Defending the Christian Worldview, Creationism, and Intelligent Design
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Defending the Christian Worldview, Creationism, and Intelligent Design

Otangelo Grasso: This is my personal virtual library, where i collect information, which leads in my view to the Christian faith, creationism, and Intelligent Design as the best explanation of the origin of the physical Universe, life, and biodiversity

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Defending the Christian Worldview, Creationism, and Intelligent Design » Astronomy & Cosmology and God » Quantum and particle physics » The Pauli exclusion principle

The Pauli exclusion principle

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1The Pauli exclusion principle Empty The Pauli exclusion principle Fri May 14, 2021 1:14 pm



The Pauli exclusion principle

The most common fermion to our everyday life is the electron, and this packing limitation of electrons has a profound influence on our world, effectively defining the subject of chemistry. This is the famous Pauli exclusion principle in action. Electrons live in certain energy levels about atoms, with two in the lowest level of an atom, known as the ground state. Why two? Electrons possess a quantized spin of ½,

The Pauli exclusion principle 1146306_orig
The fundamental tenet of quantum mechanics is that many basic phenomena at the atomic level (such as energy emission and angular momentum) appear to be quantized.  “Quantized” means that when certain properties of a system are measured, a continuous range of results are not observed, but rather a set of discrete (separate) values.  If “quanta” come in discrete units then it makes sense to count them with integers.

The idea of a spin = ½ particle was at first met with skepticism by much of the scientific community. It was not until 1928 when Paul Dirac directly derived this result for the electron from relativistic quantum mechanics that half-integer quantum numbers became widely accepted.

which can point either upwards or downwards, and so the lowest energy state can be occupied by one electron with its spin pointing upwards, as well as a second electron with its spin pointing downwards. (Classically, we define the direction of a spin with the right-hand-rule: wrap your right hand around the spinning object, with your fingers pointing with the spin. Give a thumbs-up; this defines the direction of the spin). In terms of packing electrons, this lowest level of the atom is full, and any additional electrons must go into higher levels. And as these upper levels fill, incoming electrons settle into higher and higher energy levels. What does this have to do with chemistry? Well, chemistry is about how atoms interact, and this is completely defined by the locations of the electrons in the outermost energy levels; these are the most loosely bound electrons, and it is these that can be swapped between atoms to allow them to bond and form complex molecules. It is these electrons, and the properties of their spin and orbits, that give atoms their personality. The same is true of atomic nuclei. Protons and neutrons, themselves fermions, can only be found on distinct energy levels with the nucleus, packed in accordance with the Pauli exclusion principle. This explains why, while isolated neutrons rapidly decay, a neutron inside an atomic nucleus is effectively stable. It cannot decay because no lower energy positions are available for the resultant proton. What if electrons were bosons rather than fermions? The result would be disastrous as there would be nothing to prevent all the electrons occupying the lowest level in an atom, like stuffing as many photons in the box as you can. Once again, wave chemistry – and the chemical complexity and flexibility needed by life – goodbye. These bosonic electrons would be very tightly bound to their nuclei, with little inclination to be shared with other atoms. This universe would be a sea of individual atoms floating through the cosmos, minding their own business and not getting involved in this messy work of forming molecules. However, the situation could be even more complicated! As well as the electrons, the quarks are also fermions, also possessing a spin of one-half. And this spin is imprinted (in a rather complex fashion) onto the particle they form. And both the proton and the neutron, even though they are composite objects, have a total spin of one-half, also making them fermions, and ensuring they obey the fermion rules of packing. This means that the protons and neutrons of an atom are arranged in orbits very similar to the orbits of the much more distant electrons. If quarks, and so also the protons and neutrons, had an integer spin, just like the electrons, there would be nothing to prevent all of them collapsing down and occupying the lowest energy level. Collapsing all of the protons and neutrons in your atoms is not necessarily a catastrophe; there are more important things to worry about.

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