the study that could quite literally change everything if it’s right

A new paper claims that the universe's expansion isn't accelerating. If that's true, we have to start rewriting cosmology as we know it.

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One of the few givens in cosmology is that the very fabric of space and time, driven by dark energy, is expanding at an accelerating rate. We know this by studying the glow of a very specific type of supernova called Ia, which is the result of a white dwarf accreting matter from a companion star until it tips just beyond what’s known as the Chandrasekhar Limit, or 1.4 times the mass of our sun, and its core implodes. Because this mechanism produces a really consistent burst of light no matter where it occurs, we can use them as very reliable distance markers, and those distance markers observed in a survey lined up consistent with exactly what we’d expect to see if the universe was speeding up its expansion. Why? We don’t know, but whatever is driving its accelerated expansion was given the moniker dark energy.

Plenty of papers have attempted to explain away dark energy and failed, in no small part because they would violate some other basic knowledge about the structure of the universe or have no predictive power for the behaviors we observed and can only be explained with dark energy and dark matter. But what if, posit three researchers, we try the original experiment with a larger dataset? Maybe we just didn’t look at enough supernovae and as we accumulated a lot more observations over the last two decades, it wouldn’t hurt to redo the calculations. Their results show that while you could well interpret the data as showing accelerated expansion, constant expansion is well within the error bars as well. In other words, accelerating expansion’s signal is much weaker with the larger dataset used by the researchers.

Assuming they’re correct and we have evidence of constant expansion, what exactly does this mean for the past and future of the universe? Well, it may mean that the universe is older than we think and that the Big Rip scenario is pretty much impossible. This will in turn have to slightly change our basic models of galaxy evolution, and in cosmology, even slight changes projected over billions of years and trillions of stars and galaxies add up to significant results. We would also have to rethink some of the more esoteric models for the cosmic microwave background radiation, and measurements of galaxy clusters that have been interpreted to show signs of accelerated expansion, and figure out what these new models mean. A good deal of physics would need to be at least revisited, especially on a macro scale.

But of course the obvious question is that’s the likelihood that this study has in fact come up with evidence to overturn cosmology as we know it today? Measuring the brightness of Type Ia supernovae isn’t the only evidence for accelerating expansion, after all. Considering that it’s been the consensus of some two decades of research and there have been many reviews and follow up studies, it’s tempting view this new survey with skepticism and we should ask for more and bigger reviews from our growing catalogs of observations. At the same time, CMBR maps and measurements of galaxy clusters can be a bit of a Rorschach test for those conducting them and plenty of arXiv papers have threatened to overturn cosmology by spotting something weird in the minute temperature and velocity differences in their data.

So while it is wise to assume that a paradigm-shifting result in one paper is not a good basis for overturning 20 years of research, it’s never a bad idea to analyze more data to make sure your theories withstood the test of time and more observations. The history of science is littered with questions and odd papers that questioned a consensus at the time they came out, were studied for years, scrutinized by skeptics in a spirited back and forth, and replicated by supporters until they finally became the new consensus. Out of the many papers that have set out to cast a skeptical light on dark energy, this one has the most straightforward approach and makes the fewest assumptions, none of which ask us to ignore established cosmological principles or constants, which makes it a good candidate for additional work.

# science // astronomy / astrophysics / cosmology

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