Kalimera Fotini!

I'm reading your latest hep-th/0302111 v3 [Ref. 1], and recalled your talk three years ago at Imperial College, "What the universe looks like from the inside", based on your gr-qc/9811053 [Ref. 2]. After you delivered your ideas, we talked at the cafeteria, remember?

You still firmly insist on the conjecture that "everything is (locally) finite", and I still firmly insist on my objection that you can not -- even in principle -- suggest a truly *background independent* model suitable for quantum gravity,

http://members.aon.at/chakalov/Schwarz.html#note

In your latest hep-th/0302111 of Mon, 4 Aug 2003 13:04:19 GMT, which will appear soon in Classical and Quantum Gravity [Ref. 1], you acknowledged that "QCH is not a completely background independent description", and that this crucial requirement "will not be resolved here".

Because your model involves a fixed causal structure, I'm afraid you just can't make it.

The issue is very old, it goes back to Lao-tzu: "If you realize that all things change, there is nothing you will try to hold onto". See the catch? If you introduce some fixed causal structure to describe how all things change, you need to "hold onto" something, and hence your model is not -- and can not -- be background-independent. The reason is that you firmly insist on staying confined "inside the universe" where "everything is (locally) finite".

My informal proposal which I tried to explain in the cafeteria in Imperial was about a new reference object w.r.t.w. you can have causal dynamics "inside" the universe, and a perfectly background independent description "inside" the universe. Only this hew reference object is "outside" the universe: the Holon,

http://members.aon.at/chakalov/faq.html

You wrote in gr-qc/0210086 v2 [Ref. 2]: "We only really understand the quantum mechanical evolution of ordinary systems, where an external time is always unambiguously present."

I'm afraid we don't understand it,

http://members.aon.at/chakalov/Zurek.html#note

http://members.aon.at/chakalov/Zeh.html#note

Of course, I will be all wrong if only you could get rid of any background whatsoever in your model, while staying confined "inside" the universe.

BTW I liked very much the excerpt from Boltzmann: "Every Tom, Dick and Harry felt himself called upon to devise his own special combination of atoms and vortices, and fancied in having done so that he had pried out the ultimate secrets of the Creator" [L. Boltzmann, Verh. Ges. D. Naturf. Aerzte, 1, 99 (1899)].

If some day you come to London to deliver another talk at Imperial, please drop me a line, okay? We will have a lot of fun!

Best wishes,

Dimi
http://members.aon.at/chakalov
--
Dead matter makes quantum jumps; the living-and-quantum matter is smarter.
 

References

[Ref. 1] Eli Hawkins, Fotini Markopoulou, Hanno Sahlmann, Evolution in Quantum Causal Histories, hep-th/0302111 v3

"5) The theory should be background independent. (...) Clearly, this implements the first four properties above. The fifth is more difficult (and will not be resolved here). Because it involves a fixed causal structure, a QCH is not a completely background independent description. Nevertheless, all other degrees of freedom are quantum, and with the algebraic treatment presented here this may be a step toward a truly background independent model.
...

"Everything is (locally) finite, both the dimensionality of these systems as well as the causal set. We regard this as a simple way to model the idea that there is a finite number of fundamental degrees of freedom in a finite region of the universe.
...

"It is interesting to note the multiple ways that quantum causal histories can be motivated, including:
[snip]

"3. As an alternative to the usual quantum cosmology of a wavefunction of the universe evolving according to the Wheeler-DeWitt equation. A QCH is a framework for quantum cosmology that is not restricted to globally hyperbolic spacetimes, as is the case with a WDW-type quantum cosmology. This is discussed in more detail in [15].
...

"In this new formulation, with the completely positive maps as the fundamental evolution operators, we obtain a quantum cosmology in which the universe is simply a very large collection of finite quantum systems. The information gets shuffled around, according to the causal structure. Local observers can lose information simply because, by causality, it is not available to them."
 

[Ref. 2] Fotini Markopoulou, Planck-scale models of the Universe, gr-qc/0210086 v2

"Several models of the microscopic structure of spacetime have recently been proposed. Different ones were constructed based on different motivations, but they have several features in common which I list here:

"D Quantum theory is still valid.

"E Since we are modelling the universe itself, the model should be background independent.
...

"2.2 Quantum cosmology

"An example of such a state is the Chern-Simons state in loop quantum gravity. This is to "evolve" according to the Wheeler- DeWitt equation,

   H|Psi_univ = 0;                        (2)

where  H  is the quantization of the Hamiltonian constraint in the 3+1 decomposition of the Hilbert-Einstein action of general relativity, a hermitian operator.

"There are several issues with this. First, the simple form of the equation and especially the peculiar righthand side hides the fact that we need to quantize relativity, a background-independent theory. We only really understand the quantum mechanical evolution of ordinary systems, where an external time is always unambiguously present.

"Second, equation (2) only works for spacetimes that are globally hyperbolic. Third, one can argue that  |Psi_univ>  and eq. (2) do not have a satisfactory physical interpretation:  |Psi_univ>  is the state of the entire universe and thus only accessible to an observer outside the universe (or specific observers in special universes, such as the final moment of a spacetime with a final crunch, etc). A satisfactory theory of quantum cosmology has, instead, to refer to physical observations that can be made from inside the universe (Markopoulou, 1998) (see the diagram in Fig. 5).
--
Markopoulou F, 1998, The internal logic of causal sets: What the universe looks like from the inside", Commun. Math. Phys. 211 (2000) 559-583 (gr-qc/9811053)
 

==============
 

Subject: Disordered reality in loop quantum gravity
Date: Fri, 09 Feb 2007 05:12:47 +0200
From: Dimi Chakalov <dimi@chakalov.net>
To: Fotini <fotini@perimeterinstitute.ca>
CC: loll@phys.uu.nl, lsmolin@perimeterinstitute.ca

Fotini dear,

I read your gr-qc/0702044 v1, and recalled your talk seven years ago at
Imperial College, "What the universe looks like from the inside", based
on your gr-qc/9811053. After you delivered your ideas, we talked at the
cafeteria, remember?

I guess you can't.

In your gr-qc/0702044 v1, you wrote: "A key issue facing loop quantum
gravity is the problem of the low energy limit (...)".

Why is this obsession with the low energy limit? The most acute issue is the problem with reality in GR, as recognized by Einstein long before 1915. First things first, right? See

http://www.god-does-not-play-dice.net/Xiao.html#LQG

I know from your interview in Scientific American (December 2002) that you cook very well, and that your strength is "to put things together out of nothing". But I'm sure you'll never switch to cooking, even if you lose another seven years by searching in the wrong direction.

Why don't you start with recovering reality in GR? I think it looks far more promising than the low energy limit and locality.

Take care,

Dimi
--
http://www.god-does-not-play-dice.net/Straumann.html#hobby
It is extremely difficult to induce penguins to drink warm water
John Coleman
------

=============

Subject: Re: Disordered reality in loop quantum gravity
Date: Tue, 31 Jul 2007 18:37:00 +0300
From: Dimi Chakalov <dimi@chakalov.net>
To: Fotini <fmarkopoulou@perimeterinstitute.ca>
Cc: Luca <bombelli@olemiss.edu>

RE: Class. Quantum Grav. 24 (2007) 3813-3823

Hi Fotini,

See my comments under my email from Fri, 09 Feb 2007 05:12:47 +0200,
http://www.god-does-not-play-dice.net/Fotini.html#last

If you continue to ignore my critical remarks made in the past seven years, please bear in mind that you are not ignoring 'some guy from Bulgaria', but Aristotle.
http://www.god-does-not-play-dice.net/Trautman.html#pedestrians

I will include Luca in CC: list, because you mentioned him in 'Acknowledgments'.

Take care,

Dimi
----------
 

Note: My (hackneyed, I'm afraid) remarks made in the past seven years were totally ignored, and the paper was published:

Fotini Markopoulou and Lee Smolin, Disordered locality in loop quantum gravity states, Class. Quantum Grav. 24 (2007) 3813-3823.

p. 3814: "We argue that so long as the non-local links are sufficiently uncommon, explicit non-local interactions will be difficult for local observers to detect as local effects."

pp. 3820-3821: "If we had under control a Hamiltonian operator, in the presence of appropriate boundary conditions or gauge fixing, which had been shown to be positive definite, we would be able to find the ground state and compute whether locality is disordered or not. In the absence of such a Hamiltonian, one can at least try to see if the kind of local evolution rules we find in LQG have the tendency to eliminate non-local links.

"... a long series of local moves can introduce a non-local connection to an otherwise local weave state. (...) Finally, once non-local links exist, there are exchange moves involving them which will produce more non-local links, as shown in [19, 20]. (...) (T)here is no evidence that the dynamics in LQG suppresses or eliminates non-local links, once they are present."

p. 3822: "Given that there is a range of P such that disordered locality would not be easily detectible, we can go on to investigate whether there might be consequences for cosmological problems such as dark energy or super horizon correlations. This will be the subject of future papers [20]."
--
[20] Markopoulou F, Preston-Weinstein C and Smolin L, Dark energy as a consequence of disordered locality, Preprint in preparation
 

So, we're expecting yet another preprint on the "dark energy", but without any Hamiltonian operator, "in the presence of appropriate boundary conditions or gauge fixing, which had been shown to be positive definite."

Why? Because the Greek philosopher F. Markopoulou has totally ignored Aristotle. Sad but true.

As to the claim (p. 3822) that the disordered locality "would not be easily detectible", try to detect it in the nanoworld:

M. Wautelet and D. Duvivier, The characteristic dimensions of the nanoworld, Eur. J. Phys. 28 (2007) 953-959.

There is no "disordered locality" there. Why? See above.

D. Chakalov
July 31, 2007

============

Subject: The pre-geometric background independent approach to quantum gravity
Date: Wed, 21 Mar 2007 04:54:13 +0200
From: Dimi Chakalov <dimi@chakalov.net>
To: Fotini <fotini@perimeterinstitute.ca>
Cc: Isham, Christopher J <c.isham@imperial.ac.uk>

Kalimera Fotini,

In your gr-qc/0703097 v1 posted this morning, you wrote:

"Some of the more exciting possibilities we speculated on included solving the problem of time and *deriving* the Einstein equations. Clearly this direction is in its beginning, but the basic message is that taking the idea that general relativity is an effective theory seriously involves rethinking physics without spacetime. This opens up a whole new set of possibilities and opportunities."

I believe this also brings us to our chat seven years ago at Imperial College, after you delivered your talk "What the universe looks like from the inside", based on your gr-qc/9811053. We talked at the cafeteria, remember? We need a new reference object, as I argued seven years ago, or else we simply cannot even think about the issue in the subject line. Can't do math without thinking, since our thinking is relational, and so is the theory of relativity.

In case you disagree, please see
http://www.god-does-not-play-dice.net/Straumann.html#Eric_note

and write me back.

Best regards,

Dimi