Recent content by Thomas Larsson

They say no new physics between the weak and Planck scales. There could still be new physics below the weak scale that went undetected because it interacts weakly. I am terribly rusty with this kind of calculation and I never learned it properly anyway, so am not competent to judge its...

It's been ages since I thought about these things, so some might be misremembered, but here goes. Any sensible spin model, like the Ising or q-state Potts model, is unitary. Sensible here means that that the Boltzmann weights are local and positive (so the energy is real). More formally it is...

I don't think in terms of information, but I think everything in QJT can in principle be measured locally by a single observer. There are three kinds of (partial) observables, all of which the observer can measure locally (notation as in previous post): 1. Time t, measured by a clock. 2...

Hej Fredrik, Maybe we should just agree to disagree. But before doing that, there are some points that I would like to emphasize: 1. What I have in mind is in fact very conservative. In particular, I believe the QM is exactly right. I have doubts about QFT, but it is the F rather than the...

Consider for simplicity a definite space-time split. This will break the spacetime diffeo symmetry which is my main interest, but spatial diffeos are still valid. Expand the field at time t=0 in a multi-dimensional Taylor series: \phi(x) = \sum_m {1 \over {m!}} \phi_m (x-q)^m The idea is...

Well, as I said I did not succeed in completing the program. There are a number of points where I got stuck. 1. I did not find was a nice notion of time conjugation, because a Taylor coefficient and its dual do not transform in the same way. This does of course not mean that such a notion...

As I think I have mentioned before, I consider observer dependence as implemented by Taylor expansion. A Taylor series does not only depend on the function being expanded, but also on the choice of expansion point, i.e. on the observer's position. You can consider expansions around different...

Well, I am convinced that QG is related to observation, or more precisely to the observer. The logic goes as follows: Every real experiment is an interaction between a system and an observer, and the result depends on the physical properties of both. In particular, it depends on the...

Sure, just take the usual normal-ordered expressions and apply them to the vacuum. All but finitely many of the bilinears a_{m-n}a_n annihilate the vacuum, because either n<0 or m-n<0. The same is true for the fermionic oscillators.

If you are interested in this sum because you want to calculate the central charge of the Virasoro algebra, there is an alternative method that does not involve any infinite sums at all. Instead of using the infinite sum L_m = \sum_{n = -\infty}^\infty : a_{m-n} a_n : we can define the...

http://arxiv.org/abs/hep-th/0108200" , perhaps. Page 65 looks promising.

I disagree. Every real experiment is done by someone or something, call it an observer or detector or test particle or whatever. If QG is unable to describe any real experiment, we have identified a problem. Locally, spacelikeness means that g_uv dx^u dx^v < 0. After quantization, this turns...

I had promised myself not to spend more time on online discussions, but this is a topic that I have thought quite a bit about, so here goes. In gravity, a background foliation is about as bad as a background metric. In fact, the foliation is not independent of the metric, since every...

My viewpoint is heavily influence by Rovelli's work on partial observables, with a twist. In general, we have one observer equipped with two detectors A and B. The observer makes a set of simultaneous readings (a_n, b_n); for simplicity, I assume that the corresponding operators A and B...

Re Kretschmann: Any theory can trivially be made diff invariant by adding a background metric which undergoes a compensating transformation under diffeomorphisms. Analogously, any theory can be made gauge invariant by adding a compensating background gauge field. The point with GR (or gauge...