Universe’s age discovered in landmark study on nature’s oldest light – ‘We have an answer’

Astronomers with the National Science Foundation’s Atacama Cosmology Telescope (ACT) have taken reexamined the oldest light in the known Universe. The revised cosmic observations indicate the Universe is 13.77 billion years old, plus or minus 40 million years.

The latest age estimate actually matches the one provided by the standard model of the Universe, using measurements of the same light made by the Planck satellite.

Now we’ve come up with an answer where Planck and ACT agree

Dr Simone Aiola

The latest research adds a fresh twist to an ongoing debate in the astrophysics community, says Dr Simone Aiola, first author of one of two new papers on the landmark study.

Scientist measuring the movements of galaxies in 2019 made headlines around the world after concluding the Universe is hundreds of millions of years younger than the Planck team’s prediction.

That discrepancy suggested a new model for the Universe might be required, fuelling concerns one of the sets of measurements might be incorrect.

Dr Aiola, a researcher at the Flatiron Institute’s Center for Computational Astrophysics, said: “Now we’ve come up with an answer where Planck and ACT agree.

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“It speaks to the fact that these difficult measurements are reliable.”

The age of the Universe also reveals how fast the cosmos is expanding, a number quantified by the Hubble constant.

The Atacama Cosmology Telescope data suggest a Hubble constant of 42 miles (67.6km) per second per megaparsec (approximately 3.26 million light-years).

This consequently means an object 1 megaparsec from Earth is hurtling away from the planet at 42 miles per second due to the Universe’s expansion.

This conclusion almost perfectly tallies with the previous estimate of 67.4km per second per megaparsec by the Planck satellite team.

However, it is slower than the 46 miles (74km) per second per megaparsec deduced from the measurements of galaxies.

Steve Choi of Cornell University, first author of the other paper, said in a statement: “I didn’t have a particular preference for any specific value — it was going to be interesting one way or another.

“We find an expansion rate that is right on the estimate by the Planck satellite team.

“This gives us more confidence in measurements of the Universe’s oldest light.”

Professor Erminia Calabrese, Cardiff University’s School of Physics and Astronomy and lead author of one of the papers, said: “Having worked on extracting the cosmological parameters from both ACT and Planck for almost a decade, it was very rewarding to see the two experiments agree.

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“These new results from ACT add confidence on our model of the early Universe and weigh in on the controversy with the expansion of the local universe where galaxies seem to be moving faster than what both ACT and Planck now measure.”

Like the Planck satellite, the Atacama Cosmology Telescope stars at the Big Bang’s afterglow.

This cosmic microwave background (CMB) marks a time 380,000 years after the Universe’s birth, when protons and electrons joined to form the first atoms.

If scientists can estimate how far light from the CMB travelled to reach Earth, they can calculate the Universe’s age.

However, this is easier said than done, as calculating cosmic distance is notoriously difficult.

So instead, scientists measure the angle in the sky between two distant objects, with Earth and the two objects forming a triangle.

If scientists also understand the physical separation between those objects, they can use high school geometry to estimate the distance of the objects from Earth.

Subtle variations in the CMB’s glow offer anchor points to form the other two vertices of the triangle.

Variations in temperature and polarisation resulted from quantum fluctuations in the early Universe amplified by the growing Universe into regions of varying density.

Researchers now have a strong enough understanding of the nascent Universe to realise these CMB variations should be spaced out every billion light-years for temperature and half that for polarisation.

For scale, the Milky Way galaxy is approximately 200,000 light-years across.

Suzanne Staggs, ACT’s principal investigator and the Henry deWolf Smyth Professor of Physics at Princeton University, said: “The Planck satellite measured the same light, but by measuring its polarisation in higher fidelity, the new picture from ACT reveals more of the oldest patterns we’ve ever seen.”

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