Monday, 29 April 2013

Antimatter- Something Rather than Nothing

Like skis and skates, stuff came in pairs. Pairs that annihilated one another, shared mass but differed in charge and spin. It's the Jekyll and Hyde personality of particles that corresponds to the existence of matter and antimatter; Dirac envisaged a sea of negative energy levels, each filled with a pair of electrons of opposing spin with the positron appearing as a 'hole' in the sea as a state with a positive charge and energy. While Feynman and Stueckelberg likened negative energy particles moving backward in time to positive energy antiparticles moving forward in time. But the ultimate question remains the origin of the asymmetry of matter, and why unlike a world filled with antiparticles or emptiness, we are made of matter anyways; why there is something rather than nothing. Let's look back at the early universe, before primordial nucleosynthesis and into baryogenesis; the making of baryons and antibaryons. Sakharov noted three conditions necessary for the production of the baryon asymmetry namely; the violation of baryon number, violation of C and CP symmetry and a withdrawal from thermal equilibrium. Electroweak theory, the synthesis of the electromagnetic and weak interactions, incorporates gauge symmetries useful to explaining the matter asymmetry and fulfilling the Sakharov prerequisites; just like a hot iron ferromagnet with a series of randomly spinning electrons exhibiting rotational symmetry which may be broken and magnetised when cooled and aligning the spins, the weak symmetry breaks giving W and Z bosons mass via the Higgs field and preserves the electroweak symmetry keeping photons massless. So during the early epochs, the universe must have cooled down to a critical temperature like the ferromagnet, causing the electroweak phase transition out of thermal equilibrium to form like bubbles in boiling water, breaking the symmetry. At first sight, the electroweak interaction also  seems to apparently conserve the baryon number but this may be violated in the current phase of broken symmetry via quantum tunneling but during the early universe, a barrier to fluctuation was not present and the baryon number was permitted to vary freely. But how can electroweak theory account for the differences between matter and antimatter? Like a roulette wheel likely to land in a spot of equal probability, a tilted wheel is biased toward a particular symmetry breaking much like the violation of charge conjugation (C) and parity (CP). Charge conjugation ensures the interchanging between particles and antiparticles while parity preserves spin but reverses direction; so here the CP symmetry can counteract particle production with antiparticles leading to annihilation, but how did a bit more matter than antimatter end up being made? The electromagnetic and strong interactions have C and P symmetries but the weak force violates it through the beta minus decay of kaons, thus the quark components of baryons should also be able to violate it through weak interactions and break the symmetry. Now that we've fulfilled the prerequisites via electroweak theory, it can be speculated that the initial early universe was full of a symmetric phase but as the phase transition broke the symmetry, bubbles formed and baryon number was violated out of thermal equilibrium; it may be further hypothesised that as the bubbles spread cross the universe via a plasma of particles  and antiparticles, quarks were sealed in the bubbles, leaving their baryon number unscathed  whereas the antiquarks were annihilated creating the asymmetry. However, the traditional Kobashi-Maskawa CP violation may prove inefficient as all quarks other than the 'top' are remarkably light compared the W boson; necessitating a new type of symmetry violation that will allow the weak interaction to manipulate the charge and flavour of all six quarks indiscriminate of their masses. A saga to be continued...

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