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Geraint F. Lewis

@cosmichorizons.bsky.social
1.5K followers 770 following 309 posts

Cosmologist & Galactic Archaeologist at @Sydney_Uni. Proud Silurian, Australian immigrant, & author of books about the strange universe we find ourselves in!

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Geraint F. Lewis @cosmichorizons.bsky.social · 25/09/2026
The Shortest History of Reality is now available as an audiobook. If you want to hear my words read to you in Iain Batchelor's smooth voice, this is for you!
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Reposted by Geraint F. Lewis
Corey S. Powell @coreyspowell.bsky.social · 03/09/2026
Happy Carrington Event Day to all who celebrate. On Sept 2-3, 1859, a huge solar flare hit Earth with the most intense magnetic storm on record. Auroras bloomed, magnetometers went wild, and telegraph machines sparked around the world. 🧪 link.springer.com/article/10.1...
Carrington’s (1859) carefully executed drawing of his sunspot group 520 on 1 September 1859, the first visual record of a solar flare. The initial (A and B) and final (C and D) positions of the white-light emission are indicated. Solar east is to the right. Below: Enlargement of region 520 from an early solar photograph made at Kew Observatory by Warren De la Rue on 31 August 1859.
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Reposted by Geraint F. Lewis
Tara Murphy @taramurphy.bsky.social · 16/08/2026
We are advertising a Lecturer in Radio Astronomy continuing position at @sydney.edu.au! Looking for someone to broaden and complement our existing research in #RadioAstro, and teach undergraduate #Physics. usyd.wd105.myworkdayjobs.com/en-GB/USYD_E... Deadline October 11th
usyd.wd105.myworkdayjobs.com
Lecturer in Radio Astronomy
A full-time Level B continuing position, located on the Camperdown Campus at the School of Physics Exciting opportunity to join one of the leading physics schools in the country, with outstanding staf...
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Geraint F. Lewis @cosmichorizons.bsky.social · 13/08/2026
Seeing your book in the wild is always exciting, but getting an unexpected review in your local newspaper (Blue Mountains Gazette) is really cool! #BookSky #BookTok #Nonfiction #PopularScience #Cosmology #Astronomy #Physics
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Geraint F. Lewis @cosmichorizons.bsky.social · 05/08/2026
Dear Cold-Callers - If you don't know that it's currently winter in the Southern Hemisphere, I am very unlikely to get beyond the first line of your email. Cheers - Geraint
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Geraint F. Lewis @cosmichorizons.bsky.social · 03/08/2026
Ouch - Hetherington (1980)
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Geraint F. Lewis @cosmichorizons.bsky.social · 31/07/2026
Thanks for the warm welcome on a very chilly night at Balmain Library. A great turnout, with great questions, about how we understand the nature of reality.
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Geraint F. Lewis @cosmichorizons.bsky.social · 27/07/2026
Pleased to announce that one of my books has been translated into Turkish! If you are in Türkiye, enjoy!!!
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Reposted by Geraint F. Lewis
Tara Murphy @taramurphy.bsky.social · 24/07/2026
In Sydney for National Science Week? You might be interested in this @sydney.edu.au talk with astrophysicist Geraint Lewis @cosmichorizons.bsky.social and chemist Haihui Joy Jiang. Thursday 20 Aug 6:00 pm Register here: www.sydney.edu.au/science/news... 🧪 ⚛️ 🔭
sydney.edu.au
The Impact Factor: Matter of origin
Have you ever wondered how we got here? How our Universe formed? And how life on Earth began? Join University of Sydney researchers, astrophysicist Professor Geraint Lewis and chemist Dr Haihui Joy Ji...
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Geraint F. Lewis @cosmichorizons.bsky.social · 16/07/2026
Spotted in the wild for the first time!
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Geraint F. Lewis @cosmichorizons.bsky.social · 16/07/2026
I recently appeared in Petr Lebedev's new video on Cosmic Fine-tuning. youtu.be/oi91kE_wocs?...
youtu.be
The Most Controversial Idea In Physics
YouTube video by SciencePetr
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Geraint F. Lewis @cosmichorizons.bsky.social · 03/07/2026
Unsolicited conference advice - please talk to the audience, not your slides, and stop waving the laser pointer around like a light sabre. Use it only when you really need to point something out on a slide. Oh, and you don’t have to be stuck in monotone mode.
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Geraint F. Lewis @cosmichorizons.bsky.social · 29/06/2026
Next on the reading list - by @willhaycardiff.bsky.social
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Geraint F. Lewis @cosmichorizons.bsky.social · 23/06/2026
My book, The Shortest History of Reality, publishes in North America on October 6! Preorders are 25% off at Barnes & Noble with code PREORDER25. Four days only, so don’t wait! #BNPreorder
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Geraint F. Lewis @cosmichorizons.bsky.social · 15/06/2026
Want to hear me in conversation with Dr Karl about just what reality is and how it all works? Then join us at Chatswood Library on 18th July.
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Geraint F. Lewis @cosmichorizons.bsky.social · 03/06/2026
New paper with my old student, Brendon Brewer - arxiv.org/abs/2606.01496
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Geraint F. Lewis @cosmichorizons.bsky.social · 02/06/2026
Charles Darwin on his student days at Cambridge University.
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Geraint F. Lewis @cosmichorizons.bsky.social · 01/06/2026
Winter is coming, but physics still does it's thing.
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Geraint F. Lewis @cosmichorizons.bsky.social · 30/05/2026
spacedaily.com/d-the-sun-mi... The sun doesn't look yellow, except on the horizon. It is white, as any wearer of white clothes on a sunny day can easily demonstrate.
spacedaily.com
The Sun might look yellow, but seen from space without an atmosphere filtering its light, the sun is actually white — and the yellow color we see from Earth is the result of our atmosphere scattering ...
The Sun is depicted as yellow in children’s drawings, in weather icons, on flags, and in the standard astronomical shorthand. Astronomers themselves classify it as a “yellow dwarf,” a G2V-type main se...
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Geraint F. Lewis @cosmichorizons.bsky.social · 29/05/2026
Lovely photo of the Milky Way from Tumut (taken by my eldest)
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Geraint F. Lewis @cosmichorizons.bsky.social · 27/05/2026
To be released in Australia next month, and the US in October, my new book has taken physical form! #ScienceBooks #Cosmology #Astronomy #PopularScience #Books
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Geraint F. Lewis @cosmichorizons.bsky.social · 03/05/2026
I was on a panel discussing technology and the future at the Sunshine Coast Hinterland Writers' Festival in Maleny
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Geraint F. Lewis @cosmichorizons.bsky.social · 29/04/2026
A bit of a rainbow - physics is cool!
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Geraint F. Lewis @cosmichorizons.bsky.social · 22/04/2026
I am at that grant writing stage where I am minutely adjusting figure size and deleting words almost at random to make things fit.....
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Geraint F. Lewis @cosmichorizons.bsky.social · 15/04/2026
The Southern Cross spotted on the way home.
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Geraint F. Lewis @cosmichorizons.bsky.social · 07/04/2026
Just remember that the dark side of the moon has the same metaphorical meaning as the dark side of the force and you will be ok. #astro #astrosci
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Geraint F. Lewis @cosmichorizons.bsky.social · 30/03/2026
Earlier papers on cosmological time dilation would use the word dilatation instead. Whilst they mean the same, I am glad the field has settled on dilation. #astrosci
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Geraint F. Lewis @cosmichorizons.bsky.social · 26/03/2026
Are you going to be on the Sunshine Coast in May? Do you want to hear me warble on about science and technology? Have I got the event for you!
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Geraint F. Lewis @cosmichorizons.bsky.social · 25/03/2026
Interesting perspectives on cosmology from Virginia Trimble in 1983. #astrosci
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Geraint F. Lewis @cosmichorizons.bsky.social · 07/03/2026
Time to start advertising my next book to be released in Australia at the end of June (right cover) and the US in September (left cover). A most wonderful Christmas present! #scicomm #physics #cosmology #science
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Geraint F. Lewis @cosmichorizons.bsky.social · 02/03/2026
I think it's interesting that people tell you that rockets can be used in space because of conservation of momentum, and so you don't need an atmosphere to push against, but if you ask them how and where the force is applied to the rocket, they just give you a quizzical look.
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Geraint F. Lewis @cosmichorizons.bsky.social · 27/02/2026
No it isn't.
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Geraint F. Lewis @cosmichorizons.bsky.social · 23/02/2026
New paper on the arXiv - first by PhD student Tim Adams arxiv.org/abs/2602.17957
arxiv.org
A Bayesian Exploration of the Mass of Ursa Major III: Kinematics, Rotation and their influence on the Mass to Light Ratio
We investigate the kinematics of the potential ultra-faint dwarf galaxy (UFD) UMa III/U1 using Bayesian inference to search for the signal of any potential intrinsic rotation. The magnitude of rotatio...
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Geraint F. Lewis @cosmichorizons.bsky.social · 21/02/2026
My haul from the excellent Wyrdbooks in Wentworth Falls
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Geraint F. Lewis @cosmichorizons.bsky.social · 21/02/2026
Has anyone seen a more glorious sewer cover?
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Geraint F. Lewis @cosmichorizons.bsky.social · 16/02/2026
There's no obvious reason for choosing that metric signature!
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Geraint F. Lewis @cosmichorizons.bsky.social · 13/02/2026
I made this for my PhD (sometimes last century), which shows microlensing in the Einstein Cross. It's still out there, being used :) - hyperphysics.phy-astr.gsu.edu/hbase/Astro/...
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Geraint F. Lewis @cosmichorizons.bsky.social · 09/02/2026
Brits take the Gulf Stream for granted, but to understand it's importance you just have to realise that the Titanic hit the iceberg 10 degrees *South* of Britain.
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Geraint F. Lewis @cosmichorizons.bsky.social · 06/02/2026
New paper on the arxiv - - arxiv.org/abs/2602.05070
arxiv.org
Wising up to CatWISE: using simulation-based inference to interpret the ecliptic bias and confirm the cosmic dipole excess
We apply Simulation-Based Inference ('SBI') to the cosmic dipole problem for the first time, measuring the distribution of quasar counts over the sky in the CatWISE2020 ('CatWISE') sample. We show tha...
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Geraint F. Lewis @cosmichorizons.bsky.social · 05/02/2026
Just finished Heroes (really enjoyed) and about to start Mythos (have Troy and the Odessey lined up).
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Geraint F. Lewis @cosmichorizons.bsky.social · 30/01/2026
Tim Berners-Lee talking about the invention of the world wide web at the Sydney Opera House last night. An invention that truly changed the world.
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Geraint F. Lewis @cosmichorizons.bsky.social · 14/01/2026
My airplane display has the Milky Way aligned with the Earth's equator and this really bothers me.
Aircraft display showing the Milky Way aligned with the equator of the Earth
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Reposted by Geraint F. Lewis
The Open Journal of Astrophysics @ojastro.bsky.social · 12/01/2026
New Publication at the Open Journal of Astrophysics: "Rotational Kinematics in the Globular Cluster System of M31: Insights from Bayesian Inference" by Yuan (Cher) Li & Brendon J. Brewer (U. Auckland, New Zealand), Geraint F. Lewis (U. Sydney, Australia) and Dougal Mackey doi.org/10.33232/001...
doi.org
Rotational Kinematics in the Globular Cluster System of M31: Insights from Bayesian Inference | Published in The Open Journal of Astrophysics
By Yuan (Cher) Li, Brendon J. Brewer & 2 more. This study uses Bayesian modelling to explore the kinematics of globular clusters in the Andromeda Galaxy, revealing distinct rotation patterns that sugg...
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Geraint F. Lewis @cosmichorizons.bsky.social · 08/01/2026
If you draw a circle within a square, the circle occupies 78.5% of the area. If you step up a dimension to a sphere in a cube, the relative volume of the sphere is 52.4%. As you increase the number of dimensions, the %-volume of the sphere gets smaller and smaller, and goes to zero as n->infinity.
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Geraint F. Lewis @cosmichorizons.bsky.social · 17/12/2025
Double rainbow over Rangitoto Island in Auckland #physicsinaction
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Geraint F. Lewis @cosmichorizons.bsky.social · 02/12/2025
South American Bin Chickens are prettier than the ones we have in Sydney
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Geraint F. Lewis @cosmichorizons.bsky.social · 01/12/2025
Just realised that the spell checker changed Finkelstein to Frankenstein in the General Relativity and Cosmology exam!
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Geraint F. Lewis @cosmichorizons.bsky.social · 26/11/2025
The Gravitational Astrophysics group at @sydney.edu.au
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Geraint F. Lewis @cosmichorizons.bsky.social · 17/11/2025
"You can teach a physicist finance but you cannot teach a finance person physics." - Jim Simons (en.wikipedia.org/wiki/Jim_Sim...)
en.wikipedia.org
Jim Simons - Wikipedia
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Geraint F. Lewis @cosmichorizons.bsky.social · 05/11/2025
They don't do Guy Fawkes in Australia (but I discovered this weekend that they do in New Zealand). But do we celebrate because he was captured, and the gunpowder plot failed, or because he tried?
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