For many years, it was not clear whether Einstein or Hilbert first obtained the field equations of general relativity. Hilbert's paper appeared in 1916, after Einstein's paper. But it had been submitted on November 20, 1915 – five days before Einstein's paper was submitted.
A common narrative among physicists was that Hilbert and Einstein obtained more or less the same result in parallel, with Hilbert submitting first but Einstein being responsible for the development of general relativity as a whole.
But it turns out the submission dates don't tell the whole story!
Einstein proposed three "classical" tests of general relativity: the precession of Mercury's perihelion, deflection of light by the sun, and gravitational redshift. Irwin Shapiro proposed a fourth test #OTD in 1964: the gravitational time delay of light. journals.aps.org/prl/abstract/1…
It's a simple idea: The round-trip time of a radio signal bounced off a distant object increases a little if it passes through the gravitational field of a massive object along the way.
Shapiro estimated that signals bounced off Venus or Mercury at superior conjunction, when they are on the opposite side of the sun from Earth, would experience a delay of about 200 microseconds due to the Sun's gravitational field.
Abraham Flexner, who reformed medical and science education in the U.S., founded and served as the first director of the Institute for Advanced Study, and helped many scientists — including Einstein — leave Nazi Germany, was born #OTD in 1866. ias.edu/scholars/flexn…
Parts of Abraham Flexner's 1939 essay "The Usefulness Of Useless Knowledge" feel very timely, as disingenuous attacks on science gain currency as a political tactic. ias.edu/ideas/usefulne…
The language and assumptions in Flexner’s essay are dated in parts — it was written in 1939 — but its arguments for curiosity-driven research and defense of science resonate right now.
Last year, my then-5yo heard the word "excelsior" in a cartoon and asked what it meant. I explained it to her and told her about Stan Lee. We talked about lots of characters he helped create; she wanted to know if each one was kind or mean. Later, she made this list. #Excelsior
John William Strutt, Lord Rayleigh, was born #OTD in 1842. He discovered argon, worked out the wavelength-dependence of elastic scattering of light by small particles that explains blue skies and red sunsets, and described the spectral radiance of a blackbody at long wavelengths.
It’s great that I am just seeing this three year old tweet today, since Lord Rayleigh discovered argon.
The 6yo just marched into the kitchen and solemnly announced "The superheroes are within you, your time has come" if anyone needs a premise and a tagline for a comic book.
(She was wearing her long-johns that have neon wonder woman, batgirl, and supergirl logos all over them.)
She wore the superhero long johns again tonight. I was washing dishes when I heard her say "You don't have to be tall, you don't have to be small. You just have to..." [she leaps into the kitchen] "...BE YOURSELF to be a SUPER HERO."
Carl Sagan was born #OTD in 1934. He was a planetary scientist, a dedicated and gifted science communicator, and a tireless advocate for the humanizing power of science.
Carl Sagan was prescient about many things, not just our impact on the climate but also how ignorance might be weaponized. Here, in an excerpt from “The Demon Haunted World,” is what he feared we might become.
Sagan passed away in 1996. Towards the end he emphasized two messages which are, unfortunately, still relevant today. I’m glad that we seem to have made at least a little progress on part of his first point with this last election.
IN ADDITION, @LoyolaChicago is hiring two Lecturers in Physics. These are full-time, NTT teaching positions with good benefits. If you know strong candidates, they can begin the application process here: careers.luc.edu/postings/9578
☝️Physics Twitter: Loyola is hiring multiple positions.
Wilhelm Röntgen discovered X-rays #OTD in 1895 when he noticed that emanations from a Crookes tube caused a platino-barium screen to fluoresce. The rays exposed photographic plates but were blocked by bone & metal. One early plate shows his wife's left hand.
Image: Wellcome Trust
Röntgen presented his results in December, gave a public talk in January of 1896, and by February some clinics were beginning to use X-rays as a diagnostic tool.
Image: New York Academy of Medicine (Boston Medical and Surgical Journal 134(8), February 20, 1896)
Röntgen refused to patent his discovery so that there would be no barriers to medical applications and other beneficial uses. He donated all his Nobel Prize money to his university, and then died in poverty due to mass inflation after WWI.
This is straight out of 1984. Follow @Acosta and help grow his platform to push back against these Orwellian fascists.
The first instance of the doctored video that I can find is the one posted by @PrisonPlanet. Please go to his tweet — I won’t share it — and report him. Not sure why @TwitterSafety left his account up when they dumped Infowars.
The physicist Lise Meitner was born #OTD in 1878. She discovered fission in uranium and was the first person to understand both its mechanics and implications.
Image: Atomic Heritage Foundation (photographer unknown)
Meitner’s PhD advisor at the University of Vienna was Ludwig Boltzmann -- that's the Boltzmann of S = k ln W fame. n 1907, she went to Berlin to work with Max Planck and Otto Hahn. Meitner's collaboration with Hahn would last for 30 years
Meitner handled the physics and Hahn did the chemistry. They had complementary approaches to science -- it was a partnership made for discovery. Together, they made several advances related to radioactivity. She also discovered what is commonly called the “Auger Effect” in 1922.
One nice by-product of this election is that the @HouseScience twitter account will no longer be a firehose of climate change denial and anti-science propaganda.
Just for context, there was a stretch last year where @HouseScience linked stories from or RT’d Breitbart 4x as often as it shared stories from @nature or @sciencemagazine. That’s done now.
Good news, everybody: In a few months the @HouseScience account will be run by folks who actually support science, instead of climate-change deniers, part-time Breitbart columnists, and wild-eyed conspiracy theorists.
The measured deflection of starlight by the gravitational field of the sun, confirming one of the main predictions of Einstein's general relativity, was announced at a joint meeting of the Royal Society and the Royal Astronomical Society #OTD in 1919.
The measurements were made during the total solar eclipse on May 29 of that year. Eddington led an expedition to Principe, while Crommelin led an expedition to Sobral.
Image: Arthur Eddington
Freeman Dyson submitted a lovely little two-page paper to Physical Review #OTD in 1951, demonstrating that perturbation theory in quantum electrodynamics produces a divergent series. It's an absolute classic of the field, worth taking the time to read. journals.aps.org/pr/abstract/10…
I wrote a bit about this last December, but it's embedded inside a much longer thread with lots of other stuff so let me repeat the relevant parts here.
In QED we calculate physical quantities perturbatively, as a series in a small number α (about 1/137). So if we want to know, for instance, the anomalous magnetic moment of the electron (classically it should be g=2) we get a series like:
g = 2 + (1/π) α + (0.656/π²) α² + …