God, The Time Traveller Designer Universe Maker

Lecture 6

Back to Lee Smolin

“In a background dependent theory, the properties of the elementary entities have to do with their relationships to the background. This is clear in ordinary quantum field theory, where we understand particles to be representations of the Poincare group and other externally imposed symmetries and gauge invariances. In these theories the particle states are labeled precisely by how they transform under symmetries of the background. The specification of the gauge and symmetry groups are indeed part of the background, because they are fixed for all time, satisfy no dynamical principles and do not evolve.”

Comment 14: Smolin is only talking absolute global symmetries. Local symmetries do evolve and are relational. Normally we only locally gauge the internal symmetries. We also only spontaneously break them in vacuum/ground states. The relational lesson of general relativity is to locally gauge even the space-time symmetries and perhaps spontaneously break some of them as well.

Back to Smolin:

“The search for an explanation of the properties of the elementary particles within quantum field theory and string theory has been based on three hypotheses:

Unification: All the forces and particles are different quantum states of some elementary entities.

This elementary entity was at first thought, by Einstein and his friends, to be a field, giving rise to the once maligned subject of unified •field theory. In more recent times it is thought to be a string. These are not so far apart, for a low energy approximation to a string theory is a unified •field theory. So most actual calculations in string theory involve classical calculations in unified field theories that are descendants of the theories Einstein and friends such as Kaluza and Klein studied many years ago.

But is unification enough of a criteria to pick out the right theory of nature? By itself it cannot be, for there are an infinite number of symmetry algebras, which have the observed symmetries as a subalgebra. There is however a second hypothesis which is widely believed.

Uniqueness: There exists exactly one consistent unified theory of all the interactions and particles.

If this hope is realized, then it suffices to •find that one unified theory. The first fully consistent unified theory to be found will be the only one that can be found and it will thus have to be the true theory of nature. It has even been said that, because of this, physics no longer needs experimental input to progress. At the advent of string theory, this kind of talk was very common. The transition from physics as an experimental science to physics based on finding the single unified theory was even called the passage from modern to postmodern physics.

Given that, in a background dependent theory, particles are classified by representations of the symmetries of the vacuum, it follows that the more unified a theory is the larger the symmetry of the background must be. This leads to the conjecture of

Maximal symmetry: The unique unified theory will have the largest possible symmetry group consistent with the basic principles of physics,such as quantum theory and relativity.

These three conjectures have driven much of the work in high-energy physics the last three decades. They led first to grand unified theories (large internal gauge groups), then to higher dimensional theories (which have larger symmetry groups) and also to supersymmetry.”

Comment 15: Supersymmetry is badly, probably spontaneously, broken in the actual physical vacuum of our pocket universe. Supersymmetry demands that the cosmological constant /\ = 0. That is ALL UNIFORM zero point energy density is absorbed into the coherent geometrodynamical field of Einstein. Differences of zero point energy from boundaries as in the Casimir force and Lamb shifts are of course still observable in a supersymmetric world. However, Steven Weinberg showed in the 1980’s that /\ = 0 would not allow carbon-based life to form! In fact /\ ~ 0.73 current critical density of the universe. The dark matter is ~ 0.23 current critical density. The total density is ~ critical density. Lenny Susskind predicts it will a tiny bit less giving negative space curvature. Right now we know the actual total density is equal to the critical density to an error of 2%. This /\ = 0 is the boring flat plateau (Mesa) in the cosmic landscape of megaverse, the infinity of pocket universes partitioned off from each other by causal horizons even when on the same infinite sheet inflation bubble. Our pocket universe had to have a slow roll down to the edge of a ledge on the cosmic landscape, then a sudden plunge to the low intensity anti-gravity repulsive cosmic field /\ > 0 we observe today that caused a reheating to the hot Big Bang. Note that if w = - 1 then /\ is a constant of the motion of the expanding accelerating space of our pocket universe. All other forms of energy dilute out so that in the far future /\ is 100% of the total critical density. /\ is the constant asymptote of the far future of our pocket universe if there is no metric engineering by advanced intelligence that to us looks like God! Intelligent Design is then Metric Engineering on the Grand Scale.

## Sunday, January 22, 2006

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