Subject: Signature change
Date: Tue, 18 May 2004 18:28:17 +0300
From: Dimi Chakalov <>
To: Y Jack Ng <>

Dear Jack,

It is a pleasure to read your Lecture Note "Quantum Foam and Quantum Gravity Phenomenology" [Ref. 1]. Let me try to suggest a simple idea about the signature change, which could perhaps help the students to understand the wrong assumptions that led to "spacetime foam". All you need is a brain.

For easy reading, may I suggest you to download my web site (just 3.1MB) and explore it off-line,

Once you open the front page, you'll see your name in the right navigation menu. Click on it, and you'll read this email.

The initial idea of signature change, proposed by Hartle and Hawking some 20 years ago (J.B. Hartle, S.W. Hawking, Phys. Rev. D. 28 (1983), 2960), is very important for classical GR (cf. F. Darabi, gr-qc/0405081 v1, ref. [2]).

If we imagine partitioning an *arbitrary large* cube into small cubes [Ref. 1, Fig. 1], we will end up with the paradox of Thompson's lamp,

It's a genuine self-referential logical paradox,

but is completely ignored in the holographic principle, I'm afraid.

Ensuing from the solution to the paradox of continuum proposed at the URLs above, it seems to me that the only possible way to have *successive* signature changes is to introduce a well-known atemporal medium, which you and your colleagues can easily detect with/by your brain,

This atemporal medium shows up in both GR and QM,

It is a genuine holistic phenomenon and could be the source of the so-called dark energy [Ref. 2],

It could be the the nature of gravity as well,

If we ignore it, we will be confronted with the bold hypothesis that the gravitational waves propagate within themselves, and with respect to themselves.

If we ignore it, we may never understand the nature of 3-D space in GR,

and the transition from classical to quantum,

All this is a very old story. On May 22, 1989, I had the rare privilege of discussing the nature of cognition with John Wheeler during a lunch in the cafeteria of the Physics Department of Princeton University. If "time is Nature's way to keep everything from happening all at once" (John Wheeler), we need some atemporal holder for all potential events, the 'unknown unknown' included. So, I offered him some simple brain experiments to verify the atemporal nature of human cognition, but he wasn't interested, and firmly insisted on his ideas of "quantum foam", as introduced at a gravity conference at the University of North Carolina in 1957 [Ref. 1].

I've been working on this issue in the past 15 ears. Should you or your colleagues have questions, please don't hesitate. More at GR17 in Dublin,

Kindest regards,



[Ref. 1] Y. Jack Ng, Quantum Foam and Quantum Gravity Phenomenology, gr-qc/0405078 v1. Lectures given at the 40th Karpacz Winter School on Theoretical Physics (Poland, February 2004), submitted to Lect. Notes Phys.,

"As far as (quantum gravity) phenomenology, the theme of this Winter School, is concerned, we can only say that it is not easy, but by no means impossible, to detect spacetime foam.[1] We encourage the students to find better ways to do so.

"The only quantum gravity effects we are concerned with in these
lectures are those due to quantum fuzziness -- uncertainties involving
fluctuating magnitudes with *both ± signs*, perhaps like a fluctuation
with a Gaussian distribution about zero.

p. 13: "Now that we know where the holography model stands among the quantum gravity models, we will restrict ourselves to discuss this model only for the rest of the lectures.

p. 27: "Recall that, by analyzing a simple gedanken experiment for spacetime measurements, we arrive at the conclusion that spacetime fluctuations scale as the cube root of distances or time durations. This cube root dependence is strange, but has been shown to be consistent with the holographic principle and with semi-classical black hole physics in general. We think this result for spacetime fluctuations is as beautiful as it is strange. Hopefully it is also true!

"But what is really needed is direct detection of quantum foam. Its detection will give us a glimpse of the fabric of spacetime and will help guide physicists to the correct theory of quantum gravity. The importance of direct experimental evidence cannot be over-emphasized."

[Ref. 2] Stefan Hollands, Robert M. Wald, Quantum Field Theory Is Not Merely Quantum Mechanics Applied to Low Energy Effective Degrees of Freedom, gr-qc/0405082 v1

"Rather, the puzzle is, "Why is the cosmological constant so large?" (...) This is a true puzzle. We do not have any new proposals to make here concerning the nature of dark energy. However, if dark energy does correspond to vacuum energy of an interacting quantum field, it is our view that its properties will be understood only by fully taking into account the holistic nature of quantum field theory."