Demystifying science | The mystery of the age of the Universe

Every week, our journalist answers scientific questions from readers.

Isn’t the age of the Universe much older than 13.8 billion years?
—Alain Wood

Probably not, despite studies published from time to time that estimate the Universe to be much older than 13.8 billion years.

“We estimate the age of the Universe using several methods,” explains Charles Steinhardt, an astrophysicist at the University of Copenhagen who has worked extensively in recent years on the problem of “impossible galaxies.”

The impossible galaxies are very old and more massive than expected with current models of star formation. Some were discovered by the space telescope James Webbwhich explores the far reaches of the Universe from an orbit 1.5 million kilometers from Earth.

“Colleagues have proposed that these very old and more massive galaxies than expected show that the Universe is older than 13.8 billion years,” says Steinhardt.

Over the course of several articles, the astrophysicist has shown that by modifying, for example, the quantity of matter found in the stars, the temperature of the Universe during the hundreds of millions of years after its birth and the proportion of small and large stars, one can easily explain impossible galaxies.

“Bigger stars are much brighter. But if there are more small stars compared to larger ones, we have more massive galaxies. As for the temperature, currently we use the current temperature of the Universe, 10 to 20 degrees Kelvin (i.e. – 263 to – 253 ^oVS). But it seems that 500 million years after the Big Bang [NDLR : le début de l’Univers], the temperature was 30 to 40 degrees Kelvin. And in the gas clouds where galaxies form, the temperature is higher. It modifies the galaxy formation equations. »

Ambulances

The “red shift” (redshift) and the rate of expansion of the Universe are other ways of calculating the age of the Universe. Red shift is the equivalent of the Doppler effect, which explains why the siren of an ambulance heading towards us sounds higher pitched than when it’s moving away – due to variations in sound frequencies. Celestial objects moving away from us are redder and those moving closer are bluer, due to variations in light frequencies. The oldest galaxies, and therefore the most distant, are moving away faster – and therefore are redder.

As for the speed of expansion of the Universe, it is calculated in particular in relation to the cosmic microwave background (CMB or CMB), the backdrop of the Universe, which is made up of radiation dating from the beginnings of the ‘Universe.

Last summer, an astrophysicist from the University of Ottawa, Rajendra Gupta, published in Monthly Notices of the Royal Astronomical Society a study affirming, in particular on the basis of the observations of the James Webb, that the Universe is twice as old as expected. Critics have pointed out that the model of galaxy formation it proposes does not take into account several other ways of calculating the age of the Universe, particularly in relation to the FDC. In an interview, Mr. Gupta indicated that his responses to these criticisms, particularly with regard to the FDC, were submitted to scientific journals.

“I think that more and more, we will realize that our model of galaxy formation is very incomplete,” says Laurence Perreault-Levasseur, astrophysicist at the University of Montreal, to whom The Press asked to comment on Mr. Gupta’s study. “It’s interesting to explore other theories, but how the expansion of the Universe leads to a redshift of photons is very well understood, and the physics of the CMB is also well understood. This leads us to the “standard” calculation of the age of the Universe, and I don’t think that at this point we have enough evidence to challenge this calculation. »