19th & 20th Century Scientific Advances

19th Century Science and Progress

• Science became closely associated with progress by the turn of the 19th century.

20th Century Scientific Breakthroughs

• Significant advancements in fundamental ideas occurred in the 20th century, driven by cutting-edge research.
• Discoveries were abundant, rewriting knowledge about subatomic and cosmological levels.

Wilhelm Conrad Röntgen

• German physicist who discovered X-rays in 1895.
• Discovered that electrically charged vacuum tubes emitted rays that made a fluorescent screen glow.
• These electromagnetic rays could penetrate human skin to expose photographic plates but were blocked by metal and bone.
• Awarded the first Nobel Prize in Physics in 1901.
• He never patented the X-ray and donated his prize money to scientific research.
• Also known for his contributions to mechanics, heat, and electricity.

Kitasato Shibasaburo

• Japanese physician and bacteriologist who studied in Tokyo and Berlin.
• Developed serum therapy to protect against tetanus and diphtheria.
• In 1890, he discovered that injections of tetanus serum containing antitoxin from an animal exposed to tetanus bacteria conferred immunity.
• Applied the same principle to protect against diphtheria.

Ivan Pavlov

• Russian-born scientist who transitioned from a religious career to physiology.
• Became a professor at the Military Medical Academy in St. Petersburg in 1890.
• Studied digestive secretions in dogs and discovered classical conditioning.
• Dogs learned to associate the sound of a bell with food, eventually salivating even without food present.
• This discovery is now known as Pavlovian conditioning.
• Won the Nobel Prize in Physiology or Medicine in 1904 for his groundbreaking work.

Jules Henri Poincaré

• French mathematical physicist who studied the stability of the solar system.
• Noticed that even tiny changes in initial conditions could lead to significant and unpredictable changes in outcomes (chaotic behavior).
• These findings, published as early as 1908, formed the basis for chaos theory.
• His work on electromagnetism influenced Einstein's research on relativity.

J.J. Thomson

• English physicist who made significant contributions to understanding atomic structure.
• Identified "corpuscles" (later called electrons) using a cathode ray tube.
• Showed that electrons have a negative electric charge and are 2,000 times lighter than a hydrogen atom.
• Proposed the "plum pudding model" of the atom, suggesting that a positive charge is spread throughout with electrons embedded within.
• His discoveries revolutionized theories of atoms and electricity.
• He also confirmed the existence of isotopes.

Svante Arrhenius

• Swedish physicist who studied at the University of Uppsala.
• Became a professor of physics at the University of Stockholm.
• In the 1890s, he theorized that ice ages were caused by reduced volcanic eruptions.
• Fewer eruptions would lead to lower carbon dioxide levels, cooling the Earth.
• He linked human activity (fossil fuel burning) to increased carbon dioxide and rising global temperatures, laying the groundwork for modern climate change concerns.

Henrietta Swan Leavitt

• American astronomer who studied at Radcliffe College.
• Worked at the Harvard College Observatory, analyzing the luminosity of stars from photographic plates.
• Discovered a regular pattern of brightness in Cepheid variable stars.
• Her work was instrumental in measuring the distance between Earth and other galaxies.
• Discovered over 2,400 variable stars and four novae.
• Developed a standard for photographic measurements called the Harvard Standard.
• Her contributions were largely underappreciated during her lifetime.

Harriet Brooks

• Canadian physicist who graduated from McGill University.
• Became Canada's first female nuclear physicist.
• Studied under J.J. Thomson and Ernest Rutherford, working in Marie Curie's laboratory.
• Discovered that nuclear decay can lead to the transformation of one element into another.
• Some of her findings were only attributed to her posthumously.

Annie Jump Cannon

• American astronomer who became a leading authority on stellar spectra.
• Studied physics and astronomy at Wellesley College.
• Joined the Harvard College Observatory in 1896, classifying stars.
• Pioneered a star classification system in 1901, laying the foundation for the Harvard Spectral Classification system.
• Classified over 350,000 stars during her 44 years at the observatory.

Srinivasa Ramanujan

• Indian mathematician who made significant contributions to mathematical analysis and number theory.
• Received little formal training.
• Invited to Cambridge in 1913 after sending mathematician G.H. Hardy a letter and 120 mathematical theorems.
• Awarded a Bachelor of Science degree in 1916 and became the second Indian fellow of the Royal Society.
• Sadly, he died of tuberculosis in 1920.

Erwin Schrödinger

• Austrian physicist who studied at the University of Vienna.

• Made groundbreaking contributions to quantum physics while working at the University of Zurich.

• Developed the Schrödinger wave equation, offering a new understanding of particle behavior.

• This equation showed that orbitals, shells, and subshells are probability clouds representing the likelihood of an electron's location.

• His equations of wave mechanics revolutionized our understanding of the world and formed the basis for modern quantum mechanics.

  Ronald Fisher

• British statistician and geneticist who pioneered the use of statistics in scientific experimentation.

• In 1918, he published a paper highlighting the application of statistical tools to reconcile Darwin's theory of natural selection with Mendel's experiments.

• Knighted in 1952 for his contributions to science.

Harold Urey and Stanley Miller

• American chemists who conducted a landmark experiment in 1953.
• Simulated Earth's early atmosphere in the laboratory using electrical sparks to mimic lightning.
• Their experiment showed that simple carbon-based compounds, essential for life, could be produced under such conditions.