It is one of the greatest puzzles in cosmology. Why two different methods used to calculate the rate at which the universe is expanding do not lead to the same result. A mystery known as the Hubble tension suggests that something may be wrong with the standard model of cosmology used to explain the forces in the universe.
Recent observations using the new James Webb Space Telescope (JWST) are now shaking up the debate about how close the mystery is to being solved.
In this episode of The Conversation Weekly podcast, two astronomy professors explain why the Hubble tension is so important to our understanding of the universe.
In February, Nobel Prize-winning physicist Adam Reiss published a new paper. She said the new JWST observations of distant stars match those obtained by the Hubble Space Telescope.
These stars, called Cepheids, are commonly used in one method of calculating the rate at which the universe is expanding. This method, known as the local distance ladder or the cosmic distance ladder, has been around since observations first made by Edwin Hubble himself in 1929. And it generally produces an expansion rate of about 73 km per second per mega parsec.
But the second method, using predictions of the cosmic microwave background left over from the Big Bang, consistently arrived at a different number for the expansion rate of the universe: 67 km per second per mega parsec.
Reiss said that while the new data confirmed earlier observations from the Hubble Space Telescope, the gap between the numbers remains unresolved. “What remains is the real and exciting possibility that we have misunderstood the universe,” he said.
However, a few months later, additional data from JWST, presented by Wendy Freedman, a physicist at the University of Chicago, using observations from a different set of stars, arrived at 69 km per second per mega parsec, a number closer to the cosmic microwave background number 67. Freedman is excited, that the numbers seem to converge.
Listen to The Conversation Great Mysteries of Physics podcast series to learn more about the biggest mysteries facing physicists today—and the radical proposals to solve them. Hosted by Miriam Frankel, it features interviews with some of the world’s leading scientists including Sean Carroll, Sabine Hossenfelder and Jim Al-Khalili.
Vicent MartÃnez and Bernard Jones are fascinated by the Hubble tension. Jones is Emeritus Professor of Astronomy at the University of Groningen in the Netherlands. MartÃnez, his former student, is now a professor of astronomy and astrophysics at the University of Valencia in Spain.
“The basic foundation of science that separates science from science fiction is our ability to verify the information we get,” explains Jones.
That’s why Martinez says the mystery of the Hubble tension still leads people to:
Research and imagine experiments and organize huge projects with complicated space observations to understand what is going on. In the end, it will affect your idea of ​​the entire universe, and you will probably have to change some basic component of your cosmological model.
Martinez and Jones have just written a book with their co-author Virginia Trimble about moments in history when scientists realized they had done something very wrong and had to adjust their thinking. MartÃnez thinks this could happen again with the Hubble strain:
It could be that, for example, a new theory of gravity could solve the problem of dark energy or dark matter. We must be open to these ideas.
Hear Bernard Jones and Vicent MartÃnez talk more about the Hubble strain and how it fits into the wider history of science on The Conversation Weekly podcast. The episode also features an introduction by Lorena Sánchez, Science Editor of The Conversation in Spain.
A transcript of this episode will be available soon.
This episode of The Conversation Weekly was written and produced by Katie Flood with assistance from Mendo Mariwany. Gemma Ware was executive producer. The sound design is by Eloise Stevens and our theme music is by Neeta Sarl. Stephen Khan is our global managing editor and Soraya Nandy helps with our transcriptions.
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