20th Century Flashcards
Barbara Mclintock
1902-1992.
Cytogenetics. Maize. Visualization of chromosome morphology. Transposition. Cold Spring Harbor.
Lynn Margulis
1938-2011
Symbiosis in evolution. Endosymbiosis. Mitochondria were separate organisms. Maybe chloroplasts, too? Gaia hypothesis. Married Carl Sagan.
Rosalind Franklin.
1920-1958
X-ray crystallographer.
Took photographs of crystallized DNA.
Photos used by Crick and Watson. C
King’s College.
Worked under Maurice Wilkins.
Photo 51, taken by her student, Raymond Gosling.
Died 1958 of ovarian cancer; missed out on Nobel.
Frederick Sanger.
1918-2013
Structure of insulin.
Sequencing of DNA.
Two Nobel prizes in Chemistry.
Electrophoresis.
César Milstein
8 October 1927 – 24 March 2002
Argentine biochemist in the field of antibody research.
Milstein shared the Nobel Prize in Physiology or Medicine in 1984 with Niels Kaj Jerne and Georges J. F. Köhler for developing the hybridoma technique for the production of monoclonal antibodies.
Vera Rubin
July 23, 1928 – December 25, 2016)
American astronomer who pioneered work on galaxy rotation rates. She uncovered the discrepancy between the predicted and observed angular motion by studying galactic rotation curves. Identifying the galaxy rotation problem, her work provided the first evidence for the existence of dark matter. These results were confirmed over subsequent decades.
John von Neumann
December 28, 1903 – February 8, 1957
Hungarian-American mathematician, physicist, computer scientist, engineer and polymath. Von Neumann was regarded as perhaps the mathematician with the widest coverage of the subject in his time and was said to have been “the last representative of the great mathematicians who were equally at home in pure and applied mathematics”. He integrated pure and applied sciences.
Norbert Weiner
1894-1964
American mathematician and philosopher. He was a professor of mathematics at the Massachusetts Institute of Technology (MIT).
Cybernetics.
A child prodigy, Wiener later became an early researcher in stochastic and mathematical noise processes, contributing work relevant to electronic engineering, electronic communication, and control systems.
Peter Medowar
1915-1987
British
Immunology
Tissue rejection.
Skin grafts.
Lead to organ transplants. First kidney.
Science writer.
Linus Pauling
1901 - 1994
American.
Founder of quantum chemistry, molecular biology, and molecular genetics. Nobels in chemistry and Peace.
1922 chemical engineering Oregon State. Bonding.
Caltech, P-chem. X-R diffraction. Crystals.
Europe, quantum mechanics; met Bohr, Schrodinger, Sommerfeld.
Pauling devised valence bond theory and gave chemistry its now everyday concepts of electronegativity, orbital hybridization, and resonance.
Not ionic or covalent, but how much of each.
1939 Pauling released the twentieth century’s most important chemistry book, The Nature of the Chemical Bond. Nobel 1954.
Oppenheimer had an affair with his wife.
Sickle Cell caused by an abnormal protein, hemoglobin, charge impairs oxygen affinity. Inheritance affects the properties of protein molecules.
Molecular biology and genetics.
Using paper folding and X-R diffraction, he discovered the protein alpha helix.
Thought DNA was a triple helix with the bases sticking outwards.
Survived glomerulonephritis with help af Thomas Addis, nephrologist, communist.
1950’s investigated and faced travel restrictions. 1957 got a ban on nuclear weapons testing, .
1962 Nobel Peace Prize.
UCSD chemistry professor, then at Stanford. ‘1970 Vitamin C and the Common Cold. Founding the Pauling institue of Science and MEdicine at Menlo Park.
Ernest Rutherford
Lived 1871 – 1937.
Anglo-Scott from New Zealand.
Father of nuclear chemistry and nuclear physics.
He discovered and named the atomic nucleus, the proton, the alpha particle, and the beta particle. He discovered the concept of nuclear half-lives and achieved the first deliberate transformation of one element into another, fulfilling one of the ancient passions of the alchemists.
Lord Kelvin had indicated Earth’s age could be no greater than 400 million years old. He said Earth could be older than this only if some new source of energy could be found that was heating it internally.
Rutherford identified the new source – the energy released by radioactive decay of elements. He also began the science of radiometric dating – using the products of radioactive decay to find out how old things are.
Most alpha particles shot straight through gold foil, but a few were deflected enormously, some even ‘bouncing’ straight back from the gold. Rutherford explained the effect by proposing a new model for the atom (dense nucleus), replacing the plum pudding model of his old mentor J. J. Thomson. Bohr then constructed his quantum atomic model based on this.
Element 104 is named Rutherfordium in his honor.
Lise Meitner 1878 – 1968.
Austrian. Worked at Kaiser Wilhelm Inst. w/ Otto Hahn
1909 radioactive recoil: Atomic nuclei recoil after emit alpha part.
Escaped from Germany after annexation of Austria in 1938. Went to Copenhagen. Noddak proposed fission, but Meitner did not believe.
Considered water droplet model of fission.
She sat down in the woods and began calculating the energy involved when nuclei produced by uranium fission fly apart. Her calculated energy, 200 MeV, was huge. Its source was Einstein’s famous equation: E = mc2. Meitner realized that enough mass was converted to energy during nuclear fission to produce an enormous amount of energy.
Lise Meitner was hailed as the mother of the atomic bomb by the victorious allies. She hated the title. She disapproved of the military use of nuclear fission.
S. N. Bose 1894 – 1974.
S. N. Bose founded quantum statistics in 1924 when he discovered a new way to derive Planck’s radiation law.
Bose’s method was based on the argument that one photon of light is not distinguishable from another of the same color, which meant that a new way of counting particles was needed – Bose’s statistics.
Consider the situation when you simultaneously toss two distinguishable unbiased coins. You can write the following outcomes, all of which have the same chance of happening:
Possible Outcomes: (Two Heads) or (Two Tails) or (Head & Tail) or (Tail & Head)
The chance of getting, say, two heads is 1⁄4.
BUT, if you found it impossible to tell one coin from the other, then the coins become indistinguishable. Then you find:
Possible Outcomes: (Two Heads) or (Two Tails) or (One of Each)
The chance of getting, say, two heads is now 1⁄3.
In the world of Bose statistics, the likelihood of events happening is different from our everyday expectations.
In a BEC each particle in a collection of particles exists in the same, identical quantum state – the particles are indistinguishable from one another.
In took over 70 years from Einstein’s prediction of BECs for a pure single entity to be seen.
This happened in 1995 when a gas of rubidium atoms was cooled to within a fraction of absolute zero: 1.7 × 10-7 kelvins, merging about 2,000 individual atoms into the same entity, a single super-atom, which held together for less than 20 seconds.
Erwin Schroedinger
1887 - 1961
Wave equation.
Probability function (of an electron, for instance).
Can explain quantum tunneling: Even though a particle hasn’t the energy to cross a barrier, there is a tiny probability of finding it on the other side.
Famous diffraction experiment: Even if photons are fired one at a time though slits, they will still form a diffraction pattern on the other side. Particles behaving as waves.
Heisenberg Copenhagen interpretation/Uncertainty
The Copenhagen interpretation is an expression of the meaning of quantum mechanics that was largely devised in the years 1925 to 1927 by Niels Bohr and Werner Heisenberg. It remains one of the most commonly taught interpretations of quantum mechanics.[1]
According to the Copenhagen interpretation, physical systems generally do not have definite properties prior to being measured, and quantum mechanics can only predict the probabilities that measurements will produce certain results.
The act of measurement affects the system, causing the set of probabilities to reduce to only one of the possible values immediately after the measurement. This feature is known as wave function collapse.
There have been many objections to the Copenhagen interpretation over the years. These include: discontinuous jumps when there is an observation, the probabilistic element introduced upon observation, the subjectiveness of requiring an observer, the difficulty of defining a measuring device, and the necessity of invoking classical physics to describe the “laboratory” in which the results are measured.
Alternatives to the Copenhagen interpretation include the many-worlds interpretation, the De Broglie–Bohm (pilot-wave) interpretation, and quantum decoherence theories.
There is no uniquely definitive statement of the Copenhagen interpretation. It consists of the views developed by a number of scientists and philosophers during the second quarter of the 20th Century. Bohr and Heisenberg never totally agreed on how to understand the mathematical formalism of quantum mechanics.
Niels Bohr
Lived 1885 – 1962.
Founded quantum mechanics.
In 1885 the Swiss mathematician Johann Balmer had stumbled upon a mathematical formula that predicted the wavelengths – and hence colors – of light emitted by hot hydrogen. There was no theoretical basis for the formula. It just worked!
In 1897, when Bohr was 12, J. J. Thomson discovered the electron.
In 1898 Ernest Rutherford discovered alpha and beta particles emitted by uranium.
In 1905, when Bohr was beginning his gold medal winning research, Albert Einstein unleashed a barrage of new ideas in his miracle year, writing four world-changing papers on: Brownian motion, the equivalence of mass and energy, the photoelectric effect, and special relativity.
In 1909 Ernest Rutherford discovered the atomic nucleus.
Bohr said electrons are restricted to particular circular orbits, but can jump from a lower energy orbit to a higher energy orbit by absorbing light. They can also do the opposite and fall from a higher energy orbit to a lower energy orbit by emitting light – as shown in the image below.
An electron falls from a higher energy orbit to a lower energy orbit. Energy is released as a photon of light. The difference in energy between the orbits is the same as the energy of the photon, which can be calculated using Planck’s equation, E = hf.
In classical physics, electrons could have any energy. In the new quantum physics electrons were confined to defined orbits of fixed energy. Other electron energies were forbidden.
