Webb and Hubble telescopes affirm the universe's expansion rate, but the puzzle persists

However, a persistent difference, called the Hubble Tension, is seen between the value of the constant measured with a wide range of independent distance indicators and its value predicted from the afterglow of the Big Bang. The NASA/ESA/CSA James Webb Space Telescope has confirmed that the Hubble Space Telescope's keen eye was right all along, erasing any lingering doubt about Hubble's measurements.

One of the scientific justifications for building the NASA/ESA Hubble Space Telescope was to use its observing power to provide an exact value for the expansion rate of the universe. Prior to Hubble's launch in 1990, observations from yielded huge uncertainties. Depending on the values deduced for the expansion rate, the universe could be anywhere between 10 and 20 billion years old.

Over the past 34 years, Hubble has shrunk this measurement to an accuracy of less than one percent, splitting the difference with an age value of 13.8 billion years. This has been accomplished by refining the so-called 'cosmic distance ladder' by measuring important milepost markers known as Cepheid .

However, the Hubble value does not agree with other measurements that imply that the universe was expanding faster after the Big Bang. These observations were made by the ESA Planck satellite's mapping of the —a blueprint for how the universe would evolve structure after it cooled down from the Big Bang.

NIRCam fields superimposed on Digitized Sky Survey color images for four hosts (top) and NIRCam RGB images (F090W/F150W/F277W) showing positions of Cepheids (cyan circles) (bottom). North is up and east is to the left. Credit: The Astrophysical Journal Letters (2024). DOI: 10.3847/2041-8213/ad1ddd

NGC 5468—Cepheid host galaxy. Credit: NASA, ESA, CSA, STScI, A. Riess (JHU/STScI)

Comparison of Hubble and Webb views of a Cepheid variable star Credit: NASA, ESA, CSA, STScI, A. Riess (JHU/STScI)