<P> Bilson - Thompson's original paper suggested that the higher - generation fermions could be represented by more complicated braidings, although explicit constructions of these structures were not given . The electric charge, colour, and parity properties of such fermions would arise in the same way as for the first generation . The model was expressly generalized for an infinite number of generations and for the weak force bosons (but not for photons or gluons) in a 2008 paper by Bilson - Thompson, Hackett, Kauffman and Smolin . </P> <P> Among other attempts to develop a theory of everything is the theory of causal fermion systems, giving the two current physical theories (general relativity and quantum field theory) as limiting cases . </P> <P> Another theory is called Causal Sets . As some of the approaches mentioned above, its direct goal isn't necessarily to achieve a TOE but primarily a working theory of quantum gravity, which might eventually include the standard model and become a candidate for a TOE . Its founding principle is that spacetime is fundamentally discrete and that the spacetime events are related by a partial order . This partial order has the physical meaning of the causality relations between relative past and future distinguishing spacetime events . </P> <P> Outside the previously mentioned attempts there is Garrett Lisi's E8 proposal . This theory provides an attempt of identifying general relativity and the standard model within the Lie group E8 . The theory doesn't provide a novel quantization procedure and the author suggests its quantization might follow the Loop Quantum Gravity approach above mentioned . </P>

Stephen hawking the theory of everything book summary