Uploaded September 2026 | Updated September 2026, 2 weeks ago
In the 1920s it was Edwin Hubble that first noticed that galaxies further away from us, appear to be moving away from us faster than those close by. That was eventually interpreted as not the galaxies themselves moving, but the space between us and the galaxies expanding, i.e. the Universe is expanding.
It also led to the development of the Big Bang theory for how the Universe has evolved. That took decades of endless scientific debate though, and it wasn't until the cosmic microwave background was discovered in 1964, an echo of light from the early Universe that supported the idea of the Big Bang theory, that this idea of an expanding universe became widely accepted.
So the picture in the 1990s is that the Universe is expanding at a constant rate. But then in 1998 Riess and collaborators published what would become their Nobel prize winning study, which showed as they looked at galaxies with even faster apparent speeds away from us, the galaxies were further away than you’d expect by a factor of around 10-15%.
That was eventually interpreted as space had expanded more than you’d expect from a constant expansion speed, i.e. the Universe was accelerating. And that result didn’t stand alone for very long, more evidence started to pour in through the 2000s as we got more detailed measurements of the cosmic microwave background, and as we did big galaxy surveys to map out the large-scale clustering of galaxies, all of it pointed towards a constantly accelerating expanding Universe.
But to power that, you need more energy in the Universe, something that was dubbed “dark energy” and it turns out it's more than all the normal and dark matter combined.
Video filmed on a Sony ⍺7 IV
Video edited by Martino Gasparrini: martino.freelance@gmail.com
Video produced by Marina Hui & Dr Becky Smethurst
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📚 My book, "A Brief History of Black Holes", out NOW in hardback, paperback, e-book and audiobook (which I narrated myself!): lnk.to/DrBecky
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👕 My merch, including JWST designs, are available here (with worldwide shipping!): dr-becky.teemill.com
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🎧 Royal Astronomical Society Podcast that I co-host: podfollow.com/supermassive
---
🔔 Don't forget to subscribe and click the little bell icon to be notified when I post a new video!
---
👩🏽💻 I'm Dr. Becky Smethurst, an astrophysicist at the University of Oxford. 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.
drbecky.uk.com
In the 1920s it was Edwin Hubble that first noticed that galaxies further away from us, appear to be moving away from us faster than those close by. That was eventually interpreted as not the galaxies themselves moving, but the space between us and the galaxies expanding, i.e. the Universe is expanding.
It also led to the development of the Big Bang theory for how the Universe has evolved. That took decades of endless scientific debate though, and it wasn't until the cosmic microwave background was discovered in 1964, an echo of light from the early Universe that supported the idea of the Big Bang theory, that this idea of an expanding universe became widely accepted.
So the picture in the 1990s is that the Universe is expanding at a constant rate. But then in 1998 Riess and collaborators published what would become their Nobel prize winning study, which showed as they looked at galaxies with even faster apparent speeds away from us, the galaxies were further away than you’d expect by a factor of around 10-15%.
That was eventually interpreted as space had expanded more than you’d expect from a constant expansion speed, i.e. the Universe was accelerating. And that result didn’t stand alone for very long, more evidence started to pour in through the 2000s as we got more detailed measurements of the cosmic microwave background, and as we did big galaxy surveys to map out the large-scale clustering of galaxies, all of it pointed towards a constantly accelerating expanding Universe.
But to power that, you need more energy in the Universe, something that was dubbed “dark energy” and it turns out it's more than all the normal and dark matter combined.
Video filmed on a Sony ⍺7 IV
Video edited by Martino Gasparrini: martino.freelance@gmail.com
Video produced by Marina Hui & Dr Becky Smethurst
---
📚 My book, "A Brief History of Black Holes", out NOW in hardback, paperback, e-book and audiobook (which I narrated myself!): lnk.to/DrBecky
---
👕 My merch, including JWST designs, are available here (with worldwide shipping!): dr-becky.teemill.com
---
🎧 Royal Astronomical Society Podcast that I co-host: podfollow.com/supermassive
---
🔔 Don't forget to subscribe and click the little bell icon to be notified when I post a new video!
---
👩🏽💻 I'm Dr. Becky Smethurst, an astrophysicist at the University of Oxford. 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.
drbecky.uk.com
