1. Scientific Method Predictive Testable -- Hypotheses Experimentally Reproducible Quantitative -- Uncertainties Objective and Unbiased Confirmable -- Peer Review Evaluation 9/2/09

2. Scientific Theory Speculation – untested! o The abominable snowman is a prehistoric ape o Extra-terrestrial intelligent life exists o God created the universe in 7 days Hypothesis – tested! o Gravity bends light– general relativity theory o Science is statistical – quantum theory o A “big bang” began the universe – big bang theory o Life has evolved – theory of evolution 9/2/09

3. Scientific Discovery Directed o Human genome o Laser o Transistor Serendipitous o Superconductivity o Neutrino o Penicillin 9/2/09

4. Scientific Serendipity The Neutrino Until the early part of the 20th century neutrinos were unknown. Only the study of nuclear decays revealed the existence of a yet unknown particle. Nuclear physicists studied three types of radioactivity: alpha (charged helium), beta (electrons), and gamma (high-energy light) radiation. They found that both the alpha and gamma spectrum emitted in nuclear decays were discrete. In 1930, however, James Chadwick observed that the energy spectrum of electrons (the beta particle) emitted in nuclear beta-decay was continuous. This observation could not be explained at the time. In an attempt not to abandon the fundamental conservation law of energy Wolfgang Pauli postulated a new particle to explain Chadwick’s observation. Three years later, Enrico Fermi called this new particle the neutrino and incorporated it in his theory of weak interaction. 9/2/09

5. Scientific Serendipity The Neutrino Twenty six years after Pauli’s postulate of the neutrino Frederick Reines and Clyde Cowan made the first experimental observation of neutrinos in their pioneering experiment at the Savannah River reactor for which Reines received the Nobel Prize in 1995 [9]. In their experiment they used the inverse of the beta-decay reaction which led to the neutrino postulate in 1930. Through inverse beta-decay (in which anti-neutrinos interact with protons to produce a positron and neutron) they detected anti-neutrinos from a nearby nuclear reactor. Their neutrino detector was placed at a distance of a few meters from the core of the reactor. Subsequent accelerator experiments found that there are three distinct types (or flavors) of neutrinos depending on the type of charged particle found in the neutrino-producing interaction. 9/2/09

6. Scientific Serendipity Superconductivity On July 10, 1908 at the University of Leiden, Heike Onnes succeeded in liquifying helium at a temperature of 4.2 K. By 1911, having developed a cryostat capable of maintaining the liquid at a constant low temperature, he was able to investigate the behavior of other substances at liquid helium temperatures. It was well known by this time that the electrical resistance in a metal decreased with temperature. Exactly what would happen to resistance at temperatures approaching absolute zero, however, was hotly debated. Lord Kelvin believed that the flow of electrons might stop altogether, with the electrons becoming frozen in place. The resistance at absolute zero would thus be infinitely high. Others, including Onnes, assumed that the decrease in resistance with falling temperature would continue in an orderly fashion, ultimately reaching zero at 0 K. Onnes used mercury, which he could distill into a very pure sample. He poured it into a U-shaped glass capillary tube equipped with electrodes on both ends to measure the current passing through it while it was still a liquid. As he cooled the mercury (even into a solid) Onnes found a regular decrease in resistance. At liquid-helium temperatures well higher than 0 K (absolute zero) the resistance suddenly disappeared. He assumed that a “short circuit” had occurred and replaced the U-tube with a W-shaped tube with electrodes at both ends and at the kinks, presenting four segments for measurement. He observed the same anomalous behavior and serendipitously discovered superconductivity. 9/2/09

7. Scientific Serendipity Penicillin In the early 1920s, the British scientist Alexander Fleming reported that a product in human tears could lyse bacterial cells. Fleming’s finding, which he called lysozyme, was the first example of an antibacterial agent found in humans. Like pyocyanase, lysozyme would also prove to be a dead end in the search for an efficacious antibiotic, since it typically destroyed nonpathogenic bacterial cells. Fleming’s second discovery, though, would change the course of medicine. In 1928, Fleming serendipitously discovered another antibacterial agent. Returning from a weekend vacation, Fleming looked through a set of old plates that he had left out. On one such plate, he found that colonies of Staphylococcus, which he had streaked out, had lysed. Fleming observed that bacterial cell lysis occurred in an area adjacent to a contaminant mold growing on the plate and hypothesized that a product of the mold had caused the cell lysis. 9/2/09

8. Scientific Serendipity Penicillin While Fleming generally receives credit for discovering penicillin, in fact technically Fleming rediscovered the substance. In 1896, the French medical student Ernest Duchesne originally discovered the antibiotic properties of Penicillium, but failed to report a connection between the fungus and a substance that had antibacterial properties, and Penicillium was forgotten in the scientific community until Fleming’s rediscovery. Through follow-up work, Fleming showed experimentally that the mold produced a small substance that diffused through the agar of the plate to lyse the bacteria. He named this substance penicillin after the Penicillium mold that had produced it. By extracting the substance from plates, Fleming was then able to directly show its effects. Important to its discovery was the penicillin had destroyed a common bacterium, Staphylococcus aureus. Through follow-up work, Fleming showed experimentally that the mold produced a small substance that diffused through the agar of the plate to lyse the bacteria. He named this substance penicillin after the Penicillium mold that had produced it. By extracting the substance from plates, Fleming was then able to directly show its effects. Important to its discovery was the penicillin had destroyed a common bacterium, Staphylococcus aureus, associated with sometimes deadly skin infections. 9/2/09

9. Uncertainties Gaussian Distribution μ = Mean (Average) σ = Standard Deviation 9/2/09

10. Measurements and Precision  9/2/09

11. Measurements and Precision 133.005 ± 2 What’s wrong?  9/2/09

12. Measurements and Precision 133 ± 2  9/2/09

13. Combining Uncertainties 9/2/09

14. Assignment for 09/09/09 1.The volume, V, of a small box of length a, width b and height c is given by V = abc. Calculate the mean and standard deviation of the volume if the measured values of the box dimensions are given by a = 3.00±0.03 cm, b = 2.50±0.05 cm and c = 10.00±0.1 cm. 2.A campus walkway has four straight segments of lengths a, b, c and d. Calculate the total length (mean and standard deviation) of the walkway if the measured values of the segments are given by a = 15.0±0.5 m, b = 52±1 m, c = 28.5±0.7 m and d = 44.8±0.9 m. 3.Which of the following measured quantities are expressed correctly and which are not? Explain your answers. (a) 5.06±0.1 kg (b) 7.009±0.004 mm (c) 3.0067±0.0055 km (d) 8±0.05 g (e) 85±2 mL 9/2/09