Is the Universe 13.8 or 26.7 billion years old?
Our universe is actually 27 billion years old, almost double the current age estimate
According to the “Standard Model” of cosmology, the Universe is 68% dark energy, 27% dark matter, 5% normal matter, and is 13.8 billion years old: as measured since the hot Big Bang.
Recent observations from the James Webb Space Telescope (JWST), however, have found numerous galaxies that appear early, but look surprisingly grown-up. A new theory claims to solve this “early, grown-up galaxies” problem by changing the age of the Universe to 26.7 billion years old.
That estimate is based on assuming that the ratio of matter to light output is the same between galaxies 10 billion years apart in age. The high light output of these young galaxies could also be supermassive stars that burn out very quickly, larger stars typically forming faster than smaller stars, or many other things.
Blindly assuming a linear relationship between two things, then extrapolating is how you get the Windows loading bar circa 2000.
Separately, but just as big a potential issue, the data itself may be incorrect. Previous galaxies measured at extreme redshift values were remeasured, and found to have less extreme values. This can be as simple as there aren’t that many photons from these galaxies reaching us, so a short measurement period might not be enough to get an accurate picture.