Hubble Tension Explained: Is Our Cosmological Model Breakable?

Overview

Alex McColgan from Astrum traces the story of the expanding universe, explaining how Hubble’s 1929 measurements led to the Big Bang paradigm and how today’s conflicting estimates of the Hubble constant challenge this framework. The video surveys the two main measurement paths—the cosmic distance ladder from redshift observations and the early-universe imprint in the cosmic microwave background—and highlights recent results that widen the gap rather than close it.

What is at stake

The apparent tension could imply missing physics, data systematics, or the need for a revised cosmological model. The discussion covers potential resolutions ranging from new physics ideas like evolving dark energy or decaying dark matter to a provocative, slow rotation of the universe proposed in 2025. The host emphasizes cautious openness to new concepts while preserving the core success of current cosmology.

Introduction

In this video, Astrum’s Alex McColgan reviews the Hubble constant, the rate at which the universe expands, and explains why its precise value matters for the age, size, and fate of the cosmos. The narrative travels from the historical roots of cosmology to modern measurements that test the limits of our standard model.

Hubble’s Legacy

The history begins with Edwin Hubble’s 1929 discovery that distant galaxies recede, establishing space itself as expanding. Hubble used Cepheid variables and Leavitt’s law to calibrate distances, confirming that Andromeda is outside the Milky Way and paving the way for a new cosmology. This discovery set the stage for decades of refining the expansion rate and for tying it into the Big Bang model.

Two Roads to H0

Today, there are two principal methods to measure the current expansion rate. The late-universe method uses the cosmic distance ladder, improving distance measurements to distant galaxies through standard candles like Cepheids and Type Ia supernovae, yielding a Hubble constant around 73.5 km/s/Mpc. The early-universe method rewinds to the Big Bang with the cosmic microwave background, using observations from WMAP and Planck to predict a lower H0 around 67.4 km/s/Mpc. The discrepancy between these pathways is the Hubble tension.

Recent Measurements and Implications

Independent approaches such as megamaser distances and new supernova analyses have reinforced values near the higher end, while Planck-based estimates remain lower. The tension is not merely statistical noise; it has prompted discussions about fundamental physics, including possible modifications to dark energy, dark matter, or the behavior of gravity itself, and even new physics that could reconcile the two timelines without violating known laws.

Bold Proposals and the Spin Idea

Among proposed solutions, a bold and controversial idea gaining traction in 2025 suggests a slow rotation of the universe. If real, this rotation could affect cosmic expansion histories, potentially aligning the lower early-universe predictions with higher late-time measurements. While preliminary, this idea highlights how cosmology continues to evolve when confronted with data that do not fit neatly into the standard model.

Outlook

The video concludes with a hopeful note: the Hubble tension may push physics forward rather than force a complete rewrite of cosmology. Ongoing observations, improved distance indicators, and new theoretical developments will determine whether the universe truly requires a revised framework or if the missing pieces can be explained within our current understanding.