Webb Confirms the Cosmos is Expanding Faster Than Expected

Sub : Sci

Sec: Space sector

Why in News

The James Webb Space Telescope (JWST) has confirmed findings by the Hubble Space Telescope that the universe is expanding at an unexpectedly rapid rate, termed the Hubble Tension. This raises questions about current cosmological models, especially regarding dark energy and dark matter, which constitute 96% of the universe but remain poorly understood.

What is Universe Expansion?

The universe has been expanding since the Big Bang, approximately 13.8 billion years ago. This is supported by the observation of galaxies moving away from us, confirmed by the redshift of their light.
The rate of this expansion is quantified by the Hubble Constant, which defines how fast galaxies recede per unit distance.

What is Hubble Tension?

Hubble Tension refers to the discrepancy in the measurements of the Hubble Constant derived from two primary methods:
- Early Universe Measurements: Using the Cosmic Microwave Background (CMB) radiation, which represents the universe’s state shortly after the Big Bang.
- Late Universe Measurements: Observing nearby supernovae and galaxies to calculate expansion rates.
- These methods yield conflicting values for Hubble Constant, creating a significant challenge in cosmology.

Causes Behind Rapid Expansion:

The rapid acceleration of the universe’s expansion is attributed to dark energy, a mysterious force counteracting gravity. Dark energy is believed to constitute about 68% of the universe.
Dark Radiation: Involves ghostly subatomic particles like neutrinos.
Exotic Gravity: Suggests the force of gravity may behave differently at cosmic scales.
Cosmological Constant: A constant energy density filling space, as proposed by Einstein’s General Relativity.
Quintessence: A dynamic field that evolves over time, unlike the cosmological constant.

Hypotheses Related to Rapid Expansion:

Early Dark Energy (EDE): Suggests that a form of dark energy existed briefly in the early universe, resolving both the Hubble tension and the unexpected brightness of early galaxies. This transient force could have accelerated the expansion shortly after the Big Bang before fading away.
Phantom Energy: A form of dark energy with an equation of state that leads to ever-increasing acceleration, potentially resulting in a “Big Rip.”
Interaction with Dark Matter: Some models propose interactions between dark energy and dark matter that influence the universe’s expansion rate.

Methods to Study Cosmic Expansion:

Measuring Galactic Distances: Observed galaxies containing Cepheid stars, which pulsate at regular intervals, serving as cosmic distance markers. Combined data from both Webb and Hubble for consistency.
Type Ia Supernovae: Standard candles to measure distances and expansion rates in the late universe.
CMB Measurements: Using satellites like Planck to analyse temperature fluctuations in the CMB.
Baryon Acoustic Oscillations (BAO): Patterns in galaxy distributions provide clues about expansion rates.
James Webb Space Telescope (JWST): Observes early galaxies to refine models of the early universe’s expansion.
HETDEX (Hobby-Eberly Telescope Dark Energy Experiment): Studies the influence of dark energy on the universe.

About Dark Matter:

A hypothesized form of matter that does not emit, absorb, or reflect light, making it invisible but detectable via its gravitational effects.
Constitutes 27% of the universe’s mass-energy content.
Influences galaxy formation and motion, providing the extra gravitational pull observed in galactic rotations.
Evidence: Gravitational lensing and the rotation curves of galaxies.

About Dark Energy:

A mysterious force driving the accelerated expansion of the universe.
Constitutes 68% of the universe’s mass-energy content.
Opposes gravity, causing galaxies to move apart at an increasing rate.
Evidence: Observations of Type Ia supernovae and the Cosmic Microwave Background (CMB).

About Cepheid Stars:

Pulsating stars whose brightness varies periodically, serving as “standard candles” for distance measurement.
Used to calculate distances to galaxies and determine the universe’s expansion rate (Hubble Constant).
Characteristics: Their luminosity is directly related to their pulsation period, enabling precise measurements.