9 bomb was built and dropped on Hiroshima, causing numerous deaths and catastrophic damage. The Chicago Pile Experiment As for the invention of the atomic bomb, one must mention the breakthrough in the Chicago Pile experiment. On a chilly winter day in 1942, Fermi and his colleagues placed a 6.1-meter wide by 7.6-meter high pile of graphite bricks with 6 tons of uranium metal and 40 tons of uranium-235 in the squash court under the University of Chicago football field, together with cadmium rods [1, 6, 10, 11]. The theory behind the experiment is as follows. As a neutron hits a uranium-235 atom, the latter splits into two smaller atoms and releases energy [6, 12]. This fission reaction also releases neutrons as by-products to split other uranium-235 atoms, resulting in a chain reaction to unleash gargantuan amounts of energy [6, 12]. For each mole of uranium-235 that goes under fission, the resulting products weigh approximately 0.2 grams less than the reactants [13]. By the famous equation E = mc2, this loss in mass corresponds to the conversion of order of 1013 joules of energy. In fact, the fission reaction of one kilogram of uranium-235 produces energy that is 2.5 million times greater than the energy generated by burning one kilogram of coal [13]. Therefore, for the reaction to be controllable, cadmium rods were inserted to absorb some neutrons during the reaction, thereby controlling the reaction rate and the amount of energy produced [6]. If Fermi’s calculations had been wrong and the cadmium rods had been insufficient to control the reaction, catastrophic amount of energies could have been unleashed, potentially destroying half of Chicago [6]. Fortunately, the experiment turned out to be a success, creating the first controlled, self-sustaining nuclear chain reaction. The pile was later refined by a substantial reduction in size, which made the controlled nuclear chain reaction possible to be incorporated into an atomic bomb that is small enough to be carried in an airplane. A Mistake in Fermi’s Nobel Prize The Nobel Prize is widely regarded as one of the most prestigious awards in the scientific community. Consequently, Fermi was rightfully honored with this esteemed recognition. However, there was a critical mistake concerning the scientific discovery for which Fermi received the award [14]. This is actually a story about Fermi discovering nuclear fission without realizing it. In 1938, Fermi was granted the Nobel Prize "for his demonstrations of the existence of new radioactive elements produced by neutron irradiation, and for his related discovery of nuclear reactions brought about by slow neutrons [15]." At that time, the known heaviest element was uranium with an atomic number of 92. It was believed that Fermi had successfully produced transuranic (beyond uranium) elements with atomic numbers 93 and 94 by bombarding uranium with slow moving neutrons. They called the new elements Ausenium and Heperium, respectively. However, German chemists Otto Hahn and Fritz Strassmann subsequently made a pivotal discovery that the elements produced through uranium bombardment were not novel entities, but lighter elements like barium with an atomic number of 56 [14]. In fact, uranium split into two lighter elements upon neutron bombardment, through a reaction later known as nuclear fission. Based on the discovery of nuclear fission, Hahn was awarded the Nobel Prize in Chemistry in 1944 [16]. As for the actual elements 93 and 94, they were eventually created in 1940, and named neptunium and plutonium [17]. Fermi’s Paradox One question that bugged scientists, including an intelligent physicist like Fermi, is the possible existence of extraterrestrial creatures, a.k.a. aliens. From geocentrism to realizing that we are not the center of the universe, from thinking that the Milky Way was all that there was to discovering that there are billions of galaxies [18], we should be wise enough to know that we are not special in the vast universe. Fermi proposed that if we are not unique and the Earth is young compared to the copious stars and planets out there, extraterrestrial civilizations should have evolved and colonized nearby galaxies by now [19]. Yet, where did everyone go? Before making further discoveries on this subject, Fermi died in 1954, and the question fell to other scientists. Despite ongoing research and numerous papers being published on this topic, the question remains unresolved and highly debatable. Fermi Problem During the Trinity Test, the first detonation of the atomic bomb in history, Fermi tore paper into scraps and threw them from a height of 1.83 meters [20]. While standing 16 kilometers away from the explosion site [21], he utilized their displacement shift of 2.5 meters to estimate the energy produced by the detonation through a series of deductions and calculations. Fermi’s estimate (10 kilotons of T.N.T.) was within the same order of magnitude of the true value (21 kilotons of T.N.T.) despite employing what initially seemed like an unrelated method. This led to the emergence of a new class of problems known as the Fermi problems, to be solved using this estimation method to approximate the order of magnitude of values when our knowledge is limited. It involves making educated guesses by breaking down complex problems to simpler components, with reasonable assumptions.
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