- 2784 - UNIVERSE - measuring age with the oldest light? Ancient light from the Big Bang, the start of the Universe, has revealed a precise new estimate for the universe's age: 13.77 billion years, + or - 40 million years. This new estimate is based on data from an array of telescopes in the Chilean Atacama Desert. In addition to how old it is, how fast is the universe expanding is another question?
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-------------------------- 2784 - UNIVERSE - measuring age with the oldest light
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- We need to understand the universe's expansion rate to make any sense of cosmology. Cosmology is the science of our whole universe's past, present and future. Astronomers know that a mysterious substance called Dark Energy is causing the universe to expand at an ever-increasing rate in all directions.
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- When astronomers point their telescopes into space to measure the Hubble constant rate of expansion (H0) they come up with numbers that disagree with each other, depending on the method they use.
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- In our common terms the Universe is expanding 49,300 miles per hour for every million miles of distance of space. The more space there is between us the faster the rate of recession away from us.
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- One method, based on measurements of how fast nearby galaxies are moving away from the Milky Way, produces one number for H0. Another method, based on studying the oldest light in space, the Cosmic Microwave Background (CMB), produces another different H0.
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- The data from the Planck satellite, released in 2018, were the most important measurements of the CMB before now. With an unprecedented level of precision, they showed how sharply CMB measurements of H0 disagree with measurements based on the movement of nearby galaxies.
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- Relying on data from the Atacama Cosmology Telescope (ACT) in Chile's Atacama Desert, the researchers tracked faint differences between different parts of the CMB , which appears to have different energy levels in different parts of the sky.
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- The CMB, which formed as the universe cooled after the Big Bang, is detectable in every direction in space as a microwave glow. It's more than 13 billion light-years in the distance, a relic of a time before stars and galaxies formed.
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- By combining theories on how the CMB formed with precise measurements of its fluctuations, physicists can determine how fast the universe was expanding at that moment in time. That data can then be used to calculate H0.
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- The Atacama methodically scanned half the sky between 2013 and 2016, looking particularly at microwave light. Then researchers spent years cleaning up and analyzing the data with the aid of supercomputers, removing other microwave sources that are not part of the CMB, to stitch together a full map of the CMB.
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- The other approach to calculating H0 relies on pulsing stars known as cepheids, which reside in distant galaxies and pulse regularly. That timed pulsing allows researchers to perform precise calculations of their motion and distances from Earth.
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- From a mountain high in Chile’s Atacama Desert, astronomers have taken a fresh look at the oldest light in the universe. Their new observations, plus a bit of cosmic geometry, suggest that the universe is 13.77 billion years old, give or take 40 million years.
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- This estimate matches the one provided by the standard model of the universe and measurements of the same light made by the Planck a space-based observatory that ran from 2009-2013.
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- The trouble is that research teams measuring the movements of galaxies have calculated that the universe is hundreds of millions of years younger than the Planck team predicted. That discrepancy suggested that a new model for the universe might be needed, and sparked concerns that one of the sets of measurements might be incorrect.
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- A portion of a new picture of the oldest light in the universe taken by the Atacama Cosmology Telescope. This part covers a section of the sky 50 times the moon’s width, representing a region of space 20 billion light-years across.
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-That light, emitted just 380,000 years after the Big Bang, varies in polarization. Astrophysicists used the spacing between these variations to calculate a new estimate for the universe’s age.
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- The age of the universe also reveals how fast the cosmos is expanding, a number called the Hubble Constant, HO. The Atacama measurements suggest a Hubble constant of 67.6 kilometers per second per megaparsec. This result agrees almost exactly with the previous estimate of 67.4 by the Planck satellite team, but it’s slower than the 74 inferred from the other measurements of galaxies.
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- Like the Planck satellite and its earthbound cousin the South Pole Telescope, the Atacama Telescope peers at the afterglow of the Big Bang. CMB, marks a time 380,000 years after the universe’s birth, when protons and electrons joined to form the first atoms. Before that time, the cosmos was opaque to light.
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- If scientists can estimate how far light from the CMB traveled to reach Earth, they can calculate the universe’s age. They measure the angle in the sky between two distant objects, with Earth and the two objects forming a cosmic triangle. If scientists also know the physical separation between those objects, they can use high school geometry to estimate the distance of the objects from Earth.
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- Subtle variations in the CMB’s glow offer anchor points to form the two vertices of the triangle. Those variations in temperature and polarization resulted from quantum fluctuations in the early universe that got amplified by the expanding universe into regions of varying density. The denser patches would go on to form galaxy clusters.
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- Scientists have a strong enough understanding of the universe’s early years to know that these variations in the CMB should typically be spaced out every billion light-years for temperature and half that for polarization.
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- This measurement was possible thanks to new technology. From conception to deployment at the telescope to analysis, the process has spanned nearly 10 years.
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- Astronomers still need more confidence in measurements of the universe’s oldest light. For sure it is older than dirt. More to come.
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- August 1, 2020 2784
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