It’s merely a tendency of the human mind – to accept law and order as though set it stone and abide by it religiously. After all, the simplicity of not having to process information at every instance is a luxury we can’t afford to take for granted and ignore. The art of science says otherwise. Do not accept anything as set in stone. A statement holds true only until it is proven wrong – this is a scientific theory. This harsh truth binds the threads of science and holds true in all scenarios.
This tendency favours accepting organised data over disproving it. Though beneficial at times, it hones the tendency to overlook errors and accept statements blatantly. One such victim lies in my dear realm of physics – particle physics. The victim is none other than the Standard Model of Particle Physics.
The widely accepted Standard Model provides a mathematical description of the elementary particles of matter, the electromagnetic, weak, and strong forces. It can be split into two – fermions and bosons. Fermions are the matter particles and bosons are the corresponding force carriers. We can probe deeper into the divisions and learn that fermions have two families (quarks and leptons. Similarly, bosons can also be sub-grouped however this is beyond the scope of this article).
The beauty and simplicity of the Standard Model lies in the fact that it can couple nearly ever fermion to a boson. It can explain the spins and masses of fermions and bosons. It can swiftly present all this data in a concise format. It can make predictions that match observations. All in all, it is a mass pleaser.
But mass pleasers may be deceptive.
Disappointment no. 1
The Standard Model does not include gravity. It’s that piece of the puzzle that has one of its corners abnormally shaped and simply won’t fit into the puzzle board comfortably. On the grand scale, gravity is an incredibly powerful force. It’s the force that keeps us spiralling around the Milky Way: it’s the force that drives black holes. However, upon deeper inspection, its power turns feeble.
Gravity is the weakest force we have. Its strength is such that the Standard Model seems to work adequately efficiently by merely ignoring its presence. Adding numbers we see that gravity is 1033 times weaker than the well-known electromagnetic force. There is a method to this madness - with a pinch of fortune-dust.
The lack of gravity in the standard model is a byproduct of the incompatibility of Einstein’s theory of relativity and quantum mechanics. In the context of the standard model, no theory has been able to blend the two. This includes string theory and loop quantum gravity. Particle physics seems to have slipped the checks of science by ignoring gravity due to its insignificant strength when compared to other fundamental forces. However, this incompetency cannot be taken for granted. A complete model does not exclude oddities – it supports them with an appropriate explanation.
Disappointment no.2:
Picture the puzzle scenario again. The maker has provided the pieces but there seems to be a bizarre issue. Each piece has a dramatically different size. Some large, some small, there’s no way you can build a complete picture to scale with these awkward pieces. So, what do you do? You improvise! You fit the pieces in despite the strangeness. You still see a complete picture albeit a distorted version of the expected reality. This is the Standard Model.
Dubbed the Hierarchy problem, this issue addresses the large differences in the strengths of the fundamental forces. It also highlights the issue of having a large range of masses for the elementary particles.
Tie in the Higgs Boson to this crisis to help solve the issue and quite the contrary occurs. The basic mass is taken as the mass of the Higgs Boson. This mass is adjusted and applied to the masses of each particle that it interacts with as a correction factor. The larger the mass of the particle, the larger is the correction factor associated with it. In short, take this to extremes and it breaks apart giving absurd values of correction factors. Let’s test this with the heaviest particle – the top quark. This adds an extremely large correction to the ‘theoretical’ Higgs Boson mass that leads theorists to ponder how the observed mass of the Higgs Boson was as small as it was. Nearly all my lab partners and I have encountered an uncertainty calculation that tells us something like the length of a component is 50cm give or take 50 cm. This is exactly what this scenario looks like for particle physics.
These erroneous values suggest that perhaps particle physicists are yet to discover undiscovered particles that can correct the correction itself. These undiscovered particles should cancel out the erroneous corrections to the Higgs mass from the top quark to resemble the observed mass. SUSY – more formally known as Supersymmetry – pledges to house exactly such a particle.
But particle physics may seem unwelcoming. This isn’t the first time scientists have had to face the harsh reality that expectations don’t always match reality. The correction factors due to the top quark result in an large expected value of the mass if the Higgs – close to the maximum possible energy scale of the theory i.e the grand unification scale at around 1019 GeV. The observed mass? 125 GeV. Perhaps the Standard Model is effective only at the weak scales. It is fair to say that the model itself needs corrections.
Disappointment no.3
The delicate Standard model refuses to appreciate an existing entity – it deems neutrinos massless. This is untrue. To understand this, we need to understand the concept of chirality. This property allows particles to have either left-handedness or right-handedness. Particles can switch their chirality by interacting with the Higgs field by either ditching or accepting weak hypercharge. Inevitably, this results in interactions with the Higgs boson. Simply put, a left handed electron can mutate into a right-handed electron should it collide with a Higgs Boson in the vacuum of space by getting rid of this excess weak hypercharge. This interaction is what gives it mass. Similarly, one may expect the neutrino to behave likewise. But it doesn’t. Neutrinos don’t exist in the right handed state. Left-handed neutrinos simply can’t change states – or oscillate - into right handed neutrinos. Consequently, this implies they hypothetically do not interact with the Higgs field. Hence, they may have zero mass.
Alas! This prediction was proven wrong. Neutrinos come in three flavours – electron, muon and tau, and can oscillate from one flavour to another. If neutrinos had zero mass, they’d essentially travel at the speed of light and would not experience time. The SuperKamiokande collaboration conducted an experiment that challenged this to its core. This collaboration observed neutrinos high in the atmosphere which occurred as a result of oxygen and nitrogen nuclei being bombarded by cosmic rays. These are primarily muon neutrinos. The detector, hidden beneath a rocky mountain in Japan, hold 50,000 tonnes of water. These atmospheric neutrinos interact with water nuclei to produce electrons, muons or tau leptons. The newly created particles travel faster than the speed of light in water emitting Cerenkov radiation which is then observed by the photomultiplier tube detectors. This interaction is proves that neutrinos experience time, hence they can partake in collisions. Thus, they do not travel at the speed of light nor are they massless.
Disappointment no.4
We exist. Stars exist. Galaxies exist. This shouldn’t be the case.
The universe began with a big bang. The huge burst of energy should have evolved to produce equal amounts of matter and antimatter in a phenomenon dubbed CP symmetry. When faced with each other, matter and antimatter annihilate one another. This clearly didn’t occur. All the matter we see is not made of antimatter. It’s matter.
The Standard Model cannot explain this. The CP violation, short for charge-parity violation, represents this minute imbalance that occurred at the start of the known universe giving us the universe we know. The best way to study this imbalance is to recreate the conditions of the Big Bang in a massive particle accelerator synonymous to the Large Hadron Collider at CERN. By smashing these particles together, one can study what particle it is that is left out of the blend to account for the oddness that left the universe the way it is.
An elusive particle, the heavy neutrino, seems to be an ideal candidate to explain the disparity. If observed, it has the potential to prove that for every billion pairs of matter and antimatter that existed, there is one extra matter particle. Though this is a mere ten times more mass than the mass leftover from the Big Bang, it is a reasonable estimate in a universe that is governed by uncertainty principles.
What began with plum puddings and gold foils has now advanced to massive particle accelerators. What began as curiosity has now blended into a reality which deciphers the enigmas of the miniscule, daily. The Standard Model falters a lot. It leaves blank spaces. It stammers. It hiccups – but every once in a while, it gives a speech that leaves me dumbstruck. Take the instance when the LHC observed that the Higgs Boson does indeed decay into a pair of bottom quarks. This was a prediction fresh out of the Standard Model. And it passed the test.
While science relies on this to support what is discovered, what this theory requires is a makeover to make it compatible with what the universe has to offer. Till then, it’s feet shall remain grounded on this planet, snug at the LHC.
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