Generic predictions of quantum theories of gravity

[marcus]

this just out

http://arxiv.org/abs/hep-th/0605052
Generic predictions of quantum theories of gravity
Lee Smolin
For inclusion in "Approaches to Quantum Gravity - toward a new understanding of space, time, and matter", edited by D. Oriti, to be published by Cambridge University Press

"I discuss generic consequences (sometimes called "soft predictions") of a class of background independent quantum theories of spacetime called causal spin network theories. These are theories whose kinematics and dynamics is based on the evolution of labeled graphs, by local moves, such as in loop quantum gravity and spin foam models. Some generic consequences are well known, including the discreteness of quantum geometry, the elimination of spacetime singularities, the entropy of black hole and cosmological horizons and the fact that positive cosmological constant spacetimes are hot. Within the last few years three possible generic consequences have come to light. These are:

1) Deformed special relativity as the symmetry of the ground state,

2) Elementary particles as coherent excitations of quantum geometry,

3) Locality is disordered.
I discuss some possible experimental consequences of each."

 

[marcus]

this thread is in case anyone wants to discuss Smolin's new paper (for inclusion in Oriti's book----we have a dozen or so other chapters of that book already)

http://arxiv.org/abs/hep-th/0605052
Generic predictions of quantum theories of gravity

In particular the 3 classes of prediction that he listed and what Smolin gives as

possible experimental consequences

Here are the three kinds of prediction he says he is going to mention experimental consequences of.

1) Deformed special relativity as the symmetry of the ground state,

2) Elementary particles as coherent excitations of quantum geometry,

3) Locality is disordered.

 

[marcus]

It might be interesting to discuss this paper in comparison with Distler's recent

"Falsifying String Theory Through WW Scattering"

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Smolin's paper makes the point right at the start that he is talking "soft" predictions from a class of different unification models----and that prediction can have more than one function.

Besides falsifying a definite specific model, when you have a hard prediction from that model and observation denies it----admittedly an important part of the scientific process----there can be interesting predictions which get us looking for new stuff in nature that can be observed if it is there (but which we otherwise might not have thought to look for).

Like modifications of conventional symmetry. this can have a value in its own right.

Smolin discusses this---I think in a wise and perceptive way.

He also points to cases where some certain QG theories are extremely exposed to falsification----talking hard definite predictions and it being fatal if you observation doesn't confirm.
See page 18 third paragraph "vulnerable to quick falsification".

But the whole paper is not about falsifiability! It is more general and covers a range of generic predictions----I think I counted 6 or 7, so there are others besides the 3 mentioned in the abstract.

 

[marcus]

To give an overview---some general statements.

He is talking about unification theories----or theories in progress. what he singles out as representative are graph theories in which the dynamics is described by local "moves"

a move is where you insert or delete a vertex, or you reconnect some nearby vertices in a different way.

and the labeling of the graphs can be either a Lie algebra or a quantum group (also a kind of algebra)

have to go, back later.

the surprising thing is that these kinds of graph theories are rich in prediction---like matter, or in the case of Freidel, predicting a quantum field theory in the zero-gravity limit. so there are things to check, to see if the QFT is right, or to see if it predicts the right particles.

have to clarify and edit this, back later.