The rate at which the universe is expanding, known as the Hubble constant, is one of the fundamental parameters for understanding the evolution and ultimate fate of the cosmos.
Article continues below
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 ground-based telescopes 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 variable stars.
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 cosmic microwave background radiationâ€â€a blueprint for how the universe would evolve structure after it cooled down from the Big Bang.
The simple solution to the dilemma would be to say that maybe the Hubble observations are wrong as a result of some inaccuracy creeping into its measurements of the deep-space yardsticks.
Then along came the James Webb Space Telescope, enabling astronomers to crosscheck Hubble's results. Webb's infrared views of Cepheids agreed with Hubble's optical-light data. Webb confirmed that the Hubble telescope's keen eye was right all along, erasing any lingering doubt about Hubble's measurements.
The bottom line is that the so-called Hubble Tension between what happens in the nearby universe compared to the early universe's expansion remains a nagging puzzle for cosmologists.
There may be something woven into the fabric of space that we don't yet understand. ■