A pair of recently published works show that the Universe is 13.772 billion years old (plus or minus 39 million) years old.
This is cool! He also agrees with some previous measurements of the Universe made in a similar way. Also cool.
What it is not interestingly, this does not seem to mitigate a growing discrepancy in measurements made in different ways, which are several hundred million years younger. Although it may not seem like a big deal, it is actually a big deal. Both groups of methods should be the same age and not. This means that there is something fundamental in the Universe that we lack.
The new observations were made using the Atacama Cosmology Telescope (or ACT), a six-meter antenna in Chile that is sensitive to light in the microwave part of the spectrum, between infrared light and radio waves. When the Universe was very young, it was extremely hot and dense, but after about 380,000 years after the Big Bang it cooled down enough to become transparent. It was as hot as the surface of the Sun at the time, and the light it emitted would have been more or less in the visible part of the spectrum, the kind of light we see with our own eyes.
But the universe has expanded a lot since then. This light lost a lot of energy reaching us fighting this expansion and moved to red; literally the wavelength became longer. It is now in the microwave part of the spectrum. It is also everywhere, literally in every part of the sky, so we call it the Cosmic Microwave Background or CMB.
A huge amount of information is stored in that light, so by scanning the sky for “purposes like ACT, we can measure the conditions in the Universe when it was only 380,000 years old.
ACT covered 15,000 square degrees, more than a third of the entire sky! Looking at about 5,000 square degrees in that survey, they were able to determine a lot of behavior of the young Universe, including his age. Combining this with the results obtained from the Wilkinson microwave anisotropy probe (or WMAP) they reached the age of 13.77 billion years. This is also in line with the value of the European Planck mission, which also measured microwaves in the early cosmos.
They can also measure the rate of expansion of the Universe. Enlargement was first discovered in the 1920s, and what astronomers have discovered is that an object farther away from us was moving away from us faster. Something twice as far seemed to move away from us twice as fast. This rate of expansion has become known as the Hubble constant and is measured at a distance: how fast something moves relative to how far it is.
The new observations get a value for this constant of 67.6 ± 1.1 kilometers per second / megaparsec (a megaparsec, abbreviated as Mpc, is a unit of distance convenient in some aspects of astronomy, equal to 3.26 million light years ; a little further than the distance to the Andromeda Galaxy, if that helps). So, due to cosmic expansion, an object at 1 Mpc distance should withdraw from us at 67.6 km / sec and one at 2 Mpc distance twice as long as at 135.2 km / sec and so on. far away. It’s a little more complicated than that, but that’s the essence.
And that’s a problem. There are a lot of ways to measure the Hubble constant – looking at supernovae in distant galaxies, observing gravitational lenses, observing huge clouds of gas in distant galaxies and so on – and many of them get a higher number, around 73 km / sec / Mpc. These numbers are hang up, which is reassuring in some ways, but far enough to be extremely confusing. They should agree and I disagree.
They also receive different ages for the Universe. A larger Hubble constant means that the universe is expanding faster, so it didn’t take that long to reach its current size, making it younger. A smaller constant means that the Universe is older. So while the rate of expansion may seem esoteric, it is directly related to the more fundamental concept of how old the Universe is, and the two groups of methods get different numbers.
So which is correct? This is a difficult question to answer and maybe the wrong one to ask. A better one is, why do I disagree?
There is an obvious problem and that is that both methods are correct, but they measure two different parts of the Universe. Those who look at CMB examine the Universe when it was less than a million years old. The others look at the universe when there were already a few billion age. Maybe the rate of expansion changed during that time.
In other words, maybe the Hubble constant is not. A constant, I mean.
There may be problems with the methods themselves, but they have been verified in many ways and by so many different methods in each group that this seems very unlikely at this time.
The guilt is apparently in the Universe and not in ourselves. Or, better said (I’m sorry, Bard and maybe John), the fault lies in the way we measure the Universe. He does what he does. We just have to figure out why.
A lot of work has been published on this and it is no exaggeration to say that it is one of the biggest and thorniest issues in cosmology at the moment.
A personal thought. My first job after getting my PhD was to work briefly on a part of COBE, Cosmic Background Explorer, which analyzed CMB and confirmed that the Big Bang is real. At that time, the measurements were good, but there was still room for improvement. Then came WMPA, Planck and now ACT, and these measurements are made with incredible accuracy. Astronomers call it high-precision cosmology, a kind of joke inside, because for a long time I had little idea about these numbers.
Astronomers are so good at this now that a 10% discrepancy is considered a huge problem, when in the past a factor of two was considered OK. Following this field, improving over time, was a real joy, because the better we get to it, the better we understand the Universe itself as a whole.
Yes, we have some problems. But these are big problems.
However, we hope to see them resolved soon. Because when we do, it means that our understanding will be made another big leap.