How do we know how much dark matter there is in the Universe?

From Dr. Becky.

AD – Go to to stay fully informed with the latest Space and Science news. Subscribe through my link to get 40% off the Vantage plan for unlimited access this month only. | I often get asked how do we know dark matter exists? Which is why I’ve made a video on all the observational evidence we have before (linked below)! But occasionally I’ll get asked how do we know *how much* dark matter there is, which is a really fun question. There’s many different ways we can calculate this, including the ratio between normal (baryonic) and dark matter, but in this video I just wanted to highlight three different ways astrophysicists calculate this.

Here’s my previous video on all the evidence we have for dark matter –
My previous video on whether dark matter could be made of black holes –
My previous video on whether black holes contain dark matter –
My previous video on why galaxies merge if the universe is expanding –

Allen, Evrard & Mantz (2011; review on galaxy clusters observations) –
Zwicky (1933; first virial theorem paper in German) –…6..110Z
Zwicky (1937; virial theorem applied to the Coma cluster) –….86..217Z
Alpher, Bethe, & Gamow (1948; big bang nucleosynthesis; behind paywall) –
Alpher & Herman (1950; more BBN work; behind paywall) –
Planck collaboration (2015; cosmological parameter results for our best model of the Universe) –

00:00 Introduction
02:04 Ground News AD
03:54 Method 1 – Galaxy Clusters and the virial theorem
08:49 Method 2 – Big Bang Nucleosynthesis
11:39 Method 3 – Cosmic Microwave Background
14:35 Outro
15:24 Bloopers

Video filmed on a Sony ⍺7 IV

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👩🏽‍💻 I’m Dr. Becky Smethurst, an astrophysicist at the University of Oxford (Christ Church). I love making videos about science with an unnatural level of enthusiasm. I like to focus on how we know things, not just what we know. And especially, the things we still don’t know. If you’ve ever wondered about something in space and couldn’t find an answer online – you can ask me! My day job is to do research into how supermassive black holes can affect the galaxies that they live in. In particular, I look at whether the energy output from the disk of material orbiting around a growing supermassive black hole can stop a galaxy from forming stars.