# The Nature And Practice Of Atomic Physics Philosophy Essay

The purpose of this paper is to explain how the atom and atomic physics arose and account for the basis of its on-going utility, starting from the earlier Greek philosophers until the scientists of the 20th Century and after the atomic bomb the ended World War II. The model of science applied to depicting this development is heuristics for its practical utility. This history will follow chronologically, showing how science developed and was later modified to incorporate new knowledge into its theories.

The History, Nature, Practice of Atomic Physics

Imre Lakatos (1976) posited that no theorem of mathematics is final or perfect. Once an exception is found, then the theory is adjusted to accommodate this new information. He proposed explaining mathematical knowledge based on the idea of heuristics; that is, ignoring whether a problem can be proven correct, but rather adopting a “good solution,” albeit sometimes sacrificing accuracy or precision. He essentially is describing the heuristic model, which will be applied in this chronology from atom to atomic theory. Algorithms are developed to describe a process, and subsequently modified to incorporate new technological knowledge.

The idea behind the atom goes back to the Ancient Greeks who believed that all matter was made of smaller, more fundamental things. In 460 BC, Greek philosopher, Democritus, develop the idea of atoms. He asked what would happen if you break a piece of something in half, and in half again, and so on and so forth: how many times would you have to break it before it can no longer be broken into a smaller piece. He called this small, indivisible piece, atom (άτομο) (Freeman, 1948). Unfortunately, the philosophers of that period, particularly Aristotle, dismissed his ideas as worthless (Freeman, 1948). Subsequently, there was no further interest in the atom until 1803 when John Dalton proposed what he called his atomic theory.

Dalton concurred with Democritus’ hypothesis of the immutability of the atom, and added two further hypothesis, specifically that atoms of different elements had different weights—which rejected Newton’s theory of chemical affinities, and that three different types of atoms exist, which he labeled “simple,” “compound,” and “complex.” (Greenaway, 1966). In his further work, he posited that atoms could be neither created nor destroyed, and atoms only combine in small, whole number ratios such as 1:1, 1:2, 2:3 and so on (Greenaway, 1966).

In 1897 Thomson discovered the electron and proposed a model for the structure of the atom. He posited that electrons are kept in position by electrostatic forces (Thomson, 1904). He suggested that these electrons were arranged as in a “plum pudding;” that is, each atom was a sphere filled with a positively charged fluid. The fluid was called the "pudding." Scattered in this fluid were electrons known as the "plums." The radius of the model was 10-10 meters (Hentschel, 2009).

In 1900, Planck demonstrated that when you vibrate atoms strong enough, you can measure the energy only in discrete units. He called these energy packets, quanta (Mehra & Rechenberg, 1982). He derived his formula by a statistical analysis of these quanta of energy. Each quanta contained an energy directly proportional to a constant, h, multiplied by the frequency of oscillation of the particular blackbody oscillator associated with that quanta. Using a formula that he developed, written as

I(v, T) =

where

I = energy per unit time per unit surface area per unit solid angle per unit frequency or

wavelength;

v = frequency;

T = temperature of the black body;

h = constant (6.62606896(33) x 10-34Js = 4.13566733(10) x10-15 eVs);

c = speed of light;

k = Bolzmann constant (E = ) (Mohr, et al., 2006),

calculating a value for the charge of the electron as well as the constant h. Subsequently, he discovered that because of the finite, non-zero value of h, the world at atomic dimensions could not be explained with classical mechanics (Mehra & Rechenberg, 1982). In 1905 Einstein applied this formula to light and was able to explain photoelectric affect—that is, light absorption could release electrons from atoms. He argued that under certain circumstances light behaves not as continuous waves but as discontinuous, individual particles; that is, quanta (Cassidy, 1998).

In 1905, Einstein published his paper on special relativity. It generalized Gallileo’s principle of relativity. He termed it “special” because the theory only applied to frames of reference in uniform relative motion with respect to each other (Einstein, 2008). In this theory, he expressed two postulates:

The Principle of Relativity – The laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or the other of two systems in uniform translatory motion relative to each other (Einstein, 2008).

The Principle of Invariant Light Speed – "light is always propagated in empty space with a definite velocity [speed] c which is independent of the state of motion of the emitting body" (Einstein, 2008). That is, light in vacuum propagates with the speed c (a fixed constant, independent of direction) in at least one system of inertial coordinates (the "stationary system"), regardless of the state of motion of the light source (Einstein, 2008).

The consequence of this theory are that the time lapse between two events is not invariant from one observer to another, but is dependent on the relative speeds of the observers’ reference frames (Einstein, 2008). Two events happening in two different locations that occur simultaneously in the reference frame of one observer may occur non-simultaneously in the reference frame of another observer (Einstein, 2008). The length of an object as measured by one observer may be smaller than that measured by another observer (Einstein, 2008). Velocities and speeds are not additive. He posited that as an object’s speed approaches the speed of light, an observer would see its mass appear to increase, thus making it more difficult to accelerate (Einstein, 2008). The energy content of an object at rest with mass m equals mc2. Conservation of energy implies that in any reaction a decrease of the sum of the masses of particles must be accompanied by an increase in kinetic energies of the particles after the reaction; that is, E = mc2 (Einstein, 2008).

In 1909, Rutherford conducted an experiment where he fired gold foil with helium atom nuclei—alpha () particles. Most of the -particles went straight through, but a few were deflected or bounced back. This led Rutherford to hypothesize that atoms are mostly empty. He posited that the negative electrons orbited around the nucleus of the atom similar to planets around the sun (Goldstein, et al., 2000). In 1919, Rutherford was successful in demonstrating artificial disintegration of a nucleus by firing -particles into nitrogen gas, which resulted in the production of hydrogen (Reeves, 2008).

In 1913, Bohr postulated that electrons can be bumped up to a higher shell if hit by an electron or a photon of light. Classical physics held that the electrons orbiting the nucleus should lose energy until they spiral down into the center, collapsing the atom. Bohr proposed adding to the model the new idea of quanta put forth by Planck. That way, electrons existed at set levels of energy’ that is, at fixed distances from the nucleus. If the atom absorbed energy, the electron jumped to a level further from the nucleus; if it radiated energy, it fell to a level closer to the nucleus (Smirnov, 2003). Sommerfeld hypothesized that the orbits of electrons do not have to be spherical but can also be elliptic. He further posited that the orbits don't have to lay in the same plane: they could be oriented in space on some defined directions (Eisberg & Resnick, 1985).

In 1915, Einstein developed his general theory of relativity. It addressed the issue of gravity. It described the relationship between space-time and energy-momentum. Space-time may be defined as space being three-dimensional, with the additive of time as a fourth dimension, combined in a single continuum. In this theory, Einstein assumed that space-time is curved by the presence of energy (Einstein, 2008).

Pauli, in 1925, developed his exclusion principle (Griffiths, 2004), which states that “no two electrons in the same atom can be in the same quantum state” (Schäfer, 1997). The importance of this principle is that it allows for the distinction between the different elements on the Periodic Table.

In 1926, Schrödinger theorized the concept of wave dynamics, developing a particle wave theory. (Frederic & Levi, 2006). The wave function is not physical because it cannot be measured. In this theory, the thing that is measured is the expected value of the quantum operator. This is based upon a probabilistic function (Frederic & Levi, 2006). His equation is used to described an electron’s movement through space.

In that same year, Born and Heisenberg developed a theory they called “matrix mechanics” to explain the nature of atoms. Up to this time, quantum theory described the motion of a particle by a classical orbit, with a well defined position and momentum; with the restriction that the time integral over one period of the momentum times the velocity must be a positive integer multiple of Planck’s constant (Born, et al., 1989). By applying matrix mathematics, the position, the momentum, the energy, and all the observable quantities are interpreted as matrices. This was developed on the premise that all observed sequences of physical operations may be represented by matrices whose elements are marked by two different energy levels. If one of these physical operations is measured, the result is a value, with the corresponding vector being the state of the system immediately after this measurement (Born, et al., 1989).

In 1926, Schrödinger theorized the concept of wave dynamics, developing a particle wave theory. (Frederic & Levi, 2006). The wave function is not physical because it cannot be measured. In this theory, the thing that is measured is the expected value of the quantum operator. This is based upon a probabilistic function (Frederic & Levi, 2006). His equation is used to described an electron’s movement through space.

In 1927, Heisenberg went on further to posit that no experiment could measure the position and momentum of a quantum particle simultaneously. The more precisely one of the factors may be measured, the less precisely the other can be measured. This became known as the "Heisenberg uncertainty principle" (Born, et al., 1989).

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