Catherine Heymans, the Astronomer Royal for Scotland and a professor of astrophysics at the University of Edinburgh, explores the perplexing Hubble tension—conflicting measurements impacting the universe's expansion rate. She discusses dark matter and energy's roles in this cosmological crisis and reflects on insights from the James Webb Space Telescope. The conversation also touches on the importance of observational accuracy and intriguing concepts like primordial magnetic fields and early dark energy that could reshape our understanding of the cosmos.
The ongoing Hubble tension reveals a conflict in cosmic measurements that questions either the measurement methods or the entire model of the universe.
Emerging theories, like early dark energy, are being explored to reconcile the discrepancies in the expansion rate and observations from the James Webb Space Telescope.
Deep dives
The Hubble Constant and Cosmic Expansion
The Hubble constant is crucial for determining the age of the universe, indicating how fast it is expanding. Current measurements yield two conflicting values for this constant: approximately 72 kilometers per second per megaparsec from observations of the late universe and around 67 from the cosmic microwave background. This discrepancy raises a significant issue for cosmologists, leading to questions about the accuracy of measurements or the validity of the underlying cosmic model. Understanding these numbers is essential, as they also affect our calculations regarding the universe's age, estimated at 13.8 billion years versus a younger 12.6 billion years based on varying interpretations.
Challenges with Standard Candles
Cosmologists rely on 'standard candles,' such as Cepheid variable stars and certain types of supernovae, to measure distance and speed within the universe. The methodology involves analyzing the brightness of these celestial objects to infer how far they are, while the redshift effect helps determine their velocity away from us. Factors like dust in the universe complicate these measurements, potentially leading to misinterpretations of brightness. Recent data from the James Webb Space Telescope suggests that earlier conclusions regarding the Hubble constant remain unchallenged, eliminating dust as a factor affecting measurements.
Theories Behind the Hubble Tension
The ongoing dispute over the Hubble constant has triggered various hypotheses, including the concepts of early dark energy and primordial magnetic fields, which aim to reconcile observational data with theoretical models of cosmology. The idea of early dark energy postulates that an additional force in the early universe accelerated its expansion, potentially accounting for discrepancies in observed sizes of ancient galaxies. These theories not only address the Hubble tension but also explain newfound observations from the James Webb Space Telescope regarding massive galaxies appearing earlier than predicted. As researchers pursue these complex inquiries, a breakthrough in understanding the nature of dark entities could be pivotal for advancing cosmological knowledge.
For the past 10 years cosmologists have been left scratching their heads over why two methods for measuring the universe’s rate of expansion provide totally different results. There are two possible solutions to the puzzle, known as the Hubble tension: either something is wrong with the measurements or something is wrong with our model of the universe. It was hoped that observations from the James Webb space telescope might shed some light on the problem, but instead results published last week have continued to muddy the waters. To understand why the expansion rate of the universe remains a mystery, and what might be needed to finally pin it down, Madeleine Finlay speaks to Catherine Heymans, the astronomer royal for Scotland and a professor of astrophysics at the University of Edinburgh. Help support our independent journalism at theguardian.com/sciencepod
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