Emergence of Atomic Hypothesis

The concept of Reality is very obscured in physics that now Physicist don’t even talk about Reality. Take for example Quantum Mechanics, in mid-90s, people tried to make sense out of Quantum mechanics from their notion of reality, but the outcome was so bizarre and unprecedented that physicists have left that thing to metaphysicist and philosophers.

You would’ve heard the tale of the “Fox and the grapes”, in the end the fox leaves the grapes and says, “They are sour.” In the similar ways physicists have stopped talking about reality. They make a theory, publish it and get going, not bothering to talk about the intuitive reality behind that. Sometimes our intuitious comes true and sometimes it doesn’t. One such example is the story of “The Atomicity of Matter”.

The idea that world consists of standard little parts (now we call atom) originated long ago. The atomic hypothesis existed side by side with the belief that the world consisted of a single continuous substance and it’s transformation eg: “fire”, “air” or “water”. The fact that the existence of water in different forms of solid, liquid or gas at different temperatures was taken as an example that how one substance might be able to stimulate world’s enormous variety. However, until nineteenth century the arguments for the continuum and the atomic hypothesis where mainly rhetorical; little evidence existed for either of these views.

Dalton’s Hypothesis

In 1808, John Dalton discovered that the chemical substance always combine in fixed ratio- eg: two part of Hydrogen combines with one part of Oxygen to make water, provided each of these were assigned a standard weight. Dalton proposed that these constant combining ratio represented the actual atoms whose atomic weights were proportional to standard weights. Thus, water consists of two atoms of Hydrogen and one atom of Oxygen. Dalton took these constant chemical ratios as token of an invisible atomic reality.

Believers and The Energetics

Many scientists were convinced with this theory but few prestigious opposed the atomic hypothesis on the basis that it went beyond the facts. In 1826, Dalton received the Royal Society of London’s medal of honour for the discovery of law of “chemical equivalent” and not for the hypothesis of invisible entities behind the phenomena i.e. atoms.

Chemists from different nations united to oppose the atomic hypothesis. French scientist Jean Baptise Dumas said, “It goes further than experience, and that in chemistry, we should never go further than experience.” The German chemist August Kekule, famous for the discovery of Benzene ring said, “The question whether atoms exist or not has the little significance from a chemical point of view, it’s discussion belongs rather to metaphysics.

In chemistry, we have only to decide whether the assumption of atoms as a hypothesis adapted to the explanation of chemical phenomena.” Even the defenders of the Atomic hypothesis saw little hope of directly verifying the atomic hypothesis. Because the size of these elementary entities- if they were really at all- was about thousands times smaller than the  wavelength of light, technically invisible forever.

On the other side, in the continuum hypothesis the field of chemical thermodynamics was an alternative to Atomic hypothesis. The real idea behind this was of the real underlying component of the universe- “Energy” and it’s variation forms. The two laws of thermodynamics- which requires conservation of energy and an entropy based limit on this energy’s utilization- had been extended by Maxwell & Gibbs to describe successfully the intimate details of physical and chemical reaction without the Atomic hypothesis. The ones who believed in this theory were called “Energetics”.

Debates in Journals and conferences between the supporters of atomic hypothesis and energetics were sharp and emotional- leading to the suicide of Ludwig Boltzmann.

Einstein and Brownian motion

In 1905, Albert Einstein published a paper on Brownian Motion that pointed the way to conclusive experiments bearing on the real existence of Atoms.

Whenever micron-sized particles suspended in liquid they undergo a perpetual dance whose origin had been a mystery. Early experiments on Brownian motion performed with pollen grains was believed to be of biological origin. When it was discovered that any sort of finely divided matter would show such agitation, the biological hypothesis was discarded and various physical mechanisms such as temperature gradients, surface tension, electrochemical effects were proposed but none of them quite worked and Brownian motion remained a mystery tucked away in an obscure corner of physics.

Einstein explained Brownian motion as the action of numerous atoms colliding with the Brownian particle. This explanation had been previously rejected because the atoms were millions of times less massive than the Brownian particle and their collective pressure could lead to no net motion because equal amounts of atoms were pushing in every direction.

Einstein showed that in any random direction, the relative fluctuations were inversely proportional to the square root of the numbers of samples- smaller the sample, larger the fluctuation. For a large particle, the pressure is balanced but for a smaller particle, the fluctuations were sufficient to propel it in an unpredictable direction with a predictable force. Einstein showed how this random force would vary with temperature and particle size. If atoms existed, Einstein’s theory would be able to predict the number of atoms striking a Brownian particle and it succeeded in 1913 with the counting of the number of atoms in a drop of water.

Acceptance of Atomic Hypothesis

In response to the work of Einstein, the leader of energetics (Ostwald) bowed to the experimental evidence and accepted the existence of atoms. The atomic hypothesis is thus raised to a scientifically well-founded theory. Now, we can talk about the existence of atoms with the same containing as the existence of stars. Nobody today doubts that atoms really exist.

To get familiar with more of such not so known physics theories; Click Here.