The James Webb has something new to tell us, and that is, it has managed to confirm that the universe does not expand the same everywhere. And astronomers are also surprised, because it has been thanks to Webb and Hubble that they have been able to complete this information, and it even has its own name: Hubble Tension. Since we know you love astronomy, we are going to tell you everything we know about this phenomenon as surprising as it is unsettling..
What is this “Hubble Tension”?
Let’s see, apparently there are two different ways to calculate at what rate the universe expands, and both give different results, like someone looking at the number 6 from below and thinking it is a 9, both are right.
One of the methods is based on cosmic microwave background radiation, using data from the Planck satellite. With that, it is estimated that the universe expands at about 67 kilometers per second per megaparsec. The other method is based on the so-called Cepheid stars, which are a kind of cosmic “lighthouses” that allow distances to be measured. First Hubble did it, and then Webb confirmed it, and that calculation gives a speed of 74 km/s/Mpc.
The difference between 67 and 74 may seem like nothing, but remember we are talking about science, about physics! And the worst part of all is that both ways of measuring are correct. That is, someone is right… but also wrong.
What does the James Webb do?
Until recently, many thought the difference was due to an observation error. That Hubble could be confusing the Cepheids with other stars, that there might be interferences… But James Webb, with its much more precise infrared technology, came to clear up doubts. In 2023 it confirmed that the Cepheids Hubble had measured were correctly identified. No optical errors or miscalculations, the problem was not the telescope with which they measured, it is the universe itself!
“Once the measurement errors are eliminated, what remains is the real and exciting possibility that we have misunderstood the universe” -Adam Riess, Johns Hopkins University.
And now what?
A mess! If the universe is expanding faster than the model we believed predicts, it means that there is something out there we still don’t understand. It could be a form of energy we don’t yet know, new particles, or even that the famous Big Bang did not happen the way we think, for now everything is a blessed mystery. What is clear is that, as Nobel laureate Adam Riess said, if errors have already been ruled out, what remains is the possibility that we are misunderstanding the entire history of the universe!
Teamwork between telescopes
This discovery would not have been possible without the collaboration between Hubble and Webb. More than a thousand Cepheid stars were analyzed across five different galaxies, and in all cases the results matched. The famous “cosmic ladder” with which we measure distances is still standing. But that consistency is precisely what reinforces the problem: it is no longer a one-off anomaly. It is a pattern we cannot ignore.
Many scientists no longer call it “tension,” but directly “crisis of cosmology,” is it a crisis?
What can we expect now?
There are no answers yet. Only bigger and bigger questions. It may be necessary to introduce new particles, review dark energy, or even modify Einstein’s equations, which have been the foundation of modern physics for more than a hundred years. Whatever it is, the universe is telling us that we still do not fully understand it!