As a Chemical Engineer, albeit now retired for more than 10 years, I have always had an interest in science and technology. During my retirement, as a hobby, and I think as a subconscious way to avoid Alzheimers, I have developed a love for the mysteries of theoretical physics.
Although I find modern physics irritatingly obtuse, somewhat weird and quite mysterious - I believe most physicists do as well-the manner in which the various concepts are logically explained and argued systematically calculated or experimented and presented by science writers showing great erudition is, for me, highly intriguing and interesting. Writers and speakers are always so enthusiastic about their subject.
In my first year Physics course at University, now more than 50 years ago, I was introduced to the subject through the Niels Bohr model of atomic theory. The Bohr model depicted an atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus, similar in structure to the solar system, but with attraction provided by electrostatic forces rather than gravity.
The atom (the word being derived from the ancient Greek adjective Atomos meaning 'indivisible') was considered as the building block for a growing number of irreducible chemical elements. Various experiments with electromagnetism and radioactivity showed, however, that the so-called indivisible atom was actually a cluster of various smaller particles, like electrons, protons and neutrons, which can exist separately from each other.
Extreme temperature and pressure prevents atoms from existing at all. Since atoms were found to be divisible, physicists later invented the term ‘elementary particles’ to describe the 'indivisible', though not indestructible, parts of an atom. The field of science which studies subatomic particles is now called particle physics, and it is in this field that physicists hope to discover the true fundamental nature of matter.
Under the influence of Max Planck and Albert Einstein, who postulated that light energy is emitted or absorbed in discrete amounts known as quanta, Niels Bohr modified his classical model, in which an electron could only orbit the nucleus in particular circular orbits with fixed angular momentum and energy, and at a fixed from the nucleus. Introducing the concept of quanta, an electron could make instantaneous "quantum leaps" between the fixed energy levels.
When this occurred, the light was emitted or absorbed at a frequency proportional to the change in energy, and, simply speaking, the multi-facited subject of quantum physics was introduced.
Using quantum mechanics, the concept of a particle underwent serious rethinking in light of experiments that showed that light could behave like a stream of particles (called photons) as well as being able to behave as waves. This new concept of ‘wave–particle duality’ brought about a major new principle, Heisenberg’s uncertainty principle, which stated that the position and energy cannot be measured exactly at the same time; you can measure one or the other but not both at the same time. The problem is that the observer influences the situation and this fact has been the source of great frustration for quantum scientists.
The dynamics of the known subatomic particles has been mediated by the so-called Standard Model of particle physics, which is a theory concerning the electromagnetic, weak, and strong nuclear interactions. It was developed throughout the latter half of the 20th century, and has been a model of a great collaborative effort of scientists around the world.
The current formulation was finalized in the mid-1970s upon experimental confirmation of the existence of so-called ‘quarks.’ Since then, discoveries of the ‘top quark’ (1995), the ‘tau neutrino’ (2000), and more recently the ‘Higgs boson’ (2013), have given further credence to the Standard Model. Because of its success in explaining a wide variety of experimental results, the Standard Model is sometimes regarded as a "theory of almost everything", but there are many glaring frustrating aspects not explained like the ‘emptiness’ of matter, dark matter and dark energy and no explanation of gravity.
Dark matter is thought to make up about 80 percent of the universe's matter, but little else is known about it, including its distribution in the solar system. Hints that the stuff might surround Earth come from observations of space probes, several of which changed their speeds in unexpected ways as they flew past Earth. In 2009, Steve Adler of the Institute of Advanced Studies in Princeton, New Jersey, showed how dark matter bound by Earth's gravity could explain these anomalies.
The elementary particles of the Standard Model have some intriguing names, including six ‘flavours of quarks called ‘up’, ‘down’, ‘bottom’, ‘ top’, ‘strange’, and ‘charm’ (I have yet to find out why ‘charm’). There are also six types of ‘leptons’: electrons, electron neutrinos, muons, muon neutrinos, taus and tau neutrinos. Twelve ‘gauge bosons’ exist, photons of electromagnetism, the three W and Z ‘bosoms of the weak force, and the eight ‘gallons’ of the strong force and, of course, the now famous Higgs boson.
The Standard Model also predicts the existence of an elementary Graviton particle and many other elementary particles still to be discovered.
In particle physics, the conceptual idea of a particle is one of several concepts inherited from classical physics, the world we experience, that are used to describe how matter and energy behave at the molecular scales of quantum mechanics. As physicists use the term, the meaning of the word ‘particle’ is one which understands how particles are radically different at the quantum-level, and rather different from the common understanding of the term.
The very notion of a discrete ‘particle’ has been ultimately replaced by the concept of something like wave-packet of an uncertain boundary, whose properties are only known as probabilities, and whose interactions with other ‘particles’ remain largely a mystery, even 80 years after quantum mechanics was established.
The quantum theory of small particles, i.e. they can’t be measured and can move around, has led to some strange ‘paranormal’ and ‘non-evidence’ based medicine and practices. Or some motivational speakers quantum theory implies that you just need to imagine something and this will happen.
Some of the craziest seem to do with the possibility of quantum mechanics being a feature of the functioning of human brains, including consciousness. Only time will tell whether quantum mechanics will one day have a bearing on human behavior and cognition.
Something that continues to fascinate physicists, and blows my mind, is that all the particles, believed to have formed during the Big Bang, have mirror images of themselves with the opposite polarity. Thus, for example, there is a positively charged electron, a positron. What should have happened was that all the particles should have annihilated themselves, leaving behind a total vacuum.
The fact that this has not happened is indeed strange and there are no plausible explanations. Some believe this is the root cause of dark matter and dark energy but nobody knows. This, to me, is the wonderful thing about theoretical physics; so much has been done and yet so little is known about our universe.
A famous physicist once said: “there is really only one problem in physics: there are too many physicists”! One could answer this by saying: yes, but there are still too many problems!