3 ms·

This is really interesting, because we had a lot of the machinery in place to make accurate observations, but not a lot of the theory to link them together. We'

This is really interesting, because we had a lot of the machinery in place to make accurate observations, but not a lot of the theory to link them together. We've known about sunspots since the Han dynasty and had accurate measurements of its size, distance, and temperature since the mid-1800s when spectroscopy became available. But it took Einstein himself and the legendary E=MC^2 equation to demonstrate a theoretical source of energy that powers the sun, well into the 20th century.

Finnucane 7y ago
It was definitely a conundrum for scientists. Throughout the 19th century, evidence kept piling up from geology supporting longer and longer time periods for the age of the earth, but there was no known source of energy that could keep the sun burning for that much time.
- Ididntdothis 7y ago
  Sounds a little like Dark Matter and Dark Energy today. Lots of evidence for it but nobody knows what it is.
  - hawkice 7y ago
    To be fair, the cosmological constant is a fair stab at a guess for dark energy. Like, space has an intrinsic property N that's allowed in the equations. That's a decently shaped guess.
    - Finnucane 7y ago
      Where does it say the government is limited to that?
- _bxg1 7y ago
  I wonder if anyone became worried that the sun could burn out at any time
archgoon 7y ago
Einstein did not determine that the sun was nuclear powered. That was Hans Bethe in 1939 (based on data produced by Bengt Strömgren).
- ahazred8ta 7y ago
  "In 1920, Arthur Eddington suggested hydrogen-helium fusion could be the primary source of stellar energy. ... laboratory fusion of hydrogen isotopes was accomplished by Mark Oliphant in 1932. ... the theory of the main cycle of nuclear fusion in stars was worked out by Hans Bethe." https://en.wikipedia.org/wiki/Nuclear_fusion https://en.wikipedia.org/wiki/Nuclear_fusion
- jaggederest 7y ago
  Right, I wasn't saying he did. I was trying to say that, without a theoretical framework to hang that kind of energy generation on, there was no capacity to understand what was going on. E=MC^2 is precisely that kind of theoretical framework. Pretty amazing, to me. Being able to say "It's this far away, this hot, and this large, but why?"
  - fsh 7y ago
    E=mc^2 is a consequence from special relativity, not a theoretical framework. It also has very little to do with the understand of nuclear reactions. The reason why nuclear reactions release much more energy than chemical reactions is that the binding energies inside the nucleus are much larger than inside the electron shell. Mass-energy equivalence exists in both cases.
    - pfdietz 7y ago
      Indeed. And in a Newtonian universe, it's possible that something like nuclear fusion could exist that would liberate much more than mc^2. There would be no upper limit on nuclear reaction energies set by the total rest energy of the reactants.
  - archgoon 7y ago
    I don't think thats true though. In 1903, Radioactivity had already been proposed as an explanation for the Sun's heat (2 years prior to Annus Mirabilis). The connection between E=mc^2 and nuclear reactions doesn't become clear until you start losing mass (proton + neutron) in the reactions, which doesn't happen for the reactions involved in the Sun (Carbon Nitrogen Oxygen Cycle). The connection was recognized by Lise Meitner and Otto Hahn when they discovered fission, where a mass loss does occur. However, they didn't publish their discovery until January 1939; and Hans Bethe had already been working on the Carbon Nitrogen Oxygen Cycle, and didn't need fission to account for the Sun's processes (neutron + proton mass is conserved in the relevant reactions). He was just working off of observed empirical data to make his conclusions.

Finnucane 7y ago

It was definitely a conundrum for scientists. Throughout the 19th century, evidence kept piling up from geology supporting longer and longer time periods for the age of the earth, but there was no known source of energy that could keep the sun burning for that much time.

Ididntdothis 7y ago
Sounds a little like Dark Matter and Dark Energy today. Lots of evidence for it but nobody knows what it is.
- hawkice 7y ago
  To be fair, the cosmological constant is a fair stab at a guess for dark energy. Like, space has an intrinsic property N that's allowed in the equations. That's a decently shaped guess.
  - Finnucane 7y ago
    Where does it say the government is limited to that?
_bxg1 7y ago
I wonder if anyone became worried that the sun could burn out at any time

archgoon 7y ago

Einstein did not determine that the sun was nuclear powered. That was Hans Bethe in 1939 (based on data produced by Bengt Strömgren).

ahazred8ta 7y ago
"In 1920, Arthur Eddington suggested hydrogen-helium fusion could be the primary source of stellar energy. ... laboratory fusion of hydrogen isotopes was accomplished by Mark Oliphant in 1932. ... the theory of the main cycle of nuclear fusion in stars was worked out by Hans Bethe." https://en.wikipedia.org/wiki/Nuclear_fusion https://en.wikipedia.org/wiki/Nuclear_fusion
jaggederest 7y ago
Right, I wasn't saying he did. I was trying to say that, without a theoretical framework to hang that kind of energy generation on, there was no capacity to understand what was going on. E=MC^2 is precisely that kind of theoretical framework. Pretty amazing, to me. Being able to say "It's this far away, this hot, and this large, but why?"
- fsh 7y ago
  E=mc^2 is a consequence from special relativity, not a theoretical framework. It also has very little to do with the understand of nuclear reactions. The reason why nuclear reactions release much more energy than chemical reactions is that the binding energies inside the nucleus are much larger than inside the electron shell. Mass-energy equivalence exists in both cases.
  - pfdietz 7y ago
    Indeed. And in a Newtonian universe, it's possible that something like nuclear fusion could exist that would liberate much more than mc^2. There would be no upper limit on nuclear reaction energies set by the total rest energy of the reactants.
- archgoon 7y ago
  I don't think thats true though. In 1903, Radioactivity had already been proposed as an explanation for the Sun's heat (2 years prior to Annus Mirabilis). The connection between E=mc^2 and nuclear reactions doesn't become clear until you start losing mass (proton + neutron) in the reactions, which doesn't happen for the reactions involved in the Sun (Carbon Nitrogen Oxygen Cycle). The connection was recognized by Lise Meitner and Otto Hahn when they discovered fission, where a mass loss does occur. However, they didn't publish their discovery until January 1939; and Hans Bethe had already been working on the Carbon Nitrogen Oxygen Cycle, and didn't need fission to account for the Sun's processes (neutron + proton mass is conserved in the relevant reactions). He was just working off of observed empirical data to make his conclusions.