A pair of papers Recently published It turns out that the age of the universe is 13.772 billion years (plus or minus 39 million) years.

that’s cool! It also agrees with some previous measurements of the universe that were made in a similar way. Also cool.

what is it Not What’s cool is that this doesn’t seem to mitigate the growing discrepancy in measurements made in various ways, which are hundreds of millions of years younger. While this may not seem like a big problem, it is actually a really big problem. Both sets of styles should have the same age, but they don’t. This means that there is something fundamental about the universe that we miss.

New notes were made using Atacama Cosmology Telescope (Or ACT) a delicate six-meter-long Chilean dish Light is in the microwave portion of the spectrum, Between infrared light and radio waves. When the universe was very young, it was extremely hot and denseBut about 380,000 years after the Big Bang, it has cooled enough to be transparent. It was as hot as the surface of the sun at the time, and the light it emitted was more or less in the visible part of the spectrum, which is the kind of light that we see with our eyes.

But the universe has expanded since then, a lot. This light has lost a lot of the energy we got in order to fight this expansion, and it is shifted red; Literally the wavelength has gotten longer. It is now in the microwave portion of the spectrum. It’s also everywhere, literally in every part of the sky, so we call it the Cosmic Microwave Background, or CMB.

An enormous amount of information is stored in this light, so by scanning the sky with scopes like ACT we can measure 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 from this scan, They were able to determine a lot of the behavior of the young universe, Including his age. Combine this with the results of the Wilkinson Microwave Contrast Probe (Or WMAP) have reached the age of 13.77 billion years. This also agrees with European Planck Mission Value, Which also measured microwaves from the beginning of the universe.

They can also measure the expansion rate of the universe. Expansion was first discovered in the 1920s, and what astronomers found was that an object farther from us was receding away from us faster. Something about twice the distance seems to be moving away from us twice as fast. This expansion rate became known as the Hubble constant, and is measured in velocity per distance: how fast an object is moving versus the distance it is away.

The new observations obtain a value for this constant of 67.6 ± 1.1 kilometers per second / megaparsec (megaparsec, abbreviated as Mpc), which is a convenient unit of distance in some aspects of astronomy, equal to 3.26 million light-years; a little further from the distance to Andromeda Galaxy, If that helps). So, due to cosmic expansion, an object 1 Mpc away from us should recede at 67.6 km / s, 2 Mpc away twice that at 135.2 km / s, and so on. It’s a little more complicated than this, but that’s the point.

This is a problem. There are a lot of ways to measure the Hubble constant – Looking at supernovae in distant galaxiesAnd the Gravity lens monitoringAnd the Observation of huge clouds of gas in distant galaxies, Etc – and a lot of them get an even bigger number, around 73 km / s / Mpc. these numbers close, Which is reassuring in some ways, but far apart enough that it’s very baffling. They should agree, but they don’t.

They also have different ages of the universe. The height of the Hubble constant means that the universe is expanding more quickly, so it didn’t take much time to reach its current size, making it smaller. The lower constant means the universe is older. So while the rate of expansion may seem esoteric, it is directly related to the more fundamental concept of the age of the universe, and the two groups of methods get different numbers.

So what’s the right thing? This is a difficult question to answer, and perhaps the wrong question to ask. The best is Why do not they agree?

There is an obvious problem, which is that both methods are correct, however They measure two different parts of the universe. Those looking at the CMB examine the universe when it was less than a million years old. Others look at the universe when it was really little One billion Year. The rate of expansion may have changed during that period.

In other words, the Hubble constant might not be. Mean constant.

There might be issues with the methods themselves, but they have been verified in so many and so many different ways in each group that this appears to be extremely unlikely at this point.

The fault appears to be in the universe, not in ourselves. Or, you’d better say (sorry, coolAnd maybe JohnThe error lies in the way we measure the universe. It does what it does. We just have to find out why.

Lots of papers have been published on the topic, and it is not an exaggeration to say that it is one of the thorny problems in cosmology at the moment.

Personal idea. My first job after getting my PhD was to briefly work on one part of COBE, Cosmic background explorer, Which looked at the CMB and confirmed that the Big Bang was real. At the time the measurements were fine, but there was room for improvement. Then came WMPA, Planck, and now ACT, and these measurements were made with incredible accuracy. Astronomers call it HD cosmology, and it’s kind of an inside joke, because for so long, we hardly ever had any idea of ​​these numbers.

Astronomers are so adept at this now that 10% variance is a big problem, while a factor of two per day was considered fine. Watching this field improve over time was a real pleasure, because The better we get it, the better we understand the universe as a whole.

Yes, we do have some problems. But these are big problems.

However, we hope to see it resolved soon. Because when we do, it means that our understanding has taken another big leap.