26 Anthropic Principle
199
26.2 Many Universes and the Anthropic Principle
Of course one could always ask who determined the principles, such as the
gauge symmetry, that we use to derive the standard model. Questions like
these have led to the idea of extra dimensions where the gauge forces are
related to the hidden dimensions. This was first noted by T. Kaluza and Oscar
Klein in the early part of the last century. In 1919, Theodor Kaluza extended
Einstein’s theory of general relativity to five dimensions—four space and one
time—instead of three space plus one time. The space-time metric, which was
the fundamental entity in Einstein’s theory and has ten components in four
dimensions, now has fifteen components. Kaluza identified the ten of them
with Einstein’s gravity, but of the remaining five, he could show that four of
them are like the photon field, which is a gauge field, whose generalization is
embodied in the standard model. The idea that the fifth dimension should be
small and invisible (called compactification) was suggested by Oscar Klein in
1926. Thus, it is plausible to ask whether the gauge symmetry of the standard
model, which gives rise to forces, can be derived from a theory with more than
the three familiar space dimensions.
The question then gets transformed to “where did the extra dimensions
come from?” String theory tries to answer this by using a set of theoretical
principles, which says that there have to be extra space dimensions with
the total number of space-time dimensions being either twenty six or ten.
The question becomes: what principle determined how we got to the visible
3 + 1 dimensional space-time? This is where the anthropic principle seems
to come in. One looks at the possible lowest energy states where the four
dimensional universe can exist in the string theory. String theorists have argued
that there are a huge number of such ground states (∼10
500 by some count)
and our universe is but one of them [96]. Since all these ideas are string theory
motivated, presumably the principles remain like before, i.e. extra dimensions
leading to gauge principle on compactification. The next question that arises
is what are the values of the force strength parameters in all these universes?
This is where one may invoke the anthropic principle and claim that the
distribution of strength parameters is random, and life and the universe as we
see developed only in the one we live in. It almost makes sense and may even
prove compelling. That would mean we need not strive hard to understand the
force strengths and other properties of the standard model. Science could then
come to a halt beyond making “grungy” calculations using these parameters.
199
26.2 Many Universes and the Anthropic Principle
Of course one could always ask who determined the principles, such as the
gauge symmetry, that we use to derive the standard model. Questions like
these have led to the idea of extra dimensions where the gauge forces are
related to the hidden dimensions. This was first noted by T. Kaluza and Oscar
Klein in the early part of the last century. In 1919, Theodor Kaluza extended
Einstein’s theory of general relativity to five dimensions—four space and one
time—instead of three space plus one time. The space-time metric, which was
the fundamental entity in Einstein’s theory and has ten components in four
dimensions, now has fifteen components. Kaluza identified the ten of them
with Einstein’s gravity, but of the remaining five, he could show that four of
them are like the photon field, which is a gauge field, whose generalization is
embodied in the standard model. The idea that the fifth dimension should be
small and invisible (called compactification) was suggested by Oscar Klein in
1926. Thus, it is plausible to ask whether the gauge symmetry of the standard
model, which gives rise to forces, can be derived from a theory with more than
the three familiar space dimensions.
The question then gets transformed to “where did the extra dimensions
come from?” String theory tries to answer this by using a set of theoretical
principles, which says that there have to be extra space dimensions with
the total number of space-time dimensions being either twenty six or ten.
The question becomes: what principle determined how we got to the visible
3 + 1 dimensional space-time? This is where the anthropic principle seems
to come in. One looks at the possible lowest energy states where the four
dimensional universe can exist in the string theory. String theorists have argued
that there are a huge number of such ground states (∼10
500 by some count)
and our universe is but one of them [96]. Since all these ideas are string theory
motivated, presumably the principles remain like before, i.e. extra dimensions
leading to gauge principle on compactification. The next question that arises
is what are the values of the force strength parameters in all these universes?
This is where one may invoke the anthropic principle and claim that the
distribution of strength parameters is random, and life and the universe as we
see developed only in the one we live in. It almost makes sense and may even
prove compelling. That would mean we need not strive hard to understand the
force strengths and other properties of the standard model. Science could then
come to a halt beyond making “grungy” calculations using these parameters.