Darwin’s Sorest Trouble

Darwin understood that his own theory demanded that the earth be hundreds of millions of years old.  But due to limited physics of his day, scientists at that time calculated a very young age of the sun which made Darwin doubt his theory.  In fact, due to these doubts, in later editions of  “Origin of Species”, Darwin removed all mention of timescales.  Below I will give a chronological outline of the story of how we have come to understand the Sun’s source of energy and its age.  My main source and inspiration for this post is Frank Close’s book, “Neutrino“.

2700 BC:  Ancient Egyptians view the sun as a big ball of fire — no theory of its fuel yet.  This celestial body they deified as “Ra“.
500 BCAnaxagoras, apparently found a newly crashed hot meteorite and reasoned that, coming from the sky where the only hot thing was the sun, then it must be a piece of the sun and thus the sun was made of red-hot iron.  This theory then held for more than two thousand years.
1850 ADJohn Waterstone, a schoolteacher, does calculations showing that if the Sun’s heat comes from chemical energy (cooling iron or whatever), then the sun could only last 10,000 years.  So looking for other candidates for sources of energy, he theorizes that the energy of rocks falling into the sun transferred their falling kinetic energy into heat.   But he realized there were not enough material in the solar system to power the Sun, so, in 1853 he proposed that perhaps the Sun was falling in on itself and consequently releasing energy.  Waterstone’s ideas would be picked up 10 years later by William Thomson.

Kinetic Theory of Gas

1859:  Charles Darwin publishes “On the Origin of Species“.   His theory of evolution implied that the Earth had to be more like hundreds of millions of years old.  Yet the known laws of physics could not explain how the Sun could have burned so long.

Charles Darwin

1860William Thomson[aka, Lord Kelvin] explores Waterstone’s ideas further.  First he explored the notion of material crashing into the Sun.  But he sees that even of all the planets crashed into the Sun, it would only give it 3,000 years of life.  Next he explored Waterstone’s notion of a collapsing sun’s kinetic energy, and calculates that even if the best scenario, the sun could be more than 100 million years old.

William Thompson (Lord Kelvin)

1860’s: Darwin writes the co-discoverer of natural selection, Alfred Russel Wallace, about Thomson’s work on the age of the sun and says they “have been for some time one of my sorest troubles.”

Alfred Wallace

1896: Henri Becquereldiscovers radioactivity.  1898: Marie Skłodowska Curiediscovers Radium1903: William Wilsonshows that a few grams of Radium per cubic meter of the Sun would be enough to explain its power but quickly, solar spectrum experiments showed no radium on the Sun but instead, hydrogen and helium.

Marie Curie (1898)

1905: Albert Einsteinpublished his theory of relativity and shows that mass, when converted to energy yields unbelievable energy.  E=MC↑2.

Albert Einstein 1905

1913: Earnest Rutherfordspeculates that H and He may react differently in the Sun because of its enormous temperatures and thus releasing energy in the nucleus of the atom.  Thus the Sun was thought of as a nuclear furnace though the mechanism were a mystery, the source of power was now understood.

Gold Foil experiment exposing the structure of the atom.

Earnest Rutherford

1920: Francis Aston discovered that helium had 1/120 less mass (thus given up as energy) than 4 atoms of hydrogen.   Sir Arthur Eddingtonthen proposes that hydrogen in the Sun combines to form helium and looses mass and thus yields energy.

Arthur Eddington

1939: Hans Bethe publishes his paper “Energy Production in Stars”.  He discovered the CNO cycle to explain this but then realized that the Sun was not hot enough to support this reaction (other stars are hot enough, however).  He then Bethe explored Eddington’s notion of hydrogen as the fuel and soon elaborated the P-P chain as the mechanism of our sun of converting mass into energy and thus allowing it enough fuel to last about 10 billion years.  Darwin (1809-1882) was vindicated.

Hans Bethe


Filed under Astronomy, Evolution, Science

12 responses to “Darwin’s Sorest Trouble

  1. Fascinating! I was on a hike yesterday and we were talking about Lord Kelvin. I was talking to a geologist and asked her why, if the earth is as old as she is that her core hasn’t cooled off yet. She said, “You and Lord Kelvin.” And then went on to explain why.

  2. Wow, Dan — your friend is really old!

    Pecked out quickly on my DROID phone !

  3. Be careful of those geologists with a hot core.

  4. Earnest

    Its interesting that this is still somewhat theoretical since we cannot sample the interior of the sun to verify such a process is taking place. However I haven’t heard of any better explanation of the process. Great looking post by the way.

  5. It’s amazing how recent some basic scientific understandings are. I was sort of shocked that solar fusion wasn’t known until 1939—although on reflection it made sense. The one the really gets to me is that until plate tectonics were demonstrated in the late 1960s, there was basically no explanation for anything in geology. How did the seashell fossils get to the top of Mount Everest? No clue. Wonder what we’ll figure out next?

  6. @ Earnest :
    Thanx, glad you enjoyed.
    You are right, Zeus’ little pinky could be powering the sun. Be we will never know for sure without “sampling” — but heck, even with sampling, he might move his little pinky and we could miss the truth. So without being omniscient, everything is “just” theoretical.

    @ David :
    Yeah, that would be fun to look into — what folks said about himalayan fossils prior to the 60’s. I imagine many lamas have spun wonderful stories. Heck, I even know modern day western lamas that think floating islands are mystical.🙂

  7. Yes, everyone knows the Himalayas are magic, so maybe I chose a bad example🙂

    I visited a temple in Bhutan that had a sacred dragon egg. It was a damn cool thing. It sure looked like an egg, but it was much bigger than an ostrich’s. Conceivably it was from a Madagascar elephant bird — but how would that have gotten to Bhutan? Perhaps more likely would be a dinosaur egg from the Gobi, but it seemed too new for that. Maybe it came from a dragon🙂

    What little I know about geology comes from John McPhee’s outstanding Annals of the Former World. When he wrote that (1981), there were still a few holdouts against tectonics, whom he interviewed. These dinosaurs had some alternative theory that sounded like advanced phlogistonics to me.

    Ever since reading his book, I’ve meant to follow up by reading a graduate intro geology text. (I figure I know enough physics and chemistry to skip the undergraduate stuff.) If anyone can recommend one, I’d love to hear about it — I’ve never managed to find something that looked suitable on Amazon.

  8. @ David
    That had me laughing — thanx. Sorry, I have no recommendation on geology texts. I have several very smart readers who may. Hope they have a suggestion. The only similar book on my self just now is: “A Short History of Planet Earth” by MacDougall, but it doesn’t match your bill.

    Also, I had to look up “Phlogistonics” — thanx for the tour.

  9. I like the visual aids. And I’ll be sure to check out the book.

    Just one criticism though, are you citing all that information off the top of your head? Or are you using the book? Are you using multiple sources? Perhaps citing things would make this more professional. Not only that, others who come here and read, like me, would have an easier time tracking down the information if you did.

    I mean, it’s totally up to you if you want a professional presentation (both looks and content) or if you’re just going for style points (just looks). So far it looks good.

  10. @ Tristan (if you are following comments),
    One of the main purposes of this post is coming up soon. It is not meant to be a research paper so student can copy for the term papers.🙂
    I have published papers in medical journal and public health conferences etc. I know the game very well. No need for that level of documentation here.
    Even quoting the author of the book does not prove that he is correct.
    I offer a lot of links. I hope that helps someone else.
    “Professional”, btw is an often misused word — having been a “professional” for decades.

  11. Max

    @ David,

    I read McPhee’s “Assembling California” a few years ago and it was wonderful. Mostly about the amazingly complex boundary of the Pacific and North American plates, but it gets into a global scope toward the end and gets really fantastic. The whole landscape of the planet comes alive if you can start thinking in geologic timescales. India crashing into Asia forming the Himalayans (still happening), Italy into Europe likewise building the Alps as we speak, Japan sailing toward the Aleutians at 3″ per year or something like that (might have picked up the pace recently). I highly recommend it.

  12. @ Max — thanks — I heartily concur with that recommendation! Assembling California is the last volume of The Annals of the Former World, which is available either as a series of five books or bound together as a single volume. Assembling California is probably the most exciting, but the others take you on a geological journey across the US on I-80 from New York to San Francisco, and are also a treat.

    Tying this back to Sabio’s (perhaps implicit) theme, knowing some basic geology makes it super obvious that young earth creationism can’t be right—quite apart from the evidence for evolution. And you don’t need to know geology to understand evolution, but it does help understand the fossil evidence.

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