FROM DEMOCRITUS TO EINSTEIN ON ATOMS
The lives of two famous men, Democritus (@ 430 BC) of Abdera in Greece and Albert Einstein (1879-1955) in Germany were separated by almost 2400 km and 2400 years. Were it possible for these two to meet, they might have found much in common. They were both creative thinkers who used “thought experiments” to generate hypotheses. They observed and theorized about the material world in their own very unique way. Both mused about the nature of the ultimate particles the “atoms” that make up the physical world.
Democritus (@430 BC) the Greek philosopher from Abdera in Thrace and the other philosophers of ancient Greece, were not restricted only to matters of logic, the “prime mover”, “final cause”, ethics or religion, as often they are today. In the classical Hellenic world, the purview of the “philosopher” (literally “lover of wisdom”) extended to all knowledge. So in ancient Athens, Greek philosophers were able to freely opine about the nature of matter, the heavens and planets, as well as our earth and the physical world.
Though they formulated their pronouncements without ever making a single formal observation or testing an hypothesis by experiment. (Much of Einstein’s creative work also relied on “thought experiments” from which he generated some of greatest ideas.) However, in the ancient world, the philosophical musings of these great minds were just that….untested musings . Yet these ideas concerning the nature of matter remained through the long ages, as hypotheses which cried out to be used and teated by those who followed.
Democritus viewed reality as being restricted to only the material world and for that reason his contemporaries described him as a “materialist”. Thinking about the physical world, Democritus, envisioned all matter to be comprised of minuscule building “blocks”, which were indivisible, immutable, infinite in number, as well as hard and uniform.
Democritus (or his teacher Leucippus) coined the term “atomos” ( άτομος) for these ultimate building blocks of matter. The word is formed from the root “tomos” which means to “cut or divide”, and is modified by the alpha privative prefix (“a”) which means “not”. The word can be translated as: “not able to be cut” or “indivisible”.
For Democritus, the differences in shape and size of these ultimate atomic elements determined the properties of matter. According to Democritus when material substances combined or separated they created the illusion of change, but the atoms themselves remained immutable. (To be clear, these properties of atoms as envisioned by Democritus, were based only on reason and conjecture—not on empirical evidence or testing.)
Democritus’ ideas about atoms were almost lost in the dust of time. They survived in the writings of others who criticized and lampooned his thinking. It took two millennia for humans to even begin to rise again to the level where they began to think again about the nature of matter and the ultimate particles of matter.
Two millennia after Democritus, it was an Irishman, Robert Boyle (1627-1691) who began the new intellectual process using the new “scientific method”. Boyle, was an alchemist, who is considered to be the first modern chemist, who published the “Skeptical Chymist” in 1661. Boyle was greatly influenced by the writings of philosopher Francis Bacon.
Francis Bacon(1561-1626)
In his “Novum organum” Bacon proposed that knowledge could only be advanced by a new method of inquiry. He proposed the abandonment of logic-based, deductive reasoning arguments about the material world (like Democritus’) for those based on observations, testing of proposed hypotheses ,and inductive reasoning.
It was Boyle who eventually abandoned the alchemist’s quest for the “philosopher’s stone” that would turn base metals like lead into gold and turned to the scientific inquiry of the nature of matter. Boyle based the study of chemistry on observation, measurement and reproducible experiments. For these experiments which he termed “chemical analysis”, Boyle had been greatly influenced by an English philosopher and statesman Francis Bacon.
Boyle, also promulgated a law about gases which would lead to a better understanding of matter. Boyle discovered (Boyle’s Law) that when the pressure was doubled on an “ideal gas”, kept at a constant temperature, its volume decreased by one-half. Doubling the pressure caused a decrease the volume by half. ( P1x V1 = P2xV2) Stated another way:for a fixed mass of an ideal gas at a constant temperature , the pressure is inversely proportional to the volume.
Boyle also theorized about a “corpuscular theory” of gases (and matter). These “corpuscles” or “bodies” of which Boyle’s gases seemed to be comprised were a theory that was very reminiscent of Democritus’ atomic theory.
But it took another 140 years for the Englishman, John Dalton 1776-1844, to actually reintroduced the idea of Democritus’ atoms.
Dalton began his career as a self-taught meteorologist who kept records of the change of barometric (air) pressure and how it influenced the weather. Evaluating his data about the atmosphere, which is a mixture of gases, led him to experiments from which he concluded that the total pressure of a mixture of gases is the sum of the pressures of the component gases. In 1803 he postulated a law which stated just that: Dalton’s Law states that the total pressures of a mixture of gases is equal to the sum of the partial pressures of the individual component gases, or P (total) = Pa + Pb + Pc.
Dalton had an active and inquiring mind. He investigated many and diverse topics of study. But his work with gases and how they combine eventually led him to an hypotheses in 1808 that revived Democritus’ atomic theory by concluding that gases must be composed of atoms. He suggested as well that all the chemical elements (and matter in general) must also be composed of atoms.
Dalton’s conclusions were:
a) Elements are composed of extremely small particles, he called “atoms” which can not be divided or destroyed.
b) Each element has distinctive atoms identical in size, mass and other properties.
c) Atoms can combine in chemical reactions to form molecules or compounds.
d) Atoms always combine in whole number ratios.
By comparing the weights of other elements to that of hydrogen (H), which he ascribed the value of 1 Dalton produced a table of relative atomic weights. He calculated the relative weights of other elements: nitrogen, carbon, phosphorous, oxygen, and sulfur . His weights were often one half of the weight of now known modern data. The problem with Dalton’s calculations were that he insisted on the simplest of equations. Using his method, of “the simplest is best” (or “Occam’s razor”) he formulated his molecules in the simplest possible way. He could not conceive that some gases might occur as “diatomic” molecules such as nitrogen gas (N2). Dalton imagined water to be H O, not H2O and oxygen is actually comprised of two oxygen atoms, with a notation of O2, not a single “ O” as Dalton imagined.
But the intellectual dam was breached, and only a few years later, Amedeo Avogadro (1776-1856) an Italian scientist, performed experiments that revealed the actual existence of atoms that Boyle and Dalton had just hypothesizing about. Avogadro’s experiments demonstrated that two liters of hydrogen gas, would always combine with exactly one liter of oxygen gas to produce two liters of water vapor at standard temperatures and pressures (STP). Avogadro concluded for this to occur there must be discrete particles in the gases that were combining. These particles must be the atoms of Democritus and Dalton and “corpuscles” of Boyle.
Avogadro further pointed out that the equal volumes of a pure gas at standard pressure and temperature (STP) which combined to form water vapor, may have different masses, but based on the way they combine, the volumes must contain an equal number of molecules or atoms.
In 1811 Avogadro proposed his law Avogadro’s Law, which states that equal volumes of any two gases at STP contain equal numbers of atoms or molecules. That is: the mass of a gas (differing from another) does not imply there are more or less atoms. It is the atoms or molecules which vary in weight. Since atoms or molecules combine in a very specific way, Avogadro finally proved that these invisible atoms or molecules were real. Democritus was right!
In 1827 a Scottish botanist, Robert Brown, reported observing the unexplained movement of pollen grains suspended in an aqueous solution under the high power of a light microscope. Brown who termed the jiggling motion of the pollen “Brownian Motion” could not explain these random movements.
But Albert Einstein could! It was Albert Einstein in 1905 who theorized that the random motions of the pollen grains as described by Brown must be caused by violent vibrations (the kinetic energy) of the invisible water molecules as they violently and incessantly bumped into the pollen grains. Einstein grasped on this fact to propose a way to mathematically calculate how many molecules were present, in a given volume, based on the random movements of the water molecules as measured over time. Though the atoms or molecules could not be seen, the results of their kinetic energy or their movement and impacts on pollen grains could be actually measured. Using these calculations, Einstein predicted a mathematical solution for the actual number of molecules or atoms in a given volume and led the way for this to be calculated.
These measurements and calculations by Einstein led to other experiments on tiny particles suspended in solutions by Jean Baptiste Perrin, a French scientist who in 1909, based on Einstein’s calculations actually measured how many atoms or molecules were in a standard unit of gas. Perrin called this number Avogadro’s Number. His calculations indicated this value: 6.022 x 10 23rd power for the
number of molecules, (atoms or ions) in a volume of gas equal to the molecular weight of that gas.
So finally after two millennia, we know Democritus cogitations and imaginings about the nature of matter was correct. Matter IS composed of atoms! But they are not “a tomos”. That is they are not the ultimate indivisible particle. There are “innards” to the atom! But that is another long story.
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