The Elusive Neutrino
The mystery to explain the origin of life continues to unravel
The Standard Model is our one-stop insight into three of the four fundamental forces of nature (except gravity). It achieves this through categorizing all 17 elementary particles, which act as carriers for these fundamental forces. For example, bosons are associated with the weak force.
It was the discovery of the Higgs’ Boson in 2012 that supposedly completed the Standard Model, now that scientists had identified the source of all mass in the Universe. And while this very important discovery had, and still does, its time in the spotlight, there was something more ghostly lurking right around the corner.
Fermions are elementary particles with half-integer spins, and further classified into quarks and leptons. One such lepton is the neutrino, categorized as such owing to the fact that it does not engage in strong interactions, rather just the weak and gravitational interactions. 3/17 positions in the Standard Model are occupied by the three flavors of neutrinos: the electron neutrino, the muon neutrino, and the tau neutrino. These three flavors are distinguished by the slight disparities in their masses, which together with the fact that there is nothing prohibiting neutrinos from transitioning between flavors, is responsible for the phenomenon known as neutrino oscillations. An oscillation is defined as the periodic change from one state to the other, and back again. One can envision this as motion similar to a pendulum swinging to and fro in a standing clock. From a quantum standpoint, the neutrino exists in a state of superposition of all three states simultaneously, eventually collapsing into one of those states when a measurement is made.
Neutrinos are produced in abundance as a result of radioactive decay, including natural nuclear reactions in the core of stars and artificially-induced nuclear reactions in particle accelerators. Our Sun is in fact the primary source of generating neutrinos that traverse space to reach the detectors on Earth. An intriguing dilemma posed by this neutrino journey is what is referred to as the solar neutrino problem. For the solar neutrinos detected on Earth, there also was calculated a mass difference between what was expected and what was observed. Scientists later managed to attribute this difference to the fact that neutrinos did indeed oscillate between their three flavors of different masses, enroute their journey to Earth.
Interestingly, neutrinos do not carry any electric charge but are still pivotal end-products of radioactive decay, as a way to conserve the lepton number on both sides of the reaction. They are produced in conjunction with their antiparticle, called the antineutrino. Antineutrinos also come in the same three flavors, carry no electric charge, and have the same mass as their corresponding neutrino; however, they have the opposite lepton number. While the neutrino has a lepton number 1, the antineutrino has a lepton number -1.
Both neutrinos and antineutrinos have miniscule masses, which explains why they only engage in the weak interaction and only very meekly with gravity. This is why scientists require a whole lot of them (millions to billions) in one place, in order to ascertain and distinguish their properties. Where they are not naturally generated in abundance, neutrinos are artificially manufactured. For example, the MINOS Experiment at FermiLab in the USA produces neutrinos by targeting protons at a carbon surface, that decay into mesons, which in turn decay to produce neutrinos. Because they do not bare any electric charge, only rarely interacting with matter, we feel next to nothing as billions of neutrinos pass through our bodies every second.
In reality, we may potentially have a far more inherent relationship with neutrinos. Looking back at the instant of the Big Bang, we know that matter and antimatter was produced in equal amounts, and upon contact would have annihilated each other to release vast amounts of energy. The Universe would have then just been an expanse of energies and nothing else. But that didn’t happen now, did it? How else do we explain the existence of planets and stars and everything in between? How else do we explain our own existence?
Something had to have happened to result in a kind of matter-antimatter asymmetry, such that matter particles exceed antimatter particles in number. A kind of reshuffling had to have occurred in order for an antimatter particle to morph into a matter particle, which can then justify the existence of anything but energy in the Universe. Scientists have since postulated that this phenomenon may as well have occurred, but at the very tiny scale of 1 in a billion (10 to the power of magnitude 9) antimatter particles. To put things into context, an average human comprises a billion billion billion particles (10 to the power of magnitude 27), and each of these particles itself then comes from a billion particles. That sure is a lot of particles! An especially staggering amount when we scale up to cosmological dimensions of planets and stars, for example.
But then what of this asymmetry? We know it was a matter particle, but what kind exactly? It had to have been one of the elementary particles, because those were all that existed at the time (we are looking back at a time when the Universe was about a hundredth of a millionth of a billionth of a billionth (10 to the power of magnitude -26) of a second old). In order for the antimatter particle to morph into its matter counterpart, it had to have undergone a kind of mirroring or reflection. The matter particle had to have looked something like we look when we peak in the mirror. Laterally inverted is the term. What is more is that in order for the lateral inversion to have occurred, the antimatter particle would had to have had at least three vertices. It had to have been an elementary particle bound in a three-way loop, like a triangle. This criterion alone rules out quarks, bosons, and all leptons other than the neutrino.
The neutrino is the only elementary particle with three flavors, to take up the three vertices of the triangle. The pieces start falling into place because both the neutrino and the antineutrino (its antimatter counterpart) do not carry an electric charge, and so do not require an external trigger or interaction in order to morph into each other. One assumption we make in this otherwise very empirical rhetoric, is that neutrinos tend to morph or decay into matter particles more often than into antimatter particles, which can then explain an excess of the former particle.
Another interesting and recent development regarding the neutrino has come from the NEMO experiment, working to prove the existence of the neutrino as a Majorana particle, which would mean it is its own antimatter particle. Now this would make things A LOT more simple.
While this is simultaneously bewildering and convincing, it is yet to solidify as a theory. As the titular remark at the head of this article, the neutrino is indeed an elusive particle, and not a lot is known of its extensive range of behaviors because of its somewhat inert nature. However, experiments as MINOS and NEMO are on the brink of unveiling further neutrino properties, as they further scrutinize neutrino masses and oscillations. One thing heralded true regardless, is the piqued interest of the scientific community to understand the nature of neutrinos, having come so close to attributing it to the existence of life itself.
