A recent JWST observation of a unique, gravitationally lensed Type Ia supernova called SN H0pe yielded a value for the Hubble constant of 75.4 km/s/Mpc +8.1/-5.5 km/s/Mpc.
The value of the Hubble constant (H0) directly influences estimates of the universe's age. A higher Hubble constant, such as the latest JWST-based measurement of 75.4 km/s/Mpc, implies a faster rate of expansion. This, in turn, suggests that the universe has reached its current size more quickly, indicating a younger age than estimates derived from a lower Hubble constant.
If H0 is around 75.4 km/s/Mpc, it would suggest an age closer to 13 billion years, which is younger than the roughly 13.8 billion years estimated using the lower value of around 67 km/s/Mpc from Planck's observations of the early universe's cosmic microwave background (CMB) radiation .
The persistence of this "Hubble tension" — the discrepancy between local and early-universe measurements of H0 — raises questions about whether new physics could be affecting our understanding of cosmic expansion and age. Some scientists speculate that unknown factors, perhaps related to dark energy or yet-unknown particles, might be influencing these measurements and altering our perception of the universe's timeline.
The differing measurements of the Hubble constant (H0) bring questions to the surface about our understanding of the universe's expansion and indirectly challenge certain assumptions underlying Einstein's general relativity, especially at cosmic scales. General relativity (GR) has been exceptionally successful in describing gravity and the large-scale structure of the universe, yet the Hubble tension might suggest that it could be incomplete or require modifications under extreme conditions.
In summary, while general relativity remains one of the best-tested theories of physics, the Hubble tension is a subtle yet significant signal that might hint at limitations or necessary extensions. It's possible that resolving this tension will require new physics that either builds on or reshapes our current understanding within the framework of general relativity.
