Why is it in the News?

One of the biggest mysteries in cosmology is the ‘Hubble tension’, the puzzle that the expansion of the Universe we see today doesn’t match what we think it should be from looking at the early cosmos.

What is Hubble Tension?

• The Hubble tension refers to a puzzling disagreement between two methods of measuring the universe's expansion rate, represented by the Hubble constant (H0).
• The Hubble constant describes how fast galaxies move away from each other due to cosmic expansion.
• Researchers employ two primary approaches to estimate H0: the cosmic distance ladder and analysis of the cosmic microwave background (CMB).

Cosmic Microwave Background (CMB):

• CMB constitutes a ubiquitous sea of photons, remnants of the Big Bang's aftermath.
• Scientists scrutinize CMB for temperature variations and employ intricate trigonometric techniques to analyze its large-scale properties.
• This analysis culminates in an estimation of cosmic expansion at approximately 68 (km/s)/Mpc.

Cosmic Distance Ladder:

• This method facilitates the measurement of distances to celestial objects spanning various proximity ranges.
• Notably, Cepheid variable stars, which exhibit predictable luminosity fluctuations over time, serve as crucial distance indicators.
• By gauging the brightness of Cepheid variables, researchers can infer their distances, leading to an estimation of H0 around 73 (km/s)/Mpc.

Discrepancy and Hubble Tension:

• The utilization of these two distinct measurement methods yields slightly divergent values for H0, resulting in the emergence of the Hubble tension.

Significance of the Hubble Tension:

• The presence of the Hubble tension suggests potential implications, including unexplored physical phenomena or systematic errors in measurement techniques.
• Resolving this tension is imperative to enhance our comprehension of the universe's expansion dynamics and the fundamental laws governing it.