To any living organism, the world looks like a continuous place. We are far too large to perceive atoms or molecules except through the use of special techniques and devices. Thus, when we look at a gold ring, we see a solid band of gold.
We don't see the individual atoms lined up. We don't see the discrete particles. We don't see the impurities. However, in the early 1800s, John Dalton reintroduced the concept of atoms to science and the world became discontinuous.
For much of the 19th century, the existence of atoms was a contested issue. Scientists were asked to believe in something not visible to the naked eye and, indeed, beyond the capacity of any instruments available at that time.
At the end of the 19th century, Max Planck went one step further and demonstrated that not only was matter made up of tiny particles but so is light. More to the point, light was quantized. Its photons each had a unique energy as a result of their wavelength or colour.
At the beginning of the 20th century, science was undergoing a major paradigm shift. The continuous world we perceive was being replaced by a grainy universe made up of small entities stacked one on another. The likes of Albert Einstein, Ernest Rutherford, and Niels Bohr worked long and hard to come up with an explanation for the structure of atoms and their interaction with energy or light.
Scientifically speaking, it was an amazing time to be alive as so much was yet to be discovered. But by 1913, a coherent picture of the atoms was emerging. It is the picture most of us have seen with the atom looking something like the solar system. The nucleus is the sun at the centre and the electrons orbit in rings at various energy distances from the core.
This model was not without a few problems though. For example, electrons travelling in circular orbits should emit X-rays as they are accelerating and yet none were observed. Physicists have been working at refining the model ever since. This is quantum mechanics.
A key step in its development came when Werner Heisenberg developed the uncertainty principle. In essence, it argues that certain properties do not commute. That is, mathematically and physically speaking, there are measureable properties of a system which cannot be measured at the same time. A little more accurately is these properties form an inequality with a lower limit.
For example, time and energy do not commute. The more precise the time measurement, the more uncertain the value of the energy.
We use this inequality to allow MRIs to collect a broad spectrum of frequencies simultaneously which allows scans to collect millions of data points in a very short time frame.
In the case of the atom, the uncertainty principle says that you can know the precise position of an electron but not its momentum or its exact momentum but not its position. You can either know precisely where it is but not where it is going or where it is going but not where it is.
This introduced a level of randomness to quantum theory. The electron could no longer be viewed as following a precise orbit around the nucleus, for such orbits would give both the position and the momentum of the electron precisely.
Instead, the concept of an orbital emerged through the work of Erwin Schrodinger. He started out to save modern physics from the randomness of Heisenberg by using wave mechanics and ended up with the foundational equation demonstrating the probabilistic nature of the atom and for that matter the whole universe.
This presented several problems in physics because ultimately it is a discipline devoted to finding singular definitive answers to questions about space and time.
Having randomness at the core of all that there is means that some answers will never be known.
Hence, the question of whether or not Schrodinger's cat is alive or dead. The only way to find out is to open the box and collapse the wave function. Prior to that, the cat is in a state of both alive and dead.
Collapsing the wave function leads to two equally probable outcomes and the result appears to be randomly distributed between the results. To many physicists, this is unsatisfactory as there is no apparent reason for one answer over the other. Or as Einstein put it, the Old One does not play dice with the universe.
One answer to the problem is both answers are realized and the universe splits in two creating two universes - one with an alive cat and one in which it is dead, for example.
The result is the many-universe model in which all possible realities are realized. In modern terms, this is the multi-verse in which modern science fiction and fantasy is well vested.
All because John Dalton realized atoms might be real.
