cosmic expansion, which eliminates the need for dark energy, attributing differences in light stretching to time and distance calibration rather than cosmic acceleration.

Gravitational Time Dilation and Its Role

The theory incorporates gravitational time dilation, where a clock in the emptiness of space ticks more rapidly than one within a galaxy.

The model proposes that a clock within the Milky Way runs approximately 35% slower than one situated in the average position of large cosmic voids. Consequently, billions of additional years would pass in voids, facilitating greater spatial expansion and creating the illusion of accelerated expansion as these voids increasingly dominate the universe.

Dark Energy Misconception and the Need for a New Approach

Professor David Wiltshire, the study's lead author, remarked, "Our research demonstrates that dark energy is not required to explain the apparent acceleration of the universe's expansion."

"Dark energy is mistakenly identified as variations in the kinetic energy of expansion, which is inherently uneven in a universe as heterogeneous as ours."

He added, "The study offers persuasive evidence that could address some of the fundamental mysteries of our expanding universe."

"New data could resolve the universe's greatest mystery within the next decade."

The Lambda Cold Dark Matter (ΛCDM) Model and Its Challenges

Dark energy is widely believed to be a weak repulsive force, acting independently of matter, comprising approximately two-thirds of the universe's mass-energy density.

The Lambda Cold Dark Matter (ΛCDM) model necessitates dark energy to account for the observed acceleration int he universe's expansion rate.

Researchers derived this conclusion from measurements of supernova distances in distant galaxies, which seem farther than expected without accelerated cosmic expansion.

Discrepancies in Cosmic Expansion and Hubble Tension

Nevertheless, recent observations are progressively questioning the current rate of the universe's expansion.

Initial evidence from the Cosmic Microwave Background (CMB), the afterglow of the Big Bang, reveals discrepancies between the early and current rates of cosmic expansion, a phenomenon referred to as 'Hubble tension."

New Data from DESI and Its Impact

Additionally, a new analysis of high-precision data from the Dark Energy S pectroscopic Instrument (DESI) reveals that models incorporating evolving dark energy fit the observations better than the ΛCDM model.

The Complex Structure of the Universe: A Cosmic Web

Both the Hubble tension and the new insights uncovered by DESI present challenges for models that rely on the simplified cosmic expansion law established 100 years agoFriedmann's equation.

This assumption relies on the notion that the universe expands uniformly on average, as though all cosmic structures could be blended into a homogeneous state, devoid of distinguishing features. In reality, however, the universe is characterized by a complex web of galaxy clusters arranged in sheets and filaments, interspersed with vast, empty voids.

Why Friedmann's Equation May Not Apply to Our Universe

Professor Wiltshire emphasized, "With the vast amount of data available to us today, the 21st century offers the opportunity to answer the fundamental question: how and why does a simple average expansion law emerge from such complexity?"

"A straightforward expansion law, in line with Einstein's general relativity, need not adhere to Friedmann's equation."

Testing the Timescape Model with the Euclid Satellite

The researchers asset that the European Space Agency's Euclid satellite, launched in July 2023, is equipped to test and differentiate between the Friedmann equation and the timescape alternative. However, this will necessitate a minimum of 1,000 independent, high-quality supernova observations.

Collaborating with Pantheon+ for Improved Data

The last test of the proposed timescape model in 2017 indicated that it was only a marginally better fit than the ΛCDM for explaining cosmic expansion. As a result, the Christchurch team collaborated closely with the Pantheon+ collaboration, which had meticulously compiled a catalog of 1,535 distinct supernovae.

Robust Evidence Supporting the Timescape Model

The researchers assert that the new data offers 'robust evidence' supporting the timescape model. Additionally, it could provide a convincing solution to the Hubble tension and other anomalies associated with the universe's expansion.

The Role of Upcoming Observations in Strengthening the Timescape Model

The researchers emphasize that additional observations from Euclid and the Nancy Grace Roman Space Telescope are crucial to strengthening support for the timescape model. The current focus is on leveraging this new data to uncover the true nature of cosmic expansion and dark energy.

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Thursday, November 21, 2024

desi cosmic gravity dark energy insights

DESI Data Unveils New Insights into Gravity's Cosmic Influence

DESI instrument capturing data from galaxies and quasars at the Nicholas U. Mayall Telescope, Kitt Peak National Observatory.

Overview of Gravity's Role in the Universe

The force of gravity, pivotal in shaping our universe, magnified minor early matter fluctuations into the expansive galaxy networks visible today. Recent research employing DESI data has charted 11 billion years of cosmic development, delivering the most precise large-scale test of gravity.

What is DESI?

The Dark Energy Spectroscopic Instrument (DESI) is a global collaboration involving over 900 scientists from more than 70 institutions worldwide, overseen by the U.S. Department of Energy's Lawrence Berkeley National Laboratory.

Key Findings from DESI Research

In their recent study, DESI researchers confirmed that gravity operates in line with Einstein's general relativity, supporting the prevailing cosmological model and constraining alternative theories of modified gravity, often invoked to explain phenomena like the universe's accelerating expansion typically linked to dark energy.

Gravity and Einstein's General Relativity

Testing Gravity on Cosmic Scales

"General relativity has been extensively validated on solar system scales, but testing its applicability on much larger cosmic scales is crucial," said Pauline Zarrouk, a cosmologist at CNRS and co-leader of the analysis at the Laboratory of Nuclear and High-Energy Physics (LPNHE).

Importance of Galaxy Formation Rates

"Analyzing galaxy formation rates provides a direct means to test our theories, which, thus far, remain consistent with general relativity at cosmological scales," Zorrouk added.

Neutrino Mass and Its Implications

The research additionally set new upper boundaries on neutrino mass, the only fundamental particles whose exact masses remain undetermined.

Findings on Neutrino Mass

Earlier neutrino experiments determined that the combined mass of the three neutrino types must be at least 0.059 eV/c², compared to the electron's mass of approximately 511,000 eV/c². DESI's findings suggest the sum is less than 0.071 eV/c², narrowing the range for neutrino masses.

DESI's Groundbreaking Data on the Universe's Evolution

The DESI collaboration has published their findings in multiple papers on the FSNews365 preprint server. Leveraging data from nearly 6 million galaxies and quasars, the analysis offers a glimpse into the universe's past stretching back 11 billion years.

Advancements in Structure Growth Measurement

Remarkably, DESI achieved the most precise measurement of structure growth within a single year, exceeding results that took decades to accomplish.

Exploring DESI's Inaugural Year and Major Discoveries

This study offers a deeper exploration of DESI's inaugural year of data, which, in April, unveiled the largest-ever 3D cosmic map and suggested that dark energy may evolve with time.

Insights from April's Findings

April's findings focused on baryon acoustic oscillations (BAO), a key aspect of galaxy clustering. The new "full-shape analysis" extends this work, examining the distribution of galaxies and matter across various spatial scales.

Ensuring Accuracy: The Blinding Technique

The research involved months of meticulous work and verification. Similar to the prior study, a blinding technique was employed to conceal results until completion, reducing potential unconscious bias.

Key Insights from Dragan Huterer

"Our BAO findings and the full-shape analysis are remarkable achievements," states Dragan Huterer, a University of Michigan professor and co-leader of DESI's cosmological data interpretation team.

Looking Ahead: The Future of DESI and Cosmological Research

For the first time, DESI has examined the growth of cosmic structures, demonstrating remarkable potential to investigate modified gravity and refine dark energy models. And this is just the beginning.

Dark Energy Spectroscopic Instrument imaging the night sky

DESI's Cutting-Edge Instrumentation

DESI, a cutting-edge instrument, simultaneously captures light from 5,000 galaxies. Mounted on the Nicholas U. Mayall 4-meter Telescope at NSF's Kitt Peak National Observatory, this experiment is in its fourth year of a five-year survey and aims to collect data from 40 million galaxies and quasars by its conclusion.

Anticipated Results by Spring 2025

Researchers are now analyzing data from DESI's first three years and anticipate releasing updated insights on dark energy and the universe's expansion history by spring 2025. Early findings, indicating a possible evolution of dark energy, heighten excitement for these forthcoming results.

Uncovering the Mysteries of Dark Matter and Dark Energy

Dark matter constitutes roughly 25% of the universe, while dark energy accounts for 70%. Yet, their true nature remains elusive.

Insights from Mark Maus

"It's astonishing to think that capturing images of the universe allows us to address these profound questions," noted Mark Maus, a Ph.D. candidate at Berkeley Lab and UC Berkeley, involved in theoretical and validation modeling for the analysis.

Cultural Significance of DESI's Research Location

The DESI collaboration is privileged to undertake scientific research on I'oligam Du'ag (Kitt Peak), a mountain of profound cultural importance to the Tohono O'odham Nation.

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