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One of the principles on which physicists rely is the idea of symmetry: a magnetic attraction consists of a positive and a negative charge, physical processes can happen forward (in time) or backward, particles are created with antiparticles and are destroyed with antiparticles. The idea that matter can be created from energy has been a great tool for cosmologists in postulating how the universe could have come into being. The problem is this: if every particle is created with an antiparticle counterpart, what has happened to all of the antimatter? By the rules of symmetry, there should be just as much antimatter out there as there is matter in our universe- in fact, there should be a whole universe full of it. We shouldn't have much trouble finding such a universe: at the boundary between a universe filled with matter and one with antimatter, intense gamma radiation from the interaction between the two kinds of particles should be clearly visible....but it''s not. Apart from the occasional antiproton found in cosmic rays, our universe is made up of matter and matter is all we can see. In the 1970's, under the development of GUTs (Grand Unified Theories), a prediction was made that protons are unstable and decay into positrons and pions. The pion decays into two photons, while the positron collides with an electron to produce two more photons. In this example, matter is transformed into pure radiation energy- and according to symmetry, this process can be reversed, which implies (in the ideal realm of GUTs, that is) that energy can turn into matter without the production of antimatter. While this theory hasn't exactly been embraced by modern physics, it is indicative of the attempt by most physicists to unite the highly appealing concept of symmetry with the apparent asymmetry observed in the universe. |
