Dark Energy Is Not Constant: A New Look at the Universe's Acceleration
The Universe is a grand highway where galaxies, like cars, are moving apart faster and faster. The gas pedal is controlled by mysterious dark energy.
Dark Energy as a Spring: A Model with No Tuning
In the late 1990s, Saul Perlmutter, Adam Riess, and Brian Schmidt observed supernovae and found: the universe is expanding faster and faster.
Cosmos Without Averaging: How Inhomogeneity Changes the Universe
In one hospital ward it's +40°C, in another +10°C, and on average it's +25°C. If temperature affected something nonlinearly (say, the rate of bacterial growth) the average would give a wrong prediction. The same problem arises when cosmologists describe a universe where galaxies are packed into clusters and voids yawn between them.
A Couple of Formulas Describe the Universe's Acceleration
Standard cosmology relies on the Big Bang and dark energy, but there is an alternative — the Lemaître–Tolman–Bondi model, where the Universe's expansion is explained not by a mysterious force, but by natural unevenness in the distribution of matter — clusters of…
The Universe Grew Up Unevenly
When the first stars ignited, their ultraviolet light began stripping electrons from hydrogen atoms. The universe transformed from a neutral fog into transparent plasma. This process, cosmic reionization, proceeded unevenly: slowly at first, like a fire catching in damp wood, then faster as the flames spread through dry tinder.
The Universe Was Speeding Up — Now It's Slowing Down
Imagine inflating a balloon. At first, it expands slowly; then someone gives a sharp blast of air, and it swells faster. But as the airflow weakens, the balloon's growth slows again. According to a new study, the Universe has behaved much the same way: after the Big Bang, it expanded, then suddenly accelerated, and now that acceleration is fading.
How the Universe's Expansion Rate Picks the Best Scenario
The universe in its first moments is like an inflating balloon. Cosmologists are trying to figure out what makes it puff up, and there's no shortage of ideas. One idea is to tweak Einstein's gravity slightly — adding an 'extra ingredient' that only kicks in at mind-boggling energies.
The Universe's Size and Expansion Are Uncertain
The Universe is like an inflating balloon. Quantum mechanics forbids measuring exactly how big it is and how fast it's inflating at the same time. This principle permeates the cosmos: a new equation states that the Universe's expansion and its size are linked by a fundamental uncertainty.
The Universe as a Pendulum: From Inflation to Ordinary Expansion
A pendulum chooses how to swing on its own. If you give it a strong push, it quickly returns to a smooth rhythm. If you hold it at its extreme position, it will stay there, but as soon as you let go, it resumes its usual motion.
The Breathing Universe
A hot coffee on the table cools down: heat spreads from the hot center to the edges. The authors suggest that the universe behaves in a similar way, just on scales of billions of light-years. Their model describes not the usual dark energy, but a smooth redistribution of energy within the cosmos, akin to the slow flow of heat from denser regions to rarefied ones.
How the Universe Became Smooth: Unraveling the First Moments
The birth of the universe resembles not an explosion, but a traffic jam. At first, a tiny fraction of a second after the Big Bang, space expanded sluggishly, like cars stuck in gridlock. Then came a sharp surge — accelerated expansion, which cosmologists call inflation.
Dark Matter Decays, the Universe Smooths Out
On the kitchen counter, there's a flour scale and a measuring cup for water. Individually, they're precise, but when you bake bread, the recipe calls for the perfect ratio. Astronomers have a similar dispute about the universe's expansion rate.
A Universe Without Dark Energy? A Simple Model Bypasses the Standard One
The Universe follows strict rules, like players at a table. One of them: gravity always attracts, and energy cannot be negative.
The Universe as a Distant Forest: Testing Homogeneity
The Universe resembles a dense forest: up close, individual galaxy-trees are visible, gathered into groves, but from a distance everything merges into a solid green canopy. The boundary beyond which the cosmos becomes homogeneous is called the angular scale of homogeneity: it's the size of a patch of sky from which galaxies are distributed evenly.
Dark Energy from the Depths of the Atomic Nucleus
The universe is expanding at an accelerating rate, like dough that keeps rising faster even though the yeast ran out long ago. For twenty years, astronomers have been searching for the cause and call it dark energy. But what it is remains a mystery.
New work proposes an unexpected source: the vacuum inside the atomic nucleus.
A Cosmic Compromise: One Number Settles Three Disputes
Cosmology is like an orchestra where different sections suddenly start playing out of sync. Measurements of the universe's expansion rate (the Hubble constant) from the early and late universe give different numbers.
Dark Energy: Inevitability Born of Symmetry
The explosion of a distant supernova told us something hard to believe: the universe is expanding faster and faster. The engine of this acceleration is dark energy — nearly 70% of everything that exists.
Three Faces of the Cosmos: Geometry, Growth, and the Beginning
The standard cosmological model ΛCDM (which includes dark energy and cold dark matter) is the score of a cosmic symphony. It describes how space expanded after the big bang. How dark matter clumped together. How galaxies ignited. For a long time, everything played flawlessly.
The Universe Couldn't Have Been Expanding Forever
A spotlight beam fades into the darkness, but if you trace it backward, you hit the lamp. The history of the universe might be the same: tracing its expansion backward, we run into a beginning.
Physicists took the simplest model — a universe that stretches equally in all directions, like a cube with all sides growing.