The conventional wisdom goes like this: Americans are more divided than ever. The gaps between us — Republicans and Democrats, Tea Partiers and Never Trumpers, Pelosi fans and AOC believers — seem unbridgeable.
Just how broken are we? Are these divides really as rigid as they seem? Pollsters know that if you ask the same question in two different ways, you can get two different answers; sometimes, the size of the partisan divide depends on the way you measure it.
Over the last decade, at the same time today’s political divide has been crystallizing, researchers have become aware of a small but significant split in cosmology. And just like our national divide, it’s not clear yet whether this split is truly fundamental or just a consequence of imperfect or incomplete measurement techniques.
The divide has to do with a number called the Hubble constant. Edwin Hubble, as you are not required to recall, was one of the astronomers who figured out that the universe is expanding. The farther you look from Earth, the faster galaxies seem to be rushing away, he observed. He wrote down an equation for this relationship, called Hubble’s Law, which says that the velocity at which a galaxy is receding is equal to its distance multiplied by a special number called the Hubble constant. (“Constant” is a bit of a misnomer: It’s the same everywhere, but it changes over time.) The Hubble constant helps cosmologists lock in the age, size and fate of the universe.
Hubble and his contemporaries tried to measure the Hubble constant, but their estimates were only as good as their knowledge of the true distances to other galaxies — which is to say, not very. Over the last 90 years, astronomers have improved both the accuracy and the precision of the Hubble constant measurement, and today, the margin of error stands at just a few percent. There’s just one problem: The Hubble constant comes out different depending on how you measure it.
There are two main ways to get a fix on the Hubble constant. The first involves a special kind of supernova called a Type Ia. Because they all have just about the same innate brightness, these supernovas are known in the astronomical vernacular as “standard candles.” By measuring how bright they appear from Earth, you can figure out how far away they are. Combine that with a measure of how quickly they are moving away from us, and the Hubble constant pops out.
A second, totally different way to measure the Hubble constant involves scrutinizing the cosmic microwave background (CMB), the low hum of radiation left over from shortly after the Big Bang. Very sensitive microwave telescopes, like the one on the Planck satellite, can pick out minute variations in the CMB, and from the patterns in these variations, cosmologists can read out pieces of the history of the universe, including the value of the Hubble constant.
The good news is that these two independent values of the Hubble constant are in the same ballpark: They’re less than 10 percent off. The bad news is that even that small difference is scientifically significant. So what does it mean?
Like hairline cracks that reveal problems in a house’s foundation, small observational inconsistencies sometimes turn out to mean much more. But sometimes they don’t mean much at all and are eventually put down to mistakes or miscalibrations further up the analysis chain. It’s usually safer (but less fun) to bet on the latter explanation, and researchers are now busy trying to figure out where they might have gone wrong.
One possibility is that astrophysicists have mismeasured the distances to “standard candle” supernovas. Fixing the distance to a Type Ia supernova actually requires quite a few in-between calibration steps, and at every step, there’s room for error to creep in.
The second, more interesting possibility is that the inconsistency is a sign of some previously unknown physics: Dark energy that changes over time, neutrinos beyond the standard model, decaying dark matter. Until more data come in, you can take your pick. The prospect of peering into the gap and discovering something genuinely new is tantalizing.
As for what might emerge from the political gaps between us — consensus, disintegration, cruelty — I can’t venture to guess. But here’s the thing about political gaps: Unlike cosmological ones, they have the power to make themselves real. So how broken are we? People, not data, hold the answer.
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