In "Star Wars" lore, there's a constant struggle between the dark side and the light side of the Force. Fans debate endlessly about which side is stronger. While such debates might seem futile, given that they pertain to a fictional universe, there's a real life analogue of sorts.
Our universe, too, contains both light and dark components. On the one hand, there's the light side, which consists of all that's visible and interacts with radiation — stars, quasars, planets, etc. On the other hand, a dark side looms, full of theoretical entities like dark matter and dark energy.
We know a lot more about the light side, of course. But observations of the light side reveal hints about the nature of the dark, and the more evidence we gather about this mysterious realm, the more we're realizing that understanding it isn't going to be easy.
Perhaps the biggest evidence we have that there's more to the dark side than meets the eye is the fact that our observations of the expansion rate of our universe — otherwise known as the Hubble constant — are becoming increasingly inconsistent. Different techniques we have for measuring the rate of expansion can't seem to agree.
For instance, if we measure the expansion rate by looking directly at the speed by which distant objects like supernova are moving away from us, we come up with a rate of about 73.2 kilometers per second per megaparsec (a "megaparsec" being a unit of distance equal to 3.26 million light-years). But if we attempt to calculate the expansion rate by studying the most detailed map ever compiled of the early universe — the so-called cosmic background radiation that permeates the universe in all directions — the numbers fall to between 67 and 68 kilometers per second per megaparsec.
That might not sound like a big discrepancy, but it's huge on the scale of the universe. If scientists can't figure out how to make these different measurements jive, it could mean that our biggest theories about the universe need a reboot.
Is there a missing ingredient?
One such reboot would greatly expand the scope of the universe's dark side. It's a possibility that tantalizes Lloyd Knox, a cosmologist at the University of California, Davis, who recently spoke about his research with Scientific American.
“Potentially where this is leading us is to a new ingredient in the 'dark sector,'" he said.
Knox is keen on referring to this mysterious new dark ingredient as "dark turbo," an apt description for a force that acts to hasten the universe's expansion under certain conditions, such as the conditions that were present during the years immediately following the Big Bang, when the universe was a massive plasma ball. If the universe's rate of expansion has not always been the same, then this new measurement could make all our other calculations jive.
It's also possible that Knox's dark turbo is really just another form of dark energy — the term scientists use to describe how the universe is expanding at an accelerated rate. This would mean that dark energy is way more complicated than previously thought, but that wouldn't be surprising. Knox points out that the light side of the universe contains many different types of particles and forces, and asks: Why couldn't the dark side also have complex elements?
Of course it's probably complicated. This is the universe, after all. The good news is, scientists tend to prefer questions over answers. That's just the nature of the game.
"It's much more interesting if it turns out to be fundamental new physics — but it's not up to us wanting it to be one way or another," exclaimed Wendy Freedman of the University of Chicago, who has been laboring away on the Hubble constant problem for more than three decades. "The universe doesn’t care what we think!"