It is What’s for Dinner | by Brian Koberlein



28 November 2014

Image of the cosmic microwave background.
Picture of the cosmic microwave background.

Two of probably the most mysterious phenomena in astrophysics are darkish matter and darkish vitality. Darkish matter is what holds galaxies collectively, and causes them to clump into clusters and superclusters. It is called darkish matter as a result of it doesn’t work together strongly with mild. Darkish vitality, then again, causes clusters of galaxies to increase away from one another. The ensuing cosmic growth is why distant galaxies seem like racing away from us. As a result of each of those phenomena are central to the construction of the cosmos, there have been a number of makes an attempt to attach them right into a single phenomenon. Now a brand new paper in Bodily Evaluate Letters proposes that decaying darkish matter could produce darkish vitality.

This new paper has led to well-liked science headlines questioning “Is darkish vitality consuming darkish matter?” however that’s not what the paper claims in any respect. Within the paper the authors take a look at three units of information: fluctuations within the cosmic microwave background, observations of distant supernovae, and redshift information from distant galaxies. In the usual mannequin of cosmology, often known as the ΛCDM mannequin, these three information units needs to be associated, and if you happen to plug the info into the mannequin they need to give the identical outcomes. What we discover is that they virtually agree, however not fairly. This isn’t to say that they contradict one another, merely that they don’t agree in addition to the ΛCDM mannequin says they need to.

This slight disagreement between datasets is called stress within the mannequin. There have been varied proposed options to easing this stress, corresponding to factoring in neutrino mass, however on this new work the authors suggest resolving it by linked darkish matter and darkish vitality. To do that they tweaked the ΛCDM mannequin barely. The Λ or “lambda” in ΛCDM represents the cosmological fixed that drives darkish vitality. The CDM stands for “chilly darkish matter,” which is the main mannequin for darkish matter. In the usual cosmological mannequin these two are separate and fixed, however the authors proposed that darkish matter might decay into darkish vitality (by some unknown course of) in order that over the historical past of the universe the Λ would enhance whereas the CDM decreased. The decay of 1 into the opposite could be gradual, however the authors discovered that such a decay would ease stress within the observational information.

It needs to be identified that this doesn’t show such a decay happens, solely that tweaking the usual mannequin in such away appears to raised match the info. Tweak theories are weak theories, as I’ve mentioned earlier than. However what this new work does present is that modifications of the usual mannequin are one thing value exploring. As we attempt to resolve the mysteries of darkish matter and darkish vitality, they could become two sides of the identical coin.

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