The age of the Universe can be derived by measuring its current rate of expansion and then extrapolating backwards. In practice, however, we also have to know how that expansion rate may have changed through time, and this is dictated by the matter composition and energy density of the Universe.
Fortunately, this information is embedded in the tiny temperature fluctuations found in the cosmic microwave background, the faint glow of light that fills the Universe with residual heat left over from the Big Bang.
The latest estimate, in 2021, sets the age of the Universe at 13.797 billion years, using the so-called Lambda-CDM concordance model of cosmology. This age may be a problem, however.
A study from 2013 suggested that a particular star, HD 140283 (since dubbed the ‘Methuselah star’), could be older than this; 14.46 ± 0.8 billion years. Although other studies suggest a different age, some researchers have questioned whether it’s the age of the Universe that’s in error.
The discovery of galaxies existing a mere 300 million years or so after the Big Bang, in an advanced state of evolution, also compounds this problem.
Researchers have suggested solutions. In 1929, Swiss astronomer Fritz Zwicky proposed that the redshift seen in distant galaxies wasn’t due to their motion away from us. He suggested it’s due to the gradual loss of energy by photons over vast cosmic distances.
Recently, astronomers have resurrected this idea, allowing it to coexist with an expanding Universe. In this way, it becomes possible to reinterpret the redshift as a hybrid phenomenon.
This alternative theory allows certain fundamental constants (called coupling constants) to vary over cosmic time. This changes the timescale for the formation of galaxies at high redshifts, from a few hundred million years to several billion years.
This could explain the advanced level of development observed in those ancient galaxies. This newly devised theory puts the Universe at a grand old age of 26.7 billion years old.
At present, however, there’s no known mechanism that allows photons to lose energy in the way required for ‘tired light’ theories. So, the theory is currently regarded as no more than an interesting mathematical possibility.
This article is an answer to the question (asked by Ana Castro, via email) 'How old is the Universe, really?'
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