New video: Largest-scale cosmic test ever favors dark matter over MOND

Anytime there’s a chance to subject our Universe to a new cosmic test, it’s imperative that we do it. First off, it gives the Universe a chance to surprise us: to show us something that we never could have learned unless we looked. Second off, it gives us a chance to test our underlying assumptions about the Universe: what it’s made of, what laws and rules it obeys, and how it behaves in never-before-probed ways.

And third — and perhaps most importantly — if there are rival ideas for making sense of the Universe, a new test has the potential to answer the question definitively: with data from the cosmos itself. we can finally conduct a long-awaited cosmic test: we can measure the kinetic Sunyaev-Zel’dovich effect. These measurements have the potential to test the idea of dark matter against the idea of MOND (MOdified Newtonian Dynamics), testing gravity on the largest scales and at the smallest accelerations ever. In a brand new video, I summarize the results and put them in their proper cosmic context.

Have a watch below, and read the transcript beneath it to make sure you catch every detail! Is the Universe made up of an enormous amount of dark matter, and is that responsible for the gravitational effects that we see on galactic and cosmic scales that normal matter alone can’t explain? Or is there no extra matter, and was Einstein wrong about how gravity works on the largest scales in the Universe?

The leading hypothesis is dark matter, but a rival one – MOdified Newtonian Dynamics, or MOND – paints a very different picture. In a brand new study, the largest-ever direct test of dark matter vs. MOND has just been conducted, by looking at both the large-scale structure of the Universe and the temperature properties of the cosmic microwave background together, and inferring a very difficult-to-measure effect: the kinetic Sunyaev-Zel’dovich effect.

These measurements enabled astronomers to determine, on average, how quickly two galaxies separated by a given distance accelerate towards one another: a measure of the acceleration due to gravity on the largest scales ever. When the results are obtained, on enormous cosmic scales – between 100 million and up to 750 million light-years – they were able to show that the laws of gravity behaved as Einstein’s general relativity predicted, and not as the alternative, MOND, predicts on those same cosmic scales. Get the fall print issue, shipping in October, to members only.

It’s a strong piece of evidence in our quest to uncover both how the Universe works and exactly what it’s made of, posing another colossal difficulty for alternatives to our standard picture of how reality truly is. Our main goal, always, in physics and astrophysics, is to understand the Universe as it actually is. Two of the biggest questions we know how to ask are: Over recent decades and centuries, we’ve built up a consensus picture that represents humanity’s best approximation to reality: with general relativity and quantum field theory providing the laws, and the Standard Model plus dark matter and dark energy making up the ingredients.