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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. The light, emitted just 380,000 years after the Big Bang, varies in polarization (represented here by redder or bluer colors). Astrophysicists used the spacing between these variations to calculate a new estimate for the universe’s age. Credit: ACT Collaboration |
For the last year or so, debate has raged in the Astrophysics community over the real age of the Universe, although 'raged' may be an overstatement in the sense in which it is normally used.
As always, 'raging' debate in science is conducted in quiet, polite, considerate and respectful terms and normally centres around the finer details of statistical analysis, data collection and accuracy, etc, and rarely around personality, since ad hominems have no place in rational, dispassionate debate in which facts are neutral and opinion is led by evidence.
The problem was that there were two methods for calculating the age of the universe based on how we calculate the speed at which galaxies are moving away from one another to calculate the rate of expansion of the Universe - a quantity called the Hubble Constant - and disagreement centred around how accurately we measured that constant.
One method, based on data from the Planck satellite gave 67.4 kilometres per second per megaparsec. That means an object 1 megaparsec (around 3.26 million light-years) from Earth is moving away from us at 67.4 kilometres per second due to the expansion of the universe. The other method, based on data from the Atacama Cosmology Telescope (ACT) gave a result of 74 kilometres per second per megaparsec. A similar ball-park figure but one which gave significantly different results for the age of the Universe.
The different estimates couldn't both be right. If the ACT estimate was right there was something wrong with the standard model; if the standard model was right there was something wrong with the ACT data.
This is how science progresses. New data appears to contradict the prevailing consensus so both the prevailing consensus and the new data are scrutinised to resolve the differences. If the prevailing consensus is shown to be wrong then it is abandonned in favour of a new one which better explains the facts, incuding the new data.
Now this difference has been resolved by new measurements by the ACT team which give a Hubble Constant of 67.6 kilometres per second per megaparsec - within a whisker of the Planck team's 67.4 kilometres per second per megaparsec and one which gives the age of the Universe at 13.77 billion yeaars old. In fact, on re-exmination, it turned out in this case that the 'new data' was wrong and even newer data agreed with the current consensus (or as near as makes no significant difference).
The Cornell University press release explains:
From a mountain high in Chile’s Atacama Desert, astronomers with the National Science Foundation’s Atacama Cosmology Telescope (ACT) 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.The ACT team's revised results were published in the Journal of Cosmology and Astroparticle Physics on December 30, 2020, sadly behind a paywall.
The new estimate matches the one provided by the standard model of the universe and measurements of the same light made by the Planck satellite. This adds a fresh twist to an ongoing debate in the astrophysics community, says Simone Aiola, first author of one of the new papers on the findings in the Journal of Cosmology and Astroparticle Physics. Steve Choi, Cornell Presidential Postdoctoral Fellow and researcher at the Cornell Center for Astrophysics and Planetary Science in the College of Arts & Sciences, is lead author for the paper, "The Atacama Cosmology Telescope: a measurement of the Cosmic Microwave Background power spectra at 98 and 150 GHz," published Dec. 30, 2020.
In 2019, a research team measuring the movements of galaxies 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.
“Now we’ve come up with an answer where Planck and ACT agree,” says Aiola, a researcher at the Flatiron Institute’s Center for Computational Astrophysics. “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 ACT measurements suggest a Hubble constant of 67.6 kilometers per second per megaparsec. That means an object 1 megaparsec (around 3.26 million light-years) from Earth is moving away from us at 67.6 kilometers per second due to the expansion of the universe. This result agrees almost exactly with the previous estimate of 67.4 kilometers per second per megaparsec by the Planck satellite team, but it’s slower than the 74 kilometers per second per megaparsec inferred from the measurements of galaxies.
“I didn’t have a particular preference for any specific value — it was going to be interesting one way or another,” says Choi. “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.”
But the discrepancy between the measurements suggests that either there is something missing in our cosmological model or there is something wrong with the measurements, says Michael Niemack, co-author on the two preliminary papers. While several local universe measurements find a consistently higher Hubble constant, this is the first time that two independent cosmic microwave background (CMB) measurements found consistently lower Hubble constants. (The 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.)
“The growing tension between these distant versus local measurements of the Hubble constant suggests that we may be on the verge of a new discovery in cosmology that could change our understanding of how the Universe works. It also highlights the importance of improving our measurements of the CMB with ACT as well as the future Simons Observatory and CCAT-prime projects that we are now building,” says Niemack, associate professor of physics and astronomy.
From a mountain high in Chile’s Atacama Desert, astronomers with the National Science Foundation’s Atacama Cosmology Telescope (ACT) 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.
The new estimate matches the one provided by the standard model of the universe and measurements of the same light made by the Planck satellite. This adds a fresh twist to an ongoing debate in the astrophysics community, says Simone Aiola, first author of one of the new papers on the findings in the Journal of Cosmology and Astroparticle Physics. Steve Choi, Cornell Presidential Postdoctoral Fellow and researcher at the Cornell Center for Astrophysics and Planetary Science in the College of Arts & Sciences, is lead author for the paper, "The Atacama Cosmology Telescope: a measurement of the Cosmic Microwave Background power spectra at 98 and 150 GHz," published Dec. 30, 2020.
In 2019, a research team measuring the movements of galaxies 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.
“Now we’ve come up with an answer where Planck and ACT agree,” says Aiola, a researcher at the Flatiron Institute’s Center for Computational Astrophysics. “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 ACT measurements suggest a Hubble constant of 67.6 kilometers per second per megaparsec. That means an object 1 megaparsec (around 3.26 million light-years) from Earth is moving away from us at 67.6 kilometers per second due to the expansion of the universe. This result agrees almost exactly with the previous estimate of 67.4 kilometers per second per megaparsec by the Planck satellite team, but it’s slower than the 74 kilometers per second per megaparsec inferred from the measurements of galaxies.
“I didn’t have a particular preference for any specific value — it was going to be interesting one way or another,” says Choi. “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.”
But the discrepancy between the measurements suggests that either there is something missing in our cosmological model or there is something wrong with the measurements, says Michael Niemack, co-author on the two preliminary papers. While several local universe measurements find a consistently higher Hubble constant, this is the first time that two independent cosmic microwave background (CMB) measurements found consistently lower Hubble constants. (The 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.)
“The growing tension between these distant versus local measurements of the Hubble constant suggests that we may be on the verge of a new discovery in cosmology that could change our understanding of how the Universe works. It also highlights the importance of improving our measurements of the CMB with ACT as well as the future Simons Observatory and CCAT-prime projects that we are now building,” says Niemack, associate professor of physics and astronomy.
Like the Planck satellite, ACT peers at the CMB, the afterglow of the Big Bang.
If scientists can estimate how far light from the CMB traveled to reach Earth, they can calculate the universe’s age. That’s easier said than done, though. Judging cosmic distances from Earth is hard. So instead, scientists 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.
Subtle variations in the CMB’s glow offer anchor points to form the other 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.) 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. (For scale, our Milky Way galaxy is about 200,000 light-years in diameter.)
ACT measured the CMB fluctuations with unprecedented resolution, taking a closer look at the polarization of the light. “The Planck satellite measured the same light, but by measuring its polarization in higher fidelity, the new picture from ACT reveals more of the oldest patterns we’ve ever seen,” says Suzanne Staggs, ACT’s principal investigator, at Princeton University.
As ACT continues making observations, astronomers will have an even clearer picture of the CMB and a more exact idea of how long ago the cosmos began. The ACT team will also scour those observations for signs of physics that doesn’t fit the standard cosmological model. Such strange physics could resolve the disagreement between the predictions of the age and expansion rate of the universe arising from the measurements of the CMB and the motions of galaxies.
If scientists can estimate how far light from the CMB traveled to reach Earth, they can calculate the universe’s age. That’s easier said than done, though. Judging cosmic distances from Earth is hard. So instead, scientists 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.
Subtle variations in the CMB’s glow offer anchor points to form the other 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.) 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. (For scale, our Milky Way galaxy is about 200,000 light-years in diameter.)
ACT measured the CMB fluctuations with unprecedented resolution, taking a closer look at the polarization of the light. “The Planck satellite measured the same light, but by measuring its polarization in higher fidelity, the new picture from ACT reveals more of the oldest patterns we’ve ever seen,” says Suzanne Staggs, ACT’s principal investigator, at Princeton University.
As ACT continues making observations, astronomers will have an even clearer picture of the CMB and a more exact idea of how long ago the cosmos began. The ACT team will also scour those observations for signs of physics that doesn’t fit the standard cosmological model. Such strange physics could resolve the disagreement between the predictions of the age and expansion rate of the universe arising from the measurements of the CMB and the motions of galaxies.
Science is able to resolve these differences because it is based on observable, verifiable objective evidence which is always central to any debate and in a sense referees the debate. The 'winning' side is the side that is best supported by the evidence and the only emotional commitment either side has is to the truth.
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| Lollards being burned at the stake after the Oldcastle Revolt against the Catholic Church on January 9-10, 1414. The Lollards were followers of John Wycliffe, known as the 'Morning Star of the Protestant Reformation', who produced the first English translation of the Bible which was condemned by the Pope as heretical. |
This is why science, as in this case, always converges on a single truth, no matter the starting point and why religions always diverge away from a single starting point into a myriad, mutually hostile and often warring, factions, each claiming to be the truth but entirely lacking the ability to support that claim. It is why science disagrees politely and eventually resolves its differences and moves on, and religions disagree violently and decide the issue on the strength of arms and ability to coerce and control while remaining rooted in pre-scientific, superstitious times.
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