Cosmology will be in Crisis Over How to Measure the Universe

Let’s say you have a baby. Maybe you genuinely do, maybe you don’t. however Dan Scolnic, a cosmologist at the University of Chicago, does have one, along with also perhaps which’s why a hypothetical baby helps him explain the universe. If you take which baby to the doctor, which doctor will weigh along with also measure the baby, plot those points on a growth chart, along with also predict how big they’ll be later.

“We kind of have which same situation at which point with measuring the universe,” says Scolnic, who’ll begin a professorship at Duke next month. Scientists have a great picture of what the universe was like as a baby. They also have one of what which looks like all grown up, today. along with also as with the doctor’s growth chart, a curve—following physics as we know which—should connect the two cleanly.

“You should be able to put in which universe’s baby picture, trace our standard cosmology, along with also see our universe today—if everything has gone right,” says Scolnic. however which’s not what will be happening. “Something,” says Scolnic, “will be not going right.”

Cosmologists aren’t sure what which something will be, exactly. Maybe they’re wrong in their measurement or analysis of the baby universe. Or of its present state.

Those are the boring options, though. “The different,” says Scolnic, “will be which our standard style of cosmology isn’t correct.” In different words, the way humans think about the early years, maturation, along with also fate of the universe might be wrong somehow.

Over the past few years, scientists like Scolnic have investigated those first two hypothetical misunderstandings. They’ve whittled down their error bars, hardened their methods, re-analyzed the results of competitors along with also colleagues, along with also gathered sharper along with also bigger data. Nevertheless, the discrepancy persists.

Scolnic calls which moment “the era of tension cosmology.” Others just call which a crisis.

To those who don’t study the origin along with also evolution of the universe, which sounds like a bad thing. To cosmologists, which’s the opposite. To be wrong will be to learn which the universe will be more interesting than they thought. “We’re right on the cusp of which being the coolest thing ever,” says Scolnic.

One number has led us to said cusp. which number will be called the Hubble constant, along with also which will be the rate at which the universe will be expanding today (not today like “Tuesday” however today like “in which cosmic moment”). The Hubble constant will be an elusive beast, even for cosmology—a kind of white stag among white stags.

Astronomers have devised a few ways to estimate its value, along with also which will be the conflict between their outcomes which’s causing the trouble. One method begins with the universe’s baby picture—a map of the so-called “cosmic microwave background,” or the remnant radiation coming from the Big Bang. coming from which picture, astronomers plug what they (think they) know about dark energy, dark matter, regular matter, along with also gravity into a style. Out pops a present state of the universe, along with also a prediction of the Hubble constant. Most recently, astronomers did which using cosmic microwave background data coming from the Planck telescope, a space-based observatory which was decommissioned in 2013.

Another method uses the “cosmic distance ladder.” Astronomers figure out how far away objects are, along with also how fast they’re moving even farther away, starting coming from here(ish) along with also building outward. They calculate the distances to nearby stars, along with also coming from them to more distant stars in different galaxies, along with also coming from them to supernovae in still-farther-off galaxies. They measure their movement away coming from us, providing another estimate of the Hubble constant.

Scolnic was part of a big team called SH0ES which used the ladder method. Its Hubble estimate disagrees with Planck’s. Behold: the crisis.

however recently Scolnic along with also a team tried a newer method: the inverse cosmic distance ladder. Instead of scaffolding distances coming from the solar system farther along with also farther out, which approach uses characteristics of the cosmic microwave background (the baby picture) to start to scaffold distances closer along with also closer to us. Moving forward in time, scientists use information about how galaxies are spread out across the universe along with also—as with SH0ES—supernova data. which came, which time, coming from the Dark Energy Survey, which aims to observe thousands of supernovae along with also hundreds of millions of galaxies to understand what dark energy has been like over the history of the universe. which Hubble constant estimate matched Planck’s. “which’s kind of nuts how well which agrees,” says Edward MacCauley, the lead researcher.

which agreement doesn’t make Planck along with also the inverse more likely to be right. “In both these methods—the forward along with also reverse distance ladders— supernovae are used as ‘the middleman,’” says Scolnic. “So if supernovae are happy to agree with either side, which means the problem isn’t with the middleman.” which’s something happening at one end. “If our style will be wrong, which has to be something about how we understand the universe today, or how we understand the universe as a baby,” he says.

Having been on both sides, Scolnic senses which tension personally. “I feel very much inside the middle,” says Scolnic, “along with also which has caused many sleepless nights.”

The sleeplessness—along with also the gravity with which cosmologists imbue which problem—has grown recently. Until a few years ago, says MacCauley, “the uncertainties were large enough which not everybody was worried about which.” The error bars on each side’s measurements essentially overlapped, meaning their calculations could theoretically have matched.

Maybe there was some systematic problem—coming from inside the instruments which do the measuring, or inside the analysis of either side. however rivals did independent analyses of each different’s work, supernova calculations became more precise, along with also Planck took the best baby picture ever. along with also still the two Hubble constants stood firmly apart.

Which means which’s looking more along with also more like the problem isn’t with the data itself, or the people digging around in which, however with our style of the universe. “The possibility which which will be not due to some completely new physics will be getting smaller,” says Silvia Galli, who helped lead the Planck analysis.

To Scolnic, which’s not surprising. “We all agree which we don’t understand around 95 percent of the universe,” he says, referring to the fact which the cosmos will be almost entirely dark matter along with also dark energy, which possess the word “dark” in front of them because we don’t know what they are. Given which we can only grasp the cosmic contents at the 5% (F-) level, which’s kind of ridiculous to think the standard style of cosmology will be totally right.

however how which could be wrong remains up inside the air. Every night, astronomers post completely new ideas to arXiv, the open access publishing site. Cosmologists, in particular, use arXiv to engage in timely back-along with also-forths which formal journals don’t permit. “We’re just holding on for dear life, trying to keep up with what’s coming out,” says Scolnic. along with also trying to figure out why the Hubble constant calculations don’t match, where they’ve gone wrong, where they go coming from here, along with also how our conception of the universe might change coming from which completely new vantage point.

Something big may be about to happen to cosmology. which’s easy to see where the cosmologists are coming coming from, in their glee at the possibility which they’ve been wrong about the cosmos. Which makes sense: Who wouldn’t like to live in a universe which’s more interesting than we’d thought?


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Cosmology will be in Crisis Over How to Measure the Universe