5.2 Quantum fields and unification

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The success of electroweak unification has been one of the motivations for suggesting that all three of the forces that appear in the standard model might be unified within a grand unified theory, and that a further step of unification might also incorporate gravity, thus bringing all four fundamental forces within a single superunified theory. The form that such a superunified theory might take is far from clear. Would it involve quantum fields in a curved space-time, or would something altogether more radical be required?

Figure 1.35 A possible route to superunification of the four fundamental forces. At low energies we have laboratory evidence of four forces, but the weak and electromagnetic forces are known to acquire a common strength at high energies. Perhaps this process continues. Click here for larger image (11.88kb)

For some time many hoped that an approach called string theory might provide a solution to the problem of superunification. The idea of this approach was that the basic entities were not quantized fields that filled the points of four-dimensional space-time, but rather extended objects called strings that vibrated in ten or more dimensions. There was never any experimental evidence to support this idea, but what really caused theorists to lose faith in it was the discovery that string theory is not unique. There is a strong prejudice amongst those searching for a unified theory of everything that there should only be one such theory, not a whole class of them. String theory fails to satisfy this uniqueness criterion. However, hope of string-based superunification has not been entirely lost. A new subject called M-theory is being investigated in which all of the plausible string theories appear as different aspects of a single theory - perhaps.

At the present time, the quest to find the ultimate constituents of the Universe and the laws that regulate their behaviour ends not with an answer, but with a set of loose ends. Perhaps this is as it should be in a healthy science, or perhaps it is a sign that we are heading towards a dead end. Perhaps there is no single world-view for physics to uncover, or perhaps it is not the function of physics to do so.

Question 1.7 Answer Does quantum field theory suffer from the same kind of conflict with simple realism that arose in quantum mechanics?

Continue on to 5.3 The end of physics?