never mind, the universe is still probably expanding at an accelerating rate

On further review, the study claiming that the universe is expanding at a steady rate ended up independently proving accelerating expansion.

galaxy edge on

Not too long ago, I did a writeup on a study that claimed to show evidence that the universe’s expansion is not accelerating based on an analysis of a larger dataset of Type Ia supernovae than previously done. Like every pop sci writer and ex-grad student, there was a lot of hedging of bets and ifs in the post, and it turns out for good reason. While I can claim some sort of an academic credential, my field is computer science, not astrophysics, so when an expert on the subject reviewed the same study, he found it lacking. The problem? Using redshift, or the distortion of light due to distance, from one consistent supernova type (see the first link for details on why we use Type Ia supernovae for this research) is a great start, but there are more things we know about the cosmos that limit the the results’s potential impact.

Basically, we plot the supernovae data and analyze how well they match the predictions of how they should line up according to certain models of what we think the universe looks like, and the study in question found that there was not much difference in the observations between the fit for a constantly expanding universe and one for accelerated expansion. But since we know a lot more about the universe than just where stars explode and with how big of a bang, we can focus on the difference between the error bars to tighten up the model with what we know. When we account for the known mass of the universe, which we know we have right, we limit the probabilities to a certain range within which we know the model works. We can limit the fit even more by considering that the universe is flat. And when we do that, we end up with the paper’s results neatly falling in line with the accelerating expansion model because the other models involve violating what we know about the universe’s shape, mass, and overall density to work.

So does this mean the paper challenging the consensus was a waste of time or a failure on the researchers’ part? No, not at all. In fact they were able to independently offer additional proof of existing research and even with very skeptical eyes, starting form scratch, with a new, larger dataset, end up with very similar conclusions as other researchers, conclusions that fit well with the rest of the data we have about the universe and can be tightened by two undisputed observations about our cosmos. This means we’re still stuck with dark energy and need to figure out what it is, but these results are just more proof that it’s real and we’re not getting rid of it anytime soon because there is no way to explain our observations without out. Even if the study showed constant expansion, the fact that we can’t get rid of the expansion in any of our analyses shows that there’s an unseen force driving the basic mechanics of our entire cosmos. And we now know for sure that it’s driving it to grow faster and faster…

# science // cosmology / dark energy / physics


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