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Thread: Key Discoveries in the History of Science

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    Key Discoveries in the History of Science

    This is the thread for briefish summaries of key scientific discoveries. All fields of science are eligible. No need to list the discoveries in the order of importance, but each should be a specific well-defined new advance in scientific knowledge. (Darwin's Theory of Evolution in general might not qualify, but a specific observation that contributed to his theory would.)

    I'll start with two specific discoveries in astronomy.


    1611) "Haec immatura a me iam frustra leguntur o.y."

    Both the Ptolemiac and Copernican models of the solar systems implied that Venus should have phases like the Moon, but the details varied greatly. Observation of Venus with high-quality telescopes therefore gave a way to pick between the models. Galileo Galilei had one of the best telescopes of that age and was carefully observing Venus. He didn't want to publish until his data was complete, but he didn't want to be scooped by another astronomer either!

    In December 1610, as Venus was disappearing behind the Sun, Galileo sent Johannes Kepler a letter with the above Latin sentence. (Translated, it reads "I am now bringing these unripe things together in vain, Oy!"). In January 1611 Galilelo confirmed Venus' crescent shape as it re-emerged, and revealed the anagram of this sentence: "Cynthiae figuras aemulatur mater amorum" ("The mother of love [Venus] copies the forms of Cynthia [the Moon]"). (Here's an interesting page about allegations that Kepler misinterpreted Galileo's anagrams.)

    Copernicus was correct. The Sun was the center of the solar system.

    (It is a curious fact that the Author of Shakespeare's plays took great interest in astronomy, incorporating mention of events in the 1580's and 1590's into his plays. Yet the Author mentioned no astronomical event after 1604 — including most of Galileo's great discoveries.)

    1676) Ole Christensen Rømer measured the speed of light.

    Jupiter's moon Io orbits its mother-planet once in 42 hours and 28 minutes, but due to the finiteness of light's speed and a form of the Doppler Effect, Io's orbit appears to be several seconds faster when the Earth is moving toward Jupiter, and is several seconds slower when the Earth is moving away from Jupiter. There was no need to measure this deviation of a few seconds; the cumulative deviation could be measured after months. (How did Rømer or other scientists of this era measure time? I assume they used Huygens' recently-introduced pendulum clock, but was it calibrated periodically with a sundial?)

    The orbit of each Jovian moon is affected by the other moons, and only Io worked well for this observation. Still, the perturbations aren't synchronous with Earth movement so should average out in a few years of observations. Nevertheless Rømer's supervisor — the more famous astronomer Cassini — did not accept this result. In 1729 James Bradley settled the question with a different approach.

    The two greatest mathematical physicists of that era — Christiaan Huygens (designer of afore-mentioned pendulum clock) and Sir Isaac Newton — did accept Rømer's work at once. Newton had an urgent question for Rømer — did the shadow on Io change in color as its eclipse progressed? (It didn't; light of different colors traveled at the same speed.)

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    Seriously, it all started with the control of fire and the ability to put a cutting edge on materials.

    As important today as t was at the beginning.

    Sciience is not limited to modern mathematical science.

    Steam power in the 19th century led to thermodynamics and enabled the Industrial Revolution.

    Nuclear steam power and controlled heat.

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    While Germ Theory developed over a long period of time, I think Louis Pasteur is worth a mention for proving that germ theory was not only correct, but that it was possible to not kill the germs in a medium, but also to prevent them from returning.

    While I find astrophysics and cosmology fascinating, it is utterly insignificant compared to the benefits gained from advances in medical science.

    Steven Pinker compiled a table estimating the number of lives saved by just a few discoveries in medicine:




    If we're looking for key discoveries, I'd say that's a whole keyring's worth, right there.

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    Fast-paced modern science began over a century ago, and is sometimes contrasted with Alchemy in the Middle Ages, a pseudo-science.
    However, the old dream of Transmutation of the Elements was eventually fulfilled!
    Let's review key nuclear reaction types.

    I. Single Reactant (Natural radioactivity)

    . . . . E* ⟶ F + {alpha or beta particle} + {optional gamma particle}
    Becquerel, Roentgen, Madame Marie Curie and her husband are oft-heard names from the earliest relevant studies, but it is the (then-future) Lord Rutherford who should be most revered He detected, named and later identified the alpha and beta particles. The latter he showed to be equivalent to both cathode rays and electrons. The former he identified, in a beautiful little experiment, as Helium. Little was known about the nuclei of atoms, though Rutherford's greatest discovery was (in 1911) that the nuclei are very small and very hard. He conjectured the existence of neutrons, but it was left to one of his disciples to discover them. In his elegy Bohr wept, calling Rutherford his second father.

    The result of a radioactive emission can also be radioactive. In fact there are no less than 14 radioactive isotopes between ordinary uranium and ordinary lead.

    . . . . U238*⟶Th234*⟶Pa234*⟶U234*⟶Th230*⟶Ra226*⟶Rn222*⟶Po218*⟶Pb214*⟶Bi214*⟶Po214*⟶Pb210*⟶Bi210*⟶Po210*⟶Pb206

    The net formula can be determined directly from the numbers of protons and neutrons. In this case there must be 8 alphas and 6 betas emitted.

    . . . . 92U23882Pb206 + 8 2He4 + 6 β-
    Positively-charged beta particles (anti-electrons), predicted by Dirac, were observed occasionally in the decay of light elements.

    II. Two Reactants (Neutron Production)

    Experimentalists began aiming the alpha particles they had generated at other elements. One early result (perhaps after the 1934 Joliot discovery next?) was:

    . . . . 4Be9 + 2He4 {very energetic} ⟶ 6C12 + 0n1 {Neutron}

    The energetic alpha particles are obtained from radium, polonium or radon. (In some reactions protons are produced instead of neutrons.)

    Beryllium is so eager to give up its extra neutron, that even a gamma ray suffices to trigger it:
    . . . . 4Be9 + γ ⟶ 2 2He4 + 0n1 {Neutron}

    III. Artificial radioisotope

    B](1934)[/B] Jean Joliot and his wife Irene nee Curie discover artificial radioactivity. Aluminum was coated with Alpha-emitting polonium.

    . . . . 84Po2102He4 + 82Rn206

    . . . . 2He4 + 13Al270n1 + 15P30*

    . . . . 15P3014Si30 + β+

    The first and third reactions shown are ordinary radioactivities: Polonium decays with a half-life of some months; Phosphorus-30, not found in nature, decays in 2.5 minutes. (The 3rd reaction is an example of afore-mentioned anti-electron producer.) It is the 2nd reaction that was the novel discovery: The energetic α-particles (2He4) from the 1st reaction induce ordinary aluminum to emit a neutron and transmute into the short-lived P-30.

    The ancient dream had been fulfilled! Man had created a transmutation pathway not found in nature. To prove this reaction it was necessary to come up with a chemical technique to confirm the identity of the short-lived Phosphorus very quickly. The Nobel Committee raced to award the Joliot-Curies Nobel Prizes, not quite in time for the dying Marie Curie to take a plane to Stockholm, but she did take great pleasure from her daughter's discovery.

    A flurry of other discoveries followed soon. Leo Szilard responded to (1934a) by filing for a patent on a chain-reaction bomb, though with no particular reaction to be chained. (Bombs were eventually built from U-235 and Pu-239 but neither isotope was known in 1934.

    Neutron bombardment experiments generated conflicting results. Labs with wooden benches got different results than labs with marble benches. It was Enrico Fermi who suddenly interposed a chunk of paraffin between his neutron source and the Silver he was irradiating. The carbon in the paraffin was slowing ("moderating") the neutrons and making them more active. Fermi called this his most important discovery. These results defied predictions so in 1936 Niels Bohr published a paper with a new model of the atomic nucleus. (A paper by Noddack in 1934 criticized Fermi, and claimed — correctly as it turned out — that one of his experiments had produced a new element (now called neptunium). This paper was generally deprecated; and Fermi thought he could refute it, but physicists were then using a wrong value for helium's weight so many estimates were off.)

    The most interesting reactions came with Uranium.

    IV. The discovery of atomic fission (1938-1939)
    Otto Hahn and Fritz Strassmann made a key discovery in December 1938, publishing in January 1939. Until their discovery a single nuclear reaction could produce only a single atom heavier than helium.

    Otto Hahn and Fritz Strassmann had bombarded of Uranium with neutrons and produced no less than 16 different activities; they used chemistry to attempt identification of newly-found isotopes. For example, a barium carrier can be dissolved in the reaction product; and radium (or other elements in the same column of the periodic table as barium) will precipitate out, joining barium crystals. A Geiger counter then shows which radioactivities follow into the Barium crystals. Three activities did. These were presumably either radium or some new transuranic element. Radium would be novel: With atomic number 4 less than Uranium, the U-238 would need to emit TWO alpha particles to decay to radium. Barium, with atomic number 36 away from uranium, was thought to be impossible. Hahn-Strassman tentatively named two of the radioisotopes Ra-II (half-life 14 minutes) and Ra-III (half-life 86 minutes); they focused on identifying Ra-III. The procedure was to irradiate purified uranium with slow neutrons for 12 hours, wait several hours for the Ra-II to die away, add barium chloride as a carrier, separate the barium-radium crystals and redissolve them, and finally use crystal fractionation to separate the radium. They verified that ordinary radium would indeed be isolated in this final step, but the "Ra-III" remained with the barium. Through careful chemistry, they ruled out every possibility except Barium itself. Ra-III was Barium! (This was confirmed by doing crystal fractionation on the decay product of the Ra-III.) With a publishing deadline in very late December they debated whether to replace all instances of 'radium' with 'barium' in the paper they had prepared. Hahn was in contact with Lise Meitner and her nephew Otto Frisch, who prepared a paper trying to explain this very unexpected result. Frisch invented a new word usage to describe it: fission. (On reviewing their own experiments, the Joliot-Curies noticed that they had observed fission, but failed to notice. Earlier they had overlooked their own first discovery of neutrons.)

    This was before the clamp-down on publishing results useful for atomic bombs, so Germany, Japan and Britain became immediately aware of the potential for a bomb. (Scientists in U.S.A., not then at war, were aware of the possibilities, but government dithered. When U.S. finally did respond, it went into overdrive.)

    Chain reaction: i.e. the production of more than 1 neutron for every neutron in the pile or bomb was a prerequisite for power or weapon but 2:1 multiplication of neutrons was demonstrated in 1939 (though not an actual chain reaction). Szilard applied for another atomic bomb patent; and so on. U-235 was identified by 1939; the distinction between slow neutrons and fast neutrons developed; and Bohr had another epiphany. Plutonium was discovered in 1940. The first critical mass pile was in 1941, but there was no power-mode pile until 1943 (when "xenon poisoning" was discovered).

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    I am looking at the book called The 100. A ranking of the most influential persons in history. Number 2 on the list is Isaac Newton. He discovered many things to do with optics. He
    - discovered the laws of motion
    - invented the reflecting telescope
    - integral calculus
    - the law of universal gravitation
    - worked out how to predict the orbits of the planets using maths he had developed
    - changed the way science worked.

    You wanted a list of science discoveries. That is my list.

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    Newton was certainly one of the very greatest scientists ever. In addition to items on rjh01's list, another discovery often credited to Newton is the decomposition of white light into the rainbow's colors using a prism.

    However it is said that the great Iraqi scientist Abū ‘Alī al-Ḥasan ibn al-Haytham (called Alhazen in the West) wrote up something similar (based on rainbows?) circa 1015 in his Kitāb al-Manāẓir (Book of Optics). I can't find an exact reference and am doubtful: Alhazen was highly respected by early Europeans like Roger Bacon. Galileo and Descartes. If Alhazen had made the clear claim that "white is the sum of the rainbow's colors", then why does Newton usually get the credit for this?

    Regardless of this one point, Alhazen's several discoveries about optics and vision certainly qualify as key. He has been called the greatest physicist between Archimedes and Sir Isaac Newton.

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    In the Euro-Centric vies science apered in Europe. Before the decline of the Mid East and the rise of Europe the Arabs and Prsiabs wre the place to go for science.

    Newton used Pwrsian astronomical data. I watched a show that reconstructed a Persian observatory. There was a transfer of knowledge to Europe. Newton's Laws already existed IN dfferent forms and were in print. Arabs published books on optics and algebra.

    the foundations of what we call 'the' calculus go far back in history.

    Newton-Leibniz system of notation for calculus and Newton's mechanics were the foundation for the rise of technology and modern science, Newtonian mechanics are still a mainstay of of engineering.

    The other major figure was Maxwell.

    His synthesis is the basis of modern electrical and electronic technology.

    Einstein was important, but cosmology as someone else said is really irrelevant. His real contribution was the Photo Electric Effect which showed quantization of light.

    There were many others that provided pieces of the puzzle. Fourier, Gauss, Millikan and the electron, and a long list.

    Nobody creates in a vacuum.

    I red a history of math. it is all trceable back in history. Science always follows the money. As Arab economics declined and Europe rose, science went with the money.

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    Darwin changed the way man thinks about himself.

    His ideas were so shattering many still today don't accept them.

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    Loren Eiseley's Darwin's Century is a good read to put Darwin's theories in perspective. Eiseley demonstrates how several thinkers had grasped the essential elements of Darwin's theory before Darwin wrote. Nonetheless Eiseley has great admiration for Darwin's imagination, hard work, and eloquence.

    The study of life's history was closely tied to progress in geology, the study of Earth's history. One of Darwin's chief inspirations was Charles Lyell who, though a geologist, almost produced Darwin's theory himself! He even wrote about the "struggle for existence," one of Darwin's favorite phrases. Lyell in turn learned from an 18th-century geologist who wrote the following at least a decade before Darwin was born:
    Quote Originally Posted by James Hutton
    ... if an organised body is not in the situation and circumstances best adapted to its sustenance and propagation, then, in conceiving an indefinite variety among the individuals of that species, we must be assured, that, on the one hand, those which depart most from the best adapted constitution, will be the most liable to perish, while, on the other hand, those organised bodies, which most approach to the best constitution for the present circumstances, will be best adapted to continue, in preserving themselves and multiplying the individuals of their race.
    The theme of this thread is specific discoveries or observations that led to the advance of science. Charles Lyell's observations of the strata at Mt. Etna (and the fossils therein) might qualify. These pointed to gradual geologic change rather than "catastrophes." Such gradualism was essential to Darwin's theory.

    One specific observation that surprised Darwin and affected his thinking was the diversity among different islands in the Galapagos Archipelago; see Darwin's finches. (He regretted gathering many specima without noting which of those islands they came from.)

    ~ ~ ~ ~ ~ ~

    There were two glaring objections to Darwin's theory, and he began equivocating in later editions of Origin, even embracing the possibility of Lamarckian inheritance. The discoveries which overcame these objections both qualify as key events in the development of science.

    The first objection was raised by Lord Kelvin among others. With the Earth just 25 million years old, there wasn't enough time for evolution to operate. This age was calculated from thermodynamics — if the Earth were older, more of its core heat would have dissipated. This objection was resolved when Marie Curie noticed that heat was associated with radioactivity. The Earth wasn't cooling as fast as expected because the decay of radio-isotopes replenished its heat.

    The second objection was raised by Fleeming Jenkin, a Scottish Professor of Engineering, in an anonymously-published review titled "Darwin and the Origin of Species". As seen in the linked volume (which begins with a long Memoir by Robert Louis Stevenson, one of Jenkin's students), Jenkin had very diverse interests: in addition to the review of Darwin, the book contains an essay on the meter of English poetry and an essay on the nature of truth. Jenkin also wrote on economics and linguistics; and he was a successful inventor.

    The objection Jenkin raised is that blending inheritance would imply very slow evolution: If a man with a gene for four extra inches of height marries a woman of normal height, the children inherit only half from father so would expect two extra inches of height, and the grandchildren only one inch. The new trait would fade away before much favorable inheritance could occur. Darwin was already aware of this problem, but Jenkin developed the case with much detail, and Darwin read this review with a sinking feeling.

    The refutation for Jenkin's objection was published two years before Jenkin's review! But neither Darwin nor Jenkin read it during their lifetimes. This of course was Gregor Mendel's discovery of particulate inheritance. Instead of the tall man's grandchildren each inheriting 25% of the man's extra height, most of them would get none but 25% of the grandchildren would inherit the full 4 inches! (Obviously this example is over-simplified.) Mendel's important discovery — VERY key to genetics and presented and published in a scientific journal — lay completely unnoticed for about 35 years.

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    Darwin was seriously hindered because he did not understand genetics.

    The idea of evolution was around but it was Darwin who developed credible arguments about how evolution occurs despite not understanding how traits could be passed.

    Darwin turns speculation into a science.

    A science some people living today do not accept because of the clear implications.

    Man was changed from an immutable "image of god" into a close relative of chimps and gorillas.

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