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Will Kinney Profile picture
Will Kinney
@WKCosmo
Cosmologist, physicist, dirtbag mountain biker, expat Montanan, Copernican extremist. Part of the problem.
Mar 30 • 75 tweets • 13 min read
So let me see if I can explain my skepticism here, in a way that refrains from commenting (much) on the political factors at play here, and sticks to the physics. This will be a bit of a long thread. 1/ Let's start with a historical example. The Cepheid period/luminosity relation, first discovered by Henrietta Swan Leavitt. Image
Mar 17 • 4 tweets • 1 min read
There is a fundamental disconnect between STEM and humanities/philosophy in that STEM by its nature does not value the wisdom of the ancients in any special way. We understand a lot more about Einstein's theories than Einstein did, because we have had a century to find deeper, simpler, and clearer ways to think about the physics. Contemporary scientists by and large are not confused about the things that Einstein was confused about, we are confused about new things, that Einstein barely imagined. One of the few papers by Einstein that is still worth reading for more than historical interest is the EPR paper, which remains relevant because we are still arguing about quantum entanglement and locality. But even in this case, Bell's theorem came after Einstein's death, and completely changed how we think about entanglement. The EPR paper is mostly notable because we now have experimental proof of non-local correlations in quantum mechanics that Einstein believed were impossible.
Nov 16, 2025 • 11 tweets • 2 min read
Fair question. What do we learn from gravitational waves? The form of the chirp signal is well understood from Genearl Relativity. 1/ First thing is that we don't just observe one chirp. We have a LOT of them, and that gives us information about the astrophysical population of black holes — masses, spins, distances. And almost everything we have discovered has been a surprise. 2/
Aug 22, 2025 • 25 tweets • 3 min read
So I read this book, and I thought it was very good. Image Oh no, not another book about how theoretical physics has lost its way, string theory is a failure, and new ideas are shut out. Do we really need another one?
Jun 12, 2025 • 9 tweets • 3 min read
Spoiler: it's the moment they start taking math classes. This is an astonishing statement, because the data do not even remotely support this conclusion. Image
Mar 4, 2025 • 14 tweets • 2 min read
You need to understand both General Relativity and Hubble expansion to correctly engineer Global Positioning System, which is a central part of modern civilian and military infrastructure. Here's why. 1/ GPS is a bunch of atomic clocks in orbit. You find your position by comparing the time signals from different satellites, and measuring the time delay caused by the light travel time. 2/
Dec 14, 2024 • 11 tweets • 2 min read
Why gravity is a cultural construct. 🧵 1/ Let’s start with the premise: gravity, as a concept, is not as purely objective as it seems. Yes, it’s a physical force, but the meaning we ascribe to it and the questions we ask about it are deeply rooted in cultural frameworks.
Nov 15, 2024 • 19 tweets • 4 min read
In honor of Laura Helmuth's sudden and inexplicable retirement, some greatest hits. scientificamerican.com/article/the-la…
Oct 27, 2024 • 15 tweets • 2 min read
We shall measure stellar brightness logarithmically, and it will be called the "magnitude."

- Sir, will that logarithm be base 10, or based on Napier's constant?

Neither. It shall be of the base of the fifth root of one hundred. Image - and brighter stars will have larger magnitude?

No, it shall be the opposite.
Oct 21, 2024 • 30 tweets • 6 min read
Since it has come up, a thread on "negative energy," what it means, and why it's important in physics. 1/ Negative energy shows up all the time in classical physics, for example the potential energy in Newton's theory of gravity: 2/ Image
Apr 23, 2024 • 5 tweets • 2 min read

Image Having use for this image waaaay too often lately.
Feb 24, 2024 • 46 tweets • 10 min read
Bravo to the 22.9% who (correctly) concluded that the string connecting the rocket breaks!

Contrary to what is often taught, it is perfectly possible to handle accelerated reference frames in Special Relativity. This problem is a nice example. 🧵 1/ The rocket problem was first posed by John Bell (same guy as Bell's Theorem in quantum mechanics). The story is, he posed the problem to his colleagues at CERN, and (like the poll) most of them got it wrong!
Feb 7, 2024 • 16 tweets • 4 min read
Getting a lot of replies making various claims that this is not a quantum mechanical result, and you can't assign a velocity to electrons in atomic orbitals. Nonsense! This is ALL ABOUT quantum mechanics. Allow me to explain. 1/ Let's consider the simpler system of hydrogen first. The basic properties of the hydrogen atom are a consequence of the Heisenberg uncertainty principle relating the uncertainty of the radius of the electron in orbit to the uncertainty in its momentum, 2/ Image
Sep 28, 2023 • 20 tweets • 5 min read
The string breaks. Lots of responses to the poll, most of them wrong. Image
Jul 24, 2023 • 11 tweets • 2 min read
OK, saw Oppenheimer. A few reactions, no spoilers. 1/ Image Extraordinarily well done. Nearly flawless, IMO, and one of the most important and effective pieces of #scicomm I think I have ever seen.
Jul 21, 2023 • 43 tweets • 7 min read
A few words about this paper, which was a lot of fun to write. 1/N https://t.co/PRg3YHPvDr
Image Most of the heavy lifting on this project was done on a five-week visit to @iitmadras in Chennai in January, working with my awesome collaborators L. Sriramkumar and @suvashis_maity.
Apr 28, 2023 • 23 tweets • 4 min read
So what exactly is the Planck length? A thread. 1/ Let's start with the Heisenberg uncertainty principle, which we can write like this: 2/ Image
Mar 4, 2023 • 16 tweets • 2 min read
When I teach astronomy as a Gen Ed course, I include mythology and stories from a variety of cultures and traditions, because that is part of the history of the field, and the history of the development of the scientific method. 1/ Ancient and indigenous peoples had sophisticated and deep relationships with nature. Because they were smart humans.
Feb 26, 2023 • 25 tweets • 4 min read
It's starting to look like the problem of too many big galaxies too early for LCDM is likely to be a real thing. 1/ This, of course, is categorically NOT a problem for the Big Bang. It's about how structure formed in the late universe, starting a few hundred million years after the Big Bang itself. 2/
Feb 23, 2023 • 6 tweets • 2 min read
Wish I could tweet the smell. Image Veal liver in a brandy cream sauce with bacon and onion and snow peas tonight. Image
Dec 24, 2022 • 32 tweets • 5 min read
Since I'm in Pudecherry, India, let me tell you a bit about the world's unluckiest astronomer, one Guillaume Le Gentil. This is a crazy story, so pull up a chair. 1/ The year is 1760, and our man sets out from Paris as part of an international effort to observe the 1761 transit of Venus. 2/