The Universe has been expanding since the Big Bang. Measuring the rate at which it is growing (the so-called Hubble constant) is essential to understanding its history and future. However, a strange discrepancy in the measurements of this constant has challenged scientists for several years. This mystery, nicknamed the Hubble tension, was revealed by observations carried out by different telescopes, notably the famous Hubble Space Telescope. Recently, new observations from the James Webb Telescope (JWST) have not only confirmed the existence of this anomaly, but also revealed that it may well originate from a fundamental aspect of the cosmos itself.
The Hubble constant and its measurement methods
The Hubble constant allows us to quantify the speed at which the Universe is expanding. It is essential to determine its size, age and development. Astronomers use two main methods to measure it, each with its advantages and limitations.
The first method is based on the study of cosmic microwave background (CMB), a kind of photograph of the early Universe taken about 380,000 years after the Big Bang. This microwave radiation provides valuable information about its state at that time. Using these data and theoretical models, the researchers estimated the Hubble constant to be approximately 67 kilometers per second per megaparsec (km/s/Mpc). This means that for every million light years, galaxies move away from us at a speed of 67 km/s.
The second, more recent method is based on the observation of variable stars Cepheidespulsating stars whose brightness varies regularly. These stars serve as standard candles that allow astronomers to measure distances in the closer Universe. By measuring the brightness of these stars, scientists calculated a Hubble constant d’environ 73 km/s/Mpc. This figure is therefore significantly higher than that obtained by the study of the cosmic microwave background, which creates a significant divergence. It is this difference which constitutes the famous Hubble tension.
The role of the James Webb telescope
Launched in 2021, the space telescope James Webb was designed to push the limits of astronomical measurement precision. With its infrared detection capability and its position far from Earth, it offers a more detailed view of the Universe than ever before. One of James Webb's key goals was to better measure the Hubble constant by refining observations of the Cepheids. Using the JWST, the researchers were able to reduce the margin of error of previous measurements from approximately 8 or 9% to only 2%.
Thanks to these high-precision data, astronomers have confirmed that the Hubble constant obtained by the Cepheid method is indeed around 73 km/s/Mpc, a higher value than that obtained from the CMB. This confirmation only accentuated the tension between the two values and reinforced the idea that there could be an as yet unknown phenomenon at the origin of this difference.
What explanations for the Hubble tension?
Faced with this discrepancy, several hypotheses have emerged to explain the Hubble tension. One of the avenues suggests that dark matter or primitive dark energy could be responsible for this anomaly. The idea is that these unknown phenomena, particularly in the early Universe, could have had a major impact on the expansion of the Universe and thus changed its rate of expansion at crucial times after the Big Bang.
Other speculations go even further, suggesting new properties of matter, exotic particles, even modifications in the laws of physics which govern the cosmos on a large scale. Theories such as the existence of new types of particles or primordial magnetic fields have also been proposed to try to explain this discrepancy.
Although these hypotheses are still largely speculative, they open the way to fascinating research into cosmological phenomena that were previously unimaginable. If these theories are confirmed, they could shake up our current conceptions of fundamental physics.
A mystery to solve
The Hubble voltage could be more than just a measurement anomaly, but a crucial clue for rethinking some of our most established cosmological theories. Researchers like Adam Riess, Nobel laureate and lead author of the Hubble constant study, point out that this enigma could point to a fundamental aspect of the cosmos that is still poorly understood. According to him, the cause of this discrepancy could reside in a never-before-seen feature of the Universe.
The next stages of research could not only provide a better understanding of this tension, but also change our vision of the cosmos. With its ability to collect precise data, the James Webb Telescope will continue to play a crucial role in unraveling this mystery. However, this phenomenon could also lead to discoveries that challenge fundamental concepts of cosmology, or even physics itself.
