3 ms·

The theory that hydrogen fusion powers stars is actually older than the discovery that the sun is made of (mostly) hydrogen. Eddington proposed it in 1920. It w

The theory that hydrogen fusion powers stars is actually older than the discovery that the sun is made of (mostly) hydrogen. Eddington proposed it in 1920. It wasn't necessary to assume a "mostly hydrogen" sun—his estimate was that a >5% hydrogen sun would be sufficient. https://sci-hub.se/10.1126/science.52.1341.233 https://sci-hub.se/10.1126/science.52.1341.233 The immediate historical motivation wasn't the discovery of hydrogen in the solar atmosphere, but the discovery, on Earth, that the hydrogen atom is anomalously heavy (~1% mass excess per nucleon).

perihelions 2y ago
(Eddington's is rather an astonishing paper, science aside, just for the remarkable breadth of perspective written down in one place 100 years ago. Within eight pages, he is contemplating all of: - The perspective that all of the matter life is made of may have been forged in the "crucibles" of stars; - The perspective that the timeline of the planet Earth should be expanded from ~20 million years, to multiple billions (and the specific implications for biological evolution); - The perspective that hydrogen fusion could be the energy source of future civilization—or a source of weapons that end it All of this, purely speculative theorizing, in 1920!
- ZeroGravitas 2y ago
  I think the point about the age of the earth and evolution might be backwards. Lord Kelvin had worked out that the earth might be only 20 million years old maybe 60 years earlier based on continually losing heat. But even at that earlier time biologists and geologists were suggesting that number wasn't high enough to explain what they were seeing in their fields. I think Darwin had suggested a lower bound of at least 300 million based on the erosion he saw locally.
- echelon 2y ago
  > All of this, purely speculative theorizing, in 1920! What speculative theorizing are we doing in the 2020s that we might similarly look back upon?
  - pfdietz 2y ago
    All that superstring and supersymmetry stuff. Maybe Dark Matter and Dark Energy? Inflationary cosmology. Extraterrestrial intelligence/life.

perihelions 2y ago

(Eddington's is rather an astonishing paper, science aside, just for the remarkable breadth of perspective written down in one place 100 years ago. Within eight pages, he is contemplating all of: - The perspective that all of the matter life is made of may have been forged in the "crucibles" of stars; - The perspective that the timeline of the planet Earth should be expanded from ~20 million years, to multiple billions (and the specific implications for biological evolution); - The perspective that hydrogen fusion could be the energy source of future civilization—or a source of weapons that end it All of this, purely speculative theorizing, in 1920!

ZeroGravitas 2y ago
I think the point about the age of the earth and evolution might be backwards. Lord Kelvin had worked out that the earth might be only 20 million years old maybe 60 years earlier based on continually losing heat. But even at that earlier time biologists and geologists were suggesting that number wasn't high enough to explain what they were seeing in their fields. I think Darwin had suggested a lower bound of at least 300 million based on the erosion he saw locally.
echelon 2y ago
> All of this, purely speculative theorizing, in 1920! What speculative theorizing are we doing in the 2020s that we might similarly look back upon?
- pfdietz 2y ago
  All that superstring and supersymmetry stuff. Maybe Dark Matter and Dark Energy? Inflationary cosmology. Extraterrestrial intelligence/life.