Physics We Can All Understand by John Skieswanne Parts 4 and 5.
Part 4: The Standard Model
What is the irreducible components of the Universe? If it’s made of gases and atoms and stars and rocks, are all of these made of something smaller? The answer, of course, is yes. It turns out that everything is indeed made of incredibly small components called “elementary particles”. They are the Universe’s DNA. Even your DNA’s DNA, for that matters. These components build up atoms, electrical currents, even forces such as light and inertia. And now you’re going to meet all 17 of them.
The first particle ever discovered was the electron in 1897, by Joseph John Thompson’s team. The later even published a good approximation of the electron’s mass and electric charge. This elementary particle is responsible for electrical currents. Electrons are also found surrounding the atom’s nucleus. Alternatively, a heavy version of the electron, called the muon, was spotted by Carl David Anderson in 1936. The atomic nucleus itself was discovered to contain neutrons and protons – and, later, protons were proposed to be composed of three quarks (two up quarks and one down quark) while neutrons were proposed to be composed of three quarks (one up and two downs). Later on, strange particles were discovered (for instance kaons) which were a combinaison of a strange quark with either an up quark or a down quark. In 1974 the J meson was discovered, which were composed of charm quarks. An even heavier electron (the tauon), along with top quarks and bottomquarks, were discovered in the 70s (and in the 90s for the top quark). A neutrino for the electron, the muon and the tauon were observed to exist – they act a bit like their respective particle’s luggages. When a particle decays and emits an electron, it was observed that some energy was missing, so it was proposed that a neutrino was carrying it away. Gluons were proposed to “glue” quarks together. Photons are particles of light. To explain particle decay (only a few particles can survive for longer than a fraction of a second), the W boson and the Z boson were introduced. And, most recently, the Higgs boson was introduced to account for the inertia of the particles. The latter acts a bit like a molasses which cling on a particle and give it mass. All forces in the Standard Model are explained with mathematical equations, called Special unitary groups (SU).
There you have it: 17 particles. Together these particles build up anything from the exotic Cascade B baryon to Stars, including DNA, drops of water, mountains, whole planets.
3 of these particles have an electric charge of -1 (that is, their electrical charge is equal to that of an electron): the electron, the muon, and the tauon.
Out of the 14 remaining, three other particles have an electric charge of +2/3 (that is, their electrical charge is equal to 2/3 of an electron, and has the opposite sign): the up quark, the charm quark, and the top quark.
Out of the 11 particles remaining, three other particles have an electric charge of -1/3 (that is, their electrical charge is equal to 1/3 that of an electron): the down quark, the strange quark, and the bottom quark.
W bosons have a charge of either -1 or +1, depending on the parent particle as the latter undergoes decay.
All other 7 particles have zero electric charge.
All particles (well, except the Higgs boson) have spin. The spin is the rotation of a particle on itself (as particles travel, they spin on themselves, like a bullet does after it’s been fired from a rifle) – half a spin means that the particle looks the same after 1/2 rotation. A spin of 1 means the particle basically looks the same all over. Elementary particles with an integer spin are called “bosons”, and usually they carry forces. Particles with half a spin are called “fermions”, and they compose matter. There are 12 fermions in the Standard Model. The rest are bosons.
Particles were also observed to have mass, although we don’t know for sure what’s the mass of any neutrinos (only that it’s below a certain value). Usually the mass of most particles is measured in a special unit called Mega electronVolt (MeV). 1 MeV is equal to 1.782 octillionth of a gram, or 0.000,000,000,000,000,000,000,000,001,782 gram.
Fermions which are the most normal and were discovered first, in other words, the electron, its neutrino, the up quark and the down quark, are said to be “first-generation particles”.
Fermions which were discovered a bit later, were more massive and thus were more prone to decay very fast, such as the muon (heavy version of the electron), its neutrino, the charm quark (heavy version of the up quark) and the strange quark (heavy version of the down quark), are very rare on Earth and they are said to be “second generation particles”.
Finally, super-heavy particles which were discovered last, whose mass are such that they are impossible to find unless you own a CERN-class particle accelerator, and which decay even more quickly than Generation 2 particles, include the tauon (super-heavy version of the electron), its neutrino, the top quark (super-heavy version of the up quark) and the bottom quark (super-heavy version of the down quark). These are said to be “third generation particles”.
Nearly all particles were observed to have a mate, particles whose properties are exactly the inverse of the original particles – antiparticles. Antimatter is a mirror of matter – an antielectron will have an electric charge of +1 instead of -1, an antiup quark will have a charge of -2/3 instead of +2/3. When an antiparticle meets its mate, they annihilate each other and give off two photons which carry their energy away. If you count antiparticles, the Standard Model has 30 particles. Only 4 particles (all in the boson family) don’t have antiparticles and that’s the photon, the Z boson, the gluon and Higgs boson.
Building on the Standard Model’s data, many theories has been proposed to unify this zoo of particles. String theory notices that the SM assume particles to be point-like (infinitively small), and proposes that, instead, particles are infinitively narrow strings. Others have suggested that particles were themselves composed of smaller (usually three) particles called preons.
Alot of observations, nowadays, show us that the Standard Model is getting a bit old – for instance it does not account for dark energy, dark matter, neutrino oscillation, general relativity, etc.
But, it is nevertheless the only model which has successfully united all particles under only one roof. And, in that respect, I think it should be fair for it to receive, at the very least, the title of ToNE – a Theory of Nearly Everything.
Part 5: Zero-Point Energy
Until the advent of quantum mechanics, we assumed that absolute vacuum, that is, absolute nothingness, would have no energy. Unlike matter, utter nothingness cannot form breezes like air does, it cannot carry mechanical waves like water does, it cannot get heated up like iron does. So, we thought it meant that absolute nothingness would have no energy whatsoever.
It turns out that quantum mechanics predicts otherwise. And it turns out it has been proved right. Even total emptiness still has energy – in fact, energy can never reach below a certain level. This minimum energy is called, the Zero Point Energy. Here’s the mechanism behind this energy spread across the Universe:
Imagine utter nothingness. If I was to ask you, please prove me that this nothingness is truly without any particles, you would have a rather hard time doing so. Because Heisenberg’s Uncertainty principle states that one cannot measure a particle’s value without influencing another value, it models space (and empty space) like an ocean of probabilities. This means that one has no way of proving that energy does not exist there – actually, it probably does exist at any point of space-time.
Since one can never know (because of Heisenberg’s Uncertainty Principle) if a particle (including energy particles) is or is not exactly at one place in space and time, then we can’t prove that energy is not present at any given points in space and time. Thus all of space-time has the probability of being filled with non-zero energy.
Additionally, this non-zero energy’s existence has been verified. At atmospheric pressure, you can never freeze helium-4. This is because zero-point energy is present everywhere, including the Earth, and counters the effect of the helium-4’s cooling. Even at absolute zero Kelvin, helium-4 will never become solid, because zero-point energy actually heats it up a bit. Even at its absolute zero point, energy of a system cannot reach absolute zero.
The omnipresence of the Zero-Point Energy makes it a form of energy which never need refuelling (it is present even in utter nothingness), yet always yields an output (it actively interacts with objects). This is why many energy enthusiasts reasoned that tapping into the Zero-Point Energy could solve the world’s Energy Crisis. Yet these enthusiasts received unanimous derision from the science community.
Well, allow me to explain why:
Although Zero-Point Energy is indeed, by popular definition, “free” (it never runs out, it never requires input), it is, nevertheless, a form of energy which cannot be harnessed. This is precisely because of the fact that zero-point energy is so omnipresent.
A simple analogy: Imagine a world where nothing can ever reach below room temperature. One could try to build a device to harness this heat, for instance by building a thermopile. A thermopile works by detecting a temperature difference and directly converting it into electricity. Now, if nothing outside the thermopile can reach below room temperature, then it means you’ll always have free heat to run the thermopile, right?
Well, this would be a brilliant reasoning but there is one tiny flaw in this logic: the thermopile’s components, too, can never reach below room temperature. Thus, there is no temperature difference between the source of “free heat” energy and the harnessing device. Which means, the thermopile sees zero relative heat, and thus fails to harness the energy in any workable form.
Since most devices work on potential energy (the relative difference between two level of energies), then everything having a minimum energy doesn’t solve the problem of one still needing to create actual potential differences for such devices to work.