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Oldest surviving light reveals the universe's true age

A portion of the Atacama Cosmology Telescope's new image of the cosmic microwave background
A portion of the Atacama Cosmology Telescope's new image of the cosmic microwave background
(Image: © ACT Collaboration)

 

Ancient light from the Big Bang has revealed a precise new estimate for the universe's age: 13.77 billion years, give or take 40 million years.

The new estimate, based on data from an array of telescopes in the Chilean Atacama Desert, also weighs in on one of the most important disagreements in astrophysics: How fast is the universe expanding? Described in two scientific papers, the new result gives a significant boost to one side of the disagreement, though the physicists couldn't prove the other side of the dispute wrong.

Here's the problem: Physicists need to understand the universe's expansion rate to make any sense of cosmology — the science of our whole universe's past, present and future. They know that a mysterious substance called dark energy is causing the universe to expand (at an ever-increasing rate) in all directions.. But when astronomers point their telescopes into space to measure the Hubble constant (H0) — the number that describes how fast the universe is expanding at different distances from us or another point — they come up with numbers that disagree with each other, depending on the method they use.

One method, based on measurements of how fast nearby galaxies are moving away from the Milky Way, produces one H0. Another method, based on studying the oldest light in space, or cosmic microwave background (CMB), produces another H0. This disagreement has left scientists wondering whether there's some important blind spot in their measurements or theories, as Live Science previously reported. These new results seem to show that there weren't any measurement errors on the CMB side.

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"We find an expansion rate that is right on the estimate by the Planck satellite team," which is another study of the CMB, Cornell University astrophysicist Steve Choi, lead author of one of two new papers, said in a statement. "This gives us more confidence in measurements of the universe's oldest light."

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.

These new results recalculated the CMB measurement from scratch using an entirely different set of telescope data and calculations, and came up with very similar results. That doesn't prove that the CMB measurement of H0 is correct — there could still be some problem with the physics theories used to make the calculation — but it does suggest that there aren't any measurement errors on that side of the disagreement.

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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. 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. 

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.

The ACT 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. The whole time, they "blinded" themselves to the implications of their work, they wrote in their papers, meaning they didn't look at how their choices affected estimates of H0 until the very end. Only when the full CMB map was complete did the researchers use it to calculate H0.

The new CMB map also offered a new measure for the distance between Earth and the CMB. That distance, combined with a new measurement of how fast the universe has expanded over time, allowed a precise calculation of the age of the universe.

"I didn't have a particular preference for any specific value — it was going to be interesting one way or another," Choi said.

 It's still possible, as Live Science has previously reported, that some error in those theories is messing up the  calculation. But it's not clear what the error would be.

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.

With those direct speed measurements, it's fairly straightforward to come up with a measurement of H0. There are no complicated cosmological theories involved. But it's possible, some scientists have proposed, that our region of the universe is just weirdly empty, and not representative of the whole universe. It's even possible that there are measurement issues with the cepheids, and that these cosmic measuring sticks don't work quite the way physicists expect.

For now, the true H0 remains a mystery. But CMB researchers have more ammunition for their side of the disagreement.

Both new papers describing the new analysis have been published July 14 to the preprint database arXiv and submitted for formal peer review.

Originally published on Live Science.

  • Don Nash
    So the physicists are arguing about theoretical issues that can't be proven. Not yet anyway. I love it.
    Reply
  • Mike H.
    All of the observations listed in this article are interpreted through the lens of a 100 year old paradigm, so it stands to reason that the anachronistic theory comes up short to explain what is observed...🙄
    Reply
  • TorbjornLarsson
    Cool, I saw the preliminary paper a few weeks back https://arxiv.org/abs/2004.01139 ]but I thought the result would wait a year or so!

    Even better, they confirm Planck alone - and with independent TE, EE modes (basic Planck used TT and in 2018 also BB) - and improve on the integrated result in some senses (Planck was more precise).

    On the recent expansion rate tension with mostly low-z data, the ACT starts out towards the median. The recent discovery that the H0 current expansion rate tension can be replaced by a CMB T0 current temperature tension https://astrobites.org/2020/06/27/h0-or-t0-tension/ ] is informative here: the ACT work do not extract the temperature, but they use observations of Uranus as beam calibration. The old WMAP used their beam as temperature calibration and it is that result that sits on the median of 70 km s^-1 Mpc^-1 https://iopscience.iop.org/article/10.1088/0067-0049/208/2/19 ]. So that supports the H0 <-> T0 result.

    I also twigged another source of measurement error from the paper. They note that a recalibrated and data added work on the H0LiCOW gravitational lensing low-z, high-H0 result resulted in a low-H0 result without resolving the mass density profile H0LiCOW model with https://arxiv.org/abs/2007.02941 ]. "... our new analysis does not statistically invalidate the mass profile assumptions by H0LiCOW, ...". Meaning H0LiCOW method is not very sensitive yet.

    I'm not sure measurement problems is the reason for the recent years spread, but each paper released in the area seems to accumulate evidence along those lines. I could see from the recent paper that the median H0 of 70 km s^-1 Mpc^-1 indeed do not suggest new physics, and from the figures it seems to me a H0 < 72 km s^-1 Mpc^-1 would give "same old, same old".
    Reply
  • TorbjornLarsson
    By coincidence, the Sloan Digital Sky Survey just released "the largest three-dimensional map of the universe ever created", advancing cosmology even further to 1 % uncertainty.

    "By combining SDSS data with additional data from the Cosmic Microwave Background, supernovae, and other programs, we can simultaneously measure many fundamental properties of the universe," says Mueller. "The SDSS data cover such a large swath of cosmic time that they provide the biggest advances of any probe to measure the geometrical curvature of the universe, finding it to be flat. They also allow measurements of the local expansion rate to better than one percent."

    Oddly, the papers seem to have been released to arXiv already before the weekend. The summary paper: https://arxiv.org/abs/2007.08991 .

    - Being an integrative cosmological summary based on the baryonic acoustic oscillations and the cosmic microwave background to establish flatness it reinforces the standard model nicely.
    - The structure data in the survey strongly fit dark matter evolving according to general relativity.
    - The flatness of space is now 10^-4 - yielding a universe volume at least 100 million times larger than the observable - which is just an order of magnitude from the detection limit.
    - Dark energy can be detected at 8 sigma based on accepting flatness, it is constant and yields a current expansion rate at H0 = 68.20 +/- 0,81 km s^-1 Mpc^-1. This likely means no physics since it is < 72 km s^-1 Mpc^-1 at nearly 3 sigma.

    Most exciting to me is that it is consistent with simplest selection bias ("anthropic") finetuning which they point out as possible and substantially strengthened explanation.

    "Nevertheless, the observed consistency with flat ΛCDM at the higher precision of this work points increasingly towards a pure cosmological constant solution, for example, as would be produced by a vacuum energy finetuned to have a small value. This fine-tuning represents a theoretical difficulty without any agreed-upon resolution and one that may not be resolvable through fundamental physics considerations alone (Weinberg 1989; Brax & Valageas 2019). This difficulty has been substantially sharpened by the observations presented here."


    More here: https://www.bnl.gov/newsroom/news.php?a=117340 , https://www.port.ac.uk/news-events-and-blogs/news/astrophysicists-fill-in-11-billion-years-of-universe-expansion-history .
    Reply
  • TorbjornLarsson
    Don Nash said:

    So the physicists are arguing about theoretical issues that can't be proven. Not yet anyway.

    Except that the published result show that they can test it, and has. There is one remaining tension in the data, out of thousands of explained data.

    Maybe if you tried to read the work - scientists have worked hard for it and it deserves better than unfounded dismissal.
    Reply
  • TorbjornLarsson
    Mike H. said:

    All of the observations listed in this article are interpreted through the lens of a 100 year old paradigm, so it stands to reason that the anachronistic theory comes up short to explain what is observed...🙄

    Or you can say, on the contrary, since gravity is a 400 year old paradigm that has never been rejected by data it is firm.

    Also, the current inflationary hot big bang cosmology is only 40 years old, the century old big bang theory had problems with observations at that time that we seem to have now solved. Here is a short video based on a know astrophysicist's script that explains that (but doesn't describe mechanisms): P1Q8tS-9hYoView: https://www.youtube.com/watch?v=P1Q8tS-9hYo

    Enjoy!
    Reply
  • David J Franks
    Quote from the article -

    "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."

    The radius of the observable universe is 46.5 billion light-years, The CMB is the very edge of the observable universe, so why has the article said the distance to the CMB is ~ 13 billion light-years instead of 46.5 billion light-years?
    Reply
  • SZorin
    TorbjornLarsson said:
    By coincidence, the Sloan Digital Sky Survey just released "the largest three-dimensional map of the universe ever created", advancing cosmology even further to 1 % uncertainty.

    "By combining SDSS data with additional data from the Cosmic Microwave Background, supernovae, and other programs, we can simultaneously measure many fundamental properties of the universe," says Mueller. "The SDSS data cover such a large swath of cosmic time that they provide the biggest advances of any probe to measure the geometrical curvature of the universe, finding it to be flat. They also allow measurements of the local expansion rate to better than one percent."

    Oddly, the papers seem to have been released to arXiv already before the weekend. The summary paper: https://arxiv.org/abs/2007.08991 .

    - Being an integrative cosmological summary based on the baryonic acoustic oscillations and the cosmic microwave background to establish flatness it reinforces the standard model nicely.
    - The structure data in the survey strongly fit dark matter evolving according to general relativity.
    - The flatness of space is now 10^-4 - yielding a universe volume at least 100 million times larger than the observable - which is just an order of magnitude from the detection limit.
    - Dark energy can be detected at 8 sigma based on accepting flatness, it is constant and yields a current expansion rate at H0 = 68.20 +/- 0,81 km s^-1 Mpc^-1. This likely means no physics since it is < 72 km s^-1 Mpc^-1 at nearly 3 sigma.

    Most exciting to me is that it is consistent with simplest selection bias ("anthropic") finetuning which they point out as possible and substantially strengthened explanation.

    "Nevertheless, the observed consistency with flat ΛCDM at the higher precision of this work points increasingly towards a pure cosmological constant solution, for example, as would be produced by a vacuum energy finetuned to have a small value. This fine-tuning represents a theoretical difficulty without any agreed-upon resolution and one that may not be resolvable through fundamental physics considerations alone (Weinberg 1989; Brax & Valageas 2019). This difficulty has been substantially sharpened by the observations presented here."


    More here: https://www.bnl.gov/newsroom/news.php?a=117340 , https://www.port.ac.uk/news-events-and-blogs/news/astrophysicists-fill-in-11-billion-years-of-universe-expansion-history .
    This likely means no physics since it is < 72 km s^-1 Mpc^-1 at nearly 3 sigma.
    A curious amateur here. Why would it not be a fit for the Standard Model ? Please explain.
    Reply